Dissertations / Theses on the topic 'Nutrient enrichment'

Nutrient enrichment of tropical waters constitutes an increasing threat to the health and biodiversity of coral reefs. In order to manage these ecosystems effectively, the onset of nutrient pollution has to be closely monitored. This thesis examined the possibility of using some physiological responses of hermatypic corals as an early-warning bio-assay, to detect nutrient enrichment before reef deterioration has taken place. To this aim, the physiology of the common branching coral Porites porites and the massive coral Montastrea annularis was studied both in the laboratory and on the reef under different nutrient conditions. By measuring the organic and inorganic productivity of corals and by constructing carbon budgets, it was hoped to relate differences in the fixation, allocation and utilisation of carbon to differences in nutrient regimes. Nubbins of Porites porites and explants of Montastrea annularis were chosen as the experimental units. Nubbins were obtained by cutting coral tips (approx. 20 mm), grounding their cut surface flat, and gluing them onto a perspex tile with cyanoacrylate glue. To obtain explants, a coral head was cored under a drill press fitted with a hole saw. Cores were then cut to fit, and sealed into polyethylene cups with underwater epoxy putty. A new culturing system was developed to grow corals successfully in the laboratory under completely controlled and repeatable conditions. This system (the 'photostat') consisted of glass aquaria (30x21x18 cm) placed in a constant temperature water-bath under metal halide lamps. The aquaria were fitted with specially designed air lines and coral trays to maintain a strong water motion around the corals, independent of the rate of water-flow. A peristaltic pump ensured a daily water turn-over. A new improved carbon budget methodology was developed by comparing the well established methods of Davies (1984) and Muscatine et al (1984) on Porites porites. These methodologies differed in the measurement of zooxanthellae respiration rate (Rz) and zoozanthellae growth rate (). Rz,DAVIES was found to be twice as small as Rz,MUSCATINE (RZ, MUSCATINE (RZ, DAVIES = 18.1 gC cm-2d-1 vs. Rz,MUSCATINE = 33.1 gC cm-2d-1), but this accounted for a difference of only 3% when Rz was expressed as a percentage of the total daily carbon input. By comparison, a 25-fold difference between methods occurred in the component of carbon required for the daily growth of the zooxanthellae. Davies' method measured the net rate of zooxanthellae growth (NET) from the increase in surface area, assuming a constant zooxanthellae population density. In this case NET was only 1.65 gC cm-2d-1.

The release of nutrients (nitrogen and phosphorus) via land clearing, application of fertilisers, discharge of human waste and combustion of fossil fuels, is one of the most harmful effects of anthropogenic stresses on aquatic environments. This study investigated the use of reeds as indicators of nutrient input to estuaries. Small estuaries such as the oligotrophic East Kleinemonde where the research was mostly conducted are sensitive to nutrient enrichment from septic tanks, stormwater runoff and fertiliser application to lawns in close proximity to the estuary. Nutrient concentrations were sampled at different positions, in the groundwater, at the water’s edge, in the reed bed and in the main estuary channel at five sites in the East Kleinemonde Estuary. The NH4+ and SRP concentrations showed a definite trend as concentrations decreased from the groundwater or water’s edge into the main estuary channel. Groundwater introduced nutrients to the estuary which were then taken up by the fringing reeds (Phragmites australis (Cavinelles) Trinius ex Steudel). The water column nutrients were either below detectable limits or in very low concentrations. Low TOxN concentrations were consistently found at the different sites and probably resulted from P. australis assimilating N-TOxN for growth more efficiently than N- NH4+. The roots, rhizomes, stems and leaves of the reeds were measured for δ15N as an indicator of nutrient enrichment as nitrogen stable isotope analysis of plant tissue is an effective method for assessing and monitoring septic tank and other anthropogenic inputs. All plant parts for the three sampling sessions at Site 1 (mouth region) in the East Kleinemonde Estuary had significantly higher δ15N signatures (~20 percent) than the leaves at Site 5 (upper reaches). These differences were related to the surrounding land-use of the East Kleinemonde catchment, where the lower part of the estuary has moderate to low residential development and the upper reaches are utilized mainly for livestock farming. The high δ15N signatures at Site 1 were attributed to septic tank wastewater and stormwater run-off entering the estuary. Nutrient enrichment also influenced the morphology of the reeds. Reed biomass, height and stem density was significantly higher at Site 1 compared to Site 5. Similar studies were conducted in August 2008 in the Sundays Estuary and October 2008 in the nearby Mtati and Mpekweni estuaries to see if the results were similar. iii The same patterns were found where the groundwater NH4+ and SRP concentrations were higher than the estuary channel in the Mtati and Mpekweni estuaries. In the Mpekweni and Sundays estuaries Phragmites australis leaves had high δ15N signatures (10 and 11 percent) similar to that of Site 1 in the East Kleinemonde Estuary. Lower signatures (-2 to +4 percent) were found in the Mtati Estuary. This sampling site was sheltered by a bridge with a steep slope and the concentrations were similar to Site 3 and 5 in the East Kleinemonde Estuary where the derived nutrient was the result of stormwater runoff or fertilisers. Density and biomass of reeds in the Sundays and East Kleinemonde (Site 1) estuaries were similar and this could be related to different nutrient sources, agricultural return flow and septic tank input respectively. Reeds in the Sundays Estuary were significantly taller than in the other estuaries which showed that factors such as shelter and salinity also influence reed growth and therefore morphology alone would not be a good indicator of nutrient enrichment. Indicators of nutrient enrichment are important as the status of temporarily open / closed estuaries in South Africa is threatened by deteriorating water quality. Measurements of the water column may provide an inaccurate assessment of water quality whereas macrophytes are outstanding potential indicators of nutrient enrichment as they are widely distributed, abundant and long-lived. The findings from this study indicate that δ15N concentrations in reeds can be used to indicate nutrient loading.

Atmospheric nitrogen deposition poses a serious threat to plant communities globally. Furthermore, nitrogen-induced shifts in plant community composition may create positive feedbacks via litter decomposition by the soil microbial community. These feedbacks could prevent the recovery of plant communities, even in the absence of further nutrient addition, because nutrient availability and cycling remain high. We investigated the role of nutrients and herbivores in regulating plant and soil microbial communities in the boreal forest understory in northwestern Canada. We used an experiment that began in 1990 where plots were fertilized, exclosed (herbivore reduction), or both, in a 2 x 2 factorial design. In early 2000, plots were divided in half; treatments were continued on one half, and discontinued on the other half. In 2009, we sampled plant community composition, along with carbon/nitrogen ratios and total phenolics in the plant tissue. Using phospholipid fatty-acid analyses and extracellular enzyme activity assays, we estimated the soil microbial community composition and activity. Lastly, we measured soil pH and chemistry. Overall, fertilization had significant impacts on the variables we measured; herbivore exclosures mostly had no detectable impacts. In fertilized plots, species richness declined and the plant community became dominated by Epilobium angustifolium and Mertensia paniculata. Total phenolics and the carbon/nitrogen in the plant tissue declined. The total microbial biomass declined, as did the ratio of fungi to bacteria, indicating a more bacteria-dominated food web in the soil. Extracellular enzymes involved in the breakdown of cellulose increased in activity, but those involved in the acquisition of nitrogen and phosphorus were mostly unaffected, except urease, which declined in activity. Soil pH declined significantly, and fertilizer increased the availability of many nutrients. In recovery plots, the results do not fit the predictions of a plant-soil feedback hypothesis. Instead, the system follows a “cascade of responses”, where soil chemistry recovers first, then plant tissue chemistry, followed more slowly by plant community composition. After 10 years, the soil microbial community has yet to show significant signs of recovery. These results highlight the sensitivity of the boreal forest to nutrient enrichment and demonstrate that recovery of these ecosystems may take decades.

Thesis (Ph. D.)--Ludwig-Maximilians-Universität München, 2005..
Title from PDF title page (viewed on May 13, 2006). Includes three articles co-authored with Sebastian Diehl. Vita. Includes bibliographical references.

This study was part of an ongoing investigation into the long-term effects of nitrogen enrichment and environmental stress on lowland heath ecology and nutrient cycling. The original experimental site, 4 replicate blocks of 2m x 1m plots, was established on pioneer-phase Calluna vulgaris - Deschampsia flexuosa heathland in 1996 (Cawley, 2000). Nitrogen treatments (0, 20, 60 & 120 kg N ha" yr") have been applied on a fortnightly basis, against a background deposition of -20 kg N ha'! yr" (NOx & NHy). During 1997 the plots were split and a six-month drought versus non-drought treatment introduced (full details in Cawley, 2000). The period of environmental stress experienced by the dominant C. vulgaris canopy was extended over the following two years (1998 & 1999) by a natural outbreak of Lochmaea suturalis. Zero-tension lysimeters were installed under the non-droughted half of these plots (2001), facilitating study of increased nitrogen deposition effects upon nitrogen losses through leaching.' A second set of experimental plots were started in 2000 to enable study of germination and establishment of D. flexuosa under conditions of increased nitrogen deposition and canopy gap creation in an otherwise closed C. vulgaris canopy. This study has shown that elevated, long-term deposition of atmospheric nitrogen in combination with periods of environmental stress can contribute to significant changes in the ecology and nutrient cycling of a lowland heath. Elevated nitrogen deposition was found to induce significant increases in: tissue nitrogen content of Calluna and Hypnum sp.; litter nitrogen content; the loss of nitrogen from the system through leaching. Additionally, there were significant reductions in the C/N ratio of both vegetation and soil. This could have major implications for changes in the rates of nitrogen mineralisation and immobilisation in this nitrogen-limited ecosystem. By 2001, few effects of the 1997 drought continued to be apparent in the heathland vegetation. However differences were recorded in the nitrogen content and C/N ratio of the soil components of the droughted and nondroughted plots. Some responses were not as expected, such as the transitory increase in the Deschampsia population. The predicted outcome, based on studies of other European lowland heaths, would have been for a marked transition to a Deschampsia-dominated canopy, especially in those high nitrogen (80N & 140N) treatment plots which had been droughted in 1997. Nitrogen deposition levels in excess of the critical load for dry heathlands (10 - 20 kg N ha" yr"), in combination with Calluna canopy opening induced by environmental stress, have been associated with such transitions in vegetation on Continental heaths. An equally unexpected outcome of this study was the significant recovery of the moss layer after the cessation of drought conditions in 1997. Again, reports from other European heaths have suggested that increased nitrogen deposition would normally be associated with a loss of bryophytes and cryptograms. Elevated nitrogen inputs, at this study site, have been associated with a reduction in bryophyte species diversity. Conversely, there has been a corresponding, significant, increase in the cover of nitrophilic Hypnum species.

Dissolved nutrient concentrations and invertebrate grazing activity regulate epiphytic biomass. Because epiphyton may limit light and carbon at leaf surfaces and the consequent productivity of submerged macrophytes, factors which influence epiphytic biomass may indirectly affect macrophyte abundance. I measured the simultaneous effects of water column nutrients (ambient or 3x ambient concentrations of nitrogen and phosphorus) and grazing (presence or absence of epifaunal community) on epiphyton and macrophytes seasonally in eelgrass (Zostera marina L.) microcosms on lower Chesapeake Bay. Grazing was more important than nutrients in controlling accrual of total epiphytic biomass, although effects on epiphytic components varied; numbers of diatoms responded to grazing, whereas numbers of cyanobacteria responded to nutrients. Numbers of heterotrophic microflagellates mimicked those of bacteria. The indirect effects of nutrients and grazing on macrophytes depended upon the relative magnitude of each factor and the physiological demands of the macrophyte. Under low grazer densities of early summer, macrophyte production (g m&\sp{lcub}-2{rcub}& d&\sp{lcub}-1{rcub}&) was reduced with grazer removal and nutrient enrichment independently. In contrast, under high densities of late summer, production was reduced by enrichment with grazers absent only. There were no macrophyte responses to treatment during the spring and fall, regardless of differences in epiphytic biomass; this may have been related to comparatively low light requirements of eelgrass at low temperatures. I used a simulation model to extrapolate microcosm results to predictions for community persistence. The model included ranges of environmental variables specific to lower Chesapeake Bay, where declines in eelgrass abundance in recent decades were correlated with nutrient enrichment, reduced grazer populations, and increased turbidity. Simulations indicated that neither nutrient enrichment nor loss of grazers alone would limit eelgrass survival, but together would cause community instability. Simulations indicated further that with grazers present, nutrient enrichment with a slight decrease in submarine irradiance would cause macrophyte loss. Measured rates of epiphytic accrual on artificial substrata in situ suggested that with grazers present, light reduction actually reduced the absolute rates of biomass accumulation despite nutrient enrichment. Predictions for macrophyte community stability must thus consider the relative effects of both direct (acting on macrophytes) and indirect (acting via epiphyton) environmental controls.

Thesis (Ph. D.) -- University of Maryland, College Park, 2006.
Thesis research directed by: Marine-Estuarine-Environmental Sciences. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Salt marshes are coastal ecosystem in the upper intertidal zone between internal water and sea and are widely spread throughout Italy, from Friuli Venezia Giulia, in the North, to Sicily, in the South. These delicate environments are threatened by eutrophication, habitat conversion (for land reclaiming or agriculture) and climate change impacts such as sea level rise. The objectives of my thesis were to: 1) analyse the distribution and biomass of the perennial native cordgrass Spartina maritima (one of the most relevant foundation species in the low intertidal saltmarsh vegetation in the study region) at 7 sites along the Northern Adriatic coast and relate it to critical environmental parameters and 2) to carry out a nutrient manipulation experiment to detect nutrient enrichment effects on S. maritima biomass and vegetation characteristics. The survey showed significant differences among sites in biological response variables - i.e., live belowground, live aboveground biomass, above:belowground (R:S) biomass ratio, % cover, average height and stem density – which were mainly related to differences in nitrate, nitrite and phosphate contents in surface water. Preliminary results from the experiment (which is still ongoing) showed so far no significant effects of nutrient enrichment on live aboveground and belowground biomass, R:S ratio, leaf %Carbon, average height, stem density and random shoot height; however, a significantly higher (P=0.018) increase in leaf %Nitrogen content in treated plots indicated that nutrient uptake had occurred.

The brackish Baltic Sea is a marginal environment for both marine and freshwater species. The rate of ecological differentiation is presumably high due to strong selection pressure from a gradient of decreasing salinity that has been present in its current state for only about 3 000 years. Even more recently, increased nutrient loading due to human activities has affected the growth rate of species, with potential effects on their competitive interactions and responses to other regulating factors. I have investigated the potential effects of low salinity and nutrient enrichment on the distributional ranges of two marine macroalgae with a wide distribution in the Baltic Sea, the red alga Ceramium tenuicorne (Kütz.) Wærn and the brown alga Fucus vesiculosus L.

A field study in the northern Baltic Sea indicated a strong relationship between the community structure of macroalgae and abiotic factors even on a small, local scale. The abiotic factors are potentially modulated by eutrophication, which may have a strong effect on the depth distribution and abundance of macroalgae. On a regional scale, laboratory experiments suggested that nutrient enrichment is unlikely to affect the distribution of Ceramium and Fucus along the salinity gradient. Growth in Ceramium from the Baltic Proper was enhanced by nitrate and phosphate, but the response did not override growth constraints due to low salinity. Ceramium from the Gulf of Bothnia had an inherently lower growth rate that was not positively affected by nitrate and phosphate increase. In Fucus vesiculosus, reproductive performance was impaired by nitrate and phosphate levels corresponding to ambient levels in eutrophicated areas of the Baltic Sea, when measured by their effect on zygote attachment, germination, and rhizoid development.

The wide distribution of Ceramium in the inner Baltic Sea is probably related to local adaptation, rather than a generalized tolerance of different salinity levels. Ecotypic differences were observed when comparing strains from the Baltic Proper (salinity 7 psu) and the Gulf of Bothnia (4 psu). A high rate of vegetative reproduction was evident, although sexual reproduction was occasionally observed in salinity 4. In Fucus vesiculosus, genetic and morphological analyses of sympatric and allopatric populations of the common, vesicular, morphotype and a dwarf morphotype, characteristic for the Gulf of Bothnia, showed that the dwarf morphotype represents a separate evolutionary lineage. Also, vegetative reproduction was observed in Fucus for the first time, as supported by genetic and experimental data.

The results show that the biota of the inner Baltic Sea may have unique adaptive and genetic properties, and that it is highly relevant to consider subspecies diversity in Baltic Sea management.

Determining the relative roles of top-down vs. bottom-up forces in controlling the structure of ecological communities is of primary importance because anthropogenic nutrient loading, overharvesting of consumers, and potential interactions of these forces are pervasively changing ecosystems throughout the world. Here I use both field experimentation and meta-analyses to investigate the role of predators in controlling community composition, the relative roles of herbivores vs. nutrient enrichment in controlling the abundance of benthic primary producers, and the influence of herbivore diversity on the community structure of coral reefs. On a coral reef in the Florida Keys, I showed that release from predation by large fishes and invertebrates via exclusion cages allowed population increases in the gorgonian-eating gastropod Cyphoma gibbosum which increased predation rates on gorgonian corals. To directly address the relative roles of top-down and bottom-up forces in controlling primary producers in benthic marine habitats, I used factorial meta-analysis of 54 field experiments that orthogonally manipulated herbivore pressure and nutrient loading to quantify the effects of consumers and nutrient enrichment on community structure. The relative effects of herbivores vs. nutrient enrichment were context dependant, varying with latitude, the type of primary producer, and the nutrient status of the system. To address the influence of herbivore diversity on the community structure of Caribbean coral reefs, I used manipulative field experiments over two years to show that a Caribbean reef changes dramatically as a function of herbivorous fish diversity. The effects of herbivore diversity on community structure were strong in both years of the experiment due to different diet preferences among herbivores. Higher herbivore diversity suppressed macroalgal abundance, increased abundance of crustose coralline algae, reduced coral mortality, and increased coral growth when compared to treatments with lower herbivore diversity. Complementary feeding by different fishes drove these patterns because macroalgae were unable to effectively deter feeding by fishes with different attack strategies. Thus, herbivore diversity appears to play an important role in the healthy function of coral reef ecosystems via complementary feeding of different herbivore species.

Thesis (M.S.) -- University of Maryland, College Park, 2008.
Thesis research directed by: Marine, Estuarine, Environmental Sciences Graduate Program. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Three coastal Oregon dunal lakes, Mercer Lake, Munsel Lake, and Woahink Lake, were studied in an effort to determine if eutrophication has occurred since initial studies were conducted in 1938 and to determine each lake's current trophic status. Data collected in 1991 and 1992 for phytoplankton primary productivity; chlorophyll gi phytoplankton species, biovolumes, and densities; nutrients; optical characteristics; and dissolved oxygen were compared with historical data sets. Additional data for zooplankton, benthic invertebrates, and other relevant limnological data were used to more completely characterize each lake. Phytoplankton primary productivity measurements indicate that biological productivity has increased at each lake since 1969-1971. Chlorophyll ~ concentrations appear to have increased only at Mercer Lake. Other limnological data are insufficient to determine if and to what extent these lakes have eutrophicated. Based on data collected in 1991 and 1992, the current trophic state of each lake can be described as follows: Mercer Lake is mesotrophic to eutrophic but closer to mesotrophic, Munsel Lake is oligotrophic to mesotrophic but closer to mesotrophic, and Woahink Lake is oligotrophic to mesotrophic but closer to oligotrophic.

Trends of increasing coastal eutrophication and atmospheric pCO2 require investigation to predict the combined effects on coral and reef condition and growth. Increases in nutrient concentrations have been observed over the past several decades in a number of reef systems, and it has been predicted that this will adversely affect coral growth rates. The species targeted by this research, Acropora cervicornis, is among the most important reef-builders in the Caribbean and has suffered widespread mortality in southern Florida. Approximately 192 branch tips were harvested from two local populations of A. cervicornis and maintained in the laboratory, where the growth rate was measured before, during, and after exposure to elevated levels of nitrate (N) (5 µM and 10 µM), phosphate (P) (2 µM and 4 µM), and/or pCO2 (CO2) (~700-800 µatm). During the control period, there was no significant difference in growth rate between the treatments, with a mean growth rate of 4.84 mg d-1. During Period 2, the first enrichment period, the largest decrease in growth rate was caused by the combined NPCO2 treatment (mean growth rate of 0.51 mg d-1). The least effect on growth rate was caused by the N treatment (mean growth rate of 4.39 mg d-1). During Period 3, the second enrichment period, the lowest growth rate was again found in the NPCO2 treatment tanks (mean growth rate of 0.03 mg d-1). The highest growth rate among the treatments was in the N treatment tanks (mean growth rate of 1.90 mg d-1), however there was no significant difference between the growth rates of the N, P, NP, CO2, NCO2, and PCO2 treated corals during this period. The mean growth rates in the Control tanks were 7.59 and 7.32 mg d-1 during Periods 2 and 3, respectively. During Period 4, the recovery period, the lowest growth rates were found in the combined NCO2 and PCO2 treatment tanks (mean growth rates of 1.00 and 1.02 mg d-1, respectively). The highest growth rate among the treatments was again observed in the N treatment tanks (mean growth rate of 2.75 mg d-1). The mean growth rate in the Control tanks was 7.40 mg d-1 during this period. The results of this study demonstrate that increased levels of nitrate, phosphate, and pCO2 cause statistically significant decreases in the growth rate of A. cervicornis. The effects of nitrate and phosphate appear to be concentration dependent, and the effect of pCO2 is greater than that of nutrification. Therefore, continued eutrophication and projected pCO2 increases can be expected to have negative impacts on the survival and reef building potential of this species.

Consumer-resource interactions are the basic building blocks of every food web. In spite of being a central research theme of longstanding interest in ecology, the mechanisms governing the stability and persistence of consumer-resource interactions are still not entirely understood. In particular, theoretical predictions on consumer-resource stability along gradients of temperature and nutrient enrichment diverge widely and are sometimes in conflict with empirical results. In this thesis I address these issues from the angle of the functional response, which describes a consumer’s feeding rate as a function of resource density. Specifically, I explore mechanistic, nutrient-based consumer-resource interaction models with respect to the influence of feeding behavior (the shape of the functional response), environmental temperature, nutrient enrichment, and resource quality on consumer-resource stability and persistence. In order to parameterize these models I performed extensive laboratory experiments with pairs of freshwater pelagic algae and grazers of the genus Daphnia, which are widespread, ecologically important model organisms. I found a sigmoidal type III functional response in every studied Daphnia-algae species pair. The exact form of its shape is described by an exponent b which is determined by fitting functional response models to the experimental data. A high value of b can stabilize consumer-resource systems under the otherwise destabilizing influence of nutrient enrichment, as predicted by a novel stability criterion relating b to the consumer’s prey handling time, food conversion efficiency and mortality. Estimated parameter values and, consequently, stability predictions are sensitive to the method of parameter estimation, and I propose a new estimation procedure that minimizes parameter uncertainty. Because many consumers’ feeding rates depend on temperature, warming is expected to strongly affect food web stability. In functional response experiments over a broad temperature gradient, I found that the attack rate coefficient and the maximum ingestion rate of Daphnia are hump-shaped functions of temperature. Moreover, the functional response exponent increases with warming towards stronger type III responses. Plugging these findings into a nutrient-based consumer-resource model, I found that predator persistence is a U-shaped function of temperature in nutrient enrichment-temperature space. Enrichment easily turns the system unstable when the consumer has a type II response, whereas a type III response opens up a large region of stability at intermediate, for the consumer optimal, temperatures. These findings reconcile seemingly conflicting results of earlier studies of temperature effects on consumer-resource dynamics, which can be mapped as special cases onto the enrichment-temperature space. I finally demonstrate the utility of three key model ingredients - temperature dependence of rate parameters, a mechanistic description of the dynamics of algal resources, and a type III functional response in Daphnia - by successfully implementing them in the description and explanation of phytoplankton-Daphnia dynamics in a mesocosm experiment exploring effects of warming on the spring succession of the plankton.

Includes bibliographical references (leaves 45-56).
Unimodal patterns of diversity along gradients of both disturbance and productivity rank amongst the most celebrated generalizations in ecology, known as the Intermediate Disturbance Hypothesis (IOH) and Productivity Diversity Hypothesis. However, doubt about their generality has arisen from studies that have failed to confirm the predicted patterns. Models suggest the interactive effects of disturbance and productivity on diversity to be responsible for the variability of diversity patterns.

Coastal communities will be most affected by global climate change and are important to study to understand current and future ecological processes. The current model for global climate change predicts a change in rainfall, which will alter the salinity of coastal systems. Given the presence of eutrophication in many coastal waters, it is important to understand the effects that this increase in nutrients, coupled with changes in salinity, will have on these communities. This study was conducted to understand the effect of salinity increase on the growth and herbivory of the black mangrove, Avicennia germinans, in the presence of increased nutrients. Explicitly, the effects of changing salinity (high, medium, and low) were coupled with fertilizer additions of nitrogen, phosphorus, both, or no fertilizer. Nutrient enrichment differentially affected the growth and herbivory of the plants between salinity zones. The medium salinity zone consistently produced the greatest increases in growth and herbivory. Added nutrients did not have an effect on growth in the low salinity zone. However, added nitrogen increased some growth variables in the medium salinity zone and added phosphorus increased some growth variables in the high salinity zone. Phosphorus also increased herbivory. The results point to diverse processes acting along the salinity gradient. There appears to be differential N- and P-limitation along the gradient. Additionally, the growth differences indicate abiotic and biotic limitations across the salinity gradient, with debilitating salinity acting in the high salinity zone and competition acting in the low salinity zone.

Nitrogen levels are predicted to rise dramatically in the coming decades as a result of increased deposition from the burning of fossil fuels and the large-scale conversion of nitrogen into a useable form for agriculture. Plant communities react strongly to increases in soil nitrogen, particularly in northern ecosystems where nitrogen levels are naturally very low. An experiment in northern Canada that began in 1990 has been investigating the effects of long-term nutrient enrichment (fertilizer addition) and release from herbivory (fencing). After 22 years of treatment, plant community composition has been substantially altered in fertilized plots, whereas exclusion of herbivores has had almost no detectable effects. I used this experiment to address two questions about the causes and consequences of long-term nitrogen enrichment in the boreal forest. In the first data chapter I focused on four understory species that had different levels of success in fertilized plots to investigate why some species are more successful than others under nutrient enrichment. I hypothesized that successful species would be taller, have higher specific leaf area, spurt earlier in the growing season and be more morphologically plastic than their less successful counterparts. I demonstrated that each of the two species that came to dominate fertilized plots has a different combination of traits and responses that likely gave them a competitive advantage; Mertensia paniculata has the highest specific leaf area of the four species, and E. angustifolium is tallest and exhibits morphological plasticity when fertilized by increasing biomass allocation to leaf tissue. In the second data chapter I assessed how increasing nitrogen levels has affected investment in sexual reproduction in four herbaceous understory species. Whereas plants in northern ecosystems reproduce mainly through clonal growth, rapidly changing environmental conditions and warmer temperatures will likely result in increased benefits of sexual reproduction. Fertilization increased the probability of flowering for Achillea millefolium and resulted in a higher allocation of biomass to flower parts for E. angustifolium but did not affect investment in reproduction for Festuca altaica or M. paniculata. Increased investment in sexual reproduction could give a competitive advantage to the former two species in the future.

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The omnivorous filter-feeding fish, Nile tilapia (Oreochromis niloticus), can have negative effects on water quality enhancing the eutrophication process. These effects depend on the nutrient enrichment level in the water. We carried out a mesocosm experiment for five weeks in a tropical man-made lake in Brazil to test ifthe effects of tilapias depend on of the level of nutrient enrichment. The experiment lasted for 5 weeks and a factorial 2x5 experimental design was used where the presence and absence of tilapias were manipulated in combination to 5 different levels of nutrient load in a total of 10 treatments. A two way repeated measure ANOVA was performed to evaluate the effects of time (t), tilapia (F), nutrients (NP) and the interactions among these factors on: chlorophyll a, water transparency, total phosphorous, total nitrogen, N:P ratio, zooplankton biomass and phytoplankton biovolume. The tilapia effect was evident, but nutrient enrichment didn t have any effect on the variables analyzed. Tilapia decreased the water transparency, total zooplankton biomass, calanoid copepod biomass, nauplii copepod biomass and cladocerans biomass. On the other hand, tilapia had no effect on phytoplankton biovolume. This lack of effect on phytoplankton is probably due to tilapia grazing that may counteract the positive effect of tilapia on phytoplankton via trophic cascades and nutrient recycling. Hence, a reduction in tilapia stock would not be an effective way to reduce phytoplankton biomass and improve water quality
A til?pia do Nilo (Oreochromis niloticus) ? um peixe on?voro filtrador que pode ter efeitos negativos sobre a qualidade da ?gua favorecendo o processo de eutrofiz??o. Esses efeitos negativos dos peixes on?voros filtradores devem ser dependentes do n?vel de enriquecimento da ?gua por nutrientes. N?s realizamos um experimento em mesocosmos por cinco semanas em um lago artificial tropical para testar se os efeitos das til?pias s?o dependentes do n?vel de enriquecimento por nutrientes. O experimento teve dura??o de 5 semanas e consistiu num delineamento fatorial 2x5 onde 2 n?veis de til?pia (presen?a e aus?ncia) foram manipulados em combina??o com 5 diferentes niveis (aportes) de nutrientes num total de 10 tratamentos.. Uma ANOVA bifatorial com medidas repetidas no tempo foi realizada para testar os efeitos do tempo (t), da til?pia (F) e do nutriente (NP) e os efeitos de suas intera??es sobre a clorofila a, transpar?ncia do disco de Secchi, concentra??o de f?sforo e nitrog?nio total e a raz?o entre eles (N:P), al?m do efeito sobre a biomassa da comunidade zooplanct?nica e o biovolume de fitopl?ncton. O efeito da til?pia foi evidente, enquanto o enriquecimento por nutrientes n?o mostrou efeito algum. Quando presente, a til?pia diminuiu a transpar?ncia do disco de Secchi e a biomassa total do zoopl?ncton, de cop?podos calan?ides, na?plios de cop?podos e de clad?ceros. Por?m, nenhum efeito foi detectado da til?pia sobre o biovolume do fitopl?ncton. Essa aus?ncia de efeito pode ser devido a herbivoria da til?pia que contrabalan?a os seus efeitos positivos via cascata tr?fica e ciclagem de nutrientes. Desta forma, uma redu??o do estoque pesqueiro de til?pias para promover uma melhoria na qualidade da ?gua n?o afetaria a biomassa fitoplanct?nica e consequentemente n?o atingiria o seu objetivo

Estuarine systems are of crucial importance to the provision of goods and services on a global scale. High human population densities in coastal systems have caused an increasing input of pollutants, of which nutrient pollution is of major concern. Increasingly, these areas are also impacted by physical disturbance, which can originate from anthropogenic sources (e.g. bait digging, shipping) or climate change causing increasingly frequent and intense storms. The individual impacts of such stressors on ecosystems have been investigated however their combined impacts have received less attention. Cumulative impacts of multiple stressors are unpredictable and will likely result in non-additive effects. Further, the effect of local environmental context on multiple stressors is a relatively understudied topic. Work in this thesis compared the combined impact of nutrient enrichment and physical disturbance in Scotland and Australia, using a series of manipulative field experiments. Results demonstrate that response to stressors is highly context dependent, varying between and within geographic locations. While the background levels of stress may vary, by comparing these two locations it is possible to comment on the adaptations and response that communities within different parts of the world display when subjected to additional stress. This study demonstrates that environmental context must be considered when implementing future management practices. Further work demonstrated that the impact of multiple stressors varies depending on how the stress is applied –whether stressors are applied simultaneously or whether there is a delay between two stressors. This study was among the first of its kind, assessing the implications of how multiple stressors react with each other given the order and intensity in which stressors were applied. Results demonstrated that systems can become sensitised to stress making them increasingly vulnerable to additional stress. Future research should be focussed on incorporating ecologically relevant scenarios of how stressors will impact estuaries while considering how environmental context will mediate impacts.

Twentieth century human settlement within the Tampa Bay watershed was linked to a dramatic mid-century decline in bay water quality and loss of seagrass acreage. Decades of direct and indirect nutrient discharges to the bay from phosphorus mining, fertilizer manufacturing, and wastewater treatment, as examples, impaired the estuary. In the past twenty years, regional stakeholders have worked to improve the bay water quality by reducing point and non-point source nutrient loading to the bay. Lakes within the Tampa Bay watershed may play an important role in attenuating the flow of nutrients into the bay. This study hypothesized that between 1990 and 2007 lake water concentrations of total phosphorus (TP) and chlorophyll-a, as well as the ratio of total nitrogen to total phosphorus (TN:TP), have changed for selected lakes in the Tampa Bay watershed. During this period, the watershed underwent a rapid shift in land use as groves and farms became shopping malls and new homes. A two-way analysis of variance (ANOVA) revealed that for 10 lakes clustered in the northern portion of the Tampa Bay watershed and classified as oligotrophic or mesotrophic, observed increases in water concentrations of TP and chlorophyll-a were statistically significant. For 6 lakes classified as hypereutrophic and scattered across the watershed, observed decreases in water TP concentrations were statistically significant, while chlorophyll-a concentrations did not change. For both groups of lakes, the TN:TP ratio declined significantly; however, oligotrophic and mesotrophic lakes were phosphorus-limited but hypereutrophic lakes were nitrogen-limited, based on this ratio. A second hypothesis of this study was that lake water concentrations of TP, total nitrogen (TN) and chlorophyll-a were lower in lakes that had more coverage of submerged aquatic vegetation, as vegetation suppresses re-suspension of sediments and is a reservoir for nitrogen and phosphorus and a surface for biofilms. The results of a one-way ANOVA showed that for 34 lakes within the Tampa Bay watershed, lakes with a greater than 20 percent volume infested by macrophytes (PVI), water concentrations of TP and chlorophyll-a but not TN were statistically lower than for lakes with a less than 20 PVI.

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O espinafre produzido e mais consumido no Brasil, denominado como espinafre da Nova Zelândia (Tetragonia expansa), difere significativamente do espinafre verdadeiro (Spinacia oleracea) produzido em muitos países do hemisfério norte. As diferenças ocorrem não apenas na classificação botânica, mas em muitas das características químicas dos vegetais. No presente trabalho, foram avaliados os teores de alguns nutrientes e antinutrientes contidos no espinafre comercializado na Bahia, sendo avaliados quatro diferentes procedimentos de digestão das amostras de espinafre com ácido nítrico em sistema aberto. Os resultados obtidos a partir dos diversos procedimentos de pré-tratamento da amostra foram comparados para os vários analitos investigados (Al, Ca, Fe, Cu, Zn, Mn, Mg) e indicaram vantagens da inserção de uma etapa de pré-digestão. Adicionalmente, foram realizados testes de extração dos metais sob investigação em água e em soluções com diferentes níveis de acidez na presença e ausência de agente quelante (ácido etilenodiaminotetracético – EDTA) para avaliação do nível de interação dos metais com o vegetal e, por conseguinte, a disponibilidade destes minerais. Os resultados levaram a acreditar que as interações de Mg(II), Cu(II) e Mn(II) com o espinafre seco eram fracas, enquanto que as interações com Al(III), Ca(II) e Fe(III) eram mais intensas, devido a condições mais drásticas (acidez da solução ou presença de quelante) foram necessárias para maximizar a extração destes metais. Ao considerar informações previamente reportadas sobre os elevados teores de oxalato em espinafre e seus efeitos antinutricionais, foram investigados os teores de oxalato em amostras secas oriundas de amostras de espinafre verdadeiro e espinafre da Nova Zelândia cultivado na Bahia, empregando permanganometria. Para tanto foram realizados estudos sobre as melhores condições para extração de oxalato variando a acidez da solução extratora e os resultados obtidos foram comparados com os apresentados na literatura. Finalmente, foram realizados testes para avaliação da possibilidade de enriquecimento de espinafre com íons metálicos a partir de sucessivas etapas de extração (dessorção) e concentração (sorção) do íon no vegetal. Pôde ser constatado que os maiores níveis de sorção (18 ± 3 mg g-1) e repetitividade foram obtidas para íons cálcio, possivelmente devido ao oxalato existente nos espinafres.
Salvador

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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
The Brazilian Northeast is the most vulnerable region to climatic variability risks. For the Brazilian semi-arid is expected a reduction in the overall rates of precipitation and an increase in the number of dry days. These changes predicted by the IPCC (2007) will intensify the rainfall and droughts period that could promote the dominance of cyanobacteria, thus affecting the water quality of reservoirs, that are most used for water supply, in the semi-arid. The aim of this study was to evaluate the effects of increasing temperature combined with nutrient enrichment on the functional structure of the phytoplankton community of a mesotrophic reservoir in the semi-arid, in the worst case scenario of climate change predicted by the IPCC (2007). Two experiments were performed, one in a rainy season and another in the dry season. In the water sampled, nutrients (nitrate and orthophosphate) were added in different concentrations. The microcosms were submitted to two different temperatures, five-year average of air temperature in the reservoir (control) and 4?C above the control temperature (warming). The results of this study showed that warming and nutrient enrichment benefited mainly the functional groups of cyanobacteria. During the rainy season it was verified the increasing biomass of small functional groups of unicellular and opportunists algae such as F (colonial green algae with mucilage) and X1 (nanoplanktonic algae of eutrophic lake systems). It was also observed an increasing in total biomass, in the richness and diversity of the community. In the dry season experiment there was a greater contribution in the relative biomass of filamentous algae, with a replacement of the group S1 (non-filamentous cyanobacteria with heterocytes) for H1 (filamentous cyanobacteria with heterocytes) in nutrient- enriched treatments. Moreover, there was also loss in total biomass, species richness and diversity of the community. The effects of temperature and nutrients manipulation on phytoplankton community of reservoir Ministro Jo?o Alves provoked changes in species richness, the diversity of the community and its functional composition, being the dry period which showed the highest susceptibility to the increase in the contribution of potentially toxic cyanobacteria with heterocytes
O Nordeste ? a regi?o do Brasil mais vulner?vel aos riscos da variabilidade clim?tica. Para o semi?rido brasileiro ? esperada uma redu??o nos ?ndices totais de precipita??o e um aumento no n?mero de dias secos. Tais mudan?as previstas pelo IPCC (2007) afetar?o a intensidade e dura??o de chuvas e secas que poder?o promover a domin?ncia de cianobact?rias, afetando assim, a qualidade da ?gua dos reservat?rios no semi?rido. O objetivo deste trabalho foi avaliar os efeitos do aumento de temperatura combinado ao enriquecimento de nutrientes sobre a estrutura funcional da comunidade fitoplanct?nica de um reservat?rio mesotr?fico no semi?rido, no cen?rio mais pessimista de mudan?as clim?ticas previstas pelo IPCC (2007). Foram realizados dois experimentos um no per?odo chuvoso e outro no seco. A ?gua coletada no reservat?rio foi enriquecida com nutrientes (nitrato e f?sforo sol?vel reativo) em diferentes concentra??es. Os microcosmos foram submetidos a duas temperaturas diferentes, controle (m?dia de cinco anos da temperatura do ar no reservat?rio) e aquecimento (4 ?C acima da temperatura controle). Os resultados deste trabalham mostraram que o aquecimento e o enriquecimento nutricional beneficiaram principalmente os grupos funcionais de cianobact?rias, mas tamb?m alguns grupos compostos por clorof?ceas. No per?odo chuvoso foi verificado o aumento da biomassa de grupos funcionais de algas oportunistas, como o F (algas verdes coloniais com mucilagem) e X1 (algas nanoplanct?nicas de sistemas eutrofizados). No experimento do per?odo chuvoso tamb?m foi averiguado um aumento na biomassa total, na riqueza e diversidade da comunidade. No per?odo seco houve uma maior contribui??o na biomassa relativa de algas filamentosas, com uma substitui??o do grupo S1 (cianobact?rias filamentosas n?o-heterocitadas) pelo H1 (cianobact?rias filamentosas heterocitadas) nos tratamentos enriquecidos. Al?m disso, ocorreu tamb?m perda na biomassa total, riqueza de esp?cies e diversidade da comunidade. Assim, efeitos da manipula??o da temperatura e/ou nutrientes sobre a comunidade fitoplanct?nica do reservat?rio Ministro Jo?o Alves provocaram mudan?as na riqueza de esp?cies, na diversidade da comunidade e na sua composi??o funcional, sendo o per?odo seco o que apresentou maior suscetibilidade ao aumento na contribui??o de cianobact?rias heterocitadas potencialmente t?xicas

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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
?The major aim of this study was to test the hypothesis that the introduction of the Nile tilapia (Oreochromis niloticus) and the enrichment with nutrients (N and P) interact synergistically to change the structure of plankton communities, increase phytoplankton biomass and decrease water transparency of a semi-arid tropical reservoir. One field experiment was performed during five weeks in twenty enclosures (8m3) to where four treatments were randomly allocated: with tilapia addition (T), with nutrients addition (NP), with tilapia and nutrients addition (T+NP) and a control treatment with no tilapia or nutrients addition (C). A two-way repeated measures ANOVA was done to test for time (t), tilapia (T) and nutrient (NP) effects and their interaction on water transparency, total phosphorus, total nitrogen, phytoplankton and zooplankton. The results show that there was no effect of nutrient addition on these variables but significant fish effects on the biomass of total zooplankton, nauplii, rotifers, cladocerans and calanoid copepods, on the biovolume of Bacillariophyta, Zygnemaphyceae and large algae (GALD ? 50 ?m) and on Secchi depth. In addition, we found significant interaction effects between tilapia and nutrients on Secchi depth and rotifers. Overall, tilapia decreased the biomass of most zooplankton taxa and large algae (diatoms) and decreased the water transparency while nutrient enrichment increased the biomass of zooplankton (rotifers) but only in the absence of tilapia. In conclusion, the influence of fish on the reservoir plankton community and water transparency was greater than that of nutrient loading. This finding suggests that biomanipulation should be a greater priority in the restoration of eutrophic reservoirs in tropical semi-arid regions
?O principal objetivo deste estudo foi testar a hip?tese de que a introdu??o da til?pia do Nilo (Oreochromis niloticus) e o enriquecimento por nutrientes (N e P) interagem sinergicamente ocasionando mudan?as na estrutura da comunidade planct?nica atrav?s do aumento da biomassa fitoplanct?nica e diminui??o da transpar?ncia da ?gua em um reservat?rio tropical do semi-?rido. Um experimento de campo foi realizado durante cinco semanas em vinte mesocosmos (8m3) nos quais quatro tratamentos foram alocados aleatoriamente: com adi??o de til?pia (T), com adi??o de nutrientes (NP), com adi??o de til?pia e nutrientes (T+NP) e um tratamento controle sem adi??o de til?pia ou nutrientes (C). Uma ANOVA bifatorial com medidas repetidas foi realizada para testar os efeitos do tempo, da til?pia (T) e dos nutrientes (NP) e seus efeitos de intera??o sobre a transpar?ncia da ?gua, f?sforo total, fitopl?ncton e zoopl?ncton. Os resultados mostraram que n?o houve efeito da adi??o de nutrientes sobre essas vari?veis mas houve um efeito significativo dos peixes sobre a biomassa do zoopl?ncton total, n?uplios, rot?feros, clad?ceros e cop?podos calan?ides, sobre o biovolume de Bacillariophyta, Zygnemaphyceae e algas de grande porte (GALD ? 50?m) e sobre a profundidade do disco de Secchi. Al?m disso, foi encontrado um efeito significativo da intera??o entre as til?pias e nutrientes sobre a profundidade do disco de Secchi e tamb?m sobre a biomassa de rot?feros. As til?pias diminu?ram a biomassa da maioria dos taxa zooplanct?nicos, das algas de grande porte e diminu?ram a transpar?ncia da ?gua, enquanto que o enriquecimento por nutrientes aumentou a biomassa do zoopl?ncton (rotiferos) mas somente na aus?ncia das til?pias. Portanto podemos concluir que a influ?ncia dos peixes sobre a comunidade planct?nica do reservat?rio e a transpar?ncia da ?gua foi maior do que o aporte por nutrientes, sugerindo assim que a biomanipula??o deve ter maior prioridade na restaura??o de reservat?rios eutrofizados em regi?es semi-?ridas tropicais

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Engenharia do Ambiente, perfil Engenharia Sanitária
Coastal eutrophication is a global problem which affects many natural systems and human activities throughout the world. The phenomenon of eutrophication has increased substantially due to human activities. It is caused by excess nutrients and is identified by the emergence of some symptoms. The proposed assessment will address this problem in a more specific way. The Assessment of Estuarine Trophic Status (ASSETS)methodology is going to be performed to two Northern Irish Loughs in order to rank their eutrophication status and allow a comparison with other existing methods. The data available for these systems allowed the implementation of this innovative methodology, which can provide a classification based on pressure, state and response. Thus, by considering the influences of anthropogenic activities over the coastal areas, examination of specific symptoms of the water systems and analyzing the indicators for future response, it is possible to achieve consistent results regarding the quality of the water in the “loughs” and, consequently, identify the most adequate tools to enable their proper management. By controlling the nutrient enrichment of coastal areas it is possible to avoid problems, such as, fish kills, interdiction of shellfish aquaculture, loss or degradation of sea grass beds and smothering of bivalves and other benthic organisms. As a result, many social and economical costs can be reduced. ASSETS was successfully applied to both Strangford Lough and Belfast Lough, classifying them as “Moderate”. This classification will not change their water quality status under the Water Framework Directive, Urban Wastewater Treatment Directive or Nitrates Directive, however, it is a tool to guide policy makers into better decisions in terms of future management.

Global change phenomena, such as forest disturbance and land-use change significantly affect elemental balances as well as the structure and function of terrestrial ecosystems. Inappropriate land management often causes nutrient losses and finally soil degradation and loss of soil functioning. Especially in tropical ecoregions, soil degradation by nutrient losses is widely abundant. Soil microorganisms are the proximate agents of many processes performed in soils and are regarded as sensitive bio-indicators. However, the incorporation of microbial responses to the definition of critical soil conditions is not intensively developed. In the present thesis, several data analyses of the relationships between ecosystem disturbance and land-use change (natural forest, pastures of different ages, secondary succession) and a diverse set of soil ecological characteristics in the tropical mountain rainforest region of southern Ecuador were compiled. In particular, it was tested whether soil microbial biomass and community functioning were sensitive to land-use change effects. Furthermore, an information-theoretic approach was applied to find the factors that regulate soil microbial biomass and community function. Finally, in a nutrient enrichment experiment the above- and belowground responses to N and P additions were examined. The tested research questions and results were linked to the theory of ecological stoichiometry in order to connect the research to a sound and unifying scientific basis. Soil and microbial stoichiometry were affected by both land-use change and soil depth. After forest disturbance, significant decreases of soil C:N:P ratios at the pastures were fol-lowed by increases during secondary succession. Microbial C:N ratios varied slightly in response to land-use change, whereas no fixed microbial C:P and N:P ratios were observed. Shifts in microbial community composition were associated with soil and microbial stoichiometry. Strong positive relationships between PLFA-markers 18:2n6,9c (saprotrophic fungi) and 20:4 (animals) and negative associations between 20:4 and microbial N:P point to land-use change affecting the structure of soil food webs. Significant deviations from global soil and microbial C:N:P ratios indicated a major force of land-use change to alter stoichiometric relationships and to structure biological systems. Data analysis reveals a strong impact of land-use change on soil microbial biomass, C-mineralization, gross-NH4-consumption and –production rates. According to the results of the IT-approach, combined models better describe effects of land-use change on soil microorganisms than single explanation models. Microbial resources and soil chemical environment were important pre-dictors for soil microbial biomass and community functioning. Little is known about the environmental drivers of the catalytic properties of EHEs (e.g., pH, nutrients) and their functional link to the structure of soil microbial communities. The activities of the six hydrolytic enzymes were tested. Microbial production of AP responded to the low P status of the sites by a higher investment in the acquisition of P compared to C. Three major drivers of enzyme activities were found to be significant for enzyme production: 1.) Microbial demand for P regulated the production of AP, provided that N and C were available. At the natural forest site the two-fold higher specific activity of AP pointed to a high microbial P-demand, whereas the production of AP was constrained by the availability of N and DOC after pasture abandonment. 2.) Microbial biomass that was controlled by pH and resource availability was the main driver for CBH, BG and NAG activities. 3.) Substrate induction due to increased litter inputs of herbaceous plant species seemed to regulate AG and XYL activities during secondary succession. The enzymes’ affinity to substrate, as a potentially critically enzyme kinetic parameter is understudied. The data analysis suggests that microbial communities adapted to environmental changes, demonstrated high flexibility of extracellular enzyme systems and selected for enzymes with higher catalytic efficiency compared with pure cultures. Under in situ conditions, enzyme-specific environmental drivers of the Km, e.g., the pH for XYL, the C:N ratio for AP, and the C availability for NAG were found. The data demonstrated that the higher substrate affinity of XYL and AP was associated with more abundance of Gram(-) bacteria. The catalytic efficiency of enzymes decomposing cellulose, hemicellulose, and starch positively correlated with the relative abundance of Gram(-) bacteria. The turnover rate of the tested substrates was three to four times faster at the young pasture site compared with the longterm pasture and secondary succession sites. Nutrient inputs by atmospheric deposition are known to affect terrestrial ecosystems. However, little is known about how N and P co-limited ecosystems respond to single nutrient enrichment. In this work the susceptibility of above- and belowground ecosystem compo-nents and of their linkages in an N and P co-limited pasture to N- and P-enrichment was assessed. It was tested if the plants´responses can be explained by the concept of serially linked nutrients introduced by Ågren (2004). In this concept, the control of the growth rate by one nutrient is assumed to depend on the control of a different cellular process by another nutrient. The responses of shoot and root biomass and C:N:P stoichiometry of the grass Setaria sphacelata (Schumach.) to moderate N, P, and N+P application over five years were investigated. In addition, the effects of nutrient enrichment on soil nutrient pools, on arbuscular mycorrhizal fungi (AMF) as well as on microbial biomass, activity, and community structure were tested. In order to evaluate the importance of different factors explaining microbial responses, a likelihood-based information-theoretic approach was applied. The application of N+P increased aboveground grass biomass. Root biomass was stimulated by P-treatment. Grass C:N:P stoichiometry responded by altering the P-uptake or by translocating P from shoot to root. In particular, root C:N and C:P stoichiometry decreased in P- and in N-treatment. Extractable fractions of soil C, N, and P were significantly affected by nutrient enrichment. P application increased the biomass of Gram-positive bacteria and the abundance of AMF, however, results of the IT-approach suggested indirect effects of nutrient enrichment on microbes. The responses of the N and P co-limited pasture to particular nutrient enrichment support the concept of serially linked nutrients. The present study provides evidence for the fundamental importance of P for controlling resource allocation of plants in responses to nutrient enrichment. Resource allocation of the grass rather than direct effects of nutrient additions drives changes in AMF, microbial biomass, community structure, and activity
Seit dem Übergang vom Holozän zum Anthropozän greift der Mensch immer stärker in globale und regionale Stoffkreisläufe ein. Durch die Zerstörung von Naturwäldern und Landnutzungswandel werden die Strukturen und die Funktionen der Ökosysteme stark verändert. Unangepasste Landnutzung führt zu Nährelementverlusten, die mittel- bis langfristige zur Bodendegradation und zur Reduktion von Bodenfunktionen führen. Solche Veränderungen sind insbesondere in den Tropen zu beobachten. Bodenmikroorganismen spielen in den Stoffkreisläufen eine zentrale Rolle. Zudem sind sie sensitive Bioindikatoren für den Zustand von Ökosystemen. Im Gegensatz dazu, werden die Bodenmikroorganismen noch nicht ausreichend für die Zustandsbewertung von Ökosystemen verwendet. In der vorliegenden Dissertation werden verschiedene Datenanalysen zu den Beziehungen von Landnutzungswandel (Naturwald, Weiden verschiedener Alter, sekundäre Sukzession) und den Eigenschaften der Bodenmikroorganismen in einer tropischen Bergregenwaldregion Süd-Ecuadors zusammengefasst. Ein besonderer Fokus lag darauf zu prüfen, ob die mikrobielle Biomasse und die Funktionen die von der mikrobiellen Gemeinschaft geleistet werden (z.B. Enzymaktivitäten) durch den Landnutzungswandel beeinflusst werden. Ein informations-theoretischer Ansatz wurde verwendet um verschiedene Erklärungsansätze der steuernden Faktoren vergleichend zu testen. Darüber hinaus wurden in einem Weidedüngungsexperiment die Reaktionen der ober- und der unterirdischen Ökosystemkomponenten auf die Anreicherung mit N und P getestet. Um die Ergebnisse auf eine breite wissenschaftliche Basis zu stellen wurde die Untersuchungen in den Kontext der Theorie die Ökologischen Stöchiometrie eingeordnet. Die C:N:P Stöchiometrie im Boden und in den Mikroorganismen veränderte sich durch den Landnutzungswandel und mit der Bodentiefe. Mit der Weideetablierung nahmen die C:N:P Verhältnisse im Boden deutlich ab, stiegen dann nach dem Verlassen der Weiden im Zuge der sekundären Sukzession wieder an. Das mikrobielle C:N Verhältnis variierte nur leicht, dagegen zeigten das C:P und N:P Verhältnis deutliche Veränderungen durch den Landnutzungswandel. Mit diesen Veränderungen in der Boden- und Organismenstöchiometrie waren auch Veränderungen in der Struktur der mikrobiellen Gemeinschaften verbunden. Deutliche positive Beziehungen existierten zwischen den saprotrophen Pilzen und den Protozoen. Die steigenden Mengen von Protozoen waren wiederrum mit sinkendem mikrobiellen N:P verbunden. Diese Muster weisen auf Veränderungen in den Bodennahrungsnetzten durch Landnutzungsänderungen hin. Sehr deutliche Abweichungen von globalen Mustern der C:N:P Stöchiometrie deuten darauf hin, dass der Landnutzungswandel signifikanten Einfluss auf die C:N:P Stöchiometrie ausübt. Der Landnutzungswandel beeinflusste auch die mikrobielle Biomasse, die Basalatmung, sowie die mikrobielle Aufnahme und Produktion von NH4-N im Boden. Dabei zeigten kombinierte Erklärungsansätze die adäquateren Beschreibungen der Muster. In den kombinierten Modellen zur Erklärung der mikrobiellen Biomasse und der mikrobiellen Leistungen überwogen Prädiktoren der mikrobiellen Ressourcen und der bodenchemischen Umwelt. Ein weiterer Schwerpunkt der Untersuchungen lag auf der Erfassung der Effekte des Land-nutzungswandels auf die Aktivität von extrazellulären Bodenenzymen. Bisher ist wenig darüber bekannt, welche Faktoren die katalytischen Eigenschaften steuern und beispielsweise, ob es Zusammenhänge zur mikrobiellen Gemeinschaftsstruktur gibt. Um diese Fragen näher zu beleuchten wurden sechs hydrolytische Enzyme basierend auf MUF-Substraten untersucht. Die mikrobielle Produktion von AP stand dabei in Zusammenhang mit dem niedrigen P-Status der untersuchten Böden. Das wurde besonders durch die hohe AP Produktion im Vergleich zu BG belegt. Im Allgemeinen konnten drei verschiedene Mechanismen festgestellt werden, die die Produktion der untersuchten EHEs vermutlich steuerten. 1.) Der P-Bedarf der Mikroorganismen regulierte die Produktion von AP, vorausgesetzt, dass ausreichend N und C zur Enzymsynthese zur Verfügung standen. 2.) Die Höhe der mikrobiellen Biomasse hat sich als wichtiger Faktor für die Produktion von CBH, BG und NAG gezeigt. Das deutet auf die konstitutive Produktion dieser Enzyme hin. 3.) Die substratinduzierte Produktion von Enzymen ist vermutlich entscheidend für die Aktivität von AG und XYL. Die Berücksichtigung der Enzymkinetiken, insbesondere der Michaelis-Menten-Konstante lieferte weitere Aufschlüsse über relevante Faktoren. Im Allgemeinen so scheint es, haben sich die mikrobiellen Gemeinschaften an die starken Umweltgradienten, die durch den Landnutzungswandel erzeugt worden angepasst. Im Vergleich zu den verfügbaren Daten aus Reinkulturen, wiesen die mikrobiellen Gemeinschaften der untersuchten Böden in der Regel eine deutlich höhere katalytische Effizienz auf. Auch für die Michaelis-Menten-Konstante sind die Faktoren enzymspezifisch. So ist für die Km von XYL der Boden-pH-Wert, für AP das C:N Verhältnis und für NAG die DOC-Menge entscheidend. Darüber hinaus haben sich deutliche Beziehungen zwischen der Menge an Gram(-)-Bakterien und der Substrataffinitäten von XYL und AP ergeben. Je höher die Gram(-)-Abundanz, desto höher war die Substrataffinität der Enzymsysteme. Gegenüber alter und degradierter Weiden, war der Umsatz der untersuchten Substrate im Oberboden der aktiv genutzten Weide drei- bis vierfach erhöht. In einem 5-jährigen Düngeexperiment in der Bergregenwaldregion der Anden Süd-Ecuadors wurden die Reaktionen des auf dieser Fläche N/P co-limitierten Grases (Setaria sphacelata), der Arbuskulären Mykorrhiza (AMF) sowie der Bodenmikroorganismen auf moderate N, P und N+P-Düngung untersucht. Die Zugabe von N+P erhöhte die oberirdische Biomasse (+61%) wohingegen die Wurzelbiomasse durch die Zugabe von P (+45%) anstieg. Die C:N:P Verhältnisse weisen auf veränderte P-Aufnahme oder Translokation von P in die Wurzeln hin. Im Besonderen verengte sich das Wurzel C:N and C:P in der P- und der N-Zugabe. Die aus dem Boden extrahierbaren C, N und P-Fraktionen wurden deutlich beeinflusst. Die Zugabe von P stimulierte die Biomasse Gram-(+)-Bakterien (+22%), die Abundanz der AMF (+46%) und die Brutto-N-Mineralisierung. Die Auswertungen deuten darauf hin, dass die Nährstoffanreicherung indirekt über die Veränderungen der Graswurzeln auf die Bodenorganismen wirkte. Die Ergebnisse bestätigen, dass N und P in den Reaktionen von co-limitierten Pflanzen eng miteinander verbunden sind. Vor allem aber steuert P grundlegend die Allokation von Ressourcen und wirkt damit auf andere Ökosystem-komponenten, z.B. auf die Struktur und Aktivität der Bodenmikroorganismen

Sediment records of two Italian subalpine lakes (Lake Garda and Lake Ledro) were analyzed in order to reconstruct their ecological evolution over the past several hundred years. A multi-proxy and multi-site approach was applied in order to disentangle the effects of local anthropogenic forcings, such as nutrients, and climate impacts on the two lakes and their catchments. Biological indicators (sub-fossil pigments, diatoms and Cladocera) were used to reconstruct changes in the aquatic food web and to define the lake reference conditions, while geochemical methods, i.e. wavelength-dispersive Xray fluorescence spectroscopy (WD-XRF), were used to provide quantitative information on the different physical or chemical processes affecting both lake and catchment systems. Sub-fossil pigments and diatoms, together with their respective inferred TP values, suggested very stable oligotrophic conditions in both lakes until the 1960s. The period following was affected by nutrient enrichment, which led to a drastic shift in the phytoplanktonic community. The response of sub-fossil pigments and diatoms to major climatic anomalies such as the Medieval Climatic Anomaly (MCA) and the Little Ice Age (LIA) were not pronounced, and the taxonomic composition remained relatively stable. On the contrary, these proxies showed an indirect response to climate variability since the beginning of the nutrient enrichment phase in the 1960s. In Lake Garda, the winter temperature regulates the water column mixing, which in its turn controls the degree of nutrient fertilization of the entire water column, and the related phytoplankton growth. In Lake Ledro a rapid reorganization of planktonic diatoms was observed only during the temperature recovery after the LIA, while recent temperature effects are masked by the prevailing nutrient effects. In Lake Garda, Cladocera remains responded in quantitative and qualitative terms to climatic changes, whereas in Lake Ledro they appeared to be mainly affected by variations in hydrological regimes, i.e. flood events. Cladocera remains corroborated the nutrient enrichment after the 1960s in both lakes as inferred by diatoms and pigments. In Lake Garda, the geochemical data showed a pronounced shift in elemental composition since the mid-1900s, when major elements and lithogenic tracers started to decrease, while some elements related to redox conditions and other (contaminant) trace elements increased. The general trends since the mid-1900s agree with the biological records. However, some differences recorded in the two different basins of Lake Garda reflected the effects of local conditions, both related to hydrology and sedimentation patterns. Lake Ledro showed higher short-term variability for most elements, even though some features were comparable to Lake Garda. The geochemical record of Lake Ledro revealed a major influence of human-induced lake-level fluctuations and catchment properties. This paleolimnological study allows us to place temporally restricted limnological surveys into a longer-term secular perspective, which is highly valuable for the definition of lake reference conditions. Because the restoration targets are usually based on the lake reference conditions, this study highlighted also the necessity to pay particular attention to the lake-specific sensitivity patterns. The multi-proxy and multi-site approach showed that the lake conditions of large and deep lakes in northern Italy, such as Lake Garda, are mainly driven by nutrient enrichment and/or climate change. In contrast, smaller lakes with larger catchment areas, such as Lake Ledro, are seemingly more impacted by conditions and processes occurring in the drainage basin.

Dissertação de Mestrado Integrado em Medicina Veterinária
While free-ranging gorilla populations are declining, captive gorillas face serious health issues such as obesity and heart disease. A proper dietary management is crucial to maintain healthy and thriving populations, but in captivity it can be difficult to provide diets that are both nutritionally and functionally equivalent to wild diets. During this study in Zoo Basel were evaluated two male gorillas, one silverback (16 years) and one blackback (12 years), two late-stage pregnant females (25 and 32 years) and two geriatric females (47 and 55 years). Diet adequacy was assessed through the analysis of the diet composition, individual nutrient intake, dietary enrichment program, anthropometric features and previous clinical records. Overall, the diet offered at Zoo Basel was complete and mostly adequate to the gorillas’ behavioural and nutritional needs. Some significant differences were observed between individual diets, linked to management options, individual preferences and physiologic, ageor hierarchy-related specific requirements. A list of recommendations was compiled and a sample diet was created to help correct the identified nutrient imbalances. An integrated individual analysis of diet adequacy is particularly important in a species like the gorilla, due to its complex social interactions and the need to group-feed to maintain proper levels of welfare.
RESUMO - Enquanto a população de gorilas selvagens diminui, os que estão em cativeiro deparam-se com graves problemas de saúde como a obesidade e a doença cardíaca. Uma dieta adequada é essencial para manter estas populações saudáveis, mas em cativeiro é difícil oferecer dietas nutricionalmente e funcionalmente análogas às naturais. Durante este estudo, no Jardim Zoológico da Basileia, foram avaliados dois gorilas machos, de dorso-prateado (16 anos) e de dorso-negro (12 anos), duas fêmeas em final de gestação (25 e 32 anos) e duas fêmeas geriátricas (47 e 55 anos). A adequação da dieta foi avaliada através da análise da sua composição, do consumo individual de nutrientes, do programa de enriquecimento ambiental, das características antropométricas e de registos clínicos prévios. No geral, a dieta fornecida foi completa e adequada às necessidades comportamentais e nutricionais dos gorilas. Foram observadas algumas diferenças significativas entre indivíduos, ligadas a opções de maneio, preferências individuais e requisitos específicos do estado fisiológico, idade ou hierarquia. Foi elaborada uma lista de recomendações e criada uma dieta-amostra para ajudar a corrigir os desequilíbrios identificados. Uma análise dietética integrada e individual é particularmente importante numa espécie como o gorila, devido às suas complexas interações sociais e à necessidade de serem alimentados em grupo para manter níveis adequados de bem-estar.

I investigated effects of environmental change on disease, and effects of disease on ecosystems, using a freshwater zooplankton host and its fungal parasite. This research involved lake surveys, manipulative experiments, and mathematical models. My results indicate that ecosystem characteristics such as habitat structure, nutrient availability, and quality of a host’s resources (here, phytoplankton) can affect the spread of disease. For example, a survey of epidemics in lakes revealed direct and indirect links between habitat structure and epidemic size, where indirect connections were mediated by non-host species. Then, in a mesocosm experiment in a lake, manipulations of habitat structure and nutrient availability interactively affected the spread of disease, and nutrient enrichment increased densities of infected hosts. In a separate laboratory experiment, poor quality resources were shown to decrease parasite transmission rate by altering host foraging behavior. My experimental results also suggest that disease can affect ecosystems through effects on host densities and host traits. In the mesocosm experiment, the parasite indirectly increased abundance of algal resources by decreasing densities of the zooplankton host. Disease in the experimental zooplankton populations also impacted nutrient stoichiometry of algae, which could entail a parasite-mediated shift in food quality for grazers such as the host. Additionally, I showed that infection dramatically reduces host feeding rate, and used a dynamic epidemiological model to illustrate how this parasite-mediated trait change could affect densities of resources and hosts, as well as the spread of disease. I discuss the implications of these ecosystem–disease interactions in light of ongoing changes to habitat and nutrient regimes in freshwater ecosystems.

The Chesapeake Bay, once one of the worlds most productive estuaries, has been severely impacted by human activity in the water and on the lands around it. Viewed as an ecosystem, the Bay is no longer able to support the variety and abundance of biota that it was historically able to. Several decades of research on the Chesapeake have pointed to human activities as being the principle reason for this decline. Of these detrimental activities, elevated inputs of Nitrogen and Phosphorus to the Bay were singled out as being the greatest cause of water quality deterioration. The state of Virginia is trying to reduce its annual load of Nitrogen, to the Potomac River, to 60% of what the load was estimated to be in 1985. Virginia would like to accomplish this goal at the lowest cost to its citizens. Therefore the state needs to determine the combination of nitrogen control efforts which will achieve the goal at the lowest cost. The state would also like to be able to maintain nitrogen loads at or below this cap level, indefinitely into the future. This study was undertaken with three primary objectives. The first was to project the level of annual nitrogen inputs to the Potomac River, from the state of Virginia, over the next 15 years. The second was to estimate the minimum annual costs necessary to achieve and maintain a 40% reduction in total nitrogen inputs, using the Virginiaâ s estimated 1985 inputs as a baseline. The final objective was to assess the potential cost savings that may result from using one of two alternative development patterns within the rapidly urbanizing Northern Virginia portion of the Potomac Watershed. The first alternative is prohibiting low-density development within the Northern Virginia region, and the second is to restrict all new development to be within 5 miles of an existing urban area. Study results suggest that there has been no significant progress toward meeting the nitrogen reduction goal, due to the increase in population within the watershed, over the past 13 years. To attain the goal in 1998, a minimum of $27 million, above what is currently being spent annually, would be required. Under the current land use trend within Virginiaâ s Potomac Basin, the annual cost for maintaining the goal is estimated to rise to $38 million annually, in 1998 dollars, by the year 2013. This is a 40% increase in cost. If the first alternative development pattern is adhered to over this 15-year period, then the annual cost will be $33 million, for an annual cost saving of approximately $5 million in 2013. The second alternative could achieve similar results if implemented, costing roughly $5 million less in 2013 than the annual cost per year under the current trend. These findings suggest that the use of alternative development patterns can help slow but not prevent the annual cost, of maintaining the cap, from rising. The study indicates that the reason for the continuous rise in annual cost, over this fifteen-year period, is due primarily to an increase in nitrogen loading to the Potomac that will result from the wastewater disposal needs of the growing population within the Basin. Furthermore, the state will eventually exhaust its lower cost options for reducing Nitrogen loadings, and at that point the annual cost for maintaining the Nitrogen Cap will begin to rise exponentially. Under current land use trends this rapid rise in cost is unlikely to occur within the next 15 years, and is more apt to occur sometime within the next 20 to 40 years. Once annual expenditures begin to rise exponentially it is unlikely that the state of Virginia would be able to maintain its 40% reduction goal.
Master of Science

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
According to the River Continuum Concept, in small rivers, corresponding to ~ 80% of river basins, the main energy source for the trophic chain is the material produced in riparian zones, especially leaves. This material goes through the process of decomposition, which is responsible for the nutrients cycling and maintenance of aquatic communities. In this context, the objective of this study is to investigate the effects of physical, chemical and physiological traits of plant species on microbial activity and fragmentation, and as a consequence on decomposition rates. In the first chapter we investigated the activity of Phylloicus fragmentation in relation to food resources with different leaf traits. We found that the shredders have their food activity stimulated by substrate with less amount of lignin, which facilitates fungus conditioning and promotes the palatability of the detritus. In the second chapter, we investigated the feeding preference and assimilation of C3 and C4 carbon by Phylloicus and Aegla longirostri. We found that the shredders consume more the C4 species, but do not alter its isotopic signature and the intense activity of the hyphomycetes in the leaves C4 stimulated the consumption by the shredders. In the third chapter we investigated the effect of nutrient enrichment on soil and water on leaf nutritional quality and decomposition rates. We showed that the fertilized trees promoted leaves more nutritious than leaves of unfertilized trees. In addition, we found that the effect of nutrient enrichment on water was stronger than the nutrient enrichment of leaves in the decomposition process. Within the three chapters, we verified that the activities of the shredders and fungi are influenced by the characteristics of the leaves and are related to the riparian vegetation, especially by C3 carbon. We verified that the structural compounds are determinant for the microbial colonization and consequently for the fragmentation and litter decomposition. We also verified that the enrichment of nutrients in the water may be more important for the process of leaf decomposition than the nutrients in the leaves.
De acordo com a teoria do Contínuo Fluvial, nos pequenos rios florestados, que correspondem a ~80% das bacias hidrográficas, a principal fonte de energia para a cadeia trófica é o material produzido nas zonas ripárias, especialmente folhas. Este material passa pelo processo de decomposição, que é responsável pela ciclagem de nutrientes e manutenção das comunidades aquáticas. Neste contexto, o objetivo deste estudo é investigar os efeitos dos traços físicos, químicos e fisiológicos das espécies vegetais na atividade de microrganismos e invertebrados decompositores, e como consequência nas taxas de decomposição. No primeiro capítulo investigamos a atividade de fragmentação de Phylloicus frente a recursos alimentares com características foliares diferentes. Nós constatamos que os fragmentadores têm sua atividade alimentar estimulada por substrato com menor quantidade de lignina, o que facilita o condicionamento por fungos e promove a palatabilidade do detrito. No segundo capítulo, investigamos a preferência alimentar e assimilação C3 e C4 por Phylloicus e Aegla longirostri. Constatamos que os fragmentadores consomem mais a espécie C4, porém não alteram sua assinatura isotópica. E a intensa atividade dos hifomicetos nas folhas C4 estimulou o maior consumo pelos fragmentadores. No terceiro capítulo investigamos o efeito do enriquecimento de nutrientes no solo e na água na qualidade nutricional das folhas e nas taxas de decomposição. Evidenciamos que as plantas fertilizadas geraram folhas mais nutritivas que as não fertilizadas. Além disso, averiguamos que o efeito do aumento de nutrientes na água foi mais forte do que o efeito de nutrientes das folhas no processo de decomposição. Com os três capítulos verificamos que as atividades dos fragmentadores e fungos são influenciadas pelas características das folhas e estão relacionadas com a vegetação ripária, especialmente por carbono C3. Constatamos que os compostos estruturais são determinantes para a colonização microbiana e por consequência para a fragmentação e decomposição foliar. Verificamos também que o enriquecimento de nutrientes na água pode ser mais importante para o processo de decomposição foliar do que os nutrientes nas folhas.

Abstract Community assembly results from a combination of deterministic and stochastic mechanisms, whose relative effects can vary in response to environmental heterogeneity, connectivity, disturbance regimes and anthropogenic stressors. Understanding how community assembly mechanisms vary in response to environmental changes and connectivity is crucial for the management and conservation of river ecosystems. In this thesis, I tested the effects of connectivity and natural flow disturbances on riverine invertebrate communities by assessing assembly mechanism changes in response to (I) habitat connectivity, (II) seasonal flow intermittency and (III) inter–annual hydrological variability. I also conducted a field experiment to test for (IV) the effects of human–induced nutrient enrichment on community assembly of microorganisms (diatoms and aquatic fungi) and stream ecosystem functioning under different environmental settings. Invertebrate community assembly changed gradually with habitat connectivity. While limited dispersal resulted in higher community variability in the most isolated streams, mass effects caused community homogenization in the most connected ones. Natural and human induced disturbances lead to changes in the relative importance of deterministic and stochastic factors but often through different, or even opposite, mechanisms depending on the natural background of the ecosystem and organism type considered. For instance, seasonal drying and high–flow periods in intermittent Mediterranean rivers promoted deterministic and stochastic assembly processes respectively, whereas environmental sorting and stochastic processes respectively dominated during high and low flow years in boreal streams. Diatom and fungal communities responded differently to nutrient enrichment, with detrital processes and fungal communities responding more in naturally acidic than in circumneutral streams. The results of this thesis highlight the complexity of community assembly mechanisms: they tend to be highly context dependent and temporally variable. Therefore, stream bioassessment and conservation will benefit from explicitly incorporating connectivity and natural disturbance regimes. Assessing the interactive effects of connectivity and disturbances at the river network scale would provide a greater understanding of community assembly mechanisms and river ecosystem functioning
Tiivistelmä Eliöyhteisöjen koostumus heijastelee determinististen ja stokastisten mekanismien vuorovaikutusta. Niiden suhteellinen merkitys vaihtelee suhteessa yhteisöjen kytkeytyneisyyteen sekä luontaisiin ja ihmisen aiheuttamiin häiriöihin. Yhteisöjen säätelymekanismit vaihtelevat jokiverkoston eri osissa ja tietoa tästä vaihtelusta tarvitaan jokiekosysteemien hoidon kehittämiseksi. Tässä tutkielmassa testasin elinympäristöjen kytkeytyneisyyden ja luontaisten häiriöiden (virtaamavaihtelut) vaikutuksia jokien selkärangatonyhteisöihin. Suoritin myös kenttäkokeen, jossa testattiin ihmisen aiheuttaman rehevöitymisen vaikutuksia mikro–organismeihin (piilevät, mikrobit) ja ekosysteemitoimintoihin erilaisissa ympäristöoloissa (luontaisesti happamat vs. neutraalit purot). Selkärangattomien yhteisökoostumus muuttui asteittain jokiverkostossa. Yhteisökoostumuksen vaihtelu oli suurinta eristäytyneimmissä latvapuroissa, kun taas isommissa, uomaston keskivaiheilla sijaitsevissa koskissa voimakas levittäytyminen eri suunnista (ns. massatekijät) aiheutti yhteisöjen rakenteen homogenisoitumista. Kuivuusjaksot ja niitä seuraavat korkean virtaaman jaksot edistivät determinististen prosessien merkitystä Välimeren alueen joissa, kun taas boreaalisissa puroissa Pohjois–Suomessa äärevät virtaamaolot, erityisesti poikkeuksellisen kuivat kesät, edistivät satunnaismekanismien vaikutusta. Perustuottajat (piilevät) ja hajottajat (akvaattiset sienet) vastasivat eri tavoin ravinnelisäykseen. Sienten hajotustoiminta nopeutui ravinnelisäyksen myötä, mutta vain luontaisesti happamissa puroissa. Tämän opinnäytetyön tulokset korostavat yhteisön kokoonpanomekanismien monimutkaisuutta: ne ovat usein erittäin tilanneriippuvaisia ja ajallisesti vaihtelevia. Siksi jokien ekologisen tilan arvioinnissa tulisi huomioida tutkimuspaikkojen kytkeytyneisyys jokimaisemassa