Mitigation of ecological impacts on fish of large reservoir sediment management through controlled flushing - The case of the Verbois dam (Rhône River, Switzerland).

Sediment trapping within reservoirs is a worldwide phenomenon which impairs the ecological functioning of upstream and downstream ecosystems. It also reduces reservoir water storage volume, which lessens the services dams provide such as hydropower production or flood control and questions their sustainability. Hydraulic flushing is a widely used operation to recover the reservoir volume, but ecological impacts are massive. Recently, environmental awareness led dam operators to modify their management practices: 'Controlled Sediment Flushing Operations' (CSFOs) include environmental objectives in their implementation and are designed to be less harmful for aquatic ecosystems by controlling the flow and Suspended Sediment Concentration (SSC) downstream. However, CSFOs are not yet widespread, their ecological impacts are poorly documented, and comparisons with 'classical' flushing operations are unreported. Here, we analysed impacts on fish of the first CSFO of the Verbois reservoir in 2016, both upstream and downstream of the dam, and compared these with those from the empty flushing of 2012 using the same methodology (Grimardias et al., 2017). Time-series of hydroacoustics surveys enabled us to estimate the fish abundance in the reservoir, while radiotelemetry measured movements and apparent survival below the dam for four representative species. The 2016 CSFO lasted 10 days, and released a mean Suspended Sediment Concentration (SSC) of 3.47 g·L-1 (peak = 11.98 g·L-1). The fish density as assessed by the mean acoustic scattering strength SA in the reservoir did not change significantly pre- and post-CSFO, and SA seasonal estimates of year 2016 did not differ from those of 2015 and 2017. The apparent survival estimated from capture-recapture survey of marked fish (N = 118) decreased significantly during the CSFO for all species and differed across species, while the distances moved downstream increased. By comparison with the 2012 empty flushing, the 2016 CSFO allowed fish to remain in the reservoir, while impacts below the dam were mostly behavioural rather than lethal. Overall, despite significant impacts, the CSFO advantageously replaced 'classical' flushing from an ecological viewpoint. Provided that an acceptable balance between economical, ecological and technical aspects is found, CSFO can be considered for many reservoirs while accounting for their biological and physical site-specificity.

Genetic evaluation of migratory fish: Implications for conservation and stocking programs.

Fish stocking programs have been implemented to mitigate the blockage of original riverbeds by the construction of hydropower dams, which affects the natural migration of fish populations. However, this method raises concerns regarding the genetic rescue of the original populations of migratory fish species. We investigated the spatial distribution of genetic properties, such as genetic diversity, population structure, and gene flow (migration), of the Neotropical migratory fish Prochilodus costatus in the Três Marias dam in the São Francisco River basin, Brazil, and examined the possible effects of fish stocking programs on P. costatus populations in this region. In total, 1,017 specimens were sampled from 12 natural sites and a fish stocking program, and genotyped for high-throughput sequencing at 8 microsatellite loci. The populations presented low genetic variability, with evidence of inbreeding and the presence of only four genetic pools; three pools were observed throughout the study region, and the fourth was exclusive to one area in the Paraopeba River. Additionally, we identified high unidirectional gene flow between regions, and a preferred migratory route between the Pará River and the upper portion of the São Francisco River. The fish stocking program succeeded in transposing the genetic pools from downstream to upstream of the Três Marias dam, but, regrettably, promoted genetic homogenization in the upper São Francisco River basin. Moreover, the data show the fragility of this species at the genetic level. This monitoring strategy could be a model for the development of conservation and management measures for migratory fish populations that are consumed by humans.

Long-term mark-recapture and growth data for large-sized migratory brown trout (Salmo trutta) from Lake Mjøsa, Norway.

BACKGROUND: Long-term data from marked animals provide a wealth of opportunities for studies with high relevance to both basic ecological understanding and successful management in a changing world. The key strength of such data is that they allow us to quantify individual variation in vital rates (e.g. survival, growth, reproduction) and then link it mechanistically to dynamics at the population level. However, maintaining the collection of individual-based data over long time periods comes with large logistic efforts and costs and studies spanning over decades are therefore rare. This is the case particularly for migratory aquatic species, many of which are in decline despite their high ecological, cultural and economical value. NEW INFORMATION: This paper describes two unique publicly available time series of individual-based data originating from a 51-year mark-recapture study of a land-locked population of large-sized migratory brown trout (Salmo trutta) in Norway: the Hunder trout. In the period 1966-2015, nearly 14,000 adult Hunder trout have been captured and individually marked during their spawning migration from Lake Mjøsa to the river Gubrandsdalslågen. Almost a third of those individuals were later recaptured alive during a later spawning run and/or captured by fishermen and reported dead or alive. This has resulted in the first data series: a mark-recapture-recovery dataset spanning half a century and more than 18,000 capture records. The second data series consists of additional data on juvenile and adult growth and life-history schedules from half of the marked individuals, obtained by means of scale-sample analysis. The two datasets offer a rare long-term perspective on individuals and population dynamics and provide unique opportunities to gain insights into questions surrounding management, conservation and restoration of migratory salmonid populations and freshwater ecosystems.

Using hydrodynamic and water quality variables to assess eutrophication in a tropical hydroelectric reservoir.

Few studies have examined the influence of reservoir hydrodynamics on the water quality of its limnological zones. In this study, the relationships between the operational phases and the water quality of the limnological zones were assessed for the Amazonian reservoir Tucuruí. Limnological zones were clustered by means of an artificial neural network technique, and inputs used were water quality variables, measured at twelve stations between 2006 and 2016. Generalized Linear Models (GLMs) were then used to identify the influence of the operational phases of the reservoir on the water quality of its limnological zones. The GLM with a gamma-distributed response variable indicated that Chlorophyll-a concentrations in the riverine and transitional zones differed notably from those observed in the lacustrine zone. Chlorophyll-a concentrations were significantly lower during the operational falling water phase than in the low water phase (p < 0.05). The GLM with an inverse Gaussian-distributed response variable indicated that Secchi depth was significantly lower in the riverine than in the lacustrine limnological zone (p < 0.05). Our results suggest that more eutrophic conditions occur during the operational rising water phase, and that the area most vulnerable to eutrophication is the transitional zone. We demonstrate that the use of GLMs is suitable for determining areas and operational phases most vulnerable to eutrophication. We envisage that this information will be useful to decision-makers when monitoring the water quality of hydroelectric reservoirs with dendritic patterns and dynamic operational phases.

Massive tree mortality from flood pulse disturbances in Amazonian floodplain forests: The collateral effects of hydropower production.

Large dams built for hydroelectric power generation alter the hydrology of rivers, attenuating the flood pulse downstream of the dam and impacting riparian and floodplain ecosystems. The present work mapped black-water floodplain forests (igapó) downstream of the Balbina Reservoir, which was created between 1983 and 1987 by damming the Uatumã River in the Central Amazon basin. We apply remote sensing methods to detect tree mortality resulting from hydrological changes, based on analysis of 56 ALOS/PALSAR synthetic aperture radar images acquired at different flood levels between 2006 and 2011. Our application of object-based image analysis (OBIA) methods and the random forests supervised classification algorithm yielded an overall accuracy of 87.2%. A total of 9800 km2 of igapó forests were mapped along the entire river downstream of the dam, but forest mortality was only observed below the first 49 km downstream, after the Morena rapids, along an 80-km river stretch. In total, 12% of the floodplain forest died within this stretch. We also detected that 29% of the remaining living igapó forest may be presently undergoing mortality. Furthermore, this large loss does not include the entirety of lost igapó forests downstream of the dam; areas which are now above current maximum flooding heights are no longer floodable and do not show on our mapping but will likely transition over time to upland forest species composition and dynamics, also characteristic of igapó loss. Our results show that floodplain forests are extremely sensitive to long-term downstream hydrological changes and disturbances resulting from the disruption of the natural flood pulse. Brazilian hydropower regulations should require that Amazon dam operations ensure the simulation of the natural flood-pulse, despite losses in energy production, to preserve the integrity of floodplain forest ecosystems and to mitigate impacts for the riverine populations.

Bacterial Communities in Riparian Sediments: A Large-Scale Longitudinal Distribution Pattern and Response to Dam Construction.

Sediment microbes play major roles in riparian ecosystems; however, little is known about their longitudinal distribution pattern and their responses to dam construction, the most severe human disturbance in river basins. Here, we investigated the variability of sediment bacterial communities along a large-scale longitudinal gradient and between dam-controlled and dam-affected sites in riparian zone of the Lancang River, China. The abundance, activity and diversity of sediment bacteria gradually increased in a downstream direction, but were significantly lower in the dam-affected sites than in the dam-controlled sites. The bacterial community compositions differed significantly between the upper-middle-reach and downstream sites at all control sites, and also between the dam-affected and dam-controlled sites. In the cascade dam area, the relative importance of spatial distance and environmental heterogeneity for bacterial distribution differed between the dam-controlled and dam-affected sites. Spatial distance was the primary cause of variations in bacterial community in dam-controlled site. By contrast, the environmental heterogeneity had more control over the bacterial communities than did the spatial distance in dam-affected site. Network analysis showed that the bacterial community in the dam-affected sites had lower connectivity and stability when compared with that in dam-controlled sites. These results suggest the distinct variations in sediment bacterial community in dam-affected sites, which could enhance our understanding of potential ecological effects caused by dam construction.

Responses of aquatic macrophytes to anthropogenic pressures: comparison between macrophyte metrics and indices.

Macrophyte responses to anthropogenic pressures in two rivers of Central Spain were assessed to check if simple metrics can exhibit a greater discriminatory and explanatory power than complex indices at small spatial scales. Field surveys were undertaken during the summer of 2014 (Duraton River) and the spring of 2015 (Tajuña River). Aquatic macrophytes were sampled using a sampling square (45 × 45 cm). In the middle Duraton River, macrophytes responded positively to the presence of a hydropower dam and a small weir, with Myriophyllum spicatum and Potamogeton pectinatus being relatively favored. Index of Macrophytes (IM) was better than Macroscopic Aquatic Vegetation Index (MAVI) and Fluvial Macrophyte Index (FMI) in detecting these responses, showing positive and significant correlations with total coverage, species richness, and species diversity. In the upper Tajuña River, macrophytes responded both negatively and positively to the occurrence of a trout farm effluent and a small weir, with Leptodictyum riparium and Veronica anagallis-aquatica being relatively favored. Although IM, MAVI, and FMI detected both negative and positive responses, correlations of IM with total coverage, species richness, and species diversity were higher. Species evenness was not sensitive enough to detect either positive or negative responses of aquatic macrophytes along the study areas. Overall, traditional and simple metrics (species composition, total coverage, species richness, species diversity) exhibited a greater discriminatory and explanatory power than more recent and complex indices (IM, MAVI, FMI) when assessing responses of aquatic macrophytes to anthropogenic pressures at impacted specific sites.

Spatial patterns of water quality in Xingu River Basin (Amazonia) prior to the Belo Monte dam impoundment / Padrões espaciais de qualidade de água na Bacia do Rio Xingu (Amazônia) anteriores a barragem de Belo Monte

Abstract The Xingu River, one of the most important of the Amazon Basin, is characterized by clear and transparent waters that drain a 509.685 km2 watershed with distinct hydrological and ecological conditions and anthropogenic pressures along its course. As in other basins of the Amazon system, studies in the Xingu are scarce. Furthermore, the eminent construction of the Belo Monte for hydropower production, which will alter the environmental conditions in the basin in its lower middle portion, denotes high importance of studies that generate relevant information that may subsidize a more balanced and equitable development in the Amazon region. Thus, the aim of this study was to analyze the water quality in the Xingu River and its tributaries focusing on spatial patterns by the use of multivariate statistical techniques, identifying which water quality parameters were more important for the environmental changes in the watershed. Data sampling were carried out during two complete hydrological cycles in twenty-five sampling stations. The data of twenty seven variables were analyzed by Spearman's correlation coefficients, cluster analysis (CA), and principal component analysis (PCA). The results showed a high auto-correlation between variables (> 0.7). These variables were removed from multivariate analyzes because they provided redundant information about the environment. The CA resulted in the formation of six clusters, which were clearly observed in the PCA and were characterized by different water quality. The statistical results allowed to identify a high spatial variation in the water quality, which were related to specific features of the environment, different uses, influences of anthropogenic activities and geochemical characteristics of the drained basins. It was also demonstrated that most of the sampling stations in the Xingu River basin showed good water quality, due to the absence of local impacts and high power of depuration of the river itself.

Resumo O rio Xingu, um dos mais importantes rios que constituem a bacia amazônica, é caracterizado por águas claras e transparentes que drenam uma bacia hidrográfica de 509,685 km2 com distintas condições hidrológicas, ecológicas e pressões antrópicas ao longo de seu percurso. Assim como nas demais bacias hidrográficas da Amazônia, os estudos no Xingu são raros. A eminente construção da Usina hidrelétrica de Belo Monte, a qual alterará as condições ambientais na bacia, demanda também a realização de estudos que gerem informações relevantes e que forneçam subsídios para um desenvolvimento mais equilibrado e igualitário região amazônica. Desta maneira, o objetivo deste trabalho foi analisar a qualidade de água no rio Xingu e em seus tributários focando em padrões espaciais na área de estudo pelo uso de técnicas de estatística multivariada, identificando quais parâmetros são mais relevantes nas condições de qualidade de água na bacia hidrográfica. As coletas de dados ocorreram durante dois ciclos hidrológicos completos em vinte e cinco estações de amostragem. Os dados de vinte e sete variáveis foram analisados pelos coeficientes de correlação de Spearman, análise Cluster (CA), e análise de componentes principais (PCA). Os resultados apontaram para um elevado contingente de variáveis com elevada correlação entre si (>0,7), sendo que estas altas variáveis foram retiradas das análises multivariadas por fornecerem informações ecológicas redundantes sobre o ambiente estudado. A CA resultou na formação de 6 agrupamentos, os quais foram observados por possuírem qualidade de água consideravelmente distintas pela PCA. Os resultados estatísticos permitiram identificar uma alta variação espacial da qualidade de água superficial na bacia estudada, sendo estas ocasionadas por especificidades do entorno, diferentes usos da água locais, influências de atividades antrópicas e características geoquímicas das bacias drenadas. Pode-se também evidenciar que em grande parte das estações de coleta na bacia do rio Xingu a qualidade de água superficial foi elevada, decorrente da ausência de impactos locais e do alto poder de depuração do rio.

Spatial patterns of water quality in Xingu River Basin (Amazonia) prior to the Belo Monte dam impoundment

Abstract The Xingu River, one of the most important of the Amazon Basin, is characterized by clear and transparent waters that drain a 509.685 km2 watershed with distinct hydrological and ecological conditions and anthropogenic pressures along its course. As in other basins of the Amazon system, studies in the Xingu are scarce. Furthermore, the eminent construction of the Belo Monte for hydropower production, which will alter the environmental conditions in the basin in its lower middle portion, denotes high importance of studies that generate relevant information that may subsidize a more balanced and equitable development in the Amazon region. Thus, the aim of this study was to analyze the water quality in the Xingu River and its tributaries focusing on spatial patterns by the use of multivariate statistical techniques, identifying which water quality parameters were more important for the environmental changes in the watershed. Data sampling were carried out during two complete hydrological cycles in twenty-five sampling stations. The data of twenty seven variables were analyzed by Spearman's correlation coefficients, cluster analysis (CA), and principal component analysis (PCA). The results showed a high auto-correlation between variables (> 0.7). These variables were removed from multivariate analyzes because they provided redundant information about the environment. The CA resulted in the formation of six clusters, which were clearly observed in the PCA and were characterized by different water quality. The statistical results allowed to identify a high spatial variation in the water quality, which were related to specific features of the environment, different uses, influences of anthropogenic activities and geochemical characteristics of the drained basins. It was also demonstrated that most of the sampling stations in the Xingu River basin showed good water quality, due to the absence of local impacts and high power of depuration of the river itself.

Resumo O rio Xingu, um dos mais importantes rios que constituem a bacia amazônica, é caracterizado por águas claras e transparentes que drenam uma bacia hidrográfica de 509,685 km2 com distintas condições hidrológicas, ecológicas e pressões antrópicas ao longo de seu percurso. Assim como nas demais bacias hidrográficas da Amazônia, os estudos no Xingu são raros. A eminente construção da Usina hidrelétrica de Belo Monte, a qual alterará as condições ambientais na bacia, demanda também a realização de estudos que gerem informações relevantes e que forneçam subsídios para um desenvolvimento mais equilibrado e igualitário região amazônica. Desta maneira, o objetivo deste trabalho foi analisar a qualidade de água no rio Xingu e em seus tributários focando em padrões espaciais na área de estudo pelo uso de técnicas de estatística multivariada, identificando quais parâmetros são mais relevantes nas condições de qualidade de água na bacia hidrográfica. As coletas de dados ocorreram durante dois ciclos hidrológicos completos em vinte e cinco estações de amostragem. Os dados de vinte e sete variáveis foram analisados pelos coeficientes de correlação de Spearman, análise Cluster (CA), e análise de componentes principais (PCA). Os resultados apontaram para um elevado contingente de variáveis com elevada correlação entre si (>0,7), sendo que estas altas variáveis foram retiradas das análises multivariadas por fornecerem informações ecológicas redundantes sobre o ambiente estudado. A CA resultou na formação de 6 agrupamentos, os quais foram observados por possuírem qualidade de água consideravelmente distintas pela PCA. Os resultados estatísticos permitiram identificar uma alta variação espacial da qualidade de água superficial na bacia estudada, sendo estas ocasionadas por especificidades do entorno, diferentes usos da água locais, influências de atividades antrópicas e características geoquímicas das bacias drenadas. Pode-se também evidenciar que em grande parte das estações de coleta na bacia do rio Xingu a qualidade de água superficial foi elevada, decorrente da ausência de impactos locais e do alto poder de depuração do rio.

Spatial patterns of water quality in Xingu River Basin (Amazonia) prior to the Belo Monte dam impoundment / Padrões espaciais de qualidade de água na Bacia do Rio Xingu (Amazônia) anteriores a barragem de Belo Monte

The Xingu River, one of the most important of the Amazon Basin, is characterized by clear and transparent waters that drain a 509.685 km2 watershed with distinct hydrological and ecological conditions and anthropogenic pressures along its course. As in other basins of the Amazon system, studies in the Xingu are scarce. Furthermore, the eminent construction of the Belo Monte for hydropower production, which will alter the environmental conditions in the basin in its lower middle portion, denotes high importance of studies that generate relevant information that may subsidize a more balanced and equitable development in the Amazon region. Thus, the aim of this study was to analyze the water quality in the Xingu River and its tributaries focusing on spatial patterns by the use of multivariate statistical techniques, identifying which water quality parameters were more important for the environmental changes in the watershed. Data sampling were carried out during two complete hydrological cycles in twenty-five sampling stations. The data of twenty seven variables were analyzed by Spearman's correlation coefficients, cluster analysis (CA), and principal component analysis (PCA). The results showed a high auto-correlation between variables (> 0.7). These variables were removed from multivariate analyzes because they provided redundant information about the environment. The CA resulted in the formation of six clusters, which were clearly observed in the PCA and were characterized by different water quality. The statistical results allowed to identify a high spatial variation in the water quality, which were related to specific features of the environment, different uses, influences of anthropogenic activities and geochemical characteristics of the drained basins. It was also demonstrated that most of the sampling stations in the Xingu River basin showed good water quality, due to the absence of local impacts and high power of depuration of the river itself.

O rio Xingu, um dos mais importantes rios que constituem a bacia amazônica, é caracterizado por águas claras e transparentes que drenam uma bacia hidrográfica de 509,685 km2 com distintas condições hidrológicas, ecológicas e pressões antrópicas ao longo de seu percurso. Assim como nas demais bacias hidrográficas da Amazônia, os estudos no Xingu são raros. A eminente construção da Usina hidrelétrica de Belo Monte, a qual alterará as condições ambientais na bacia, demanda também a realização de estudos que gerem informações relevantes e que forneçam subsídios para um desenvolvimento mais equilibrado e igualitário região amazônica. Desta maneira, o objetivo deste trabalho foi analisar a qualidade de água no rio Xingu e em seus tributários focando em padrões espaciais na área de estudo pelo uso de técnicas de estatística multivariada, identificando quais parâmetros são mais relevantes nas condições de qualidade de água na bacia hidrográfica. As coletas de dados ocorreram durante dois ciclos hidrológicos completos em vinte e cinco estações de amostragem. Os dados de vinte e sete variáveis foram analisados pelos coeficientes de correlação de Spearman, análise Cluster (CA), e análise de componentes principais (PCA). Os resultados apontaram para um elevado contingente de variáveis com elevada correlação entre si (>0,7), sendo que estas altas variáveis foram retiradas das análises multivariadas por fornecerem informações ecológicas redundantes sobre o ambiente estudado. A CA resultou na formação de 6 agrupamentos, os quais foram observados por possuírem qualidade de água consideravelmente distintas pela PCA. Os resultados estatísticos permitiram identificar uma alta variação espacial da qualidade de água superficial na bacia estudada, sendo estas ocasionadas por especificidades do entorno, diferentes usos da água locais, influências de atividades antrópicas e características geoquímicas das bacias drenadas. Pode-se também evidenciar que em grande parte das estações de coleta na bacia do rio Xingu a qualidade de água superficial foi elevada, decorrente da ausência de impactos locais e do alto poder de depuração do rio.