Tesi sul tema "Salinisation"

Mestrado em Biologia Aplicada<br>As global climate patterns change, so will freshwater availability. Specially, salinisation of freshwater costal ecosystem is a major point of concern; either by surface flooding or by groundwater intrusions of seawater. This may be potentiated by the decrease of freshwater availability provoked by longer drought periods, evaporation, and increased freshwater extraction (for example for agriculture and other human uses). According, the present work aimed at evaluating how freshwater organisms responded to an increase in salinity. To achieve this main objective two specific goals were delineated: (i) to compare the toxicity of seawater with a surrogate (NaCl), commonly used in laboratory toxicity assays, to two standard freshwater species, and (ii) to assess if an association exist between resistance to chemical contamination and to increased salinity; since many populations, predicted to experience future increased salinity, are presently exposed to chemical contamination. To accomplish the first objective the sensitivity of the green algae Pseudokirchneriella subcapitata (Korshikov) F. Hindák and of the cladoceran Daphnia magna Straus to NaCl and to natural seawater was evaluated. Growth rate for P. subcapitata, and mortality, time to release the first brood, body size, total reproduction, and intrinsic rate of natural increase for D. magna, were monitored after exposing these species to two series of solutions with an increasing gradient of salinity. One series of solutions was established with a natural seawater sample and the other with NaCl dissolved artificial media. To address the second objective, four cloned lineages of Daphnia longispina O.F. Müller, exhibiting different sensitivities to lethal levels of copper, were exposed to a gradient of lethal and sublethal levels of salinity, established with the salt NaCl. The same endpoins described for D. magna were also monitored for D. longispina. The obtained results showed that NaCl exerted a higher toxicity to P. subcapitata (LOEC of 5.9mS/cm and 9.6mS/cm, respectively for NaCl and seawater) and to D. magna (LC50,48h of 9.88mS/cm and 11.32mS/cm; and EC50 for total reproduction of 8.9mS/cm and 10.4mS/cm, respectively for NaCl and seawater) than the natural seawater. These data suggest that the use of NaCl as a surrogate for seawater to predict, in laboratory, the effects of seawater intrusion in freshwater is a protective approach as it simulates a “Worst Case Scenario” of exposure. An association between resistance to copper and to NaCl was not observed for the tested cloned lineages of D. longispina (r < 0.92 and p > 0.08), though the two clonal lineages most resistant to copper also exhibited the highest sensitivity to sublethal levels of NaCl (determined as the EC20 for total reproduction). Finally, obtained data demonstrated that D. longispina was more sensitive to increased salinity (LC50,48h of 2.85g/L to 2.48g/L or, conductivity values of LC50,48h of 5.50mS/cm to LC50,48h= 4.57mS/cm which correspond respectively to the highest and lowest recorded values in these assays) than the standard species (D. magna), highlighting the importance of using autochthonous species for the ecological risk assessment of secondary salinisation.<br>À medida que os padrões climáticos se alteram também a disponibilidade de água doce se irá alterar. Como tal, a salinização de ecossistemas costeiros, principalmente os dulçaquicolas, torna-se um ponto de preocupação fundamental. Quer devido ao aumento de intrusões de água do mar por inundação ou por intrusões salinas através dos lençóis freáticos, quer devido à diminuição de entrada de água doce, provocada por períodos mais prolongados de seca, evaporação e aumento do uso de água para actividades antropogénicas. De acordo com o exposto, o presente trabalho pretendeu avaliar as respostas de organismos dulçaquicolas a alterações provocadas pelo aumento de salinidade. Para atingir este objectivo principal foram delineados dois objectivos específicos: (i) comparar a toxicidade de água do mar com a do sal NaCl, comummente usado em laboratório como substituto de água do mar e (ii) averiguar uma possível correlação entre a resistência a contaminação química (cobre) e a aumento de salinidade; uma vez que muitas das populações que se prevê virem a ser afectadas por salinização estão, presentemente, já expostas a contaminação química. Para abordar o primeiro objectivo, a alga verde Pseudokirchneriella subcapitata (Korshikov) F. Hindák e o cladócero Daphnia magna Straus foram expostos a dois gradientes crescentes de salinidade estabelecidos com água do mar natural e com NaCl dissolvido num meio artificial.. No ensaio com a alga verde unicelular foi avaliada a inibição do crescimento; no ensaio com D. magna foram avaliados os seguintes parâmetros: mortalidade, tempo decorrido até libertar a primeira ninhada, comprimento corporal, reprodução total, taxa de crescimento intrínseco. Para atingir o segundo objectivo, foram seleccionadas quatro linhagens do cladócero Daphnia longispina O.F Müller com sensibilidades diferentes a níveis letais de cobre. As quatro linhagens foram expostas a um gradiente de concentrações, letais e sub-letais, de NaCl. Neste ensaio foram analisados os mesmo parâmetros descritos anteriormente para o ensaio com D. magna. Os resultados demonstram que o sal NaCl apresentou maior toxicidade do que a água do mar natural, quer para P. subcapitata (LOEC de 5.9mS/cm e de 9.6mS/cm, respectivamente para NaCl e água do mar), quer para D. magna (LC50,48h de 9.88mS/cm e LC50,48h= 11.32mS/cm; e EC50, para reprodução total, de 8.9mS/cm e 10.4mS/cm, respectivamente para NaCl e água do mar). Estes dados sugerem que o uso de NaCl, em laboratório, como um substituto de água do mar deve ser considerado como uma abordagem protectora, uma vez que simula um cenário de maior toxicidade. Não foi observada uma associação significativa entre maior resistência a cobre e a NaCl nas linhagens de D. longispina testadas (r < 0.92 and p ≥ 0.08), apesar de as duas linhagens mais resistentes a cobre apresentarem as maiores sensibilidades a níveis subletais (para reprodução total) de NaCl. Finalmente, os dados obtidos demonstram que D. longispina é mais sensível ao aumento de salinidade (o intervalo de valores de LC50,48h calculados foi de 2.85g/l a 2.48g/l de NaCl, correspondente a valores de conductividade de 5.50mS/cm e 4.57mS/cm, respectivamente) que a espécie padrão (D. magna), salientando a importância do uso de espécies autóctones na avaliação de risco ecológico em situações de intrusões salinas.

Dryland salinity is increasing in the upper catchments of central and northern New South Wales, Australia. Consequently, salts may be exported downstream, which could adversely affect cotton irrigated-farming systems. In order to assess the potential threat of salinity a simple salt balance model based on progressively saline water (i.e., ECiw 0.4, 1.5, 4.0 and 9.0 dS/m) was used to simulate the potential impact of salinisation due to the farming systems. The study was carried out in the lower Namoi valley of northern New South Wales, Australia. A comparison has been made of the various non-linear techniques (indicator kriging, multiple indicator kriging and disjunctive kriging) to determine an optimal simulation method for the risk assessment. The simulation results indicate that potential salinisation due to application of the water currently used for irrigation (ECiw) is minimal and may not pose any problems to sustainability of irrigated agriculture. The same results were obtained by simulation based on irrigation using slightly more saline water (ECiw 1.4 dS/m). However, simulations based on irrigation using water of even lower quality (ECiw of 4 and 9.0 dS/m), shows potential high salinisation, which will require management inputs for sustainable cropping systems, especially legumes and wheat, which are used extensively in rotation with cotton. Disjunctive kriging was the best simulation method, as it produced fewer misclassifications in comparison with multiple-indicator kriging and indicator kriging. This study thus demonstrates that we can predict the salinity risk due to application of irrigation water of lower quality than that of the current water used. In addition, the results suggest here problems of excessive deep drainage and inefficient use of water might be a problem. The second part of this thesis deals with soil information required at the field scale for management practices particularly in areas where deep drainage is large. Unfortunately, traditional methods of soil inventory at the field level involve the design and adoption of sampling regimes and laboratory analysis that are time-consuming and costly. Because of this more often than not only limited data are collected. In areas where soil salinity is prevalent, detailed quantitative information for determining its cause is required to prescribe management solutions. This part deals with the description of a Mobile Electromagnetic Sensing System (MESS) and its application in an irrigated-cotton field suspected of exhibiting soil salinity. The field is within the study area of part one of this thesis-located about 2 km south west of Wee Waa. The EM38 and EM31 (ECa) data provide information, which was used in deciding where soil sample sites could be located in the field. The ECa data measured by the EM38 instrument was highly correlated with the effective cation exchange capacity. This relationship can be explained by soil mineralogy. Using different soil chemical properties (i.e. ESP and Ca/Mg ratio) a detailed transect study was undertaken to measure soil salinity adjoining the water storage. It is concluded that the most appropriate management option to remediation of the problem would be to excavate the soil directly beneath the storage floor where leakage is suspected. It is recommended that the dam not be enlarged from its current size owing to the unfavourable soil mineralogy (i.e. kaolin/illite) located in the area where it is located.

Dryland salinity is increasing in the upper catchments of central and northern New South Wales, Australia. Consequently, salts may be exported downstream, which could adversely affect cotton irrigated-farming systems. In order to assess the potential threat of salinity a simple salt balance model based on progressively saline water (i.e., ECiw 0.4, 1.5, 4.0 and 9.0 dS/m) was used to simulate the potential impact of salinisation due to the farming systems. The study was carried out in the lower Namoi valley of northern New South Wales, Australia. A comparison has been made of the various non-linear techniques (indicator kriging, multiple indicator kriging and disjunctive kriging) to determine an optimal simulation method for the risk assessment. The simulation results indicate that potential salinisation due to application of the water currently used for irrigation (ECiw) is minimal and may not pose any problems to sustainability of irrigated agriculture. The same results were obtained by simulation based on irrigation using slightly more saline water (ECiw 1.4 dS/m). However, simulations based on irrigation using water of even lower quality (ECiw of 4 and 9.0 dS/m), shows potential high salinisation, which will require management inputs for sustainable cropping systems, especially legumes and wheat, which are used extensively in rotation with cotton. Disjunctive kriging was the best simulation method, as it produced fewer misclassifications in comparison with multiple-indicator kriging and indicator kriging. This study thus demonstrates that we can predict the salinity risk due to application of irrigation water of lower quality than that of the current water used. In addition, the results suggest here problems of excessive deep drainage and inefficient use of water might be a problem. The second part of this thesis deals with soil information required at the field scale for management practices particularly in areas where deep drainage is large. Unfortunately, traditional methods of soil inventory at the field level involve the design and adoption of sampling regimes and laboratory analysis that are time-consuming and costly. Because of this more often than not only limited data are collected. In areas where soil salinity is prevalent, detailed quantitative information for determining its cause is required to prescribe management solutions. This part deals with the description of a Mobile Electromagnetic Sensing System (MESS) and its application in an irrigated-cotton field suspected of exhibiting soil salinity. The field is within the study area of part one of this thesis-located about 2 km south west of Wee Waa. The EM38 and EM31 (ECa) data provide information, which was used in deciding where soil sample sites could be located in the field. The ECa data measured by the EM38 instrument was highly correlated with the effective cation exchange capacity. This relationship can be explained by soil mineralogy. Using different soil chemical properties (i.e. ESP and Ca/Mg ratio) a detailed transect study was undertaken to measure soil salinity adjoining the water storage. It is concluded that the most appropriate management option to remediation of the problem would be to excavate the soil directly beneath the storage floor where leakage is suspected. It is recommended that the dam not be enlarged from its current size owing to the unfavourable soil mineralogy (i.e. kaolin/illite) located in the area where it is located.

[Truncated abstract] Land clearing is known to increase runoff, and in many dryland landscapes is also associated with rising saline watertables, causing increased stream salinity and degrading riparian vegetation. The limited understanding of how river morphology responds to these changes and the potential for vegetation-based strategies to offer river management options under these conditions, has prompted this research. In southwestern Australia the severity of salinity and recent nature of land clearing provides an appropriate setting to investigate river response. A data-based, multidisciplinary methodology was applied to determine how land clearing and landscape salinisation has altered landscape sensitivity through changes in erosive potential, system connectivity and material threshold mechanisms, and how these affect patterns of river response. The study investigated the responses of morphologically similar reaches across fifty two study sites in the Kent River and Dalyup River catchments, in the south coastal rivers region of Western Australia. Land clearing was found to have significantly altered the hydrologic regime and erosive potential in both frequency and magnitude, with flow becoming more perennial, and increased annual discharge, flood peaks and bankfull flow frequency. While sediment transport rates have also increased since land clearing, they remain low on a global scale. Human response to a reduced rainfall regime and related water security pressures has caused large hillslope areas to be decoupled from the main channels by bank and farm dam construction, and have reduced downstream transmission of change. ... By contrast, steeper-sloped mid-catchment areas with minimal vegetation degradation caused by salinity are associated with higher erosive potential. A more erosive response is observed in these reaches where floodplains have been cleared for agricultural purposes. A conceptual model of vegetation growth across the salinity gradient observed in the study catchments was developed, and applied to selected river styles to assess the potential that vegetation-based strategies offer for river management. This work identifies the unsuitability of river restoration strategies, but the potential for river restoration or remediation in a saline landscape. Hydraulic modelling demonstrated that river rehabilitation strategies such as improving the vegetation condition of the riparian buffer using native or commercial species on areas elevated above saline flow can stabilise reaches. For river styles in wide and flat valleys, there is limited potential for vegetation-based river rehabilitation under the current salinity gradient. Field observation and modelling suggest that river remediation may offer geomorphic management options in salt-affected reaches through channelisation to lower watertables, and further research on this is warranted. This work found a consistent response for river styles across the two study catchments. Based on the understanding of river response and the potential for vegetation-based river management for each style, this research offers a regional-scale tool for river management in a saline landscape.

Les aquiferes cotiers, part non negligeable des ressources en eau des bassins sedimentaires en france, ont subi des changements de gradients hydrauliques et de proprietes hydrodynamiques, en reponse aux periodes de decharge/recharge dues aux variations du niveau marin et/ou aux forcages anthropiques. Cette etude a pour objectif principal la comprehension des conditions de recharge et de decharge a l'origine des eaux salees reconnues sur trois sites : les aquiferes du dogger des cotes de la manche (caen) et de l'atlantique (marais poitevin), ainsi que l'aquifere des sables astiens (cap d'agde). Pour les trois sites, les eaux douces recentes sont marquees par une anthropisation des aires de recharge. Le long d'une ligne d'ecoulement, les signatures geochimiques dependent de la nature des formations aquiferes et relevent des interactions eau-roche. Les temps de residence des eaux douces evoluent de l'actuel (site atlantique) a la limite de la methode du 1 4c (site de la manche). Les eaux de l'aquifere des sables astiens montrent une gamme d'ages holocene, determinee par le 1 4c et le 2 2 6ra. De l'actuel a 3 ka, les ages 1 4c et 2 2 6ra sont identiques. Au dela, les ecarts observes peuvent etre associes a une sous-estimation de la production de 2 2 6ra in-situ, mais plus vraisemblablement, a l'effet tampon- 1 4c lors de l'equilibration isotopique avec la matrice. D'origine marine, la signature des eaux salees reconnues sur les trois sites a ete modifiee par interaction avec des horizons tourbeux, par echange cationique, ou par apport de carbone d'origine profonde. Ces processus de salinisation sont lies a un debordement marin en plaine ou a une drainance d'eau carbo-gazeuse provenant d'un aquifere profond. Les intrusions marines affectant des sites de l'atlantique et de la manche ont pu etre associees a la transgression flandrienne (respectivement 8 ka et 4,8-10,8 ka b. P. ). Pour les sables astiens, le temps ecoule depuis le melange profond eau-co 2 a pu etre estime a 0,5-3 ka.

The thesis looks at landscape evolution and salinisation in the Bamganie-Meredith region of Victoria. The importance of reducing waterlogging is stressed if successful land management is to be achieved.<br>Master of Applied Science

This thesis presents the results of a computational study on salt transport and accumulation in crop root zone. The main objective of this study is to examine the impacts of past land use on the environment and to examine the effect of irrigation water on the rising of groundwater level and the subsequent salinity problem in rice growing area under given climatic conditions. A special focus has been such impacts in the Wakool irrigation area, NSW, Australia. To this end, a computational model for the assessment and prediction of salinisation in agricultural areas has been developed. This modelling system consists of a land surface scheme (ALSIS) for simulating unsaturated soil moisture and moisture flux, a groundwater flow model (MODFLOW) for estimating the spatial and temporal variations of groundwatertable, a surface flow model (DAFLOW) for calculating water flow in river networks, a module for calculating solute transport at unsaturated zone and a 3-D model (MOC3D) for simulating solute transport in groundwater as well as a module for calculating the spatial and temporal distributions of overland flow depth during wet seasons. The modelling system uses a finite difference linked technique to form a quasi three dimensional model. The land surface scheme is coupled with the groundwater flow model to account for the interactions between the saturated and unsaturated zones. On the land surface, the modelling system incorporates a surface runoff model and detailed treatments of surface energy balance, which is important in es-timating the evapotranspiration, a crucial quantity in calculating the moisture and moisture fluxes in the root zone. Vertical heterogeneity of soil hydraulic properties in the soil profile has been considered. The modelling system has the flexibility of using either Clapp and Hornberger (1978), Broadbridge and White (1988), van Genuchten (1980) or Brooks and Corey (1966) soil water retention models. Deep in the soil, the impact of groundwater table fluctuation on soil moisture and salinity in the unsaturated soil is also included. The calibration and validation for the system have been partially performed with observed groundwater levels in the Wakool irrigation area. The applications of the model to theWakool region are made in two steps. Firstly, a one-dimensional simulation to a selected site in the Wakool irrigation area is carried out to study the possible impact of ponded irrigation on salinisation and the general features of salt movement. Secondly, a more realistic three-dimensional simulation for the entire Wakool region is performed to study the spatial and temporal variations of root zone soil salinity under the influence of past land use from 1975 to 1994. To allow the assessment and prediction of the effects of ponded rice irrigation water (which contains salt) on soil salinity in the area, several hypothetical scenarios using different qualities of water for rice irrigation are tested. To facilitate comparative analysis of different scenarios, a base case is defined, for which irrigation water is assumed to be free of salt. The simulated results show that irrigation increases overall recharge to groundwater in the Wakool irrigation area. The use of ponded irrigation for rice growing has a substantial effect on salt accumulation in the root zone and the rising of groundwater level, indicating that irrigation at rice bay is a major budget item for controlling soil salinity problem in the local area.

In South Western Sydney (which encompasses the study area), New South Wales, Australia, salinity is a major emerging urban problem and is primarily related to rising groundwater level. This eight-chapter thesis focuses on the factors influencing salinity and its processes in the Mount Annan, Currans Hills and Narellan Vale areas, and investigates both the present three-dimensional (3-D) groundwater flow pattern and that expected to occur in the area as a result of future urban expansion. The chemical and physical analyses carried out on the soil samples collected from the study areas, and the groundwater level and electrical conductivity data have been interpreted in a comprehensive integrated manner to identify factors and processes influencing salinity, and to develop a reliable and detailed hydrogeological conceptual model. A new method has been developed for groundwater recharge estimation for unconfined aquifers under the assumption that groundwater recharge is solely due to rainfall. The method is capable of estimating groundwater recharge and drainage and predicting groundwater levels from time series of observed groundwater level data and rainfall events. The method can produce non-unique solution. Despite the non-uniqueness, the estimated recharges do not suffer large variations. A 3-D groundwater flow model has been developed by calibrating the measured groundwater level data using the MODFLOW code. The groundwater flow maps constructed from the 3-D calibration results have shown that the flow pattern is collectively controlled by topography and recharge, and varies in space and time, which likely suggests that the salinisation process, which is influenced by the lateral and vertical groundwater movements, varies in space and time. Analysis has revealed that future urbanisation likely results in changes in the subsurface water balance. Conclusions and suggested avenues for future research are drawn in Chapter 8.

Secondary salinisation is a anthropogenic process that is increasingly disrupting the health of freshwater ecosystems in Australia. In a continent where supplying future water resources for a growing population is challenging, secondary salinisation not only makes freshwater ecosystems unsuitable for human use, but may also have substantial negative impacts on aquatic biota. A large body of research in Australia and overseas has found that increasing salinisation is associated with a loss of biodiversity in freshwater ecosystems. However, most of these studies are based on salinity tolerance tests conducted in the laboratory, which determine physiological effects of salinity without considering the synergistic impacts of other existing stressors in the system. The south of Western Australia is a biodiversity hot spot, but has been severely impacted on by secondary salinisation. Only 44% of flow in the 30 largest rivers in the Southwest Coast Drainage Division is fresh and more than half of the rivers in the region can be classified as brackish or saline. Among these rivers, the Blackwood River is the second largest in the region, has the highest discharge and contains all eight native riverine fish species which are endemic to the south-west. More than 85% of the river catchment has been cleared and salinity has an annual upward trend throughout the upper catchment and in the main channel of the lower catchment, while lower catchment tributaries remain fresh. In this study, I have used a combination of field and laboratory studies to investigate the impacts of increasing salinity on the biological performance of native and exotic freshwater fishes in different parts of the Blackwood River. Eleven species of fish were captured in the Blackwood River during the study; Galaxias occidentalis, Gambusia holbrooki, Leptatherina wallacei, Pseudogobius olorum, Edelia vittata, Tandanus bostocki, Nannatherina balstoni, Bostockia porosa, Afurcagobius suppositus, Galaxiella munda and Oncorhynchus mykiss. The greatest diversity of fish species (G. occidentalis, G. holbrooki, L. wallacei, P. olorum, E. vittata, T. bostocki, N. balstoni, B. porosa and A. suppositus) was found in the main channel of the lower catchment, where salinity typically varies between 2 and 5 ppt. Eight species (B. porosa, E. vittata, G. occidentalis, N. balstoni, T. bostocki, A. suppositus, G. munda and O. mykiss) were found in freshwater tributaries of the lower catchment, where salinity is always less than 0.5 ppt. In the upper catchment, where salinity varied from 7 ppt to over 31 ppt, only four species of fish were captured; the native riverine species G. occidentalis, the introduced G. holbrooki and the euryhaline species L. wallacei and P. olorum. For the four species of fish that were distributed throughout the Blackwood River (G. occidentalis, G. holbrooki, L. wallacei and P. olorum), I investigated the size, morphology, life-cycle, diet and rate of parasitism between populations in the upper and lower catchment. All four fish species have relatively short life spans and this was more evident in the case of G. holbrooki and P. olorum in which 100% (n = 558) and 98% (n = 163), respectively, were classified as 0+. Forty-five percent of L. wallacei (n=788) and 41% of G. occidentalis (n=942) were classified as 0+. Significant numbers of G. occidentalis (46%) and L. wallacei (43%) were found in their second year of life, while this number was only 2% for P. olorum. No L. wallacei (n = 776) older than three years were captured in this study, while 1% (n = 937) of G. occidentalis were recorded as four years old. Spawning of L. wallacei in the upper catchment peaked by mid spring, while fish in the lower catchment delayed spawning until early summer. There were no significant differences between spawning time of G. occidentalis and P. olorum populations in the upper and lower catchments of the Blackwood River, although biannual spawning of P. olorum was only recorded in upper catchment sites. The breeding season of G. holbrooki in both the upper and lower catchments of the Blackwood River lasted for a period of at least six months (from October to beyond March). Dietary analyses of all four fish species from the upper and lower catchments of the Blackwood River revealed their opportunistic feeding behaviour. Overall, the highest diversity of invertebrate fauna was recorded in the diet of L. wallacei, while the lowest diversity was recorded in P. olorum. Crustaceans including Amphipoda, Copepoda, Cladocera and Ostracoda, made up a greater proportion of the diet of all four fish species in the salt affected upper catchment than in the lower catchment. There were significant differences between the dietary compositions of all fish species in both upper and lower catchments. The eggs or larvae of native fishes were not commonly found in the diet of G. holbrooki, although dietary analysis showed that this species is clearly in competition with native fish fauna. Over all, five species of macroparasites, including nematodes, trematodes and cestodes, were found in association with the four fish species studied. The highest prevalence of parasite infections were recorded in the native species G. occidentalis (5.9%), P. olorum (5.7%) and L. wallacei (2.8%) with the lowest prevalence in the introduced G. holbrooki (0.2%), despite G. holbrooki making up approximately 77% of the fish population in the river. This reduced parasite diversity in introduced species, compared with native hosts, has also been reported in a wide range of other taxa, and may contribute to the competitive advantage of introduced pest species. There was a correlation between the distribution of one species of parasite, Diplostomum sp., and position of its fish intermediate host in the catchment. This trematode, which has a complex life-cycle involving a number of different hosts, was mainly restricted to the freshwater tributaries, occurred rarely in the main channel of the lower catchment where the salinity was relatively low and was never found in the salinised upper catchment. Despite the circumstantial evidence from field studies that the current pattern of fish distributions in the Blackwood River has been influenced by secondary salinisation, salinity tolerances of native freshwater fishes have not previously been measured under controlled laboratory conditions. The acute salinity tolerance of populations of G. occidentalis from the upper and lower catchments of the Blackwood River was studied experimentally, and compared with the tolerance of two other native fish species; E. vittata which is found in the main channel of the lower catchment, but not in the upper catchment; and N. balstoni which is restricted to a single small, freshwater tributary of the lower catchment. Nannatherina balstoni was found to have the lowest salinity tolerance with EC50 = 8.2 ppt and EC95 = 9.3 ppt. This confirms that the upper catchment of the Blackwood River, where the salinity was significantly higher than this range throughout most of the year, is unsuitable for this species and this may explain its absence from most of the catchment. The salinity tolerance of both E. vittata (EC50 = 14.5 and EC95=15.6) and G. occidentalis (EC50 = 14.6 ppt and EC95 = 15.8 ppt) was considerably higher than that of N. balstoni (LC50 = 8.2 ppt and LC95 = 9.2 ppt). It is possible that the eggs, larvae or juvenile stages of E. vittata are more sensitive to salinity than adults and this prevents this species from establishing its life-cycle in the upper catchment of the Blackwood River. Additionally, the greater dispersal capabilities of G. occidentalis may enable it to maintain its life-cycle in the upper catchment by moving into refuge areas as salinity increases. This study has provided valuable insight into the impact of secondary salinisation on the biological performance of freshwater fishes in south-western Australia. These impacts are likely to be further exacerbated by continued increases in salinisation and reduced rainfall due to climate change.

Secondary salinisation has affected large areas of inland southwestern Australia, and in particular, low lying aquatic areas; causing the loss of freshwater submerged macrophyte communities and their replacement by salt-tolerant species. At high salinities, the salt-tolerant macrophyte-dominated ecological regime may be replaced by a regime dominated by benthic microbial communities, further reducing the structural and functional diversity of salinised wetland ecosystems. There is little prospect of restoring salinised systems to a freshwater state, meaning that saline macrophyte dominated wetlands have a heightened structural and functional importance in this landscape. Prior to this study, little was known about the drivers for change from one ecological regime to another in salinising wetlands or about rates of ecosystem response to these drivers. This study used experimental and observational data from seven saline wetlands in order to identify some of the potential mechanisms for the transition between the salt tolerant submerged macrophyte-dominated regime and the benthic microbial community-dominated regime. The applicability of existing conceptual models for ecological regime shifts was then tested against these data. Some of the mechanisms responsible for the formation and maintenance of the macrophyte-dominated regime were explored by examining the effects of salinity on germination and flowering in a series of salt-tolerant submerged macrophytes. The initiation and dominance of benthic microbial communities over a range of salinity and wetting regimes was also examined. The results suggested that macrophyte communities are unlikely to develop in seasonally-drying wetlands at high salinities (>45 ppt), but will usually germinate and establish well at lower salinities. It was also predicted that although benthic microbial communities can survive and grow across a wide range of salinities, they are likely to be outcompeted at low salinities by macrophytes or by phytoplankton blooms if water column nutrient levels are high. However, water permanence may facilitate benthic microbial community dominance. Existing conceptual models of ecological regime transitions, such as the alternative regimes model, did not account for the effect of water regime on the dynamics of seasonally-drying systems. Therefore, a new conceptual model incorporating the interaction between hydrology and salinity in seasonally-drying wetlands was proposed.

L'objectif de ce travail est de préciser les processus responsables de la salinisation des aquifères côtiers captifs en réponse aux variations du niveau marin (passées, futures) et aux pressions anthropiques. <br />Cette étude a été réalisée sur l'aquifère profond captif de Camargue dans le cadre de l'ORE RESYST. Cet aquifère présente des salinités élevées atteignant celle de la Méditerranée à proximité de la côte. Deux approches ont été menées conjointement : (i) une étude hydrodynamique en régime permanent et transitoire pour préciser le fonctionnement hydrogéologique de l'aquifère (flux, conditions aux limites, propriétés hydrodynamiques) et (ii) un suivi des traceurs naturels hydrochimiques et isotopiques (18O, 2H, 13C CMTD, 3H et 14C CMTD) permettant de déterminer l'origine de la salinité de l'aquifère. <br /> Ce travail a mis en évidence le rôle de la partie libre de l'aquifère (aquifère de Crau) dans l'alimentation de l'aquifère captif. La forte augmentation de la salinité de l'aquifère captif depuis 1969 est ainsi principalement reliée à des baisses de charge naturelles ou anthropiques de l'aquifère de Crau. L'aquifère captif est soumis à des transferts de pression rapide depuis la mer mais également le Rhône qui s'accompagnent de transferts de masse très lents. En s'appuyant sur les rapports ioniques et isotopiques, ce travail a permis de démontrer que les fortes salinités de l'aquifère captif s'expliquent par un mélange eau douce/eau de mer fortement modifié par des interactions géochimiques : échanges de bases, processus de dégradation de la matière organique sédimentaire (sulfato-réduction, méthanogénèse), phénomènes de précipitations. Le temps moyen de séjour des eaux, supérieur à une cinquantaine d'année, témoigne de l'influence d'une intrusion marine ancienne en relation avec la dernière transgression marine (Holocène supérieur).

L'objectif de ce travail est de préciser les processus responsables de la salinisation des aquifères côtiers captifs en réponse aux variations du niveau marin (passées, futures) et aux pressions anthropiques. Cette étude a été réalisée sur l'aquifère profond captif de Camargue dans le cadre de l'ORE RESYST. Cet aquifère présente des salinités élevées atteignant celle de la Méditerranée à proximité de la côte. Deux approches ont été menées conjointement : (i) une étude hydrodynamique en régime permanent et transitoire pour préciser le fonctionnement hydrogéologique de l'aquifère (flux, conditions aux limites, propriétés hydrodynamiques) et (ii) un suivi des traceurs naturels hydrochimiques et isotopiques (18O, 2H, 13CCMTD, 3H et 14CCMTD) permettant de déterminer l’origine de la salinité de l'aquifère. Ce travail a mis en évidence le rôle de la partie libre de l’aquifère (aquifère de Crau) dans l'alimentation de l'aquifère captif. La forte augmentation de la salinité de l'aquifère captif depuis 1969 est ainsi principalement reliée à des baisses de charge naturelles ou anthropiques de l'aquifère de Crau. L'aquifère captif est soumis à des transferts de pression rapide depuis la mer mais également le Rhône qui s'accompagnent de transferts de masse très lents. En s'appuyant sur les rapports ioniques et isotopiques, ce travail a permis de démontrer que les fortes salinités de l'aquifère captif s'expliquent par un mélange eau douce/eau de mer fortement modifié par des interactions géochimiques : échanges de bases, processus de dégradation de la matière organique sédimentaire (sulfato-réduction, méthanogénèse), phénomènes de précipitations. Le temps moyen de séjour des eaux, supérieur à une cinquantaine d’année, témoigne de l'influence d'une intrusion marine ancienne en relation avec la dernière transgression marine (Holocène supérieur)<br>This study deals with the salinization of confined coastal aquifers in relation with sea level variations (past, future) and human pressures. The deep confined aquifer of Camargue has been studied in the framework of the ORE RESYST. This aquifer shows high salinities reaching that of the Mediterranean Sea near the shoreline. Two approaches have been jointly carried out: (i) an hydrodynamic study in steady and transient flow to understand the hydrogeological behaviour of the aquifer (flows, boundary conditions, hydrodynamic properties) and (ii) a monitoring of hydrochemical and isotopic natural tracers (18O, 2H, 13CCMTD, 3H and 14CCMTD) to determine the origin of the salinity of the aquifer. This work highlights the influence of the unconfined part of the aquifer (Crau aquifer) on the recharge of the confined aquifer. Thus, the high increase of salinity in the aquifer since 1969 is mainly due to natural or anthropogenic head depletion within the Crau aquifer. The confined aquifer shows rapid pressure transfers both from the Sea and the Rhone River whereas mass transfers are very low. Ionic and isotopic ratios highlight that strong salinities of the aquifer are due to a freshwater/seawater mixing, which is highly modified by geochemical interactions: cationic exchange, sedimentary organic matter degradation (sulphate reduction, methanogenesis), precipitation phenomena. The mean residence time of water is higher than fifty years and reflects the influence of a former marine intrusion related to the last marine transgression (upper Holocene)

Groundwater salinity is widespread in Western Sydney; however, little is known about the processes which cause it. This thesis explored many features of the shallow groundwater system using a range of hydrogeological, geochemical and statistical techniques. Geostatistical analysis of historical data highlighted that 53.6% of the study region had shallow groundwater with an electrical conductivity exceeding 2,000µS/cm. Salinisation hazard mapping indicated that 0.66% of the region has a high salinisation hazard and 54.2% has a moderate salinisation hazard. The high-temporal-resolution dataset collected for this study, allowed the recharge and salt source (modern rainfall) to be identified, plus mechanisms of salt accumulation (cyclic process of evaporation and re-dissolution driven by high rates of evapotranspiration and clay-rich soils), and transport. From this, a geochemical model identifying the processes contributing to groundwater salinisation, and a conceptual model of the hydrogeological system were developed. Multivariate analysis identified seven water-types, their geographical distribution, and the causes of temporal variability for each water-type. Saline groundwater was found in many parts of the landscape, though temporal variability was generally limited. The monthly comparison approach, which analyses temporal variability, was developed for this study. This method increased our understanding of system variability and its causes, ultimately improving the conceptual model. The conceptual model generalises the geographical distribution of water-types based on landscape features, while temporal variability is related to water-types. The model significantly improves our understanding of the groundwater system, and our ability to manage it. Additionally, this study has illustrated that groundwater salinity arising from evaporative processes could be more wide-spread than currently thought, and may not be confined to arid or semi-arid environments.

Spicers Creek catchment is located approximately 400 km west of Sydney in the Central West region of New South Wales, Australia. Dryland salinity has been recognised as a major environmental issue impacting soil and water resources in the Central West region of NSW for over 70 years. Due to the geological complexity of the catchment and the presence of high salt loads contained within the soils, groundwater and surface waters, the Spicers Creek catchment was identified as a large contributor of salinity to the Macquarie River catchment. Over fifty-two dryland salinity occurrences have been identified in the Spicers Creek catchment and it appears that dryland salinity is controlled by the presence of geological structures and permeability contrasts in the shallow aquifer system. Combinations of climatic, geological and agricultural factors are escalating salinity problems in the catchment. The main aim of this thesis was to identify the factors affecting salinisation processes in the Spicers Creek catchment. These include the role of geological structures, the source(s) of salts to the groundwater system and the geochemical processes influencing seepage zone development. To achieve these aims a multidisciplinary approach was untaken to understand the soils, geology, hydrogeology and hydrogeochemistry of the catchment. Investigative techniques employed in this project include the use of geophysics, soil chemistry, soil spectroscopy, hydrogeochemistry and environmental isotopes. Evaluation of high-resolution airborne magnetics data showed a major north-east to south-west trending shear zone. This structure dissects the catchment and several other minor faults were observed to be splays off this major structure. These structures were found to be conducive to groundwater flow and are influencing the groundwater chemistry in the fractured aquifer system. Two distinctive groundwater chemical types were identified in the catchment; the saline Na(Mg)-Cl-rich groundwaters associated with the fractured Oakdale Formation and the Na-HCO3-rich groundwaters associated with the intermediate groundwater system. The groundwater chemistry of other deep groundwaters in the catchment appears to be due to mixing between these end-member groundwaters within the fractured bedrock system. The spatial distribution of electrical conductivity, Cl-, Sr2+ and 87Sr/86Sr isotopic ratios showed the correlation between saline groundwaters and the location of faults. Elevated salinities were associated with the location of two crosscutting fault zones. The spatial distribution of HCO3-, K+, Li+ and ?????3CDIC highlighted the extent of Na-HCO3-rich groundwaters in the catchment and showed that these groundwaters are mixing further east than previously envisaged. These findings show that Na(Mg)-Cl-rich groundwaters are geochemically distinctive and have evolved due to extensive water-rock interaction processes within the fracture zones of the Oakdale Formation. These saline groundwaters contain elevated concentrations of trace elements such as As, V and Se, which pose a potential risk for water resources in the area. 87Sr/86Sr isotopic ratios indicated that the source of salinity to the Na(Mg)-Cl-rich groundwaters was not purely from marine or aerosol input. Salt is most likely contributed from various allochthonous and autochthonous sources. This research found that the main mechanism controlling the formation of dryland salinity seepage zones in the Spicers Creek catchment is due to the presence of geological structures. These groundwater seepage zones act as mixing zones for rainfall recharge and deeper groundwaters. The main sources of salt to the seepage zones are from deeper Na(Mg)-Cl-rich groundwaters and rainfall accession. The major importance of this research highlights the need for an integrated approach for the use of various geoscientific techniques in dryland salinity research within geologically complex environments.

Thesis (DPhil)--Stellenbosch University, 2002.<br>ENGLISH ABSTRACT: Freshwater is the most fundamental of all life-supporting resources that determine our social, economic and political wellbeing. It is, however, only a small percentage of the world's water resources and is also unevenly distributed. Arid regions make-up about forty percent of the world's land area and have a large proportion of the world population, however, they only have a small fraction of the freshwater compared to other areas. Conventional freshwater sources in arid environments such as surface water in rivers, lakes and dams are often seasonal, available mainly during the rainy season. Equally, only a small part of the rain (0 - 5% of rainfall) infiltrates into groundwater reserves, and even this groundwater displays high rates of salinisation such that the end-water is too saline for human consumption. The poor quality of groundwater in arid regions is generally understood, however, it is always assumed that this is mainly a problem in areas where surface water does not occur. The study investigates seasonal groundwater salinisation in ephemeral (seasonal) river sources in some parts of Namibia and aims to derive a better understanding of the nature of this problem and how it affects people in these areas. It also looks at some possible solutions to the problem with the aim of informing water managers and scientists who are responsible for formulating solutions for water supply to areas in arid regions. These solutions are designed to take advantage of available opportunities in the study areas namely; the abundant supply of solar energy, alternative sources of freshwater such as fog and general atmospheric moisture, and adaptations for water collection in animals that inhabit these regions. The results show that groundwater in shallow ephemeral river sources of the Namib Desert and the Cuvelai delta in North central Namibia display high seasonal variation in Total Dissolved Solids (TDS) and chemical composition. The lowest TDS values are recorded during the rainy season, mainly after the first rains in the high rainfall areas and only after flood events in the lower rainfall regions. The groundwater salinity increases during the remainder of the year and in most cases becomes too saline for drinking purposes. The investigations of possible solutions indicate that small-scale photovoltaic reverse osmosis; solar distillation and fog collection could be used to address the seasonal shortage of potable water in these areas. The low-pressure (6 bar) reverse osmosis desalination experiments show that it is possible to operate the unit on a solar-driven pump to produce enough water to cover the typical daily water demand of a village in the Namib Desert. This unit would produce about 4600 litres per day (l/day) of 500- mg/l TDS product water, which exceeds the water production of similar world-leading small-scale RO units in Australia and The Canary Islands. The results also show that the cost of solar distillation units (solar stills) can be reduced sufficiently to make them a viable option for water supply to individual households in these rural areas. The study also found that fog is a feasible alternative source of freshwater in some of the study areas. The fog water is generally of 'A' quality drinking water according to the WHO-derived Namibian Drinking Water Quality Guidelines (NDWQG) and can be used directly or mixed with the saline groundwater to provide potable water. Mixing of the above-mentioned waters is particularly suitable in the Central Namib Desert because the period of high groundwater salinity coincides with that of peak fog deposition. The results also show that fog water can be collected with vanous polymeric greenhouse shade netting that can be easily obtained, and provides guidelines on the correct percentage shade coefficient and weave of possible fog collector mesh to intending users of fog collection technology in areas where the polypropylene mesh that is used in Standard Fog Collectors is not available. The investigations of surface properties of fog-harvesting beetles and experiments with various prototype collectors show that it is possible to increase water production in fog collectors existing today. The hydrophobic surface conditions as were found on the cuticles of fog-basking beetles (Onymaeris unguicularis and Onymacris bieolor) would enhance formation and runoff of large fog droplets on the collector surface. The prototype extractor-fan- and cooling system-based collectors show that it is possible to increase fog collection on polymeric meshes about three times and also that a comparable volume of atmospheric moisture can be collected even when there is no fog, up to a relative humidity of about 40%. In conclusion the study emphasizes that groundwater salinity in arid regions is at times a seasonal problem that should be considered in water supply strategies for these regions. Also that atmospheric moisture is a feasible alternative source of freshwater in some arid regions that often exceeds rainfall several times and should be considered as an important aspect of the strategies to address water problems in these areas. The study strongly recommends that scientists, engineers and water managers in these regions should always investigate the available opportunities such as climatic conditions (e.g. fog deposition) and adaptations for water collection/conservation that are found in the endemic plants and animals in order to develop sustainable solutions to this problem. They should also constantly update themselves on developments/opportunities that arise in the larger water industry that could be of benefit to water supply initiatives for remote areas in developing countries. Lastly, the study serves to better the understanding of the nature of groundwater salinity in arid environments that are dependent on seasonal surface flow for water supply as well as to contribute to the formulation of solutions to this problem in these areas, particularly in west coast hyper arid environments where conventional sources of freshwater are most inadequate. It also emphasises the role of materials science (polymers) and environmental engineering as well as that of UNESCO associated scientific institutions in the formulation of sustainable solutions to some of the current water problems in arid regions. Keywords: Arid lands, hydrochemistry, sources of freshwater, desalination, atmospheric moisture<br>AFRIKAANSE OPSOMMING: Vars water is die mees fundamentele van aIle lewensonderhoudende natuurlike hulpbronne wat ons sosiale, ekonomiese, en politieke welstand bepaal. Dit is egter slegs 'n klein gedeelte van die totale waterbronne van die wereld, en is boonop baie oneweredig versprei. Natuurlike waterarm gebiede (woestyne en halfwoestyne) beslaan ongeveer veertig persent van die landoppervlakte van die aarde en word bewoon deur 'n relatief groot persentasie van die wereldbevolking, maar beskik oor slegs 'n klein gedeelte van die varswater in vergelyking met ander gebiede. Konvensionele bronne van varswater in waterarm gebiede, soos oppervlaktewater in riviere, mere en darnme, is dikwels seisoenaal, en slegs beskikbaar gedurende die reenseisoen. Verder beland slegs 'n klein gedeelte van die reenval (0 - 5%) in die ondergrondse waterreserwes, en selfs hierdie grondwater vertoon 'n hoe mate van versouting, sodat die eindproduk te brak is vir menslike gebruik. Die swak gehalte van grondwater in waterarm gebiede word algemeen verstaan, maar daar is tot nog toe aanvaar dat dit oor die algemeen slegs 'n probleem is in gebiede waar oppervlaktewater me voorkom nie. Hierdie studie ondersoek seisoenale grondwaterverbrakking in seisoenale rivierbronne in sekere dele van Namibie en beoog om 'n beter begrip te formuleer van die aard van die probleem en hoe dit die inwoners van hierdie gebiede raak. Daar word ook ondersoek ingestel na moontlike oplossings vir die probleem, met die doel om 'n inligtingsbron vir waterbestuurders en wetenskaplikes wat verantwoordelik is vir die formuleer van oplossings vir watervoorsiening in waterarm gebiede daar te stel. Hierdie oplossings is ontwerp om voordeel te trek uit die beskikbare geleenthede in die ondersoekgebiede, naamlik; die oorvloedige beskikbaarheid van sonenergie, altematiewe bronne van varswater soos mis (Eng. "fog") en atmosferiese vog in die algemeen en aanpassings (Eng. "adaptations") vir die opvang van water wat voorkom by diere, veral insekte, in hierdie gebiede. Die resultate toon dat grondwater in die vlak seisoenale rivierbronne van die Namibwoestyn en die Cuvelai-delta in noordsentraal Namibie hoe seisoenale variasie in totale opgeloste stowwe (TVS) en chemiese samestelling vertoon. Die laagste TVS-waardes word waargeneem tydens die reenseisoen, hoofsaaklik na die eerste reen in die hoe-reenvalgebiede en eers na vloede in die lae-reenvalgebiede, Die soutgehalte van die grondwater neem toe gedurende die res van die jaar en in die meeste gevalle verbrak die water tot ondrinkbare vlakke. Die ondersoek na moontlike oplossings dui aan dat kleinskaalse fotovoltaiesgedrewe tru-osmose, sondistillasie en die opvang van mis (Eng."fog collection") aangewend kan word om die seisoenale tekort aan drinkwater in hierdie gebiede aan te spreek. Die laedruk (6 bar) tru-osmose-ontsoutingseksperimente wys dat dit moontlik is om die eenheid met behulp van 'n sonkraggedrewe pomp te bedryf en voldoende water te lewer vir die tipiese daaglikse drinkwaterbehoeftes van 'n nedersetting in die Namibwoestyn. Hierdie eenheid sal sowat 4600 liter per dag (l/d) water, met 'n TVSwaarde van 500 mg/I, lewer. Dit is aansienlik meer as die lewering van soortgelyke eenhede in Australie en die Kanariese Eilande. Die resultate wys ook dat die koste van sondistillasie-eenhede genoegsaam verminder kan word om dit 'n lewensvatbare opsie vir watervoorsiening aan enkelhuishoudings in die plattelandse gebiede te maak. Die studie het ook bevind dat die opvang van mis 'n toepaslike alternatiewe bron van varswater is in sekere van die studiegebiede. Die miswater is oor die algemeen 'A' -gehalte drinkwater vol gens die Namibiese gehalteriglyne Vir drinkwater (gebasseer op bepalings van die Wereldgesondheidsorganisasie) en dat dit net so, of vermeng met brak grondwater, gebruik kan word as drinkwater. Vermenging is besonder geskik in die sentrale Namibwoestyn, aangesien die periode van hoe grondwaterverbrakking saamval met die piek van benutbare misneerslag. Die resultate toon ook aan dat miswater opgevang kan word met verskeie tipes polimeriese skadunet, wat maklik verkrygbaar is, en verskaf riglyne vir die optimale skadu-koeffisient en weefpatroon van moontlike misvangsnette vir voomemende gebruikers van misvangstegnologie in gebiede waar die polipropileennet wat in die standaard miskollekteerders gebruik word nie, beskikbaar is nie. Die ondersoek van oppervlakeienskappe van mis-koesterkewers (Eng. "fog harvesting beetles") en eksperimente met verskeie prototipe versamelaars toon dat dit moontlik is om die waterproduksie van bestaande kollekteerders te verhoog. Die hidrofobe oppervlaktetoestande soos gevind op die opperhuid van die mis-koesterkewers (Onymacris unguicularis en Onymacris bicolor) bevorder die vorming en afloop van groot misdruppels op die versameloppervlak. Die prototipe suigwaaier- en verkoelerstelselgebasseerde versamelaars toon dat dit moontlik is om die misvogversameling op polimeriese nette tot drie maal te verhoog en dat 'n vergelykbare volume atmosferiese vog versamel kan word, selfs in die afwesigheid van mis, tot by 'n relatiewe humiditeit van ongeveer 40%. Ten slotte benadruk die studie dat grondwatersoutgehalte in waterann gebiede soms 'n seisoenale probleem is, en dat dit in ag geneem moet word in watervoorsieningstrategiee vir sulke gebiede. Dit benadruk ook dat atmosferiese vog 'n bruikbare alternatiewe bron van varswater kan wees in sekere areas, waar dit dikwels verskeie male meer is as reenval, en gesien behoort te word as 'n belangrike aspek in strategiee om waterprobleme in hierdie gebiede aan te spreek. Die studie beveel sterk aan dat wetenskaplikes, ingenieurs en waterbestuurders in hierdie gebiede altyd die beskikbare geleenthede soos klimaatstoestande (bv. misneerslag) en aanpassings vir vogvangslbewaring wat voorkom by inheemse plante en diere sal navors om sodoende onderhoudbare oplossings vir die probleem te vind. Hulle behoort deurlopend op hoogte te bly met ontwikkelings/geleenthede wat ontstaan in die wyer waterindustrie, wat van waarde kan wees in by waterverskaffmgsinisiatiewe vir afgelee gebiede in ontwikkelende lande. Laastens dien die studie om 'n beter begrip daar te stel van die aard van grondwatersoutvlakke in waterarm gebiede wat afhanklik is van seisoenale oppervlaktevloei vir watervoorsiening sowel as om 'n bydrae te lewer tot die formuleer van oplossings tot die probleem in hierdie gebiede, veral in die hiperdroe omgewings aan die Namibiese weskus, waar konvensionele waterbronne mees onvoldoende is. Dit benadruk ook die rol van materiaalkundige wetenskappe (polimere) en omgewingsingenieurswese sowel as die UNESCO-geassosieerde wetenskaplike instellings in die formulering van volhoubare oplossings vir sommige van die huidige waterprobleme in waterann gebiede. Sleutelwoorde: Waterarm gebiede, hidrochemie, bronne van varswater, ontsouting, atmosferiese vog

Les zones humides côtières sont caractérisées par des variations spatiales, temporelles, et liées aux changements globaux, de la salinité. Ces variations de salinité peuvent influencer négativement la biodiversité très riche des zones humides côtières. C’est particulièrement le cas pour les amphibiens, caractérisés par un tégument perméable et de faibles capacités de dispersion. Si la sensibilité des amphibiens à la salinité est bien connue, elle a majoritairement été déterminée dans le cadre du salage des routes, sur des communautés qui sont naïves à l’exposition au sel. Néanmoins, les populations côtières d’amphibiens, exposées régulièrement à ces variations de salinité, devraient présenter une tolérance à ce paramètre environnemental en réponse à des processus d’adaptation locale. Nous avons examiné comment la salinisation des milieux côtiers influence l’écologie, la physiologie, le comportement et le développement des amphibiens côtiers. A tous les niveaux d’intégration (communautés, populations, individus), nous avons montré des impacts négatifs de l’exposition au sel, affectant la composition de la communauté, la distribution des individus, leur croissance, leur développement, leur physiologie et leur comportement. Cependant, les communautés, les individus adultes, et les larves, sont tous capables de résilience physiologique et comportementale au travers de mécanismes de compensation. Nos travaux ont permis une meilleure compréhension des effets des variations de la salinité sur la biodiversité des zones humides côtières, et d’apporter des pistes de gestion pour compenser les effets de ce changement global<br>Coastal wetlands are characterized by spatial, temporal, and global change-related variations in salinity. These variations in salinity can negatively impact the biodiversity of coastal wetlands. This is particularly the case for amphibians, characterized by a permeable integument and low dispersal abilities. Although amphibians’ sensitivity to salinity is well known, it has mainly been studied in the context of road de-icing salt, in communities that are naive to salt exposure. Nevertheless, coastal populations of amphibians, regularly exposed to these salinity variations, should express a higher tolerance to this environmental parameter in response to local adaptation processes. We investigated how salinization of coastal environments influences the ecology, physiology, behaviour and development of coastal amphibians. At all levels of integration (community, population, individual), we have shown negative impacts of salt exposure, affecting the composition of the community, the distribution of individuals, their growth, their development, their physiology and their behaviour. However, communities, adult individuals, and larvae all expressed physiological and behavioural resilience through compensatory mechanisms. Our work has led to a better understanding of the effects of salinity variations on coastal wetlands’ biodiversity, and to provide management options to compensate for the effects of this global change

South Africa is a semi arid country and the provision of water clean water to a steadily growing population is currently one of the major challenges facing governmental organisations. Water resources in South Africa are subject to many forms of pollution. resulting in eutrophication and salinisation. Hence, there is a need to monitor chemical and organic pollution in South African rivers. Chemical monitoring is expensive and not all the elements of water quality can be monitored and measured in a particular sample. The synergistic effects of water quality determinants cannot be demonstrated if only the chemical composition of a water resource is monitored. Biological monitoring can provide a rapid indication of water quality and at a lower cost than traditional monitoring. Organisms within a river are exposed to all water quality variables present in a system and can provide an integrated reflection of the health of their environment. Diatoms are found in all aquatic ecosystems and have demonstrable responses to many of the elements of water quality that have been identified as causing aquatic pollution. These elements include total dissolved solids, pH and plant nutrients such as nitrates and phosphates. The relationship between the structure of a given diatom community and the water quality to which the community is exposed, has lead to the development of several indices of water quality. Diatom indices of aquatic pollution have been developed in France, Belgium, Germany, Britain and Japan. Existing diatom indices have been tested for use in Finland, Poland, Britain, the Himalayas and South America. Several diatom indices were tested in this study for application in the Vaal and Wilge Rivers. The tested diatom indices correlated well with measured water quality variables such as pH and the chemical variables responsible for eutrophication and salinisation. The demonstrated correlations were comparable to those demonstrated by European authors. Several indices proved successful in indicating general water quality, namely the Biological Diatom lndex (BDI), the Specific Pollution sensitivity lndex (SPI) and the Generic Diatom lndex (GDI). The Eutrophication and Pollution lndex (EPI) successfully indicated levels of plant nutrients together with the ionic composition measured at various sites in the Vaal and Wilge Rivers. It is recommended that these indices be further tested in different regions within South Africa.<br>Thesis (M. Omgewingswetenskappe)--North-West University, Potchefstroom Campus, 2004.

L'extension d'une salinité chlorurée sodique en bas de topographie au Nord-est de la Thai1ande est un des problèmes importants pour les agriculteurs et une inquiétude pour les pouvoirs publics. Cette salinisation sodique met en danger l'agriculture et l'environnement, et dégrade les sols. Ces sols ont toujours été peu fertiles, sableux et hydromorphes, ce qui a été expliqué par le processus de ferrolyse. La salinisation et la ferrolyse, semblent les deux pédogenèses importantes pour l'évolution des sols des bas fonds. La première est une voie saline alcaline. La seconde est une voie acide. L'objectif de ce travail, est de mieux connaître l'interaction entre la sodisation et la ferrolyse, et particulièrement le rôle du sodium et du fer ferreux sur les argiles. Cette étude est menée sur une séquence de sols de rizière du bassin versant de Phra Yun au Nord-est de la Thaïlande. La recherche a été réalisée en trois étapes. La première étape est l'étude du comportement de floculation - dispersion des argiles dans des solutions sodiques et ferreuses au laboratoire. La deuxième étape est une caractérisation de l'évolution de la solution du sol in situ, au cours de la culture du riz en saison des pluies. La troisième étape est la description et l'analyse des sols de la séquence. Enfin, ces différents résultats sont confrontés et des conclusions en sont tirées. Les résultats des expériences de floculation montrent que l'effet du fer ferreux sur la floculation des argiles est identique à celui du calcium. Une concentration de 0. 67 mmol L-1 de fer ferreux suffit pour floculer les argiles quels que soient les autres cations présents. Cette concentration est fréquemment atteinte dans les sols de rizière. Le fer ferreux peut donc jouer un rôle efficace de floculant des argiles en milieu sodique. Seules les kaolinites bien cristallisées ne sont jamais dispersées. Le suivi de la solution des sols in situ montre que les argiles autre que la kaolinite bien cristallisée sont dispersées en haut de séquence et dans les horizons supérieurs des sols non rizicultivés. Les horizons médians et inférieurs restent salés ce qui permet de floculer les argiles. Les horizons supérieurs des rizières cultivées sont lessivés par la riziculture, ce qui devrait permettre la dispersion des argiles, mais généralement la molarité en fer ferreux est suffisante pour éviter la dispersion. En favorisant le lessivage et la dissolution des oxydes par réduction, la riziculture favorise a priori la réalisation de la première étape de la ferrolyse. La description des profils de sols et l'observation des circulations d'eau en saison des pluies montre un gradient textural d'amont en aval, et vertical dans les profils. Tous les profils présentent un contraste textural entre un horizon de surface très sableux et les suivants. Les profils sont plus argileux et compacts d'amont en aval. Des figures de migration d'argile sont observables dans tous les horizons. L'analyse des sols et des argiles montre une proportion étonnamment élevée de minéraux 2 : 1 pour le climat tropical de mousson de la région. La fraction argileuse est de petite taille et de grande réactivité. Les particules sont plus fines d'amont en aval, et de plus grande réactivité, la smectite devenant le type minéralogique dominant. Aucun des caractères de la ferrolyse n'apparaît. En revanche, la migration des argiles et des limons est évidente. La phase analytique permet de conclure sur la genèse des sols étudiés, qui peut être expliquée par la dispersion et le transport des particules en suspension. Ces deux mécanismes sont contrôlés par les concentrations en sodium et en fer ferreux de la solution des sols, sur lesquelles la riziculture exerce une forte influence<br>Soil salinity extension in Northeast of Thailand is a huge problem for the farmers and the Thai authorities. It endangers both the agriculture and the environment, and is cause to almost irreversible. Soil degradation. Low fertility sandy soils were however reported long time before the salinity started to spread, and explained by the ferrolysis process. Both salinization and ferrolysis seem to be the important soil genesis processes forming the lowland soils. The first process leads to alkaline soils, whilst the second leads to acid soils. This study therefore focuses on the interactions between the two processes, namely sodication and ferrolysis, and particularly on the role of sodium and ferrous iron on clay weathering. It is driven in a paddy soil sequence in Phra Yun basin, Northeast of Thailand. This work was carried out in three steps. The first step is the study of clay tlocculationdispersion behaviour in sodium and ferrous iron electrolytes in the laboratory. The second step is the in situ characterization of the soil solution compositions, during rice cropping and rainy season. The third step is the description and analysis of the soil sequence. Finally, these different results are compared and conclusions are taken. The results show that the effect of ferrous iron on the tlocculation of clay is quite identical to calcium. The flocculated clays are well-crystallized kaolinite and dispersed clay is smectite and disordered or small kaolinite. A maximum ferrous iron concentration of 0. 67 mmol L-1 is necessary to flocculate the clays whatever the other cations in the electrolyte. Such a concentration is currently reached in rice-cropped soil solution, thus suggesting that rice cropping may prevent clays to disperse. The field soil solution monitoring shows that ferrous iron concentration increase upon reductive dissolution of oxides during rainy season, and other cations are leached due to heavy rainfalls and tlooding in rice fields. Both reductive dissolution and salt leaching are enhanced by rice cropping. The clays are likely to disperse in the non cropped and non saline profiles or leached surface horizons, and to flocculate in saline deep horizons or rice-cropped and reduced surface horizons. Thus rice cropping is likely to both enhance the conditions for the fust step of ferrolysis, and balance the dispersive effect of sodium by increasing the ferrous iron content of the soil solution. The description of the soil sequence shows that the soil clay and silt content increase from top to bottom of sequence and profiles. Many clay dispersion and clay precipitation features, such as clay cutans, appear in the horizons. Clays seem to mostly accumulate in the medium, compact horizons of the bottom part of the sequence. The soil and clay analyses agree with these observations. The mean particle size continuously decreases with depth and topography. Conversely, the reactivity of the clay increases, smectite being the major clay type down the sequence. All results agree to show that ferrolysis has a limited effect in forming these soils, though they belong to soil series that are typically considered as ferrolysed. The role of ferrolysis might thus be overestimated is assessed oruy by hydromorphic conditions and profiles wit low CEC and contrasting textures. The soils of the sequence form by clay and silt translocation, which is mostly controlled by sodium and ferrous iron content in the soil solution. Rice cropping has thus a great impact on soil forming

Dans l'ouest du maroc, entre casablanca et azemmour (au sud-ouest de casablanca) s'etend sur 65 km la plaine de la chaouia cotiere. Celle-ci connait une exploitation agricole tres importante. Les eaux souterraines qui representent les seules ressources en eau de la region sont trop mineralisees (jusqu'a 10 g. L#-#1) pour l'alimentation en eau potable et pour l'irrigation. L'objectif de cette etude est donc de rechercher la ou les causes de cette salinite. L'utilisation d'un modele mathematique a differences finies cale sur deux etats hydrodynamiques en regimes permanent et transitoire nous a permis d'evaluer les parametres hydrodynamiques de l'aquifere: transmissivite et coefficient d'emmagasinement, et de realiser des simulations previsionnelles qui serviront a une gestion rationnelle des ressources en eau de la region. L'utilisation de traceurs chimiques (cl#-, br#-) et des isotopes stables (#1#8o, #2h) montre que les eaux souterraines de la chaouia cotiere sont d'origine essentiellement meteorique. La salinite elevee des eaux souterraines ne s'explique pas par le phenomene d'invasion marine qui est limite ponctuellement a quelques puits cotiers. De meme la salinisation des eaux ne peut etre due a un phenomene d'evaporation des eaux avant et durant leur infiltration ou a la dissolution de roches evaporitiques. L'essentiel de cette salinite a pour origine le lessivage des sels abandonnes dans le sol lors de la transpiration des plantes. Le tracage naturel par les isotopes radioactifs (#3h, #1#4c) des eaux souterraines de la chaouia cotiere a permis d'estimer leur temps de sejour moyen a 5020 ans. Cependant existent des eaux dont le temps de sejour moyen est superieur a 100 ans. Ces eaux suivent des cheminements plus lents dans des zones particulieres au sein de la circulation generale de la nappe, et limitees a des particularites hydrogeologiques locales. Le faible taux de renouvellement des eaux de la nappe et leur recyclage par l'irrigation favorise l'augmentation de leur charge saline

This study investigates coal discard cover soil fertility and its potential for degradation, particularly in terms of its salinisation and acidification potential. Seven rehabilitated coal discard dumps in the Witbank, Ermelo and Newcastle regions were used as study areas. All areas were rehabilitated with a cover soil layer, revegetated and annually fertilised with nitrate fertilisers, super phosphate, kraal manure and lime. Performance guideline for pH of 5.5-(6.5 i0.5)-7.5 and electrical conductivity guideline of preferably less than 200 mS.rn-' but not higher than 400 mS.m-' were set based on literature information. Soil chemical data from a three-year fertilisation programme were used to assess the fertility of the cover soil surface (0-150mm). Data collected over a three year period as well as additional electrical conductivity and pH measurements from the cover soil surface, subsoil, cover soil/coal contact zone and underlying coal itself were used to assess the occurrence of salinisation and acidification of the cover soil. The soil fertility varied significantly among dumps as well as over the three years. Results indicated an increase in ammonium acetate extractable macro elements (calcium, magnesium and potassium). With the exception of manganese, no micro-element toxicities were recorded. Iron concentrations were slightly elevated in some of the sandy cover soil layers. No increase in soluble nitrogen (nitrate and ammonium) was found and most soluble nitrogen was in the form of nitrates. In general the Bray extractable phosphate increased during the study period. It can be predicted that with the following fertiliser programme increases of exchangeable macro-elements as well as available phosphorus can be expected. The study could not indicate an increase in adsorbed or available nitrogen. Organic carbon was initially not analysed therefore no comments can be made whether organic matter increased. Four of the seven dumps surveyed had comparably similar organic carbon levels to the background samples. Overall the fertiliser programme increased the electrical conductivity and decreased the acidity of the cover soil surface. Acidity and salinity was in general not a problem at the surface of the cover soil and pH was even slightly higher in cover soil samples. The acidity and especially salinity increased at the subsoil and so did the sulphate concentrations. Calcium and magnesium sulphate were predominantly responsible for higher electrical conductivity measurements. The percentage exchangeable sodium was also predominantly less than 2% indicating that sodicity is not currently a problem in cover soil. Soil fertility was satisfactory for vegetation growth and macroelement concentrations were in the correct ratio although calcium was slightly high. An elevated sulphate concentration, in comparison to the natural grassland soils, as well as a high salinity and high acidity in the subsoil layers indicate that salinisation and acidification could deteriorate without proper management. A slightly acidic cover soil can also be attributed partially to its natural acidic pH due to the wellweathered and leach property of burrow pit. Higher than recommended salinity levels were found in subsoil samples but the occurrence of acidification of the subsoil was more dump specific. In relation to acidity and salinity guidelines only the cover soil of one dump was concerning and the larger dumps subsoil acidity and salinity were elevated. The following management strategies are proposed: a) The acidification potential, and therefore the pyrite content of the coal discard must be considered during decisions making on the rehabilitation method (clay barriers), topsoil depth, maintenance and mine closure potential. b) The occasional monitoring of the subsoil's and coal contact acidity is recommended, although not much can be done to stop acidification after cover-soil placement. c) To ensure a more sustained from of nitrogen supplementation over the long term the use of selected legumes should be investigated. Research in Europe and Australia suggested that nitrogen fixation could contribute substantially to the nitrogen for plant uptake. d) The physical properties of the topsoil (bulk density 8 soil compaction) are also being neglected and needs to be assessed occasionally and interpreted together with chemical analyses. Observations in other studies indicate that this could be the most fundamental problem for vegetation growth and not necessarily soil fertility, since soil physical properties could have a major impact on root development. Key words: Coal discard, mine rehabilitation, soil fertility, topsoil degradation, salinisation, and acidification<br>Thesis (M. Environmental Management)--North-West University, Potchefstroom Campus, 2004.

Thesis (MSc)--Stellenbosch University, 2015.<br>ENGLISH ABSTRACT: Several areas in Namaqualand are affected by elevated levels of salinity; including the shallow alluvial aquifers along the Buffels River catchment. The chemistry of rainwater that recharges these aquifers has low salt-loads, but the groundwater system is very saline. The shallow alluvial aquifers are an important source of water for several communal areas along the river both for domestic and agricultural purposes. Groundwater is also used for the copper and diamond mining activities along the river. Prior to this study, the sources of salinity to the alluvial aquifers and whether salinity can be remediated has not been determined. Possible salinity sources included seawater intrusion, evaporitic salts dissolution, concentrations by evaporation, deep aquifer brines, dissolution of minerals from the aquifer geology as well as salts from anthropogenic activities (i.e. mining). The source(s) of salinity to the groundwater has been determined using the geochemical as well as the isotopic tracers. The ratios of major ions (i.e. Na/Cl) as well the oxygen (18O), hydrogen (2H), 36Cl/Cl, and 87Sr/86Sr isotopes were used in determining the possible solute sources. In addition to these, the chloride mass balance (CMB) method was used to determine the recharge rates to the alluvial aquifers. Furthermore, the groundwater age of the alluvial aquifers was determined using the tritium (3H) isotope. The groundwater samples have high 87Sr/86Sr ratios, which are in the same ranges as the 87Sr/86Sr ratios in the surrounding granitic rocks indicating water-rock interactions. The 36Cl/Cl ratios are low and indicate the dissolution of old salts. The 18O and 2H stable isotopes of groundwater show an evaporative trend with respect to the LMWL, which indicate that groundwater has been evaporated before or during infiltration. Salinity to the shallow alluvial aquifers was found to be mainly derived from the dissolution of rock mass and concentration by evaporation process. The groundwater is relatively young, but there is mixing between old water recharged prior to bomb testing and recently recharged groundwater in some boreholes. The Chloride mass balance (CMB) method assumes atmospheric chloride is the only source of chloride to the aquifers. However, there is additional chloride to these alluvial aquifers from rock mass dissolution. The estimated recharge rates by CMB method (0.1-3.4mm/a) are therefore underestimated. A simulation model was used to determine the recharge rates based on the annual precipitation that will yield the current measured chloride concentrations in the groundwater. Recharge was found to range from 1-5% of the annual precipitation, which is also low. The CMB method therefore gives significant recharge rate estimates, but they are not accurate and need to be supported by another method.<br>AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.

Em regiões nas quais a irrigação é intensiva, visando o aumento da produção de culturas, a fertirrigação é uma prática muito utilizada como uma alternativa para a adubação, proporcionando o menor grau de risco possível. Entretanto, a aplicação excessiva de adubos, via fertirrigação, pode elevar o risco de salinização dos solos, especialmente pela aplicação indiscriminada de fertilizantes. Nem sempre as chuvas que ocorrem em campo aberto são suficientes para lavar os sais do solo. O volume de água necessário para a lavagem de recuperação de um perfil de solo é calculado em função da salinidade inicial do solo, do nível final desejado, do tipo de solo e da profundidade de solo a recuperar, do método de aplicação da água de irrigação e da concentração de sais da água de lavagem. O objetivo desse trabalho foi avaliar o desempenho de equações empíricas para recuperação de solo salinizado, em sistema de lixiviação contínua e intermitente, para o a caso de lâminas de lavagem de sais fertilizantes. O experimento foi conduzido em lisímetros tubulares com a superfície protegida com plásticos, localizados em uma área a campo aberto, pertencente às dependências do Departamento de Engenharia de Biossistemas da Escola Superior de Agricultura \"Luiz de Queiroz\" - ESALQ/USP, Piracicaba - SP. O estudo consistiu em três etapas: 1) Salinização dos solos armazenados em lisímetros tubulares de concreto, impermeabilizados em seu interior; 2) Recuperação dos solos salinizados; e 3) Medição das concentrações dos sais nos solos após o procedimento de dessalinização e comparação dessas com as previstas por fórmulas empíricas. Os tratamentos foram compostos pela combinação de dois fatores em esquema fatorial de 2x5, sendo duas formas de recuperação do solo (R1=continua e R2=intermitente) em cinco níveis inicias de salinidade no solo (S1=2,0: S2=4,0: S3=6,0: S4=8,0 e S5=10,0 dS m-1). O delineamento experimental adotado para o experimento foi o de blocos ao acaso, com 6 repetições. Tecnicamente, é possível o uso de lavagem de solos salinizados como estratégia de manejo da irrigação, sendo essa bastante satisfatória. Dentre as equações avaliadas, a que apresentou melhor performance na recuperação do solo salinizado foi a de Volobuyev, fornecendo respostas mais coerentes aos resultados obtidos experimentalmente. De maneira geral, as equações testadas foram mais eficientes no sistema de recuperação intermitente; no sistema continuo, os valores calculados para as lâminas de lavagem foram todos subestimados para condições estudadas.<br>In regions where irrigation is intensive, aimed at increasing crop production, fertigation is a practice widely used as an alternative to the fertilizing, with the lowest possible level of risk. However, the excessive application of fertilizers, via fertigation can raise the risk of salinization of soils, especially indiscriminate application of fertilizers. Not always the rains that occur in open country are enough to wash the salts from the soil. The volume of water required for washing recovery of a soil profile is calculated on the basis of initial soil salinity, final level desired, type of soil and depth of soil to recover, method of application of irrigation water and concentration of salts in the wash water. The objective of this work was to evaluate the performance of empirical equations for soil recovery in continuous and intermittent leaching system, for the determination of fertilizer salts wash blades. The experiment was conducted in lysimeters with tubular plastic-protected surface, located in an area in open field, belonging to the Department of Biosystems Engineering from Escola Superior de Agricultura \"Luiz de Queiroz-ESALQ/USP, Piracicaba - SP. The study consisted of three steps: 1) Salinisation of soils stored in lysimeters concrete tubular, waterproofed inside; 2) salinized soil recovery; and 3) measurement of concentrations of salts in the soil after the procedure of desalination and comparison of these with those provided by empirical formulas. The treatments were composed by the combination of two factors in factorial scheme of 2 x 5: two forms of recovery (R1=R2 = continuous and flashing) in five levels of salinity in the soil (S1=2.0: S2=4.0: S3=6.0: S4=8.0 and S5=10.0 dS m-1). The experimental design adopted for this experiment was random blocks with 6 repetitions. Technically, it is possible the use of salinized soils washing as irrigation management strategy, quite satisfactory. Among the equations evaluated, the best presented performance at salinized soil recovery was Volobuyev, providing coherent answers to the results obtained experimentally. In general, the equations tested were more efficient in the intermittent recovery system; the system keep the values calculated are praying all underestimated for studied conditions.

Two sites on each of four intermittent streams of differing salinities flowing through wandoo woodland were sampled to examine the effects of salinisation on the structure and function of the macroinvertebrate communities. A range of physicochemical parameters were measured and leaf packs were used to measure the rates and types of leaf decomposition in the streams…

Cette etude a pour objectif l'analyse des mecanismes de salinisation, alcalinisation et sodisation des sols irrigues. A l'echelle du profil de sol, elle vise a identifier les phenomenes hydro-geochimiques et leurs interactions et a comprendre leur evolution dans le cas des sols rizicoles de l'office du niger (mali). La demarche s'appuie sur des experimentations en milieu controle, des suivis de terrain et sur la modelisation numerique des processus. Un modele numerique mecaniste integrant les processus hydrogeochimiques selon des lois cinetiques a ete developpe en couplant un modele deterministe de transfert d'eau et de solutes et un modele geochimique integrant les processus de precipitation/dissolution des mineraux et d'echanges cationiques. Les resultats obtenus a partir d'observations faites sur un monolithe de sol en infiltration montrent l'importance de considerer les couplages entre ecoulement et processus geochimiques pour expliquer les evolutions chimiques observees dans la solution du sol. Dans ce sol structure, les echanges cationiques ont, en particulier, un fort impact sur l'evolution de la concentration des elements dans la solution du sol. Le modele numerique a ete cale a partir de ces experimentations. Les resultats du calage montrent que les evolutions des concentrations simulees et observees sont voisines mais qu'il subsiste, dans le cas des solutes reactifs, des ecarts entre les valeurs simulees et observees. Les processus d'echanges et de precipitation/dissolution de mineraux sont egalement mis en evidence dans des sols rizicoles irrigues. Les caracteristiques hydro-geochimiques de deux profils de sol ont ete suivis pendant une annee de culture. Pendant la periode de submersion, on note une forte augmentation de l'alcalinite dans la solution du sol que les seuls processus de precipitation/dissolution de mineraux et d'echanges cationiques ne suffisent pas a expliquer. L'hypothese de l'existence de processus d'oxydo-reduction influant sur la balance alcaline du sol est discutee. L'ensemble des processus geochimiques et des mecanismes de transfert est alors etudie au regard des pratiques d'irrigation de ces sols.

Pour aborder la complexité de la relation agriculture-environnement, un modèle économique est couplé à un modèle biophysique. Le modèle bio-économique ainsi conçu pour une région semi-aride nous a permis de tirer des riches enseignements. Sur le plan empirique, la simulation des formules tarifaires binômes de l'eau a mis en exergue les conflits d'intérêts entre des agriculteurs cherchant à maximiser leurs revenus et un gestionnaire de la ressource en eau soucieux d'améliorer la couverture de ses charges. Alors que la simulation des politiques environnementales a mis en évidence que aucun effort de dépollution n'est envisageable sans que cela engendre une perte de revenu des exploitants. Sur le plan théorique, nous démontrons que la fonction d'externalité est désormais non-convexe et risque ainsi de compromettre l'efficacité de certaines politiques environnementales. Dans ce cas, l'éco-conditionnalité liée à la rotation des cultures paraît une piste intéressante à explorer.

Dans le cadre de la stratégie tunisienne d’optimisation de la réutilisation des eaux usées traitées (EUT), plusieurs périmètres agricoles irrigués ont été créés. Le risque de l’irrigation des cultures par les EUT dépend d'une part, de la qualité des EUT et d'autre part, de la nature de la couverture pédologique et des pratiques culturales (type et rotation des cultures). L’objectif de ce travail est d’évaluer l'impact de cette irrigation sur les sols et les plantes dans le périmètre d'El Hajeb, réutilisant les EUT de la STEP de Sfax depuis 1989. Deux types de sols bien représentés dans le périmètre ont été étudiés : un calcisol isohumique et un fluvisol calcique. Des analyses physicochimiques et pédologiques ainsi qu'un bilan géochimique des éléments majeurs et métalliques (EM) ont été faits pour les deux types de sol. Les plantes échantillonnées sur les deux sites sont de deux types; fourragères (sorgho et luzerne) et pérennes (oliviers). Elles ont été caractérisées par leurs contenus en éléments majeurs et métalliques. L’irrigation par les EUT a affecté les deux types de sols de différentes manières. Cependant, dans les deux cas, on note un effet de salinisation. Au niveau du calcisol (parcelle OTD) irrigué depuis 15 ans, l’impact négatif de la salinisation est tamponné par le fait qu’il soit bien drainant. Pour le fluvisol (parcelle BZ) à texture lourde et irrigué depuis 4 ans seulement, la salinisation est plus marquée et l'ESP atteint même le niveau critique de 15%. Si cette augmentation de salinité n'a pas affecté, jusqu'à présent, les rendements des cultures, elle a, par contre, déjà inhibée la décomposition de la MO. Pour les deux types de sols, la mobilité verticale des éléments métalliques (EM), que ce soit en terme de migration en profondeur ou de transfert vers les plantes, est relativement faible et se limite aux horizons de surface des sols. Il reste difficile de discerner les apports anthropiques du fond géochimique naturel en éléments métalliques. En se limitant à l’étude du niveau de surface du calcisol (cinq premiers centimètres), il s'avère que la variabilité latérale des EM s’explique par l'orientation du système d'irrigation appliqué (submersion à la raie). La biodisponibilité des EM est gouvernée par le taux de MO dans le sol et la distance par rapport au canal d'arrivée des EUT. Le taux d’éléments métalliques absorbés par les deux plantes fourragères dépend principalement du type de plante alors que les accumulations des éléments métalliques dans les feuilles d'oliviers sont statistiquement non significatives<br>In the framework of Tunisian strategy for optimizing the treated wastewater reuse (TW), several irrigated agricultural areas have been created. The risk of TW crop irrigation depends on the one hand, to the TW quality and on the other hand, to the soil type and agricultural practices (type and crop rotation). In the El Hajeb area, TW deriving from the Sfax wastewater treatment plant is reused since 1989. The aim of this work is to evaluate the impact of the TW irrigation on soil and plants. Two soil types were analyzed for they cover the main study area: isohumic calcisol and calcic fluvisol irrigated respectively over 15 and 4 years. Several parameters have been characterized in the studied soils: physicochemical proprieties, geochemistry, major and metallic elements (ME). For both soil sites, two plants types have been sampled; forages plants (sorghum and alfalfa) and perennial plants (olives tree). Contents in major and metallic elements were also analyzed in the Plants samples. TW irrigation has affected both studied soils in different manners. However, in both cases the salinity has been increased. At the calcisol (OTD site), the negative impact of the salinity increase is buffered by the good permeability. For the clayey textured fluvisol (BZ site) irrigated for only 4 years, the salinity increase is more pronounced and the ESP reached the critical level of 15%. If this salinity increase has not affected crop yields by present, it has already inhibited SOM decomposition. For both soil types, the metallic elements (ME) mobility, both in terms of migration with depth or of transfer to the plants, is relatively low and limited to surface soil level. It remains difficult to discern the anthropogenic inputs from natural background of metallic elements. Limiting the study to the surface soil layer only (0-5 cm), it appears that the lateral variability of ME was induced by the irrigation system orientation (surface furrows). Whereas, the ME bioavailability is governed by the SOM level and the distance from the inlet of TW channel. Finally, determination of the rate of ME accumulation in tissues of two forages (alfalfa and sorghum), has shown that the metal uptake level depends mainly on the plant type. While, accumulations of metallic elements in leaves of olive trees are not significant to a statistical point of view

Variable groundwater quality in complex aquifer-aquitard systems presents a challenge for sustainable groundwater development. In the Lower Murrumbidgee alluvial fan of the Murray-Darling Basin in semi arid inland Australia, shallow groundwater is saline (12000 &micro S/cm) and locally contaminated by nitrate. Deep fresh aquifers (150 &micro S/cm), developed as an irrigation water supply, were thought to be protected from downwards leakage by laterally extensive aquitards. However, hydrochemical sampling, augmented by historic data, revealed that aquifer salinisation (400 to 4000 &micro S/cm) had occurred at some sites to 50 m depth since the mid 1980s. Aquitard windows, landscape depositional features at a scale of 10s to 100s of metres which are rarely detected by conventional investigations, were proposed as conduits for rapid downwards leakage in stressed systems. Intensive research was conducted at the Tubbo site where downhole geophysical logging and minimally disturbed cores were used to describe a saline clayey silt to 15m depth, an indurated clayey sand and 2 deep deposits of hard clayey silt. Fracturing was inferred by the scale dependency of aquitard permeability (Kv 10E-11 to 10E-6 m/s). Lithological variation near the surface was delineated by electrical imaging which revealed a 40m wide aquitard window beneath a veneer of smectite clay. Intensive monitoring of groundwater pressures in six piezometers (23-96 m depth) near the Tubbo irrigation bore and two other peizometers upgradient, indicated that the indurated clayey sand formed an effective hydraulic barrier but the deep silty deposits were spatially discontinuous. Groundwater samples were collected before, three times during, and after the 1998-99 irrigation season. A large, but delayed TDS increase occurred in the shallow aquifer and small pulses of saline water were sustained in the middle aquifer but shortlived in the deep aquifer. Hydrochemical and isotopic data dC-13, dH-2, dO-18, C-14 and H-3) showed the middle aquifer mixing with the deep aquifer, though retaining the signature of a palaeowater. Hydrochemical changes were accounted for with PHREEQC inverse mass balance models for the shallow aquifer. Mixing of aquifer water with 20-70% saline porewater from the upper aquitard occurred, together with ion exchange and NaCl dissolution. Based on an axisymmetric radial FEFLOW model, 5-30% of the volume pumped was accounted for by vertical leakage from the middle aquifer. Leakage from the shallow aquifer was small but significant, as it allowed high salinity water to migrate. Permeability and compressible storage measurements (Ss 10E-5 to 10E-4 /m) were used to constrain model calibration, and to show that direct mixing occurred mainly via aquitard windows at depth, and between the shallow and middle aquifers via leaky boreholes. Fracture flow and aquifer-aquitard interaction by diffusion were of secondary importance.

Ce bassin HELP-UNESCO situé en zone semi-aride à régime de mousson est représentatif des zones densément peuplées où des problèmes de réduction de la quantité et de forte minéralisation des eaux souterraines sont identifiés. Ses aquifères sont fortement sollicités pour l'irrigation depuis 1970 aux dépens des systèmes d'irrigation traditionnels. Après avoir validé et complété une base de données géoréférencées notre travail a permis de : caractériser le fonctionnement hydrologique, quantifier le terme de recharge vers les aquifères, quantifier le système aquifère multicouche, retracer son évolution depuis sa mise en exploitation (1950-2006). La pérennité de la ressource en eau est gravement menacée, notamment par une intrusion saline qui pourrait en quelques mois envahir la moitié de l'aquifère. Son arrivée aurait été jusqu'à présent retardée en raison de l'existence d'une poche d'eau douce "offshore". Il est donc urgent de mettre en place une gestion rationnelle des ressources en douce sur ce bassin.

The distribution pattern of diatoms from lakes and streams of varying salinity in the south-west of Western Australia was investigated. A total of 95 water bodies were sampled and separated into freshwater (<3 ppt), hyposaline (3-20 ppt), mesosaline (20-50 ppt) and hypersaline (>50 ppt). The south-west and specifically the inland wheatbelt region has been severely influenced by secondary salinisation, due to clearing of native vegetation for agriculture. There has been little research on diatom communities from salt-affected systems, with this data providing the basis for the development of an inference model based on species optima and tolerance limits to salinity.Physico-chemical variables measured from the study sites were collated and assessed. Salinity ranged from freshwater (0.04) to hypersaline (156.80 ppt), and pH ranged from acidic (2.90) to alkaline (10.51). Dissolved oxygen levels were recorded from 1.11 to 18.67 mgL[superscript]-1, water temperature from 6.30 to 28.10 ºC and peripheral vegetation scores from 1 (little or no cover) to 5 (dense cover). Analysis of variance (ANOVA) showed that salinities were significantly higher in standing waters located further inland, compared to flowing waters in high rainfall areas. Hypersaline wetlands displayed significantly lower dissolved oxygen levels, higher water temperatures and reduced peripheral vegetation, compared to freshwaters. The pH of hypersaline sites was also significantly lower, associated with surrounding land use or underlying geology. The data collected provides important baseline information, with implications for aquatic biota.The community structure of diatoms in relation to varying salinity concentration was explored. An artificial substrate collector (JJ periphytometer) was used to standardise sampling and ensure diatom assemblages were representative of ambient water quality. A total of 217 taxa were identified with the highest diversity observed in freshwater sites (up to 33 species), and limited to less than 15 in hypersaline waters. According to BIOENV, salinity was the key factor influencing diatom community structure. SIMPER analysis found a number of discriminating taxa between salinity ranges, specifically between assemblages from freshwater and hypersaline sites. Taxa such as Achnanthidium minutissimum and Gomphonema parvulum were indicative of freshwaters. In comparison, Amphora coffeaeformis and Nitzschia ovalis were associated with hypersaline water bodies.Diatom community structure was also examined from 20 hypersaline wetlands in the wheatbelt region with varying pH. Characteristic taxa including Amphora coffeaeformis, Hantzschia sp. aff. baltica and Nitzschia ovalis showed a wide tolerance to salinity and pH, or hypersaline acidic conditions. BIOENV analysis found there were no observable differences between diatom assemblages in relation to salinities above 50 ppt and that pH was highly correlated to species composition. The increasing occurrence of acid saline lakes is of concern and is most likely attributable to deep drainage practices and continued use of fertilisers in agricultural areas.A diatom-based transfer function was developed from the south-west dataset, to document species optima and tolerance limits to salinity. CCA analysis showed that salinity accounted for a significant and independent amount of variation in the diatom data enabling an inference model to be derived. The most successful model was generated using tolerance-downweighted weighted averaging, with a high coefficient of determination and low prediction errors that remained high after jackknifing. The optima of freshwater diatoms were similar to those reported from other regions of the world, although the optima of hypersaline species tended to be higher. Comparatively, the model performed very well, with the potential to be applied in future paleolimnological studies.In conclusion, this study has shown diatoms to be effective biomonitoring tools, providing the basis for future sampling strategies that assess the biodiversity of salt-affected water bodies in Western Australia. Potential indicator species from different salinity ranges were identified and the sensitivity of diatoms allowed for the development of a statistically robust inference model for the south-west. The reported optima and tolerance limits of important taxa may be further explored to evaluate the success of remediation measures implemented for secondary salinised systems in this region.

Dans ce travail, on expose les résultats concernant trois aquifères alluviaux (Tuban, Bana et Hadramoute) en République Démocratique Populaire du Yémen, sous climat aride et semi-aride. Cette étude a pour objet l'investigation des eaux des nappes libres, à partir des données hydrochimiques et isotopiques. L'interprétation de ces données apporte des éléments de réponses relatifs sur -L'origine et l'évolution de la salinité des eaux souterraines dans les nappes considérées. La minéralisation est essentiellement due à la dissolution. -Les conditions de recharge des eaux souterraines et l'effet éventuel de l'évaporation. Homogénéisation efficace des apports successifs dans les systèmes Faible évaporation. - Le temps de transit de l'eau souterraine Des apports par des eaux plus anciennes (nappe des grès) expliquent le vieillissement "apparent" le long de la vallée de l'Hadramoute. Un système de type multicouches à perméabilité variable jouerait le même rôle sur le transfert de l'eau (Tuban et Bana).

L’organisation géomorphologique actuelle du Bassin de Kairouan (Tunisie centrale) commande le fonctionnement de nombreux processus naturels actuels comme c’est le cas du processus de la salinisation et le ruissellement diffus et concentré. Mais ces processus ne dépendent pas seulement de la géomorphologie : le climat et les activités humaines interviennent aussi. Ce travail essaye tout d’abord de comprendre les processus actuels du fonctionnement géomorphogénique du Bassin de Kairouan, puis de mettre en évidence l’impact de la structuration géomorphologique du fonctionnement des milieux et du développement agricole sur le développement de la salinité et enfin d’évaluer la vulnérabilité à l’érosion, partiellement en relation avec la salinité, le risque de ruissellements et les caractéristiques topographiques. La méthodologie utilisée est différente en fonction de la thématique, pour l’organisation géomorphologique du Bassin de Kairouan, la méthodologie consiste à utiliser les cartes topographiques, des cartes géologiques et l’imagerie satellitaire afin de créer une carte géomorphologique, un MNT et une carte des pentes. Pour cartographier l’extension actuelle de la salinité dans les plaines alluviales de Kairouan, la méthodologie utilisée est fondée sur l’utilisation simultanée d’une image Landsat ETM acquise le 08 février 2001, des données de terrain, des mesures de la salinité et des données géomorphologiques. Il ressort de cette application que les séquences géomorphologiques effectuées en fonction de l’organisation spatio-temporelle des modelés indiquent des taux de sel élevées dans les formations superficielles des alluvions actuelles, un très léger taux de salinité dans les formations alluviales des cônes d’épandage holocène et une absence de salinité dans les formations superficielles de matériaux pléistocènes. Il existe également un enrichissement en sel vers la profondeur dans les modelés pléistocènes et holocènes. La méthodologie pour définir les aires sensibles au risque érosif agricole dans le Bassin de Kairouan consiste à déterminer premièrement les grandes unités texturales des formations superficielles à partir de notre carte géomorphologique en nous appuyant également sur les résultats d’analyses granulométriques. La carte pédologique de Belkhodja (1970) et les travaux de Bahri (1982) ont éventuellement servi à compléter nos données. Les textures sont définies d’après le diagramme triangulaire des textures. Ces textures sont traduites en aptitude à la battance. Le dernier objectif cherche à déterminer la distribution des classes de sensibilité à l’érosion diffuse et le risque érosif en intégrant l’occupation des sols, la carte des pentes et tout l’aspect éolien et hydroéliens. Il ressort de cette étude l’importance du risque érosif agricole dans le Bassin de Kairouan. Le secteur Nord Ouest est globalement le plus exposé aux risques érosifs du fait que les parcelles de céréales et les terrains de parcours se localisent principalement sur les aires à fort et moyen risque de battance en relation avec des pentes élevées<br>The current geomorphological Basin Kairouan (Central Tunisia) controls the operation of many existing processes such as the process of salinization and diffuses runoff and concentrated. But these processes do not only depend on the geomorphology: climate and human activities also play. This work tries first to understand the processes operating géomorphogénique Basin Kairouan, then highlight the impact of the geomorphological structure of the operating environment and agricultural development on the development of salinity and assess the vulnerability to erosion, partly in relation to salinity, the risk of runoff and topography. The methodology used is different depending on the theme for the organization Geomorphologic Basin Kairouan, the methodology is to use topographic maps, geological maps and satellite imagery to create a geomorphological map, a DEM and a map slopes. To map the current expansion of salinity in the alluvial plains of Kairouan, the methodology used is based on the simultaneous use of a Landsat ETM image acquired on 08 February 2001, data from field measurements of salinity and geomorphological data. It appears from this application as the geomorphological sequences carried out according to the spatio-temporal models show rates high in salt formations superficial alluvia present a very slight rate of salinity in the alluvial formations cone spray Holocene, and a lack of salinity in the surface formations of Pleistocene materials. There is also an enrichment of salt to the depth in the modeled Pleistocene and Holocene. The methodology to identify areas susceptible to erosion risk in the agricultural basin of Kairouan is to determine the first large surface textural formations from geomorphological map drawing also on the results of granulometric analysis. The soil map of Belkhodja (1970) and the work of Bahri (1982) may have served to complement our data. The textures are based on the triangular diagram of textures. These textures are translated into the ability to battance. The latter seeks to determine the distribution of classes of sensitivity to erosion and erosion risk by integrating land use, slope map and aspect and wind hydroéliens. This study revealed the importance of agricultural erosion risk in the Basin of Kairouan. Sector North West is generally the most exposed to risk of erosion because the plots of grain and the lands are located mainly in areas with high and medium risk battance in conjunction with high slopes

Este estudo visou avaliar o contributo da sementeira direta (SD) e de culturas de cobertura (CC) durante o Inverno na atenuação do risco de salinização/sodização do solo, em solos com má drenagem interna, perspetivando o aumento de regadio proporcionado pelo Alqueva. O aumento da estabilidade estrutural do solo e a redução da evaporação direta que a SD e as CC normalmente atribuídas a este sistema proporcionam, poderão contribuir para uma menor acumulação de sais no solo durante o verão e uma maior lavagem durante o inverno. Para testar a hipótese de trabalho instalou-se um ensaio com dois sistemas de preparação do solo: sementeira direta sobre cultura de cobertura (SD/CC) e o sistema convencional (SC) (chisel e grade de discos), subdivididos em dois regimes hídricos e em dois níveis de salinidade da água de rega (respetivamente 0,7 dS m-1 e 2,0 dS m-1), com uma razão de adsorção de sódio (SAR) de 3. Ao contrário do esperado a CC mostrou uma tendência para aumentar o teor de sais no outono-inverno por redução da fracção disponível para a lavagem, mas evidenciaram-se as suas vantagens na proteção da estrutura superficial do solo e na capacidade de impor ciclos de secagem, contrariando a tendência do solo permanecer sempre húmido em regadio. O fator mais importante foi a salinidade da água de rega, comprovando que a qualidade da água é determinante na sustentabilidade do regadio na área de influência de Alqueva. A utilização da rega com teores moderados de sais (CE de 0,7 dS m-1) mostrou riscos de salinização do solo na sequência de outono-invernos secos. A SD aumentou significativamente o teor de matéria orgânica e poderá ter proporcionado uma melhoria na estrutura do solo, que poderá explicar a tendência de uma maior lavagem de sais de outono-inverno, nos dois anos de pousio, seguintes ao ensaio; Direct Drilling and cover crops on soil salinity control in irrigated crops ABSTRACT: This study aims to evaluate the contribution of no-till (SD) and cover crops (CC) during winter in mitigating the risk of salinity/sodicity of the soil, in soils with poor internal drainage in irrigated area under the influence of Alqueva. The increased soil structural stability and the reduction of direct evaporation that SD and CC should allow, may contribute to a lower accumulation of salts in the soil during the summer and to increase the leaching of excess salts during the winter. To test the working hypotheses it was installed an experiment with two tillage systems - No-till associated to a winter cover crop (SD/CC) and conventional system (SC) (chisel plow plus and disc harrows ), divided into two water regimes and two levels of water salinity (respectively 0.7 dS m-1 and 2.0 dS m-1), with a adsorption sodium ratio (SAR) 3. Contrary to expectations CC showed a tendency to increase the salt content of the soil during the period of fall-winter, but showed advantages in protecting the structure of soil surface and the ability to impose drying cycles, contrary to the soil trend to always remain wet when irrigated. The most important factor was the salinity of irrigation water, indicating that water quality is crucial for the sustainability of irrigation in the area of influence of Alqueva. Irrigation water with moderate levels of salt (CE 0.7 dS m-1) showed a risk of soil salinization when the following autumn-winter was dry. The SD/CC significantly increased the organic matter content and may have provided an improvement in soil structure that could explain the faster leaching of salts from the soil during autumn winter period, in the two years after the experiment when the soil was left under fallow.

The distribution pattern of diatoms from lakes and streams of varying salinity in the south-west of Western Australia was investigated. A total of 95 water bodies were sampled and separated into freshwater (<3 ppt), hyposaline (3-20 ppt), mesosaline (20-50 ppt) and hypersaline (>50 ppt). The south-west and specifically the inland wheatbelt region has been severely influenced by secondary salinisation, due to clearing of native vegetation for agriculture. There has been little research on diatom communities from salt-affected systems, with this data providing the basis for the development of an inference model based on species optima and tolerance limits to salinity. Physico-chemical variables measured from the study sites were collated and assessed. Salinity ranged from freshwater (0.04) to hypersaline (156.80 ppt), and pH ranged from acidic (2.90) to alkaline (10.51). Dissolved oxygen levels were recorded from 1.11 to 18.67 mgL-1, water temperature from 6.30 to 28.10 °C and peripheral vegetation scores from 1 (little or no cover) to 5 (dense cover). Analysis of variance (ANOVA) showed that salinities were significantly higher in standing waters located further inland, compared to flowing waters in high rainfall areas. Hypersaline wetlands displayed significantly lower dissolved oxygen levels, higher water temperatures and reduced peripheral vegetation, compared to freshwaters. The pH of hypersaline sites was also significantly lower, associated with surrounding land use or underlying geology. The data collected provides important baseline information, with implications for aquatic biota.<br>The community structure of diatoms in relation to varying salinity concentration was explored. An artificial substrate collector (JJ periphytometer) was used to standardise sampling and ensure diatom assemblages were representative of ambient water quality. A total of 217 taxa were identified with the highest diversity observed in freshwater sites (up to 33 species), and limited to less than 15 in hypersaline waters. According to BIOENV, salinity was the key factor influencing diatom community structure. SIMPER analysis found a number of discriminating taxa between salinity ranges, specifically between assemblages from freshwater and hypersaline sites. Taxa such as Achnanthidium minutissimum and Gomphonema parvulum were indicative of freshwaters. In comparison, Amphora coffeaeformis and Nitzschia ovalis were associated with hypersaline water bodies. Diatom community structure was also examined from 20 hypersaline wetlands in the wheatbelt region with varying pH. Characteristic taxa including Amphora coffeaeformis, Hantzschia sp. aff. baltica and Nitzschia ovalis showed a wide tolerance to salinity and pH, or hypersaline acidic conditions. BIOENV analysis found there were no observable differences between diatom assemblages in relation to salinities above 50 ppt and that pH was highly correlated to species composition. The increasing occurrence of acid saline lakes is of concern and is most likely attributable to deep drainage practices and continued use of fertilisers in agricultural areas.<br>A diatom-based transfer function was developed from the south-west dataset, to document species optima and tolerance limits to salinity. CCA analysis showed that salinity accounted for a significant and independent amount of variation in the diatom data enabling an inference model to be derived. The most successful model was generated using tolerance-downweighted weighted averaging, with a high coefficient of determination and low prediction errors that remained high after jackknifing. The optima of freshwater diatoms were similar to those reported from other regions of the world, although the optima of hypersaline species tended to be higher. Comparatively, the model performed very well, with the potential to be applied in future paleolimnological studies. In conclusion, this study has shown diatoms to be effective biomonitoring tools, providing the basis for future sampling strategies that assess the biodiversity of salt-affected water bodies in Western Australia. Potential indicator species from different salinity ranges were identified and the sensitivity of diatoms allowed for the development of a statistically robust inference model for the south-west. The reported optima and tolerance limits of important taxa may be further explored to evaluate the success of remediation measures implemented for secondary salinised systems in this region.

Exotic pine plantations are a major landuse within the coastal lowlands of southeast Queensland, extending from close to the shoreline to the hinterland ranges. These plantations are within a sub-tropical climatic zone, and in most years, the summers are appreciably wetter than the winters. This terrain, in general, has been highly weathered and the soils are poor in nutrients. Environmental factors such as the climate, topography and weathering profile (including soil) are found to be important controls on vadose zone hydrology, which, in turn, has a great impact on tree growth and consequently on the design of management practices. This research project takes a holistic approach to investigate the influence of these environmental factors at different scales, and is designed to fulfil the following objectives: (1) To build a spatial model of forest productivity for the entire Tuan Toolara State Forest (TTSF), southeast Queensland, by analysing the spatial patterns of many environmental variables that may have controls on soil water distribution. (2) To determine how some of these environmental factors are responsible for the development of water-logging and soil salinisation by examining in detail an area of low site index that is severely affected by these two processes. (3) To develop a model to assess the risks of water-logging spatially and temporally. A multiple regression model was constructed to predict the forest productivity (measured by the value of site index, the average dominant tree height at 25 years of age). The independent variables were derived from a digital elevation model (elevation, slope, curvature, hillshade, flow accumulation and distance to streams), γ-ray spectrometry (potassium, thorium and uranium), and interpolated rainfall. The model explained up to 60% of the variance in the site indices and produced predictive maps of site index for two species: P. elliottii Engelm. and Queensland hybrid, a P. elliottii × P. caribaea Morelet hybrid. The model also identified the lowest site index area at the northern Tuan State Forest (NTSF), likely due to a greater risk of water-logging and salinisation. The NTSF area is of low relief and, therefore, the focus has been on the vertical controls of deep weathering profile. The methodology included setting up a network of groundwater bores screened at different depths within the weathering profile, characterising the profile (mineralogy, EC, and pH) and the groundwaters within it (water levels, physico-chemical parameters, major and minor ions). It is found that water-logging is caused by perched groundwater formed on top of the ferricrete or mottled saprolite after prolonged rainfall. Localised salinisation is related to the discharge of brackish groundwater occurring within the mottled saprolite. The deep aquifer within the coarse saprolite is fresh and not responsible for salinisation, a situation that differs from many other settings in Australia. The ability of using the Soil and Water Assessment Tool (SWAT) computer model to simulate soil water balance and to assess the risks of water-logging was tested in a selected catchment in the TTSF. The model successfully simulated stream flow at 2 weirs for a period of 6 years; the achieved R2 were 0.752 and 0.858, respectively. Long-term simulation for a 30-year period showed that there are pronounced seasonal patterns in rainfall and evapotranspiration as well as in soil water. For mature plantation with slopes of 3-15%, the mean annual duration of water-logging ranged from 161 days in the humus podzols, to 110 days in the gleyed podzolic, and to 90 days in the yellow podzolics. The outcomes of this research suggest that forest management can be strongly supported by understanding the impacts of these environmental factors (e.g. climate, topography and weathering profile) on vadose zone hydrological processes; the selection of optimum approach will depend on the research objective or purpose. The models and analytical tools that were developed or tested here have the potential to be successfully applied elsewhere if the input data are available.

Exotic pine plantations are a major landuse within the coastal lowlands of southeast Queensland, extending from close to the shoreline to the hinterland ranges. These plantations are within a sub-tropical climatic zone, and in most years, the summers are appreciably wetter than the winters. This terrain, in general, has been highly weathered and the soils are poor in nutrients. Environmental factors such as the climate, topography and weathering profile (including soil) are found to be important controls on vadose zone hydrology, which, in turn, has a great impact on tree growth and consequently on the design of management practices. This research project takes a holistic approach to investigate the influence of these environmental factors at different scales, and is designed to fulfil the following objectives: (1) To build a spatial model of forest productivity for the entire Tuan Toolara State Forest (TTSF), southeast Queensland, by analysing the spatial patterns of many environmental variables that may have controls on soil water distribution. (2) To determine how some of these environmental factors are responsible for the development of water-logging and soil salinisation by examining in detail an area of low site index that is severely affected by these two processes. (3) To develop a model to assess the risks of water-logging spatially and temporally. A multiple regression model was constructed to predict the forest productivity (measured by the value of site index, the average dominant tree height at 25 years of age). The independent variables were derived from a digital elevation model (elevation, slope, curvature, hillshade, flow accumulation and distance to streams), γ-ray spectrometry (potassium, thorium and uranium), and interpolated rainfall. The model explained up to 60% of the variance in the site indices and produced predictive maps of site index for two species: P. elliottii Engelm. and Queensland hybrid, a P. elliottii × P. caribaea Morelet hybrid. The model also identified the lowest site index area at the northern Tuan State Forest (NTSF), likely due to a greater risk of water-logging and salinisation. The NTSF area is of low relief and, therefore, the focus has been on the vertical controls of deep weathering profile. The methodology included setting up a network of groundwater bores screened at different depths within the weathering profile, characterising the profile (mineralogy, EC, and pH) and the groundwaters within it (water levels, physico-chemical parameters, major and minor ions). It is found that water-logging is caused by perched groundwater formed on top of the ferricrete or mottled saprolite after prolonged rainfall. Localised salinisation is related to the discharge of brackish groundwater occurring within the mottled saprolite. The deep aquifer within the coarse saprolite is fresh and not responsible for salinisation, a situation that differs from many other settings in Australia. The ability of using the Soil and Water Assessment Tool (SWAT) computer model to simulate soil water balance and to assess the risks of water-logging was tested in a selected catchment in the TTSF. The model successfully simulated stream flow at 2 weirs for a period of 6 years; the achieved R2 were 0.752 and 0.858, respectively. Long-term simulation for a 30-year period showed that there are pronounced seasonal patterns in rainfall and evapotranspiration as well as in soil water. For mature plantation with slopes of 3-15%, the mean annual duration of water-logging ranged from 161 days in the humus podzols, to 110 days in the gleyed podzolic, and to 90 days in the yellow podzolics. The outcomes of this research suggest that forest management can be strongly supported by understanding the impacts of these environmental factors (e.g. climate, topography and weathering profile) on vadose zone hydrological processes; the selection of optimum approach will depend on the research objective or purpose. The models and analytical tools that were developed or tested here have the potential to be successfully applied elsewhere if the input data are available.

Les eaux souterraines représentent environ 98% des eaux douces potentiellement disponibles pour l'homme sur notre planète, en faisant donc une ressource fondamentale de nos sociétés. Du fait du changement climatique et du fort lien existant entre le climat et le cycle de l'eau, une préoccupation légitime est née concernant l'impact potentiel de ce changement climatique sur les ressources en eau. À ce jour, des évidences de plus en plus nombreuses appuient le fait que les modifications des conditions climatiques se répercutent sur le cycle hydrologique. L'identification de la sensibilité des eaux souterraines aux variations climatiques est donc devenue indispensable. Or, le climat est un système hautement complexe dont les variations, contrôlées par de nombreux facteurs à la fois naturels et anthropiques s'effectuent sur toutes les échelles de temps. Les modifications climatiques ne sont donc pas un phénomène nouveau, les eaux souterraines ont par conséquent subi dans le passé les effets de ces variations climatiques, elles en subissent actuellement les changements et subiront celles à venir. Les travaux développés dans cette thèse ont abordé cette problématique visant à caractériser la sensibilité de la ressource en souterraine face aux variations climatiques. À l'aide de l'analyse de traceurs environnementaux à l'échelle régionale, les impacts d'évènements climatiques majeurs intervenus sur les derniers millions d'années (transgression marine et période glaciaire) sont mis en évidence au sein du système hydrogéologique actuel. Puis, à l'aide de modélisation hydrogéologique, l'impact du changement climatique est étudié à travers les relations particulières existantes entre l'eau souterraine et les compartiments de surface et l'océan. Toutes ces études mettent en avant la sensibilité de la ressource en eau souterraine aux variations climatiques en termes de qualité (salinisation) et de quantité (baisse des niveaux d'eau). Les ressources hydrogéologiques sont particulièrement sensibles aux variations climatiques et hydrologiques (modifications de recharge, intrusions eau de mer…) ainsi qu'aux facteurs non climatiques (activités humaines). La gestion de cette ressource nécessite donc de considérer à la fois les risques climatiques et non climatiques ainsi que de prendre en compte l'adaptation à long terme de ces systèmes<br>Groundwater resources represent approximately 98% of global freshwater resources available for humans on our planet; therefore groundwater is fundamental resource of our societies. Due to climate change and strong link between climate and the cycle of water, an understandable concern is appeared about the potential impacts of climate change on water resources. Nowadays, growing body of evidence supports the fact that changes in climatic conditions (temperature, precipitation, evaporation…) impact the hydrologic cycle and consequently groundwater resources. The identification of groundwater sensibility to climate variations has become essential. The climate is a highly complex system where its variations drive by many factors both natural and human occurs on all time scales. Climatic changes are not a new phenomenon, groundwater resources have already been impacted by effects of climatic variations, are impacting presently and will be in the future. The work carried out under this thesis covered this problematic to characterize the groundwater resources sensibility to climate variations. With the help of environmental tracers analyzed at the regional scale, impacts of major climate events occurred since the last millions years (marine transgression and glacial period) have been identified in the current hydrogeologic system. Then, support by hydrogeological modeling the impact of climate change has been studied through the specific relationships between groundwater and surface water bodies and ocean. All these studies highlight the important sensibility of groundwater resources to climate variations in terms of quality (salinization) and quantity (lower water levels). Hydrogeological resources are particularly sensitive to climate and hydrological variations (recharge changes, seawater intrusion…), as well as to non-climatic factors (human activities). Thus groundwater resources management needs to consider both climatic and non-climatic risks and the long-term adaptation of these systems

Un intérêt croissant est porté aux conséquences des modifications du climat et de la température sur les milieux aquatiques continentaux. Une augmentation de la salinité des eaux est envisagée dans un contexte de changements globaux, due en particulier à l'augmentation de l'évaporation, la remonté du niveau marin et des aquifères souterraines, les changements d'occupation des sols et les processus d'érosion des bassins versants. Malgré cette perspective, le rôle de la salinité dans les écosystèmes d'eaux douces est mal connu, en particulier au niveau d'écosystèmes situés en climat tempéré. L'objectif principal de ce travail doctoral est de contribuer à une meilleure connaissance du rôle et des conséquences de l'augmentation de la salinité sur la faune des eaux. Des spécificités régionales ont permis d'étudier in situ, le rôle de la salinité dans la régulation de la biodiversité des communautés de macroinvertébrés d'une rivière, la Meurthe, présentant sur une faible distance géographique (environ 19 Km) un important gradient de salinité (0,2 à 2,6 g. L-1). La première partie de ce travail documente nos connaissances sur l'évolution des communautés de macroinvertébrés le long du gradient de salinité en terme de biodiversité et de structure mais aussi en termes de caractéristiques bio/écologiques des peuplements macrobenthiques. L'impact de la salinité a été mis en évidence à partir d'une concentration en sels supérieure à 1,4 g. L-1 avec, notament, l'installation d'espèces exotiques. Dans une seconde partie, des études aux niveaux populationnel et individuel ont permis d'expliquer les changements observés à l'échelle communautaire, notamment par l'intermédiaire de tests de tolérance à la salinité réalisés en conditions contrôlées sur 60 taxons appartenant à l'ensemble des groupes faunistiques. Plusieurs outils diagnostiques tels que l'utilisation d'habitats sentinelles et de substrats artificiels adaptés à l'étude de la salinisation ont été développés au cours de ce travail. Des investigations originales ont également été réalisées sur la possibilité d'utiliser des mesures d'asymétrie fluctuante en tant qu'indicateur d'instabilité de développement des populations naturelles soumises à un stress salin<br>One of the consequences of the climat changes and rising temperatures on continental aquatic environments will be an increase their salinity levels. This salinization process is due to multiple factors such as an increase of evaporation, a rise of the sea level and the subterranean aquifers or a change of land use and erosonial process of drainage basins. In spite of its importance, the role of the salinity in freshwater ecosystems is poorly known, in particular in temperate ecosystems. The main objective of this sudy is to improve our knowledge of the role and consequences of a rising salinity on the freshwater biota. A particular section of the Meurthe River allowed us to study on the field the role played by the salinity in the regulation of biodiversity of the macroinvertebrate community. This section of 19 Km presents a salinity gradient ranging from 0. 21 to 2. 60 g. L-1. The first part of this study document our knowledge on the change of macroinvertebrate communities along a salinity gradient in term of biodiversity and structure but also in terms of bio/ecological characteristics of macroinvertebrate assemblages. In the second part, the study is focused on the populationnal and individual scales to explain the observed changes in community scale, especially by using some laboratory tests of the salinity tolerance of 60 taxa belonging to all faunistic groups. From a practical point of view, we explored several bioassessment tools adapted to the study of salinization process such as the bused of sentinel substrate and artificial substrates. Some inovative investigations have also been realized on the use of fluctuating asymmetry to highlight developmental instabilities in natural population submitted to a salinity stress

La forte croissance démographique (~3%.an-1) observée au cours des dernières décennies en Afrique subsaharienne a engendré la conversion de grandes étendues de savane arborée en cultures pluviales ou irriguées et la diminution de la durée des jachères. Afin de déterminer l'impact de tels changements d'usage du sol sur la recharge des nappes phréatiques, la zone non saturée a été investiguée pendant trois ans (2009-2011) pour deux régions du Niger (sud-ouest et sud-est) aux conditions climatiques et géomorphologiques différentes.Une approche expérimentale in-situ a tout d'abord permis de caractériser qualitativement les propriétés de la zone non saturée et les flux hydriques associés (profondeur 0-10 m) pour les principaux usages du sol : savane naturelle ; jachère ; culture pluviale de mil ; et culture irriguée de poivron. Des profils granulométriques et de résistivité électrique apparente ont été réalisés et des suivis temporels de la teneur en eau et du potentiel matriciel du sol ont été mis en place. A partir des résultats et de la synthèse des données ainsi recueillies, deux analyses détaillées ont été proposées.Afin de quantifier le différentiel de recharge diffuse entre une jachère à Guiera senegalensis et une culture pluviale de mil (Pennisetum sp.) au sud-ouest Niger, une modélisation à base physique via le code Hydrus-1D a été appliquée. Dans un premier temps, une inversion basée sur la méthode GLUE a permis d'établir les densités de probabilité pour les paramètres hydrodynamiques de la zone non saturée ; dans un second temps, des simulations pluriannuelles (2 × 100 ans) du drainage profond (0-10 m) lors d'une transition jachère-mil ont été réalisées. Il a ainsi été montré que l'expansion des surfaces cultivées en mil pourrait se traduire par une augmentation du drainage profond, de 20 à 25 mm.an-1 après un délai de 35 à 60 ans.Afin d'étudier les conséquences des mises en culture pluviales et irriguées sur le potentiel de salinisation des sols et des eaux souterraines au sud-est Niger, les concentrations en ions majeurs dissous dans l'eau des pores de la zone non saturée ont été mesurées, puis comparées à la composition géochimique des apports d'eau associés (pluie, eau d'irrigation). Il a été ainsi mis en évidence que la mise en culture pluviale a un effet négligeable sur la qualité des eaux interstitielles et souterraines tandis que l'irrigation est associée à un enrichissement de l'eau de la zone non saturée en solutés qui pourrait induire, à terme, une salinisation de la nappe par lessivage des sols devenus salins/sodiques<br>In semiarid sub-Saharan Africa, the rapid population growth (~3%.yr-1) during the past few decades has resulted in land clearing and large-scale conversion from savannah and fallow to rainfed or irrigation crop fields. The traditional duration of fallow has been also shortened. In order to estimate the impact of these land use changes on groundwater recharge, the vadose zone was investigated during three years (2009-2011) for two regions located in Niger (south-west and south-east).A qualitative analysis was first carried out for identifying vadose zone properties and for characterizing the corresponding water fluxes (0-10 m depth) for the main land use types: natural savannah; fallow; rainfed millet crop; and irrigated sweet pepper crop. Grain size and electrical resistivity profiles were established and soil water content and matric potential were monitored. Based on the results of this analysis, two more detailed investigations were performed.In southwestern Niger, in order to estimate changes in diffuse recharge from a fallow with Guiera senegalensis to a rainfed millet crop (Pennisetum sp.), a physically-based modeling with Hydrus-1D code was completed. Probability density functions were first built for the soil hydraulic parameters based on the GLUE approach; then, deep drainage (0-10 m depth) was simulated for a 2 × 100 year time-period including a fallow-millet conversion. It was shown that the increase in millet crop areas could result in an increase in deep drainage from 20 to 25 mm.yr-1 after a delay of 35 to 60 years.In southeastern Niger, in order to assess the impact of rainfed and irrigated cropping development on soil and groundwater salinization, major ion concentrations in pore water of the vadose zone were measured and compared with the geochemical composition of water inputs (rainfall, irrigation). It was shown that rainfed cropping does not affect soil water and groundwater quality whereas irrigation results in an increase of solutes concentrations in soil pore water, which could lead to a groundwater salinization at mid-term through soil leaching

L'archipel de Kerkennah, situé dans le Golfe de Gabès en Tunisie, est composé d'une dizaine de petites îles dont le relief est très plat et la lithologie meuble et fragile. Les espaces les plus bas sont occupés par des sebkhas, espaces salés et stériles. L'évolution du climat et l'élévation relative du niveau de la mer ainsi que les évolutions importantes des modes de vie et de production locaux ont conduit à des changements dans l'occupation du sol. Cette thèse vise à comprendre l'évolution de la vulnérabilité liée à la mobilité du trait de côte et à la salinisation des sols depuis les années 1960. Des études diachroniques de photo-interprétation et télédétection ont été réalisées afin d'observer et mesurer l'évolution de l'occupation du sol, du trait de côte et de l'extension des surfaces de sebkhas. Il est apparu que les côtes subissent majoritairement une érosion significative (0,12m/an) et que les surfaces de sebkhas s'étendent. Ces phénomènes physiques, associés au: évolutions de l'occupation des sols et aux modes de gestion parfois peu adaptés, ont conduit à une augmentation de la vulnérabilité liée à la mobilité du trait de côte et à la salinisation des sols. Les résultats d'un questionnaire, proposé à 139 personnes, laissent penser que la population locale perçoit le retrait de la côte et la salinisation des sols comme étant des phénomènes préoccupants et dangereux. Ainsi le contexte local est plutôt cohérent avec des phénomènes dommageables réels et une population qui semble les connaître. Cependant, la gestion littorale dans l'archipel ne semble prendre en compte ni la vulnérabilité existante, ni la perception et les connaissances de la population locale<br>CThe Kerkennah archipelago, located in the Gabes Gulf in Tunisia is composed of 10 little islands with a very low landforms a soft and fragile lithology. The lowest areas are occupied by sabkha, which are sterile and salty. The climate evolution, the relative sea level rise and the important evolution in the local production mode and lifestyle caused changes in the land use. In this context, we tried to understand the evolution of vulnerability linked to the coastline mobility and to the soil salinization since the 60's. Diachronic studies of photointerpretation and remote sensing have been performed to observe and quantify the evolution of land use, of the position of the coastline and of the extension of the sebkhas. From this studies and field data, it was found that the coasts are undergoing significant erosion (0. 12m/y) and that the sabkha are extending. Those physical phenomena associated to the evolutions of land use and to management methods sometimes unadapted, conduct to the increase of the vulnerability linked to the coastline mobility and the soit salinization. The results of a survey proposed to 139 people suggest that the local population perceives the coastline retreat and the soil salinization as worrying and dangerous phenomena. So the local context is quite consistent with real damaging phenomena and a population that seems to be aware of it. However the littoral management in the archipelago doesn't seem to take into account neither the vulnerability nor the perception and the knowledge of the local population. So, even if the integrated coastal zone management is recommended in Tunisia, it is not set up in Kerkennah

La premier thématique a pour objectifs :1) de tracer l’origine de la salinité des eaux des aquifères karstiques en milieu côtier méditerranéen,2) de quantifier les proportions de mélange entre les eaux salées et les eaux karstiques,3) de discriminer les traceurs géochimiques pour identifier et modéliser les processus de salinisation d’aquifères karstiques côtiers. La seconde thématique a pour objectifs:1) d’établir les [As] d’origine naturelle des eaux de surface et des eaux souterraines, 2) de quantifier le niveau de contamination en arsenic de ces eaux et sa variabilité spatio-temporelle 3) de tracer l’origine naturelle ou anthropique de la pollution en As à l’aide d’outils isotopiques adaptés. les origines de la salinité identifié inclue i) des venues d’eaux profondes salées ii) des venues profondes d’eau salées remontant vers la surface par une faille majeure normale. Le 36Cl/Cl a permis d’identifier l’origine profonde des eaux salées et une recharge d’eau météorique infiltrée lors de la période des essais thermonucléaires. La modélisation PHREEQC permet de différentier le mélange avec une eau profonde salée de celui avec une eau de mer actuelle. Le 87Sr/86Sr montre un comportement conservatif pour tracer l’origine des eaux salées dans les aquifères karstiques. Les traceurs Cs, Rb, Li et B permettent de différentier les trois origines identifiées de la salinité. Les données acquises sur la contamination en As soulignent une augmentation nette et pérenne des [As] à partir des anciens sites de traitement minier réhabilités. Les rapports 87Sr/86Sr et δ18O et δ2H se révèlent dans ce cas un traceur très discriminant de l’origine naturelle ou anthropique de l’arsenic<br>The first theme has for objectives: 1) to trace the origin of the salinity of the waters of the karst aquifers in coastal environment mediterraneen,2) to quantify the mixing proportions between salt waters and the waters karstiques,3) to discriminate the geochemical tracers to identify and model the process of salinization of aquifers coastal karst. The second theme has for objectives:1) to establish the [hast] of natural origin of surface waters and groundwater, 2) to quantify the level of contamination by arsenic in these waters and its spatial and temporal variability 3) to trace the natural or anthropogenic origin of pollution in hast to the aid of isotopic tools adapted. the origins of the salinity identified include i) of came from deep waters salted ii) of come deep water salted dating back toward the surface by a major flaw normal. The 36Cl/Cl has allowed us to identify the origin of deep saline waters and a recharge of meteoric water infiltrated during the period of thermonuclear tests. The PHREEQC modeling used to differentiate between the mixture with a deep water of salt that one with a sea water current. The 87SR/ 86Sr shows a conservative behavior for tracing the origin of saline waters in karst aquifers. The plotters Cs, Rb, Li and B allows to differentiate the three origins identified of salinity. The data acquired on the contamination in hast underline a net increase and perennial of [hast] from the ancient sites of mining processing rehabilitated. The reports 87SR/ 86Sr and δ18O and δ2H will reveal in this case a chartplotter very discriminant of natural or anthropogenic origin of arsenic

Das übergeordnete Ziel dieser Studie ist es, die Auswirkungen des Eindringens von Salzwasser auf den Reisanbau bei unterschiedlichen Salzgehalten zu analysieren und zu untersuchen, wie Veränderungen in den Reissortenoptionen innerhalb der nördlichen zentralen Küstenregion Vietnams dazu beitragen können, diese Auswirkungen zu reduzieren. Auf Böden mit hohem Salzgehalt, die für den Reisanbau nicht mehr geeignet sind, werden geeignetere Anpassungsstrategien gefordert, indem die Präferenz der Landwirte für verschiedene Anbaufolgen und die Faktoren, die ihre Präferenzen im Zusammenspiel mit verschiedenen Salzgehaltsstufen beeinflussen, untersucht werden. Die Studie untersuchte die Auswirkungen des Salzgehalts auf den Mittelwert und die Variabilität der Reiserträge in vier Gemeinden der Provinz und untersuchte mögliche Änderungen im Portfolio der Reissorten, die Erträge zu steigern und gleichzeitig die Ertragsvariabilität zu verringern. Außerdem wurden die Auswirkungen des Salzwassereinbruchs auf die Produktivität und die technische Effizienz der Reisfarmen im Untersuchungsgebiet bewertet. Im Gegensatz zu bestehenden Studien wurden in dieser Untersuchung die Auswirkungen der Bodenversalzung analysiert. Salztolerante Reissorten können die Erträge sichern, solange der Salzgehalt moderat ist, sind aber ungeeignet, sobald der Salzgehalt hoch ist. Dies führte zur Durchführung eines dritten methodischen Ansatzes, der mit Hilfe eines Choice-Experiments Informationen über die Präferenzen und Motivationen der Reisbauern für die Wahl zwischen dem Portfolio der lokal möglichen adaptiven und transformativen Optionen generierte. Die Adoptionsergebnisse der Befragten bei verschiedenen Versalzungsgraden wurden ebenfalls simuliert. Die Ergebnisse zeigen, dass sich der Salzgehalt negativ auf die Reiserträge auswirkt, zu einer Erhöhung der Variabilität der Erträge beiträgt und die technische Effizienz von Reis in Abhängigkeit von den Reissorten verringert.<br>The overall objective of this study is to analyze the impact of saltwater intrusion on rice cultivation at different salinity levels and it also explores how changes in the rice cultivar options within the north central coastal region of Vietnam can help to reduce these impacts. In soils with high salinity levels which are no longer suitable for rice cultivation, more suitable adaptation strategies are called upon through examining farmers’ preference for different crop sequences and the factors affecting their preferences in the interaction with various levels of salinity. The study investigated impacts of salinity on mean and variability of rice yields in four communes of Thua Thien Hue Province and looked at possible changes in the portfolio of rice cultivars, which would offer farmers the potential to increase yields and decrease yield variability simultaneously. I also evaluated the impact of saltwater intrusion on the productivity and technical efficiency of rice farms in the study area. Contrasting to existing studies, this research analyzed season-differentiated impact of soil salinity. Salt tolerant rice varieties can secure yields as long as salinity levels are moderate but are inappropriate once salinity becomes severe. This led to the conduct of third methodological approach that generated information about rice farmers’ preferences and motivations for choosing among the portfolio of locally feasible adaptive and transformative options using a choice experiment. The respondents’ adoption outcomes at different salinity levels were also simulated. The results showed that salinity has negative impact on rice yields, contributes to an increase in variability of yields and reduces rice technical efficiency depending on rice varieties.