Ecological effects of flow and temperature regimes on fish communities in temperate rivers

Les organismes aquatiques sont adaptés à une grande variabilité hydrique et thermique des rivières. Malgré ceci, la régulation des eaux suscite des changements aux débits qui peuvent provoquer des impacts négatifs sur la biodiversité et les processus écologiques en rivière. Celle-ci peut aussi causer des modifications au niveau des régimes thermiques et des caractéristiques de l’habitat du poisson. Des données environnementales et biologiques décrivant l’habitat du poisson existent, mais elles sont incomplètes pour plusieurs rivières au Canada et de faible qualité, limitant les relations quantitatives débit-température-poissons à un petit nombre de rivières ou à une région étudiée. La recherche menée dans le cadre de mon doctorat concerne les impacts de la génération d'hydroélectricité sur les rivières; soit les changements aux régimes hydriques et thermiques reliés à la régulation des eaux sur la variation des communautés ichtyologiques qui habitent les rivières régulées et naturelles au Canada. Suite à une comparaison d’échantillonnage de pêche, une méthode constante pour obtenir des bons estimés de poisson (richesse, densité et biomasse des espèces) a été établie pour évaluer la structure de la communauté de poissons pour l’ensemble des rivières ciblées par l’étude. Afin de mieux comprendre ces changements environnementaux, les principales composantes décrivant ces régimes ont été identifiées et l’altération des régimes hydriques pour certaines rivières régulées a été quantifiée. Ces résultats ont servi à établir la relation significative entre le degré de changement biotique et le degré de changement hydrique pour illustrer les différences entre les régimes de régulation. Pour faire un complément aux indices biotiques déjà calculés pour l’ensemble des communautés de poissons (diversité, densité et biomasse des espèces par rivière), les différences au niveau des guildes de poissons ont été quantifiées pour expliquer les divers effets écologiques dus aux changements de régimes hydriques et thermiques provenant de la gestion des barrages. Ces derniers résultats servent à prédire pour quels traits écologiques ou groupes d’espèces de poissons les composantes hydriques et thermiques sont importantes. De plus, ces derniers résultats ont servi à mettre en valeur les variables décrivant les régimes thermiques qui ne sont pas toujours inclues dans les études hydro-écologiques. L’ensemble des résultats de cette thèse ont des retombées importantes sur la gestion des rivières en évaluant, de façon cohérente, l’impact de la régulation des rivières sur les communautés de poissons et en développant des outils de prévision pour la restauration des écosystèmes riverains.

Ecological effects of flow and temperature regimes on fish communities in temperate rivers

Les organismes aquatiques sont adaptés à une grande variabilité hydrique et thermique des rivières. Malgré ceci, la régulation des eaux suscite des changements aux débits qui peuvent provoquer des impacts négatifs sur la biodiversité et les processus écologiques en rivière. Celle-ci peut aussi causer des modifications au niveau des régimes thermiques et des caractéristiques de l’habitat du poisson. Des données environnementales et biologiques décrivant l’habitat du poisson existent, mais elles sont incomplètes pour plusieurs rivières au Canada et de faible qualité, limitant les relations quantitatives débit-température-poissons à un petit nombre de rivières ou à une région étudiée. La recherche menée dans le cadre de mon doctorat concerne les impacts de la génération d'hydroélectricité sur les rivières; soit les changements aux régimes hydriques et thermiques reliés à la régulation des eaux sur la variation des communautés ichtyologiques qui habitent les rivières régulées et naturelles au Canada. Suite à une comparaison d’échantillonnage de pêche, une méthode constante pour obtenir des bons estimés de poisson (richesse, densité et biomasse des espèces) a été établie pour évaluer la structure de la communauté de poissons pour l’ensemble des rivières ciblées par l’étude. Afin de mieux comprendre ces changements environnementaux, les principales composantes décrivant ces régimes ont été identifiées et l’altération des régimes hydriques pour certaines rivières régulées a été quantifiée. Ces résultats ont servi à établir la relation significative entre le degré de changement biotique et le degré de changement hydrique pour illustrer les différences entre les régimes de régulation. Pour faire un complément aux indices biotiques déjà calculés pour l’ensemble des communautés de poissons (diversité, densité et biomasse des espèces par rivière), les différences au niveau des guildes de poissons ont été quantifiées pour expliquer les divers effets écologiques dus aux changements de régimes hydriques et thermiques provenant de la gestion des barrages. Ces derniers résultats servent à prédire pour quels traits écologiques ou groupes d’espèces de poissons les composantes hydriques et thermiques sont importantes. De plus, ces derniers résultats ont servi à mettre en valeur les variables décrivant les régimes thermiques qui ne sont pas toujours inclues dans les études hydro-écologiques. L’ensemble des résultats de cette thèse ont des retombées importantes sur la gestion des rivières en évaluant, de façon cohérente, l’impact de la régulation des rivières sur les communautés de poissons et en développant des outils de prévision pour la restauration des écosystèmes riverains.

Periphyton as an indicator of restoration in the Everglades

Periphyton communities dominate primary production in much of the Florida Everglades wetland and therefore contribute to soil production, ecosystem metabolism and secondary production as well as the composition of dependent communities. Decades of research in the Everglades have supported research findings from other wetland types that cumulatively show that periphyton communities respond very rapidly to alterations in the two dominant drivers of wetland structure and function—hydrology and water quality. Hydrology controls periphyton productivity and composition by regulating moisture availability, substrate types available for colonization and supply of nutrients. Nutrients, particularly the limiting nutrient in this system, phosphorus (P), control levels of production and community composition. Because periphyton communities are well-established to be related to hydrology and water quality, an indicator was developed based on three periphyton attributes: abundance, quality (i.e., nutrient content) and community composition. This assessment tool offers a qualitative assessment of ecosystem response to potential changes in management activities at a time scale appropriate for active management. An example is provided of how the indicator can be used to assess the current water quality and hydrological conditions from high-density spatial surveys. Detected patterns of deterioration align with expectations derived from model predictions and known sources of nutrients and unnatural hydrologic regimes. If employed adaptively in ecosystem management, this tool can be used to both detect and react to change before the system has been irreparably altered.

Water Uptake Patterns of an Invasive Exotic Plant in Coastal Saline Habitats

Schinus terebinthifolius Raddi (Schinus) is one of the most widely found woody exotic species in South Florida. This exotic is distributed across environments with different hydrologic regimes, from upland pine forests to the edges of sawgrass marshes and into saline mangrove forests. To determine if this invasive exotic had different physiological attributes compared to native species in a coastal habitat, we measured predawn xylem water potentials (Ψ), oxygen stable isotope signatures (δ18O), and sodium (Na+) and potassium (K+) contents of sap water from plants within: (1) a transition zone (between a mangrove forest and upland pineland) and (2) an upland pineland in Southwest Florida. Under dynamic salinity and hydrologic conditions, Ψ of Schinus appeared less subject to fluctuations caused by seasonality when compared with native species. Although stem water δ18O values could not be used to distinguish the depth of Schinus and native species' water uptake in the transition zone, Ψ and sap Na+/K+ patterns showed that Schinus was less of a salt excluder relative to the native upland species during the dry season. This exotic also exhibited Na+/K+ ratios similar to the mangrove species, indicating some salinity tolerance. In the upland pineland, Schinus water uptake patterns were not significantly different from those of native species. Differences between Schinus and native upland species, however, may provide this exotic an advantage over native species within mangrove transition zones.

Loaxahatchee Impoundment Landscape Assessment (LILA): Tree Island Experiments and Management; May 1, 2005 to September 4, 2009: Final Report

Hydrologic modifications have negatively impacted the Florida Everglades in numerous significant ways. The compartmentalization of the once continuously flowing system into the Water Conservation Areas (WCAs) caused disruption of the slow natural flow of water south from Lake Okeechobee through the Everglades to Florida Bay. The ponding of water in the WCAs, the linking of water flow to controlled water levels, and the management of water levels for anthropogenic vs. ecological well-being has caused a reduction in the spatial heterogeneity of the Everglades leading to greater uniformity in topography and vegetation. These effects are noticeable as the degradation in structure of the Everglades Ridge and Slough environment and associated Tree Islands. In aquatic systems water flow is of fundamental importance in shaping the structure and function of the ecosystem. The organized patterns of parallel orientation of ridges, sloughs, and tear-drop shaped tree islands along historic flow paths attest to the importance of water movement in structuring this system. Our main objective was to operate and manage the LILA facility to provide a broad potential as a research platform for an integrated group of multidisciplinary, multi-agency scientists collaborating on multifunctional studies aimed primarily at determining the effects of CERP water management scenarios on the ecology of tree islands and ridge and slough habitats. We support Everglades water management, CERP, and the Long-Term Plan by defining hydrologic regimes that sustain healthy tree islands and ridge and slough ecosystems. Information gained through this project will help to reduce the uncertainty of predicting the tree island and ridge and slough ecosystem response to changes in hydrologic conditions. Additionally, we have developed the LILA site as a visual example of Everglades restoration programs in action.

Cape Sable Seaside Sparrow Habitat Monitoring and Assessment - 2010 Final Report

For the last two decades, the Cape Sable seaside sparrow (CSSS), a federally endangered species, has been a pivot point for water management operations in the Everglades, primarily because a decline in sparrow population in the early 1990s was attributed in part to managementinduced alterations in hydrologic regimes. With a goal of understanding the response of landscape-level processes to hydrological restoration and its interaction with fire, a study intended to monitor vegetation structure and composition throughout the marl prairie landscape has been conducted since 2003 with funding from U.S. Army Corps of Engineers (USACE). In the first three years (2003-2005), vegetation structure and composition was characterized in relation to the existing hydrologic regime and fire history. During 2006-2010, vegetation was resampled to assess vegetation change within the sparrow habitat. This document summarizes the vegetation change pattern observed between the two sampling periods in sub-population A, C, E and F, emphasizing the work accomplished in FY 2010.

Monitoring of Tree Island Condition in the Southern Everglades: Annual Report 2011

Tree islands, a prominent feature in both the marl prairie and ridge and slough landscapes of the Everglades, are sensitive to large-scale restoration actions associated with the Comprehensive Everglades Restoration Plan (CERP) authorized by the Water Resources Development Act (WRDA) 2000 to restore the south Florida ecosystem. More specifically, changes in hydrologic regimes at both local and landscape scales are likely to affect the internal water economy of islands, which in turn will influence plant community structure and function. To strengthen our ability to assess the “performance” of tree island ecosystems and predict how these hydrologic alterations would translate into ecosystem response, an improved understating of reference conditions of vegetation structure and function, and their responses to major stressors is important. In this regard, a study of vegetation structure and composition in relation to associated physical and biological processes was initiated in 2005 with initial funding from Everglades National Park and South Florida Water Management District (SFWMD). The study continued through 2011 with funding from US Army Corps of Engineers (USACOE) (Cooperative Agreement # W912HZ-09-2-0019 Modification No.: P00001).

Landscape Pattern – Marl Prairie/Slough Gradient: Vegetation Composition along the Gradient and Decadal Vegetation Change Pattern in Shark Slough: Annual Report 2012

In the southern Everglades, vegetation in both the marl prairie and ridge and slough landscapes is sensitive to large-scale restoration activities associated with the Comprehensive Everglades Restoration Plan (CERP) authorized by the Water Resources Development Act (WRDA) 2000 to restore the south Florida ecosystem. More specifically, changes in hydrologic regimes at both local and landscape scales are likely to affect vegetation composition along marl prairie-slough gradient resulting in a shift in boundary between plant communities in these landscapes. To strengthen our ability to assess how vegetation would respond to changes in underlying ecosystem drivers along the gradient, an improved understanding of reference conditions of plant community structure and function, and their responses to major stressors is important. In this regard, a study of vegetation structure and composition in relation to physical and biological processes along the marl prairie-slough gradient was initiated in 2005, and has continued through 2012 with funding from US Army Corps of Engineers (USACOE) (Cooperative Agreement # W912HZ-09-2-0018 Modification No.: P00002). This study addresses the hypothesis with respect to RECOVER-MAP monitoring item 3.1.3.5 – “Marl Prairie/Slough Gradients; patterns and trends in Shark Slough marshes and associated marl prairies”.

Classification of natural flow regimes in the Ebro basin (Spain) by using a wide range of hydrologic parameters

Clasificación de tipos de régimenes naturales de caudales a partir de parámetros de tres componentes del régimen fluvial: magnitud, frecuencia y duración.

Automation of DEM Cutting for Hydrologic/Hydraulic Modeling, TR-631, 2015

Hydrologic analysis is a critical part of transportation design because it helps ensure that hydraulic structures are able to accommodate the flow regimes they are likely to see. This analysis is currently conducted using computer simulations of water flow patterns, and continuing developments in elevation survey techniques result in higher and higher resolution surveys. Current survey techniques now resolve many natural and anthropogenic features that were not practical to map and, thus, require new methods for dealing with depressions and flow discontinuities. A method for depressional analysis is proposed that uses the fact that most anthropogenically constructed embankments are roughly more symmetrical with greater slopes than natural depressions. An enforcement method for draining depressions is then analyzed on those depressions that should be drained. This procedure has been evaluated on a small watershed in central Iowa, Walnut Creek of the South Skunk River, HUC12 # 070801050901, and was found to accurately identify 88 of 92 drained depressions and place enforcements within two pixels, although the method often tries to drain prairie pothole depressions that are bisected by anthropogenic features.

Regimes de precipitação na América do Sul: uma revisão bibliográfica

Como a América do Sul se estende por diferentes latitudes e possui formas de relevo variadas, proporciona a atuação e o desenvolvimento de diferentes sistemas atmosféricos, os quais contribuem para a não homogeneidade climática da região. Portanto o objetivo deste estudo é apresentar uma revisão dos sistemas atmosféricos que atuam nos diferentes setores do continente sul-americano e que contribuem para a precipitação.

Signatures of oxygen on Cu(3)Au(100): From isolated impurity to oxide regimes

We analyze the scanning tunneling microscopy (STM) signatures for the O/Cu(3)Au(100) surface from the low-coverage (isolated impurity) to high-coverage (oxide) regimes. First-principles calculations show that oxygen signatures switch from dark to bright spots as the oxygen coverage increases. This behavior is nicely traced back to a change in the oxygen orbital character of the Fermi-level electronic states. Our results allow for the chemical identification by STM of oxygen and copper atoms in the fully ordered O/Cu(3)Au(100)-c(2x2) surface.

Crossover between the extended and localized regimes in stochastic partially self-avoiding walks in one-dimensional disordered systems

Consider N sites randomly and uniformly distributed in a d-dimensional hypercube. A walker explores this disordered medium going to the nearest site, which has not been visited in the last mu (memory) steps. The walker trajectory is composed of a transient part and a periodic part (cycle). For one-dimensional systems, travelers can or cannot explore all available space, giving rise to a crossover between localized and extended regimes at the critical memory mu(1) = log(2) N. The deterministic rule can be softened to consider more realistic situations with the inclusion of a stochastic parameter T (temperature). In this case, the walker movement is driven by a probability density function parameterized by T and a cost function. The cost function increases as the distance between two sites and favors hops to closer sites. As the temperature increases, the walker can escape from cycles that are reminiscent of the deterministic nature and extend the exploration. Here, we report an analytical model and numerical studies of the influence of the temperature and the critical memory in the exploration of one-dimensional disordered systems.

Kondo screening regimes of a quantum dot with a single Mn ion

We study the Kondo and transport properties of a quantum dot with a single magnetic Mn ion connected to metallic leads. By employing a numerical renormalization group technique we show that depending on the value of ferromagnetic coupling strength between the local electronic spin and the magnetic moment of the Mn, two distinct Kondo regimes exist. In the weak-coupling limit, the system can be found in a completely screened Kondo state describing a local magnetic moment decoupled from the rest of the system. In contrast, in the strong-coupling regime the quantum dot spin and the local magnetic moment form a single large-spin entity partially Kondo screened. A crossover between these two regimes can be suitably tuned by varying the tunnel coupling between the quantum dot and the leads. The model investigated here is also suitable to study magnetic molecules adsorbed on a metallic surface. The rich phenomenology of these systems is reflected in the conductance across the system.

Rotifer abundance, biomass, and secondary production after the recovery of hydrologic connectivity between a river and two marginal lakes (Sao Paulo, Brazil)

Rotifera density, biomass, and secondary production on two marginal lakes of Paranapanema River were compared after the recovery of hydrologic connectivity with the river (Sao Paulo State, Brazil). Daily samplings were performed in limnetic zone of both lakes during the rainy season immediately after lateral inflow of water and, in the dry period, six months after hydrologic connectivity recovery. In order to identify the factors that affect rotifer population dynamics, lake water level, volume, depth, temperature, transparency, dissolved oxygen, pH, alkalinity, conductivity, suspended solids, nutrients, and chlorophyll-a were determined. Variations of water physical and chemical factors that affect rotifer population were related to the lake-river degree of connection and to water level rising after drought. The water lateral inflow from the river resulted in an increase in lake water volume, depth, and transparency and a decrease in water pH, alkalinity, and suspended solids. The lake with the wider river connection, more frequent biota exchange, and larger amount of particulate and dissolved materials was richer and more diverse, while rotifer density, biomass, and productivity were lower in both periods studied. Density, biomass, and secondary production were higher in the lake with the smaller river connection and the higher physical and chemical stability. Our results show that the connectivity affects the limnological stability, associated to seasonality. Stable conditions, caused by low connectivity in dry periods, were related with high density, biomass and secondary production. Conversely, instability conditions in rainy periods were associated to elevated richness and diversity values, caused by exchange biota due to higher connectivity. (C) 2008 Elsevier GmbH. All rights reserved.