Spatio-temporal changes in water quality in the Guarapiranga reservoir (São Paulo, Brazil): insights from a long-term monitoring data series.

The provision of drinking water in metropolises is a challenge that requires programs for continuous monitoring of water quality and processes that impact the land cover of the watershed. In this work, we investigated through multivariate statistical analysis the temporal and spatial trends of several variables, not yet explored in a data series that includes 42 years (1978-2020) of monitoring in the hydrographic basin of the Guarapiranga reservoir, in the São Paulo Metropolitan Region-SPMR (Brazil). This reservoir is the source of drinking water for 3.8 million people and plays a strategic role in the social, environmental, and economic structure at SPMR. Our results point to the continuous degradation of water quality in the reservoir, although with different causes and spatio-temporal aspects. Between the 1970s and 1980s, variables associated with erosion/silting played a more critical role. From the 1990s, the introduction of N and P intensified, and the concentration of thermotolerant coliforms increased. The loss of quality is mainly associated with the progressive advance of urban settlements without planning combined with the inefficient initiatives to control domestic sewage pollution. If there is no rapid and comprehensive intervention, there is a risk that the Guarapiranga reservoir may become unsuitable for drinking water supply and other types of use in the future. This scenario will represent a critical obstacle to regional development and the quality of life of the population.

A long-term study on zooplankton in two contrasting cascade reservoirs (Iguaçu River, Brazil): effects of inter-annual, seasonal, and environmental factors.

BACKGROUND: In reservoirs, zooplankton strongly interact with the physical and chemical characteristics of water, and this interaction is mainly influenced by climate variation and the different methods used to manage the dam water level. Therefore, the aim of this study was to evaluate how the distinct operating modes of two cascade reservoirs affected the richness, abundance, and composition of zooplankton, both spatially (intra and inter-reservoirs) and temporally (annual and seasonal). In this study, the upstream reservoir (Salto Santiago) operates using the storage method, with a water retention time (WRT) of 51 days, whereas the downstream reservoir (Salto Osório) operates using the run-of-river method, with a WRT of 16 days. METHODS: Zooplankton samples were collected for 16 consecutive years from the two reservoirs located on the Iguaçu River, Brazil. A total of 720 samples were collected. Four-way ANOVAs were used to determine the differences in richness and abundance of the zooplankton among years, periods, reservoirs, and environments. Multidimensional non-metric scaling (NMDS) and an analysis of similarities (ANOSIM) were used to describe similarity patterns in species composition. Finally, a canonical correspondence analysis (CCA) was used to select the environmental predictors that best explained the variation in zooplankton abundance data. RESULTS: We identified a total of 115 taxa in this study, and rotifers were the richest group. In contrast, the copepods were the most abundant. The four-way ANOVA results showed significant differences in the species richness and abundance of the zooplankton among years, periods, reservoirs, and environments. The NMDS ordination and ANOSIM test indicated that the largest differences in zooplankton species composition were annual and seasonal differences. Finally, the CCA showed that these differences were mainly associated with changes in water transparency, temperature, and the chlorophyll a, phosphorus, and total dissolved solids concentrations. DISCUSSION: Inter-annual changes in zooplankton species composition showed that over time, large filters-feeders (e.g., large daphinids and calanoid copepods) were replaced by small cladocerans (e.g., bosminids) and generalist rotifers. The highest species richness was associated with the fluvial environment, whereas the highest abundance was associated with the transitional and lacustrine reservoir environments. Variations in water temperature, nutrients, and food availability explained the annual and seasonal changes in community structure, whereas variations in the water flow characteristics of the environments explained the longitudinal changes in the richness and abundance of zooplankton in reservoirs. The differences in zooplankton structure between the two reservoirs can be explained by the functional differences between the two systems, such as their WRTs and morphometrics.

Storage or Run-of-river Reservoirs: Exploring the Ecological Effects of Dam Operation on Stability and Species Interactions of Fish Assemblages.

Water level variation has an important role in the biology of fish species, driving behavior, feeding, and reproduction both in natural and modified environments. In reservoirs, different dam operation schemes result in alternative patterns of water level fluctuations. Storage (STR) reservoirs accumulate water and can vary the water level unpredictably, whereas this variation is more discrete in run-of-river (ROR) reservoirs. For this reason, ROR reservoirs are commonly presumed to be less environmentally harmful than STR reservoirs. We used multivariate autoregressive models (MAR) to compare the stability and species interactions of fish assemblages from two reservoirs under alternative operation schemes, using long-term data (15 years). We hypothesized that the lower variability of water level in the ROR reservoir would coincide with a more stable fish assemblage than in the STR reservoir. Contrary to our expectation, the MAR properties related to resilience and resistance indicated that the fish assemblage from the ROR was less stable than that from the STR reservoir. This suggests that the absence of water level variation limits the potential direct (movement and reproduction of fish) and indirect (primary production and nutrient input) benefits for fish that arise from the temporal environmental heterogeneity. Most importantly, this study highlights the need to reexamine the implications of ROR reservoirs on the health of aquatic communities. At least for fish, management actions should include varying the water level in a regime as similar as possible to the natural flow regime of the river, in order to improve the state of assemblages.

Impact of copper sulfate application at an urban Brazilian reservoir: A geostatistical and ecotoxicological approach.

A landscape ecotoxicology approach was used to assess the spatial distribution of copper in the recent bottom sediment (surficial sediment) of a Brazilian subtropical reservoir (the Guarapiranga reservoir) and its potential ecotoxicological impacts on the reservoir ecosystem and the local society. We discuss the policies and procedures that have been employed for the management of this reservoir over the past four decades. Spatial heterogeneity in the reservoir was evaluated by means of sampling design and statistical analysis based on kriging spatial interpolation. The sediment copper concentrations have been converted into qualitative categories in order to interpret the reservoir quality and the impacts of management policies. This conversion followed the Canadian Water Framework Directive (WFD) ecotoxicological concentration levels approach, employing sediment quality guidelines (SQGs). The SQG values were applied as the copper concentration thresholds for quantitative-qualitative conversion of data for the surficial sediment of the Guarapiranga. The SQGs used were as follows: a) interim sediment quality guideline (ISQG), b) probable effect level (PEL), and c) regional reference value (RRV). The quantitative results showed that the spatial distribution of copper in the recent bottom sediment reflected the reservoir's management policy and the copper application protocol, and that the copper concentrations varied considerably, ranging from virtually-zero to in excess of 3gcopper/kgds. The qualitative results demonstrated that the recent bottom sediment was predominantly in a bad or very bad condition, and could therefore have impacts on the local society and the ecosystem. It could be concluded that the management policy for this reservoir was mainly determined by the desire to minimize short-term costs, disregarding long-term socioeconomic and environmental consequences.

Downstream passage of fish larvae and eggs through a small-sized reservoir, Mucuri river, Brazil

In South America, one important symptom of the failure of fish passages to sustain fish migratory recruitment is the inability of eggs and larvae to reach the nurseries. This is especially so when the breeding areas are located upstream of a reservoir, and the floodplain is downstream of the dam. Therefore, the transport of fish larvae and eggs across reservoir barriers is a key factor in the development of effective conservation strategies. In this paper, we evaluate the potential for migratory fish larvae and egg transportation across a small size reservoir in eastern Brazil. We sampled fish daily between 15th October 2002 and 15th February 2003 (spawning period) in the Mucuri River, immediately upstream of the reservoir and downstream of the Santa Clara Power Plant dam. Our study was the first to indicate the possibility of successful larval passage through the reservoir of a hydroelectric reservoir and dam in South America, and showed that the passage of migratory fish larvae was associated significantly with residence time of water in the reservoir. The relatively short water residence time and elevated turbidity of the Santa Clara's reservoir waters during the rainy season certainly contributed to the successful passage, and can be considered as key factors for a priori evaluations of the feasibility of a downstream larval passage.

Downstream passage of fish larvae and eggs through a small-sized reservoir, Mucuri river, Brazil

In South America, one important symptom of the failure of fish passages to sustain fish migratory recruitment is the inability of eggs and larvae to reach the nurseries. This is especially so when the breeding areas are located upstream of a reservoir, and the floodplain is downstream of the dam. Therefore, the transport of fish larvae and eggs across reservoir barriers is a key factor in the development of effective conservation strategies. In this paper, we evaluate the potential for migratory fish larvae and egg transportation across a small size reservoir in eastern Brazil. We sampled fish daily between 15th October 2002 and 15th February 2003 (spawning period) in the Mucuri River, immediately upstream of the reservoir and downstream of the Santa Clara Power Plant dam. Our study was the first to indicate the possibility of successful larval passage through the reservoir of a hydroelectric reservoir and dam in South America, and showed that the passage of migratory fish larvae was associated significantly with residence time of water in the reservoir. The relatively short water residence time and elevated turbidity of the Santa Clara's reservoir waters during the rainy season certainly contributed to the successful passage, and can be considered as key factors for a priori evaluations of the feasibility of a downstream larval passage.

Downstream passage of fish larvae and eggs through a small-sized reservoir, Mucuri river, Brazil

In South America, one important symptom of the failure of fish passages to sustain fish migratory recruitment is the inability of eggs and larvae to reach the nurseries. This is especially so when the breeding areas are located upstream of a reservoir, and the floodplain is downstream of the dam. Therefore, the transport of fish larvae and eggs across reservoir barriers is a key factor in the development of effective conservation strategies. In this paper, we evaluate the potential for migratory fish larvae and egg transportation across a small size reservoir in eastern Brazil. We sampled fish daily between 15th October 2002 and 15th February 2003 (spawning period) in the Mucuri River, immediately upstream of the reservoir and downstream of the Santa Clara Power Plant dam. Our study was the first to indicate the possibility of successful larval passage through the reservoir of a hydroelectric reservoir and dam in South America, and showed that the passage of migratory fish larvae was associated significantly with residence time of water in the reservoir. The relatively short water residence time and elevated turbidity of the Santa Clara's reservoir waters during the rainy season certainly contributed to the successful passage, and can be considered as key factors for a priori evaluations of the feasibility of a downstream larval passage.

Efficiency and selectivity of a trap and truck fish passage system in Brazil

The construction of fish passages has been one of the strategies adopted by the Brazilian energy sector in order to diminish the effects of barriers on fish communities. However, studies of the efficiency of these mechanisms are scarce. The present study evaluated the efficiency and selectivity of the first trap and truck fish passage system in Brazil, installed in Santa Clara Dam, Mucuri River. The species composition in the Santa Clara Dam fish lift was compared to the original composition of Mucuri River fish fauna and with the populations that gather downstream of the dam during the reproductive season. The proportion of previously tagged individuals translocated by the lift was used to estimate its efficiency. During the 2003/2004 reproductive period, 67,841 individuals of 32 species passed through the lift, which corresponds to 66% of the lower Mucuri river fish richness. Less than 0.5% died or were injured during the passage. When compared to the river's population, less representative captures of smaller individuals and marine species were observed. However, the composition and structure of the community in the fish lift was quite similar to those downstream of the dam during the reproductive season. The estimated efficiency of the fish lift ranged from 0.2% for Pogonopoma wertheimeri to 16.1% for Leporinus conirostris reaching an average of 7% for all migratory species.

A construção de passagens para peixes tem sido uma das estratégias adotadas pelo setor elétrico como forma de diminuir os efeitos de barramentos sobre as comunidades de peixes. No entanto, trabalhos de avaliação da eficiência destes mecanismos são escassos. Neste trabalho são avaliadas a eficiência e seletividade do primeiro elevador com caminhão tanque instalado no Brasil, na Usina Hidrelétrica de Santa Clara. A composição de espécies no elevador foi comparada com aquela original do rio, e com a das populações que se aglomeram a jusante da barragem, durante a estação reprodutiva. A proporção de indivíduos previamente marcados transpostos pelo elevador foi utilizada como forma de estimar sua eficiência. Durante o período reprodutivo (2003/2004) 67841 indivíduos de 32 espécies de peixes passaram pelo elevador, o que corresponde a 66% da riqueza do baixo curso do rio Mucuri. Destes, menos de 0,5% morreram ou foram feridos durante a passagem. Quando comparado com as populações do rio, foram observadas no elevador capturas menos representativas de indivíduos de pequeno porte e de espécies marinhas. No entanto, a composição e estrutura da comunidade no elevador foram bastante similares àquela observada a jusante da barragem durante o período reprodutivo. A eficiência estimada para o elevador variou de 0,2% para Pogonopoma wertheimeri até 16,1% para Leporinus conirostris, sendo de 7% para o conjunto de espécies migradoras.