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1
Bernal, Berenguer Susana. "Nitrogen storm responses in an intermittent Meditterranean stream." Doctoral thesis, Universitat de Barcelona, 2006. http://hdl.handle.net/10803/1436.
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The amount of dissolved inorganic nitrogen delivered to streams and groundwater has substantially increased in the last decades due to anthropogenic impacts. This fact has stimulated research on processes related to the nitrogen cycling in order to elucidate the ability of terrestrial and aquatic ecosystems in controlling nitrogen loads. Some of these studies pointed out during storms streamwater chemistry is significantly altered. However, because of the inherent difficulty of an extensive field experimental setting for dealing with episodic storms, studies focused on hydrological processes or stream solute dynamics during storms rely on a very limited number of events. Hydrobiogeochemical processes have been mainly studied in temperate experimental catchments and little attention has been paid to Mediterranean catchments. Recent studies have stressed the fragility of Mediterranean regions in front of the global change and because of that Mediterranean regions should become hot spots for present and future studies.The main goal of the present thesis was to study the variability of nutrient dynamics, in particular nitrogen, during stormflow in relation to baseflow conditions in Fuirosos, an intermittent stream draining a small Mediterranean catchment (Part I). As a secondary objective (Part II), solute dynamics in Fuirosos were compared with those measured at one of its main tributaries, the Grimola stream. Biotitic granodiorite was an important fraction of the Fuirosos catchment, whereas the Grimola catchment was underlain by leucogranite. The Fuirosos stream had an alluvial zone and it was flanked by a well developed riparian forest, whereas the Grimola stream had not a significant alluvial zone, neither a well developed riparian area. Thereby, the effect of (i) catchment size, (ii) lithology and (iii) the presence of an alluvial-riparian zone on stream hydrogrochemistry were assessed by comparing the Fuirosos and Grimola streams.
The Fuirosos Stream Watershed, a relatively undisturbed Mediterranean ecosystem that can not be considered a N-saturated catchment, leaks to the stream most of the nitrogen loss in the form of nitrate (57 %). This figure contrast with that reported for other pristine tropical and humid catchments where nitrogen export is mainly in the form of dissolved organic nitrogen. In particular, nitrate is mainly mobilized during stormflow conditions (from 52 % to 80 % of the annual yield). Contrastingly, most of the dissolved organic carbon export occurs during baseflow conditions (from 40 to 70 % of the annual yield). These results point to a decoupling between soil nitrification and nutrient uptake by biota, which brings about the leaking of nitrate to the stream. Hydrochemistry in this Mediterranean intermittent stream is highly variable within and in between years. The antecedent moisture conditions and the magnitude of storm events are key factors on shaping the hydrological responses to storm events. However, storm episodes that occur during similar climatological and hydrological conditions produce different streamwater chemistry depending upon the time of the year. This is so, mainly because of the influence of the summer drought period on streamwater chemistry. Both, the mixing model (EMMA) and the spectral analysis approaches, point out that groundwater is the most important contributor to stormflow in Fuirosos. Nonetheless, the EMMA approach emphasizes how stream water and nitrate sources vary throughout the year. Our results stress the importance of sampling storms during all seasons to draw general conclusions about watershed processes. The mixing model shows that nitrate is retained by biota in the Fuirosos alluvial zone only when streamflow is lower than 80 l/s. Above this threshold, the system is not efficient in retaining nitrate arriving from the catchment. This result might be keep on mind when establishing the importance of near- and in-stream processes for regulating catchment nitrate loads since a major fraction of the annual nitrate export usually occurs during stormflow conditions in many catchments. The spectral analysis also shows that the variability of stream nitrate concentrations is more damped in Fuirosos than in Grimola. This is attributed to the buffer effect that biota has on nitrate concentrations in the Fuirosos alluvial zone, which retards its delivery in relation to the Grimola catchment.
"Efecte de les pluges en la dinàmica del nitrogen en una riera intermitent i mediterrània"
La quantitat de nitrogen dissolt que arriba avui dia als nostres rius i aqüífers és substancialment major a la de fa un parell de dècades a resultes de l'activitat antròpica. Aquest fet ha estimulat força la recerca dels processos relacionats amb el ciclatge del nitrogen, amb la intenció d'esbrinar la capacitat que tenen els ecosistemas terrestres i aquàtics per controlar les càrregues de nitrat que els hi arriben. Alguns d'aquests estudis indiquen que durant les tempestes s'altera de forma substancial la química de l'aigua del riu. Això no obstant, la major part dels treballs realitzats es recolzen en un nombre limitat d'episodis, donada la dificultat inherent al mostreig intensiu de camp a l'hora d'estudiar les respostes hidrològiques i la dinàmica dels soluts durant les crescudes. Tradicionalment, la comunitat científica s'ha dedicat a l'estudi dels processos hidrobiogeoquímics de regions temperades i tropicals, i desafortunadament, les conques Mediterrànies no han estat objecte de la seva atenció. Estudis recents alerten de la fragilitat de les regions Mediterrànies enfront del canvi global, i per tant, urgeixen els estudis focalitzats en aquests ecosistemes.
El principal objectiu d'aquesta tesi ha estat l'estudi de la variabilitat de la dinàmica dels nutrients, en particular del nitrogen, durant les crescudes en relació a la seva dinàmica en condicions de cabal basal en una riera intermitent, Fuirosos, en una conca Mediterrània. La hidrologia i la dinàmica dels soluts a la riera de Fuirosos s'ha comparat amb les de la Grimola, un dels seus efluents més importants. Hi ha diferències litològiques notables entre les dues conques. A més la riera de Fuirosos té zona al.luvial i està flanquejada per un bosc de ribera ben desenvolupat, mentre que la riera de Grimola no té zona al.luvial ni tampoc una zona riberenca ben diferenciada. Per tant, els efectes de (i) la mida de la conca, (ii) la litologia, i (iii) la presència d'una zona al.luvial i riberenca sobre la hidrobiogeoquímica d'un riu, van poder ésser contrastats comparant les rieres de Fuirosos i Grimola. L'estudi es va realitzar al Parc Natural del Montnegre-Corredor al Vallès Oriental entre els anys 1998 i 2004.
2
Nhim, Tum. "Variability of intermittent headwater streams in boreal landscape : Influence of different discharge conditions." Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-183137.
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Dynamic expansions and contractions of stream networks can play an important role for hydrologic processes as they can connect different parts of the landscape to the stream channels. However, we know little about the temporal and spatial variations of stream networks during different flow and wetness conditions. This study focuses on the contraction and expansion of stream networks during different flow conditions in the boreal Krycklan catchment, located in Northern Sweden. The stream network and initiation points were extracted from a gridded digital elevation model (DEM) of 5-meter resolution, and then compared with the stream network initiation points (heads) observed during the spring flood (freshet) period in 2012. From the results of the study, it was clearly seen that the observed stream heads and the stream heads appearing in the stream network map extracted from DEM did not agree very well. 49% of the total observed stream heads (49) fell onto the low order stream branches and headwater streams derived from the DEM. Only few of them exactly matched the modeled stream heads. Moreover, the modeled stream network was much denser than the observed stream network, and so the simple raster based dynamic model developed could not well represent the dynamic stream network extension in the real system. Most headwater streams in the study catchment were man-made ditches, which were dug to drain water wetlands and to increase forest productivity. The majority of observed stream heads were formed by seepage from the saturated surrounding soils, while only a few of them were formed by saturation overland flow. On the other hand, the dynamic stream network derived from the DEM suggested that the number of streams of lower order and their lengths was sensitive to change in streamflow, especially during the high flow episode.
3
Willard, Eric Hillman Tharsing. "Temperature and relative humidity gradients of intermittent and perennial tributaries in Northern California." [Chico, Calif. : California State University, Chico], 2009. http://hdl.handle.net/10211.4/108.
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Bogan, Michael T. "Hurry up and wait: life cycle and distribution of an intermittent stream specialist (Mesocapnia arizonensis)." UNIV CHICAGO PRESS, 2017. http://hdl.handle.net/10150/626268.
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Species inhabiting intermittent streams must have life-history traits that confer resistance or resilience to flow cessation or drying. However, we lack basic life-history information for most aquatic invertebrate species, especially those from intermittent streams. I documented the life cycle and distribution of an unusual winter stonefly species, Mesocapnia arizonensis (Capniidae). The species was first described from 6 localities in 1969, but its natural history remained enigmatic. I surveyed >90 streams across the southwestern USA, documented the life cycle of M. arizonensis at 1 locality, and experimentally rehydrated dry streambed sediment in search of dormant stoneflies at another locality. Field surveys expanded the number of localities from 22 to 98, most of which were intermittent with flow durations as brief as 3 mo/y, and extended the known range of the species by 800 km. Nymphs were abundant within days of flow resumption, grew rapidly as a single cohort, and started emerging as adults 42 d after flow resumed. The brief appearance of a 2(nd) cohort of tiny nymphs 1 mo before the stream dried indicates direct hatching of at least some eggs. I failed to find dormant stoneflies in the top 30 cm of dry stream sediment, suggesting that M. arizonensis undergoes dormancy deep in the substrate, putting it safely out of reach of scouring summer floods that occur between favorable winter seasons. The remarkable ability of M. arizonensis to survive in short-flow duration streams and to endure multiple consecutive dry years, suggests that the species is well prepared for the drier climatic conditions predicted to occur across its range.
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Bonjour, Sophia. "Influence of Fishes on Macroinvertebrate Communities in Prairie Stream Permanent Water Refugia." OpenSIUC, 2018. https://opensiuc.lib.siu.edu/theses/2348.
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Physical factors, such as hydrologic variability, are major structuring forces of prairie stream communities. Macroinvertebrate and algae densities can both decrease sharply in response to floods and drying. Less is known about the influences of biological factors, such as fishes. The influence of fishes on macroinvertebrate communities varies with environmental factors and other biologic interactions, ranging from neutral to strong negative effects on some populations, and the strength of these interactions sometimes appear linked to hydrology. Drying intermittent streams leave permanent water refugia that may be hotspots for interactions between fishes and invertebrates. Effects of fishes on macroinvertebrate communities may vary with invertebrate life cycle stages (e.g., larvae, emerging adults, colonizing adults). I examined macroinvertebrate communities (benthic and emerging) and algal biomass across a range of permanent stream pool sites at Konza Prairie Biological Station with naturally varying densities of fishes. I also manipulated fish densities in a mesocosm experiment to address how fishes may also be effecting colonization during recovery from hydrologic disturbance. Fish biomass had a negative impact on invertebrate abundance, but not biomass or taxa richness, in natural pools. Total fish biomass was not correlated with total insect emergence in natural pools, but orangethroat darter (Etheostoma spectabile) biomass was inversely correlated with emerging Chironomidae biomass (r2 = 0.43, p = 0.047) and individual midge body size (r2 = 0.61, p = 0.014). Predatory fish biomass and a date interaction appeared in top linear models, indicating fish may also delay insect emergence from natural pools. Fish presence reduced abundance of colonizing insects (p < 0.001) and total invertebrate biomass (p = 0.001) in mesocosms. Mesocosm insect communities in pools without fishes were characterized by more Chironomidae, Culicidae, and Corduliidae (p < 0.001 for all). Chlorophyll-a increased between sampling dates in mesocosms, but did not differ between treatments. Not all life stages showed the same response to fishes, illustrating the need for understanding life histories in order to interpret the influence of fishes. Understanding how fishes in prairie streams affect ecosystem structure and function is critical for conservation and management of remaining grassland streams. Results suggest fishes can influence colonization and community structure in prairie stream pools, which serve as important refugia during hydrologic disturbance and source areas for colonists during recovery.
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Taylor, Ritchie Don. "Water Quality Aspects of an Intermittent Stream and Backwaters in an Urban North Texas Watershed." Thesis, University of North Texas, 2002. https://digital.library.unt.edu/ark:/67531/metadc3206/.
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Pecan Creek flows southeast through the City of Denton, Texas. Characterized as an urban watershed, the basin covers approximately 63.5 km2. Pecan Creek is an intermittent stream that receives nonpoint runoff from urban landuses, and the City of Denton's wastewater treatment plant, Pecan Creek Water Reclamation Plant, discharges effluent to the stream. Downstream from the City of Denton and the wastewater treatment plant, Pecan Creek flows about 6,000 m through agricultural, pasture, and forested landscapes into Copas Cove of Lake Lewisville, creating backwater conditions. Pecan Creek water quality and chemistry were monitored from August 1997 to October 2001. Water quality was influenced by seasonal, spatial, climatic, and diurnal dynamics. Wastewater effluent discharged from the Pecan Creek Water Reclamation Plant had the greatest influence on water quality of the stream and backwaters. Water quality monitoring of Pecan Creek demonstrated that dissolved oxygen standards for the protection of aquatic life were being achieved. Water quality modeling of Pecan Creek was completed to assess future increases in effluent flow from the Pecan Creek Water Reclamation Plant. Water quality modeling indicated that dissolved oxygen standards would not be achieved at the future effluent flow of 21 MGD and at NPDES permitted loadings. Model results with application of a safety factor indicated that the maximum allowable concentrations for a 21 MGD discharge would be 2.3 mg/L of ammonia and 7.0 mg/L of biochemical oxygen demand at summer conditions. Drought conditions that occurred from 1998 to 2001 reduced water levels in Lake Lewisville and impacted dissolved oxygen water quality in Pecan Creek. Water quality observations made during the period of drought allowed for the development of a model to estimate the zone of the dissolved oxygen sag in Pecan Creek based on reservoir elevation. Finally, monitoring results were analyzed with nonparametric statistical procedures to detect water quality changes in the backwater area of Pecan Creek, as influenced by storm events.
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Belli, Joseph P. "Movements, habitat use, and demography of Western Pond Turtles in an intermittent central California stream." Thesis, San Jose State University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10011666.
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Western Pond Turtles, Emys (Actinemys) marmorata, were captured (n=173) in 2011 (wet year) and 2012–2013 (successively drier drought years) along upper Coyote Creek, an intermittent stream in central California. Males outnumbered females 2.8:1, juveniles less than 120 mm long made up 26% of captures, growth rates varied among individuals, and little growth occurred in turtles older than 10 years. I radio-tracked turtles from May 2011 through August 2013 to ascertain movements and seasonal habitat use. Males had much larger home ranges than females (means of 2281 m for males and 501 m for females in 2012), and males moved extensively in April and May, during the apparent breeding season. Turtles preferred deep and complex pools, complex runs, and backwaters. Turtles left the stream for upland habitats in late spring and summer as stream flow ceased and pool connectivity was broken. There was substantial variation in departure dates among individuals and between wetter and drier reaches. Mean departure date was 16 August in 2011, but decreased to 20 July in 2012 and 28 June in 2013, as the drought intensified. Upland sites were mostly within 100 m of the stream, beneath dried leaves and/or thatch, and on slopes varying from flat to over 40%. Turtles remained upland for almost seven months in 2011–2012, although there was much variation. Mean return to stream dates were 27 February (males) and 16 March (females).
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Rutledge, Charles Jerry 1941. "Physiological Ecology, Population Genetic Responses and Assemblage Stability of Fishes in Two Southwestern Intermittent Stream Systems." Thesis, University of North Texas, 1991. https://digital.library.unt.edu/ark:/67531/metadc277808/.
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Six sites within the Denton and Hickory Creek watersheds were sampled over three years to assess the impact of seasonal intermittent stream conditions on the ichthyofauna. An integrated approach using field and laboratory techniques was employed to evaluate the responses of the fishes.
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Chapman, Lauren J. (Lauren Jeanette). "Population ecology of the fish Poecilia gillii in an intermittent tropical stream : the effects of seasonal flooding." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74330.
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This thesis demonstrates how the intermittent nature of seasonal tropical fresh waters facilitates and impedes the dispersal of fish and how the variability among residual dry season pools affects the dynamics of isolated populations. I focused on the seasonal ecology of Poecilia gillii from pools in a steep gradient, intermittent stream in Costa Rica. Water temperature and dissolved oxygen concentration were affected by season, by between-pool differences, and by the interaction between seasonal and spatial influences. Seasonal flooding resulted in a catastrophic loss of fish from most pools. Population loss was influenced by the susceptibility of the pools to flooding and population density, with mortality occurring primarily in nearby desiccating "graveyard" pools. Pools increased in population size and density over the 5-month post-flood study period, and their densities converged to their pre-flood values. Variability in the rate of increase among pools was related to water quality and population density. Striking changes in the size and abundance of males over the season suggest social influences on maturation in Poecilia gillii.
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Lubbers, Hannah R. "Impacts of Urbanization and Flow Permanence on Headwater Stream Macroinvertebrates (Hamilton County, Ohio)." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1243026143.
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Bautts, Susan Marie. "An investigation of metal concentrations in waste rock piles, stream water, benthic macroinvertebrates, and stream bed sediments to assess long-term impacts of intermittent precipitation events in the Lefthand Creek watershed, northwestern Boulder County, Colorado." Diss., Connect to online resource, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1433516.
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Vander, Vorste Ross. "The hyporeic zone as a primary source of invertebrate community resilience in intermittent alluvial rivers : evidence from field and mesocosm experiments." Thesis, Lyon 1, 2015. http://www.theses.fr/2015LYO10259/document.
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Un paradigme émergent prédit que les perturbations influencent les processus qui déterminent l'organisation des communautés. L'assèchement des rivières (disparition complète d'eau de surface pour une durée déterminée) est une perturbation naturelle affectant les cours d'eau dans de nombreuses régions du monde. De plus en plus de cours d'eau pérenne s'assèchent en réponse aux changements globaux. Toutefois, l'effet de ces assèchements sur les communautés aquatiques et les processus impliqués dans leur résilience restent mal quantifié et mal compris. A travers quatre études allant de suivis de terrain à des expérimentations in-situ et des mésocosmes en laboratoire, une résilience exceptionnelle des communautés d'invertébrés a été mesurée dans huit rivières alluviales. La zone hyporhéique semble être la principale source de recolonisation expliquant la forte résilience de ces communautés. En laboratoire, l'augmentation de la température et de la compétition intra-spécifique entraine une migration de Gammarus pulex dans la zone hyporhéique. L'augmentation de la profondeur de la zone hyporhéique lors d'assèchements pourrait réduire la résilience et avoir des effets sur les fonctions de l'écosystème (décomposition de litière). Ces résultats montrent que les assèchements n'ont pas toujours des effets sévères sur les communautés d'invertébrés des rivières alluviales qui semblent même très résilientes. La zone hyporhéique joue un rôle primordial dans la résilience des communautés des cours d'eau. Un accent devrait être mis sur la protection de la zone hyporhéique dans les rivières alluviales afin de préserver cette capacité de résilience face aux changements globauxUnderstanding community response to disturbance is essential to identifying processes that determine their assembly and to predicting the future effects of climate change on biodiversity and ecosystem functions. Drying (complete loss of surface water) is a natural disturbance affecting 50% of rivers worldwide and is occurring more in perennial rivers due to climate change. However, its effects on aquatic invertebrate communities and the underlying processes contributing to their resilience (i.e. return to pre-drying or undisturbed levels) have not been well quantified. Using 4 congruous field and mesocosm experiments to quantify community resilience and identify its primary sources in environmentally harsh alluvial rivers. First, I found communities in 8 alluvial rivers were highly resilient to moderate and severe drying. Second, I showed that the hyporheic zone (saturated interstitial sediments) can be the primary source of colonists, promoting high community resilience. Third, I found high water temperature and intraspecific competition caused Gammarus pulex, a common benthic detritivore, to migrate into the hyporheic zone. Fourth, I found increasing depth to the water table diminished the hyporheic zone’s role as a source of colonists by reducing survival of G. pulex. My results support an emerging concept that harsh ecosystems are highly resilient and indicate that the effects of drying on biodiversity and ecosystem functions could vary across river systems. In alluvial rivers, the hyporheic zone can contribute strongly to community resilience and management should focus on protecting and restoring vertical connectivity to maximize resilience to climate change
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Sarremejane, R. (Romain). "Community assembly mechanisms in river networks:exploring the effect of connectivity and disturbances on the assembly of stream communities." Doctoral thesis, Oulun yliopisto, 2018. http://urn.fi/urn:isbn:9789526218632.
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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 functioningTiivistelmä 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
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Guarch, Ribot Alba. "Dissolved organic matter fluctuations in an intermittent headwater stream: from storm oscillations to decadal hydrological changes = Fluctuacions de la matèria orgànica dissolta en un riu de capçalera intermitent : de crescudes a canvis hidrològics decennals." Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/406137.
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Dissolved organic matter (DOM) is an important source of carbon for aquatic microorganisms and it regulates many biogeochemical processes. Therefore, changes in river DOM concentration and properties could notably affect the functioning of fluvial and coastal ecosystems and alter the global carbon cycle. The DOM in headwater streams is strongly influenced by hydrology, as a consequence of the modification of catchment flow paths with high discharges. During storm events, the catchment hillsides are washed and terrigenous DOM is transported to rivers. In the Mediterranean region, the precipitation regime and evapotranspiration strongly modulate fluvial hydrology, which shows low discharges in summer and even flow disappearance. These dry–wet cycles of conditions affect many ecological and biogeochemical processes.
In this thesis, I analyse a long time series of discharge and DOM data from Fuirosos, an intermittent headwater stream in NE Spain. My aim is to examine the relationship between DOM and hydrology at different temporal scales. First, I characterise the hydrological regime of this Mediterranean stream. A decrease in discharge was revealed, although trends in temperature and precipitation were not significant. In contrast, I did not find a clear temporal trend in dry period duration. However, rewetting has been significantly delayed, moving from September to October. The frequency of storm events decreased over the interval 1998–2015, showing a significant positive relationship with solar activity with a 2-year lag.
Dissolved organic carbon (DOC) concentration saw a slight decrease during the study period, which was opposed to that observed in boreal systems. This pattern might respond to a reduction of terrigenous DOC input from forest hillsides as a consequence of the decrease in flushing episodes. The DOC temporal dynamics during the rewetting was regulated by dry period duration. Discharge oscillations explained up to 50% of total DOC variability during the wet period. Notably, this weight of discharge increased significantly over the years.
DOM quality was also explored, and described in terms of absorbance and fluorescence properties. Most of the DOM properties were strongly related to discharge, revealing the input of allochthonous, degraded, aromatic, humic and large-molecular DOM under high flow conditions. However, these relationships were altered during drying and rewetting periods. The DOM responses at the individual storm event scale were highly heterogeneous. Multiple linear regression and commonality analyses showed that, in addition to the magnitude of storm episodes, antecedent hydrological conditions, namely pre-event basal flow and the magnitude of the previous storm event, played a significant role in regulating the trends and shapes of DOM–discharge hysteresis.
Finally, I identified the differences and similarities in the DOM–discharge relationships between the intermittent Mediterranean stream analysed herein and a perennial Alpine stream with higher mean discharge (Oberer Seebach). The DOM in Fuirosos was significantly more concentrated, more terrigenous, more degraded, more aromatic and more humified. The sign of the global DOM–discharge response was the same in both streams. However, discharge was a more robust predictor of DOM variability in Oberer Seebach. In fact, low flow and rewetting periods in Fuirosos introduced considerable dispersion into the relationship. During snowmelt
in Oberer Seebach the sensitivity to discharge also decreased or disappeared. The flushing/dilution patterns were essentially associated with the magnitude of storm events in Fuirosos. In contrast, the DOM quality change was more coupled to basal flow conditions in Oberer Seebach, while the storms were behind the DOC oscillations.
This study attests to the importance of generating and analysing long-term and high-frequency biogeochemical series, which allow relationships between DOM and hydrology to be explored in intermittent headwater streams that are subjected to extreme hydrological regimes.La matèria orgànica dissolta (MOD) és una important font de carboni per als microorganismes aquàtics i regula molts processos biogeoquímics. La MOD en els rius de capçalera està modelada principalment per la hidrologia. A la regió mediterrània, el règim de precipitació i evapotranspiració impacta fortament la hidrologia fluvial, que mostra cabals baixos a l’estiu i pot arribar fins i tot a la seva desaparició. En aquesta tesi hem analitzat un sèrie temporal a llarg termini de cabal i MOD a Fuirosos, un riu de capçalera intermitent al NE de la Península Ibèrica. El nostre objectiu era examinar la relació entre la MOD i la hidrologia en diferents escales temporals. Primer, vam caracteritzar el règim hidrològic d’aquest riu mediterrani. Al llarg de l’estudi es va revelar una disminució del cabal, no vam trobar una tendència temporal clara en la durada de la sequera i la freqüència de les crescudes va disminuir en l’interval 1998–2015. La concentració de carboni orgànic dissolt (COD) ha patit una lleugera disminució durant el període d’estudi, cosa que contrasta amb el que s’ha observat en sistemes boreals. La dinàmica temporal del COD durant el període de transició va ser regulada per la durada del període sec. La qualitat de la MOD també va ser explorada, i descrita en termes de propietats d’absorbència i fluorescència. La majoria de les propietats de la MOD van ser clarament relacionades amb el cabal. No obstant, aquestes relacions van ser alterades durant els períodes de fragmentació i de transició. A més de la magnitud dels episodis de crescuda, les condicions hidrològiques prèvies juguen un paper significatiu perquè regulen les tendències i formes de les histèresis MOD–cabal. Per acabar, vaig identificar les diferències i semblances en les relacions MOD–cabal entre el riu mediterrani intermitent analitzat i un riu perenne alpí amb un cabal mitjà superior (Oberer Seebach). Aquest estudi testifica la importància de generar i analitzar sèries biogeoquímiques de llarga durada i alta freqüència, que permeten explorar les relacions entre la MOD i la hidrologia en rius de capçalera intermitents que estan subjectes a règims hidrològics extrems.
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Timoner, Amer Xisca. "Stream biofilm responses to flow intermittency." Doctoral thesis, Universitat de Girona, 2014. http://hdl.handle.net/10803/283569.
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Streams experiencing a recurrent non-flow phase (i.e., flow intermittency) are characteristic of world regions with arid and semi-arid climates, where Mediterranean regions are part of. During non-flow streambed sediments, and consequently, microorganisms inhabiting these sediments are exposed to desiccation. These microorganisms, assembled in biofilms, lead a substantial part of the ecosystem processes. They recycle the carbon materials, intervene in the nutrient cycles and are on the base of the food web, fueling energy to the higher trophic levels. The aim of this tesis is to understand how biofilms respond to flow intermittency in order to unravel the consequences of the increasing spatial and temporal extent of flow intermittency, as a consequence of the global change, on the biogeochemical cycles and on the ecosystem functions in temporary streams. Structural and functional biofilm responses were analyzed at the cellular level (algae and bacteria), as well as at the whole biofilm responses (autotrophic vs heterotrophic processes) in two different field studiesEls rius que experimenten una fase sense cabal (intermitència fluvial) són característics de les regions del món amb climes àrids i semi-àrids, com ara les regions de la Mediterrànies. Durant la fase seca es produeix la dessecació de la llera del riu i conseqüentment els microorganismes que creixen sobre aquests sediments estan exposats a la dessecació. El conjunt d’aquests microorganismes es coneix com a biofilm, el qual juga un paper clau en el processament de la matèria orgànica i en els cicles del carboni i nutrients, A més són a la base de la xarxa tròfica aportant energia als nivells tròfics superiors. L'objectiu principal d'aquesta tesi és entendre el funcionament del biofilm quan es dona la fase seca, pas clau per entendre i predir les implicacions que tenen els períodes creixents sense cabal en els cicles biogeoquímics i en el funcionament de l’ecosistema. Les respostes estructurals i funcionals del biofilm des d’un punt de vista cel·lular (algues i bacteris), així com també en el conjunt del biofilm (processos autotròfics i heterotròfics) es van investigar mitjançant dos estudis de camp
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Hellum, Aren. "Intermittency and the viscous superlayer in a single stream shear layer." Diss., Connect to online resource - MSU authorized users, 2006.
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Colls, Lozano Miriam. "Biofilm responses to flow intermittency in Mediterranean rivers." Doctoral thesis, Universitat de Girona, 2020. http://hdl.handle.net/10803/670845.
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Currently, global change is promoting the spatiotemporal occurrence of temporary streams, altering fluvial ecosystem function and structure, and the ecosystem services they provide. To effectively protect fluvial ecosystems, a detailed understanding of the effects of hydrological regime changes on their biodiversity and functioning is needed. Organisms inhabiting temporary streams are directly affected by their hydrological regime, including the stream biofilm. Biofilms are associations of microorganisms and they are of particular relevance in temporary streams because of their diversity, abundance, and key role in ecosystem processes. Therefore, understanding biofilm response to hydrological regime variability is key to understand the implications of increasing non-flow periods on fluvial ecosystems. The results of this thesis demonstrate the non-flow duration as a key influence on the structure and functioning of river biofilms, the importance of maintaining photoautotrophic stream biodiversity to preserve stream ecosystems functioning and the protective role of canopy cover to protect these communitiesEl canvi global està promovent l’aparició de rius intermitents, alterant funcionament, estructura i serveis ecosistèmics dels sistemes fluvials. Per a protegir efectivament els ecosistemes fluvials, es necessita un coneixement detallat dels efectes del canvi de règim hidrològic sobre la seva biodiversitat i funcionament. Els organismes que habiten els rius temporals estan directament afectats pels canvis hidrològics, inclòs el biofilm. Els biofilms són associacions de microorganismes i particularment rellevants als rius temporals per la seva diversitat, abundància i paper en processos ecosistèmics. Així, entendre la resposta del biofilm a la variabilitat del règim hidrològic és clau per entendre les implicacions del increment del període sec als ecosistemes fluvials. Els resultats d'aquesta tesi demostren la duració del període sec com a vector d'estructura i funcionament del biofilm, la importància de mantenir la biodiversitat fotoautòtrofa per preservar el funcionament ecosistèmic i el paper protector de la coberta vegetal sobre aquestes comunitats
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McIntyre, Rebecca Elise Sinclair. "Soil biogeochemistry and flooding in intermittent streams of the semi-arid Pilbara region." University of Western Australia. School of Plant Biology, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0115.
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[Truncated abstract] Most of Australia, and large areas of many other continents, is drained by intermittent rivers and streams, however comparatively few biogeochemical studies have been completed for these systems. Intermittent, dryland streams are highly dynamic environments subject to unpredictable and sporadic flow. Natural disturbance from lengthy drought periods and sudden floods are typical for these systems. Without adequate baselines for natural disturbances, it is difficult to quantify other effects from anthropogenic disturbance such as dewatering, land clearing, and urbanisation, or climate change. This thesis presents work from a four-year study examining the biogeochemistry of nitrogen (N), phosphorus (P) and carbon (C) in soils and sediments of two intermittent streams (Barnett Creek and Pirraburdoo Creek) in the Pilbara region of north-west Australia. The Pilbara is an area of ancient geology and highly weathered environments that is undergoing rapid development yet is poorly understood from an ecological perspective. The principal objectives of this thesis were to determine: i) how flooding affects the spatiotemporal patterns of nutrients in intermittent stream landscapes; ii) the role of flooding in N and C mineralisation and microbial dynamics; and iii) the connections between benthic algae, microbes and nutrient availability in channel sediments. To address these objectives, three field studies and two incubation experiments were conducted. Field studies at Barnett Creek indicated that flooding reduced the spatial heterogeneity of available soil nutrients and microbes in the stream landscape, and that topography (relative elevation) in the stream landscape was of less importance in influencing nutrient and microbial patterns than flooding or landscape position. ... Field studies at Pirraburdoo Creek indicated that microbial biomass and activity increased in benthic algal mats during mat senescent stages, and decreased after flooding when mat biomass peaked. Benthic algae grew rapidly in gravel run environments after flooding, while declining in pools, and demonstrated moderate N limitation and strong P limitation. Pools had two to eight times greater NO3-N, three to five times more total N, and two to three times more labile P, OC and total C than either pools after flooding, or runs before or after flooding. Hence, the pools at Pirraburdoo Creek represented a local, interflood store of nutrients in otherwise nutrient-poor landscape, when connectivity to upstream reaches or upland environments was weak or non-existent. This thesis provides the first detailed analysis of soil and sediment biogeochemical responses to flooding for intermittent streams in the Pilbara region and for semi-arid Australia. Further pressing questions raised by this work include: What is the key pulse size and frequency for maintaining Pilbara riparian communities as well as soil microbial function? How do the spatio-temporal nutrient and microbial patterns observed persist over (i) multi-decadal scales, (ii) mega-spatial (larger landscape to regional) scales, (iii) different flood frequency-magnitude regimes, and (iv) different stream sizes? Stream biogeochemistry is a burgeoning field, and it is therefore reasonable to expect such existing gaps in knowledge may be addressed in the near future.
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McKenzie-Smith, Fiona Julie, and n/a. "Habitat and Hydrological Variability in Sub-Tropical Upland Streams in South-East Queensland." Griffith University. Australian School of Environmental Studies, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20030725.142256.
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Headwater streams are extremely vulnerable to the consequences of land-use change as they are tightly coupled with the surrounding landscape. Understanding the natural processes that influence the structure and function of these ecosystems will improve our understanding of how land-use change affects them. Benthic substratum habitat was investigated in a sub-tropical headwater stream by quantifying temporal change to sediment texture of surface sediments (less than 10cm), over four years. Hydrological characteristics were also surveyed in detail, as hydrological regime is a primary determinant of sediment transportation. Additionally, measures of hydro-geological features - hydraulic conductivity and groundwater depth were made in order to explore features of sediment habitat that extend beyond the sediment-water interface. Whilst the typical discharge pattern was one of intermittent base flows and infrequent, yet extreme flood events associated with monsoonal rain patterns, the study period also encompassed a drought and a one in hundred year flood. Rainfall and discharge did not necessarily reflect the actual conditions in the stream. Surface waters were persistent long after discharge ceased. On several occasions the stream bed was completely dry. Shallow groundwater was present at variable depths throughout the study period, being absent only at the height of the drought. The sediments were mainly gravels, sand and clay. Changes in sediment composition were observed for fine particulates (size categories less than 2mm). The grain size change in the finer sediment fractions was marked over time, although bedload movement was limited to a single high discharge event. In response to a low discharge regimen (drought), sediments characteristically showed non-normal distributions and were dominated by finer materials. High-energy discharge regimes (flood) were characterised by coarsening of sands and a diminished clay fraction. Particulate organic matter from sediments showed trends of build-up and decline with the high and low discharge regimes, respectively. Benthic habitats were described according to prevailing hydro-geological parameters. Faunas from sediment substratum samples were associated with identified habitat categories. The fauna reflected the habitat variability in terms of hydrological disturbance of the substratum structure and intermittency of discharge. An applied multivariate procedure was used to correlate temporally changing environmental parameters and faunal abundance data. Faunas were correlated with a group of variables dominated by either discharge variables or sediment textural parameters. Sediment characteristics that affect substratum quality and substratum preference at the micro-scale were investigated via hypotheses testing. A model of carbon loss was used to determine how long particulate organic matter could potentially sustain microbial activity under experimental conditions. An estimate of up to 200 days was determined from this laboratory experiment. Secondly, enriched carbon isotopes were used in a field-based experiment to establish a link between sediments and macrofauna. Enrichment via organic sediments was found for various detritivorous and carnivorous taxa. In the 'third' experiment, artificial treatments were applied to elucidate substratum preference. Fauna was offered the choice of variable quantities of clay and/or quality of organic matter. There were no significant preferences found for the different substratum treatments, although further investigation is needed and a different outcome from this method may be achieved under more benign field conditions than those encountered during this experiment. Finally, the study was set within a context of the primary features of scale. Climate and hydrological features, including linkages with the alluvial aquifer and terrestrial ecosystem, and their potential to change within 'ecological time' are perceived as critical to understanding the role of benthic sediment substratum.
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Nicholas, Hillary Dianne. "Estimating Surface Water Presence and Infiltration for Intermittent Streams in the Semi-arid Southwest." Thesis, The University of Arizona, 2012. http://hdl.handle.net/10150/238891.
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Ephemeral streams with spatially and temporally variable flow are important ecological settings in semi-arid desert environments that until now have been poorly characterized. Our quantitative analysis explores how intermittent stream hydrology varies across geomorphic (mountain streams to desert washes) and climatic gradients (150-400 mm precipitation) in Southern Arizona. Stream channels were instrumented for the first time with a co-deployment of vertical profiles of subsurface temperature sensors, and electrical resistance (ER) sensors on the bed surface. HYDRUS 1-D was used to simulate vertical unsaturated flow, and differences along hydrologic, topographic, and climatic gradients were compared. Annual surface water presence varied < 1%-82% of the year, and reach-normalized infiltration water volumes were 20,000-2,500,000 m³/(km y). Surface water presence was correlated with geomorphic gradient, and infiltration volumes were correlated with surface water presence. This sensor co-deployment method has shown that ER sensors alone are necessary to estimate infiltration in semi-arid, poorly-sorted, coarse desert channels.
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McLeod, Anna L. "Colonisation pathways of an intermittently flowing stream in relation to a changing flow regime and seasonality." Thesis, University of Canterbury. Zoology, 1998. http://hdl.handle.net/10092/6592.
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Invertebrate colonisation pathways were investigated in relation to a changing flow regime and seasonality in a stream with an intermittently flowing lower course at Cass, inland Canterbury. Benthic, drift, hyporheic and non-aquatic adult invertebrate faunas were sampled over a 12 month period, from November 1996 to November 1997. During this period, the stream channel in the lower, grassland reach dried up for three months, from late January to late April, and recolonisation of this reach was assessed following flow resumption. Colonisation pathways operating in both forest and grassland sections of the permanently flowing upper reach were also assessed.
At the perennially flowing forested and grassland sites, invertebrate drift, oviposition by flying adult insects, and vertical migration from the hyporheos all contributed to colonisation of the benthos. Assemblages of invertebrates using the three pathways and the two riparian biotopes (forest and grassland) differed to varying degrees, with drift and flight activity of potential colonists being greatest during summer.
Invertebrate drift from the perennially flowing upper reaches and
oviposition by flying adults appeared to be the main sources of colonists of the intermittent grassland reach when flow resumed in autumn following a three month dry period. The hyporheic zone was of limited importance as a refuge when the channel dried up, since subsurface water disappeared rapidly following the loss of surface flow. Recolonisation of the benthos was gradual, as both drift and ovipositing adults contributed relatively low numbers of colonists in late autumn and winter.
Local conditions, particularly substratum type (which affects hyporheic drainage) and proximity to permanent water bodies (sources of colonists), were important determinants of the colonisation pathways used by invertebrates following flow resumption in the intermittent reach. It will be important to take such local factors into consideration when making predictions about recolonisation pathways operating in other New Zealand streams and rivers.
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Creed, Cari K. "Identifying Controls on Patterns of Intermittent Streamflow in Three Streams of the American Southwest| A Geospatial Approach." Thesis, University of Louisiana at Lafayette, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10681171.
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Despite a rising interest in intermittent river systems, landscape influences on long-term wetting and drying patterns of streamflow are not well understood. There has been a significant increase in the presence of intermittent rivers worldwide due to climate change and subsequent increases in groundwater abstraction, and these effects are intensified in already arid regions such as the American Southwest. Consequently, the spatial extent of wet and dry reaches of Arizona’s Agua Fria River, Cienega Creek, and San Pedro River has been documented by citizen scientists for several years. Citizen science involves the use of trained members of the public for data collection, and the analysis of datasets produced from citizen science projects have become a huge asset to the scientific community. Here, we synthesize the most current data (1999–2016) to determine what stream and valley characteristics act as drivers for patterns of surface water flow. Geologic, geomorphic, and land cover characteristics of these rivers were analyzed via aerial imagery and Digital Elevation Models within ArcGIS 10.3 in conjunction with the Soil and Water Assessment Tool model. Principal Component Analysis was used in order to assess trends across sites. A set of landscape intermittency metrics was produced and then further analyzed using Multiple Linear Regression. We found that land cover had a significant (p-value < 0.01) positive correlation with reach average (i.e., the proportion of channel wet). Physical watershed and channel characteristics each had a negative correlation with both intermittency metrics (i.e., wet/dry status and reach average). However, their results were not significant to the 0.05 level. This study begins to shed light on the drivers of landscape intermittency patterns of desert streams and demonstrates the utility of citizen science in regard to the study of intermittent river systems.
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Alhamdi, Sabah Falih Habeeb. "INTERMITTENCY EFFECTS ON THE UNIVERSALITY OF LOCAL DISSIPATION SCALES IN TURBULENT BOUNDARY LAYER FLOWS WITH AND WITHOUT FREE-STREAM TURBULENCE." UKnowledge, 2018. https://uknowledge.uky.edu/me_etds/116.
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Measurements of the small-scale dissipation statistics of turbulent boundary layer flows with and without free-stream turbulence are reported for Reτ ≈ 1000 (Reθ ≈ 2000). The scaling of the dissipation scale distribution is examined in these two boundary conditions of external wall-bounded flow.
Results demonstrated that the local large-scale Reynolds number based on the measured longitudinal integral length-scale fails to properly normalize the dissipation scale distribution near the wall in these two free-stream conditions, due to the imperfect characterization of the upper bound of the inertial cascade by the integral length-scale. When a length-scale based on Townsend's attached-eddy hypothesis is utilized to describe the local large-scale Reynolds number near the wall, the description of the Reynolds number scaling was determined to be significantly improved and agreed with that found in homogeneous, isotropic turbulence. However, the scaling based on Townsend's attached-eddy hypothesis agreed best for the lowest 40% of the boundary layer thickness and then it degraded due to the loss of the validity of the attached eddy-hypothesis and the onset of external intermittency.
A surrogate large-scale found from turbulent kinetic energy and mean dissipation rate improved the scaling of the dissipation scales, relative to the measured integral length-scale. The probability density functions of the local dissipation scales were calculated. When the three local large-scale Reynolds numbers are used for normalization, the one based on the longitudinal integral length-scale and the one based on the length-scale of attached-eddy hypothesis provide support for the existence of a universal distribution of the local dissipation scales up to the edge of the outer region of the turbulent boundary layer, which scales differently for inner and outer regions. However, the probability density functions of the local dissipation scales normalized by these two large-scale Reynolds numbers are deviated in interface locations for the flow without free-stream turbulence due to external intermittency.
The surrogate large-scale provided the best agreement throughout the entire depth of the boundary layer. However, in the outer part of the boundary layer, a significantly reduced collapse in the scaled probability density functions was shown due to bias in the calculation introduced by the intermittent presence of laminar flow in the time series. To support that intermittency argument, injection of the free-stream turbulence was determined to improve the distribution of these normalized probability density functions in the intermittency locations for the flow regime without free-stream turbulence.
In addition, unlike in channel flow, in the outer part of the turbulent boundary layer, the normalized distributions of the local dissipation scales were observed to be dependent on wall-normal position. This was found to be attributable to the presence of external intermittency in this outer part as the presence of free-stream turbulence was found to restore the scaling behavior by replacing the intermittent laminar flow with turbulent flow.
Thus, the influence of external intermittency on the scaling of the dissipation scale distribution was examined in greater detail for the laminar free-stream condition. Probability density functions of the dissipative scales were compared with, and without, accounting for the external intermittency using an intermittency detection function. Results showed that accounting for the external intermittency produces restores universality in the shapes of the probability density functions at the same wall-normal location at different instances in time. In addition, properly scaling the dissipation-scale-distribution collapses the probability density functions calculated at different wall-normal locations. This improvement in the scaling of the dissipation-scale-distribution supports prior observations of universality of the small-scale description of the turbulence for wall-bounded flow.
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Carpenter, Forrest Michael. "Understanding the Importance of Intermittently Fragmented Stream Habitat for Isolated Westslope Cutthroat Trout (Oncorhynchus clarki lewisi) in the Colville National Forest, Washington." PDXScholar, 2016. http://pdxscholar.library.pdx.edu/open_access_etds/3315.
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Climate change and anthropogenic effects have vastly reduced Westslope Cutthroat Trout (Oncorhynchus clarki lewisi, WCT) habitat throughout their range, including the Colville National Forest in northeastern Washington where this study was conducted. Many native salmonid populations have declined in abundance since the early 1900s due to a variety of climate- and human-driven forces. Westslope Cutthroat Trout are especially sensitive to habitat loss or degradation and to climate change. Together, climate change, habitat degradation, and non-native salmonid invasions are contributing to increasingly fragmented WCT populations. Ongoing and predicted future warming trends are expected to further fragment these populations and isolate them in headwater stream reaches, with populations in the spatial margins of their distributions facing greater risk. Native salmonid populations are often separated or isolated by natural or artificial upstream migration barriers (i.e., waterfalls, culverts, etc.). Prior to continuing conservation and management actions targeting WCT, it is imperative to understand habitat requirements of this keystone species in fragmented areas. Field survey data were collected in the summer of 2015 on channel geomorphic characteristics and WCT presence/absence in 26 streams located in the Colville National Forest. A clear spatial separation was observed between Eastern Brook Trout (Salvenius fontinalis, EBT) and WCT above four culvert road crossings and the habitat in both of these areas was compared statistically to identify explicit differences. This dataset was also analyzed using logistic regression modeling to determine the best habitat predictors of the presence of isolated WCT populations existing upstream of these crossing. In general, stream habitat in the Middle and South Forks of Mill Creek had low large substrate, high fine sediments, and exhibited pool-riffle channel morphology. Pool habitat supporting isolated WCT was significantly smaller, in terms of volume and surface area, than pool habitat supporting sympatric populations of WCT and EBT, largely due to the headwater nature of channel units supporting isolated WCT populations. Additionally, due to the extreme drought conditions during 2015, stream flow was substantially diminished in the study area causing these reaches to be highly fragmented and largely disconnected from the rest of the stream channel. Fine sediments were generally higher in headwater reaches supporting isolated WCT, including in pools and riffles, which was unexpected, mainly because they exist above sediment delivery points in the longitudinal extent of the system.
Logistic regression analysis indicated that the presence of isolated WCT populations was primarily positively associated with an increase in large wood and boulders, and negatively associated with increasing gravel, bedrock, habitat unit length, depth, and width (Significant x2, R2=0.174, misclassification rate = 14.9%, α=0.05). The final model correctly predicted 37.5% of isolated WCT presence observations and 96.5% of the WCT/EBT presence observations significantly better than by chance alone (k=0.81). This model, in fact, may be useful in identifying limited habitat due to the fragmented nature of the channel units supporting IWCT. Large wood and boulders were positively correlated to WCT presence, likely because both are important in the formation of pools and cascades. Channel unit length, width, depth, active channel width as well as gravel and bedrock substrates, were all negatively associated with WCT presence. This suggests that isolated WCT are primarily associated with small headwater cascades with complex shelter, which may provide greater thermal and predation refuge compared to shallow glide or large pool habitats. Future model analysis should include additional habitat variables such as water temperature, stream gradient, and species interactions to strengthen the prediction of Westslope Cutthroat Trout presence. Overall, I concluded that differences in stream habitat above and below blocking culverts are not driving Westslope Cutthroat Trout distributions in the study area due to confounding factors such as the presence of problematic barriers and small sample size. I also conclude that future conservation and management decisions specific to WCT should prioritize complex cascade habitat in headwater stream reaches because of the type and quantity of habitat they may provide, especially during severe drought or low flow conditions.
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Rosset, Véronique, Albert Ruhi, Michael T. Bogan, and Thibault Datry. "Do lentic and lotic communities respond similarly to drying?" WILEY, 2017. http://hdl.handle.net/10150/625362.
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Disturbance is a central factor shaping composition, structure, and dynamics of local communities. Drying is a disturbance that occurs in aquatic ecosystems globally and can strongly influence their communities. Although the effects of drying may depend on ecosystem connectivity and the dispersal abilities of resident species, there have been no comparisons of community responses to drying between lentic and lotic ecosystems across different climates. Here, we predicted that drying would have stronger effects on aquatic communities in isolated lentic ecosystems than in dendritic lotic ecosystems, owing to the higher hydrological connectivity of the latter, and that drying would have stronger effects on passive than on active dispersers, because of the potentially higher recolonizing ability of the latter. We tested these predictions by comparing alpha diversity, phylogenetic relatedness, and beta diversity for active and passive dispersers, in both ecosystem types across five climatic regions. Drying caused greater declines in alpha diversity in lentic than in lotic ecosystems. Communities that experienced drying were more similar to one another than those of perennial sites, and this pattern was especially pronounced in lentic ecosystems. In contrast, drying did not influence the contributions of turnover and richness gradients to beta diversity. Additionally, dispersal mode did not influence community responses to drying. Relatively weaker effects of drying in lotic compared to lentic systems were likely due to the hydrological connectivity among perennial and temporary river sites, which may facilitate dispersal of organisms to escape drying and recolonize rewetted sites. Collectively, our results suggest that habitat connectivity may ameliorate (and fragmentation may worsen) the impacts of drying disturbance. This is an important finding in light of increasing drying and concomitant aquatic habitat fragmentation under global change.
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Loustau, Emilie. "Effet des facteurs environnementaux sur la nature des EPS, la capacité de sorption du cuivre et le potentiel de résilience de biofilms phototrophes simplifiés." Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30148.
Full textAbstract:
Les biofilms phototrophes, principale signature trophique benthique des rivières à écoulement rapide, offrent un panel de services écologiques en lien avec les processus d'autoépuration (nitrates, pesticides, pollutions métalliques, etc.). Cependant, leur fonctionnement est fortement perturbé par les pressions anthropiques croissantes qu'ils subissent, notamment celles associées à la présence d'éléments traces métalliques (ETM) ou encore l'interruption séquentielle de l'écoulement de surface. Dans un contexte de changement global avéré, la réponse des communautés phototrophes est au centre des préoccupations pour la gestion de ces milieux, tant pour leur qualité chimique qu'écologique. L'objectif de ce travail de thèse est de comprendre les réponses physiologiques des microorganismes phototrophes benthiques à des facteurs d'environnement révélateurs de changements globaux (lumière, température, phosphore) ainsi qu'à l'application d'un multi- stress combinant l'exposition à des ETM (Cu et Zn, appliqués seuls ou en cocktail) suivie d'un assèchement prolongé du biofilm. Les réponses physiologiques sont centrées sur la biomasse, l'activité photosynthétique et la production d'EPS (substances polymériques extracellulaires), en abordant ces processus par l'aptitude de tolérance et de résilience des communautés. Le choix s'est porté sur trois espèces phototrophes benthiques, une cyanobactérie (Phormidium autumnale), une diatomée (Nitzschia palea) et une algue verte (Uronema confervicolum). Un système expérimental adapté à la culture en biofilm au sein de microcosmes à écoulement de surface libre (mini-canaux hydrauliques) a permis de contrôler l'ensemble des paramètres des expérimentations. La première étape a consisté à mettre au point une méthode d'extraction des EPS de la matrice de biofilm tout en préservant l'intégrité cellulaire des microorganismes phototrophes. L'analyse de la réponse physiologique de biofilms phototrophes mono-espèce face à une exposition au Cu et/ou au Zn a permis de montrer les différences de sensibilité des espèces phototrophes testées. Puis, la capacité de sorption du Cu par ces mêmes biofilms phototrophes s'est révélée être dépendante des facteurs environnementaux, via la modulation des EPS produites et de leur nature. Enfin, l'application d'un double-stress, conjuguant l'exposition au Cu suivie d'un assèchement du biofilm, permet également de mesurer des réponses de résilience lors de la remise en eau, elles-mêmes modulées par les facteurs environnementaux testés. Globalement, les biofilms phototrophes mono-espèce testés présentent des capacités de tolérance et de résilience différentes avec des réponses de modulation de la quantité et de la nature des EPS produitesPhototrophic biofilm, the main benthic signature of fast-flowing rivers, provide an important number of ecosystem services related to self-purification mechanisms (nitrates, pesticides, metal contaminations, etc.). However, their functioning is strongly disturbed by the increasing anthropogenic pressures, particularly by the presence of traces metals (TM) or the sequential interruption of surface flow. In the context of global change, the response of phototrophic communities should be considered for river management, in term of chemical and ecological properties. The aim of this thesis was to understand the physiological responses of benthic phototrophic microorganisms to environmental parameters involved in global change (light, temperature, phosphorus) as well as their response to a multi-stress combining the exposure of biofilms to TM (Cu and Zn, alone or in cocktail) by the prolonged drying of biofilm. Physiological responses of biofilm (biomass, photosynthetic activity and EPS production (extracellular polymeric substances)) were studied to analyze the tolerance and resilience capacities of communities. Three benthic phototrophic species were chosen: the cyanobacteria Phormidium autumnale, the diatom Nitzschia palea and the green algae Uronema confervicolum. Cultures of biofilm in free surface flow microcosms (hydraulic mini-channels) allowed to control all the experimental parameters. The first step was to develop a method for EPS extraction from the biofilm matrix while preserving the cell integrity of phototrophic microorganisms. Subsequently, the study of physiological responses of monospecific phototrophic biofilm exposed to Cu or/and Zn showed different sensitivities of phototrophic species. Then the sorption capacity of Cu by these species depended on environmental parameters, via the modulation of EPS production and composition. Finally, the double-stress characterised by Cu exposition followed by drying biofilm induced also resilience responses when rewetting, modulated by the environmental parameters. Overall, the monospecific phototrophic biofilms studied present different tolerance and resilience capacities by modifying the abundance and composition of EPS produced
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Lee, Yu Man. "Amphibian communities and physical characteristics of intermittent streams in old-growth and young forest stands in western Oregon." Thesis, 1997. http://hdl.handle.net/1957/34085.
Full textAbstract:
Intermittent, headwater streams recently have been recognized as important
components of forest ecosystems and have been provided increased protection by the
Northwest Forest Plan. However, few studies have examined their distribution,
dynamics, and ecological roles, such as habitat for wildlife. My goal was to provide
additional information on the ecology of intermittent streams in the Pacific Northwest. I
examined and compared hydrologic, water quality, and physical characteristics of 16
intermittent streams in old-growth and young forest stands in the central Cascade Range
in western Oregon. I documented amphibian communities and habitat associations in
these streams during spring and summer. I used comparisons of current habitat
conditions and amphibian communities between stand types to gain insight into potential
impacts of timber harvesting on these stream systems.
Of the streams surveyed in old-growth and young forest stands, relatively few
(23%) were designated as intermittent based on my definition which included presence of
a definable channel, evidence of annual scour and deposition, and lack of surface flow
along at least 90% of the stream length. Intermittent streams in old-growth stands
exhibited the following characteristics: (1) annual flow pattern in which streams started
to dry in May and June and were mostly dry by July; (2) lengthy annual flow durations
(range 6-11 months); (3) cool and stable daily stream temperatures; (4) primarily coarse
substrates, such as cobbles and pebbles; (5) streamside vegetation comprised of
predominantly coniferous overstories, and plant species associated with uplands or dry
site conditions, such as Oregon-grape and salal, as well as riparian areas or wet site
site conditions, such as Oregon-grape and salal, as well as riparian areas or wet site
conditions, such as red alder, oxalis, red huckleberry, and vine maple (Steinblums et al.
1984, Bilby 1988); and (6) low to moderate densities of large wood, mostly moderately- and
well-decayed. Study streams in young forest appeared to dry about one to two
months later than the streams in old growth but had similar annual flow durations. They
also were characterized by higher daily stream temperatures, similar diel fluctuations,
finer substrates, more deciduous overstory and herbaceous understory cover, and lower
densities of moderately-decayed large wood. Differences in habitat conditions between
stand types may be attributed to timber harvesting as well as discrepancies in
physiographic and geological factors, such as elevationgradient, and soil type.
Amphibian communities in spring and summer were comprised primarily of the
Cascade torrent salamander (Rhyacotriton cascadae), Dunn's salamander (Plethodon
dunni), and Pacific giant salamander (Dicamptodon tenebrosus). Amphibian
communities in streams in young forest stands exhibited different species composition
and seasonal patterns in total density from those in old growth. Cascade torrent
salamanders and Dunn's salamanders maintained similar densities and biomass between
spring and summer by potentially adopting drought avoidance strategies. Species
differed in their use of habitat types and associations with habitat features. In general,
amphibian species were positively correlated with percent surface flow, water
depth, intermediate-sized substrates and negatively associated with overstory canopy
cover, elevation, and wood cover.
Results of my study suggest that intermittent streams may warrant protection for
their potential effects on downstream habitat and water quality and for their role as
habitat for aquatic species, such as amphibians. Streamside vegetation should be
maintained along intermittent channels to provide shade protection for water temperature
regulation and sources of large woody debris and other allochthonous energy input, to
help stabilize slopes, and to minimize erosion and sedimentation. At a minimum,
intermittent stream channels should receive protection from physical disturbance during
timber harvesting operations. However, since intermittent stream systems are highly
variable, management should address individual site conditions and vary accordingly.Graduation date: 1997
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Hennigar, Julie Michelle. "Effects of anthropogenic alterations to ephemeral and intermittent headwater drainage features on downstream fish communities." Thesis, 2012. http://hdl.handle.net/10012/6964.
Full textAbstract:
Headwater drainage features (HDFs) in the GTA are commonly subjected to land-use modifications including agricultural uses and urbanization. A temporal study design approach was used to test whether the runoff being exported from previously modified HDFs differed from runoff exported from less disturbed forested channels. Drift nets were deployed in the permanent reaches of streams and in the HDF channels, to give an indication of the quality and quantity of drifting materials. Gastric lavage was used to remove stomach contents from creek chub living downstream from HDFs and these contents were used to determine if invertebrates in HDF runoff could act as food immediately upon reaching fish-bearing sections of stream. Reaches of streams associated with forested HDFs were found to have more fish than either those associated with agricultural or urban HDFs (203, 184 and 145 fish per forested, agricultural and urban site, respectively). Sites associated with forested catchments also had a greater number of salmonids per site. Conditions of high flow in the stream and the HDF coincided with an increased quantity of drifting invertebrates in all site types and land uses, as well as a decrease in the proportion of creek chub with empty stomachs. Overall, aquatic Diptera were the most numerous invertebrates captured in drift nets and in the stomach contents of creek chub. Hymenoptera, terrestrial Oligochaeta and Diplopoda also made major contributions to the diets of creek chub. Results indicate that HDFs in all land uses are exporting both aquatic and terrestrial invertebrates to main streams at times of high flow. Creek chub consume more prey at times of high flow, and this often includes terrestrial invertebrates, which must have been imported from terrestrial sources to the aquatic environment, however the degree to which they are exported by HDFs is still not clear. The series of complex interactions occurring at the HDF/main stream interface requires further study.