Long-term study of reservoir cascade in Southeastern Brazil reveals spatio-temporal gradient in fish assemblages

In reservoir cascades, effects on fish assemblages are expected to strengthen over time and transfer from one reservoir to an adjacent one. To test this, fish assemblage data from 23 years of monitoring in the Araguari reservoir cascade system, upper Paraná River basin, were analyzed. From 1993 to 2015, 72 fish species were recorded in the studied reservoirs, representing five orders and 19 families. In all, 58 species were native to the basin and 14 non-native (10 from other Brazilian basins and four from other countries). The results showed a clear reduction in richness of native and migratory fish species and an increase of non-native species, following reservoir formation. Migratory species richness was higher in reservoirs that presented habitats similar to lotic stretches or tributaries upstream of the impounded area. A clear tendency for native species’ decline and non-native fish abundance to increase, was observed in a downstream direction. Fish assemblages became increasingly dissimilar as reservoirs became more distant from each other (longitudinal gradient) and were dominated by small and medium sized species. Alongside biogeographic factors and the presence of non-piscivorous non-native species, reservoir area and age were found to be important drivers of variation in fish assemblage structure. Results from this study help to clarify the potential accumulated impacts of reservoirs cascades on fish diversity, which must be carefully considered in river basin inventories for hydropower plants, and reinforces the importance of long-term monitoring, considering longitudinal and lateral dimensions of the basin

Optimizing hydropower dam location and removal in the São Francisco River basin, Brazil to balance hydropower and river biodiversity tradeoffs

To support eco-friendly hydropower planning in developing regions, we propose a spatial optimization model for locating dams to balance tradeoffs between hydropower generation and migratory fish species richness. Our model incorporates two special features. First, it is tailored to the dispersal of tropical migratory fishes, which require long, unimpeded river stretches to complete their life-cycle. To model fish with this type of dispersal pattern, we introduce the concept of a river pathway, which represents a novel way to describe river connectivity. Second, it combines decisions about dam placement and removal, thus facilitating opportunities for hydropower offsetting. We apply our model to the São Francisco River basin, Brazil, an area of hydropower-freshwater biodiversity conflict. We find that dams have reduced weighted migratory fish richness 51% compared to a pre-dam baseline. We also find that even limited dam removal has the potential to significantly enhance fish biodiversity. Offsetting the removal of a single dam by the optimal siting of new dams could increase fish richness by 25% above the current average. Moving forward, optimizing new dam sites to increase hydropower by 20%, rather than selecting the fewest number of dams, could reduce fish species losses by 89%. If decisions about locating new dams are combined with dam removal, then a win-win can even be achieved with 20% greater hydropower and 19% higher species richness. Regardless of hydropower targets and dam removal options, a key observation is that optimal sites for dams are mostly located in the upper reaches of the basin rather than along the main stem of the São Francisco River or its main tributaries

Reliability of arterialized venous blood samples

The venous blood samples collected from the hand and from the ear lobule after heating have been used as a substitute of the arterial blood samples. Objective: The aim of this study was to determine the efficiency and reliability of this method during rest and exercise. Methods: The venous blood samples were collected (n = 14, 22 ± 3 yr., 71.3 ± 15.5 kg) on the back of the hand before and after immersion in warm water (41-43° C). ANOVA and Tukey post hoc test (P < 0.05) were used for statistical analysis. Results: The arterialized blood samples were signficantly lower on the [Lac] (-0.45 ± 0.49 mmoW 1); [HCO3] (-1.04 ± 2,76 mmoM'1) and PC02 (-5.51 ± 7.4 mmHg) in contrast an increment on the pH (0.040 ± 0.044), P02 (30.3 ± 26.2 mmHg) and %S02 (18.9 ± 18.1%) was perceived. No differences were found among the variables, except for P02, when measured in three differents moments. The lactate concentration in ear lobule capillary blood samples did not differ of the arterialized blood samples, and showed strong correlation (r = 0.95) during progressive exercise on cycle ergometer. Conclusion: The heating hand technique for arterialized blood samples was useful and reliable to study acid-base balance during rest and effort.Amostras de sangue venoso coletadas do dorso da mão após o aquecimento vêm sendo empregadas como substitutas para as coletas arteriais. Objetivo: Determinar a eficiência e confiabilidade desta manobra durante o repouso e no esforço. Métodos: Coletou-se amostras venosas do dorso da mão e do lóbulo da orelha de 14 sujeitos (22 ± 3 anos; e 71,3 ± 15,5 kg) antes e após a imersão por 15 minuto em água a 41-43 °C. Os dados foram tratados pela ANOVA com o teste post hoc de Tukey e análise de regressão para P medidas em três diferentes momentos. As concentrações do lactato no sangue capilar do lóbulo da orelha e do sangue venoso arterializado não diferiram e apresentaram forte correlação (r = 0,95) durante o esforço escalonado no ciclo ergômetro. Conclusão: O método do aquecimento da mão é útil e confiável para estudos do equilíbrio ácido-base, no repouso e no esforço

Multi-scale assessment of human-induced changes to Amazonian instream habitats

Context Land use change and forest degradation have myriad effects on tropical ecosystems. Yet their consequences for low-order streams remain very poorly understood, including in the world´s largest freshwater basin, the Amazon. Objectives Determine the degree to which physical and chemical characteristics of the instream habitat of low-order Amazonian streams change in response to past local- and catchment-level anthropogenic disturbances. Methods To do so, we collected field instream habitat (i.e., physical habitat and water quality) and landscape data from 99 stream sites in two eastern Brazilian Amazon regions. We used random forest regression trees to assess the relative importance of different predictor variables in determining changes in instream habitat response variables. Results Multiple drivers, operating at multiple spatial scales, were important in determining changes in the physical habitat and water quality of the sites. Although we found few similarities in modelled relationships between the two regions, we observed non-linear responses of specific instream characteristics to landscape change; for example 20 % of catchment deforestation resulted in consistently warmer streams. Conclusions Our results highlight the importance of local riparian and catchment-scale forest cover in shaping instream physical environments, but also underscore the importance of other land use changes and activities, such as road crossings and upstream agriculture intensification. In contrast to the property-scale focus of the Brazilian Forest code, which governs environmental regulations on private land, our results reinforce the importance of catchment-wide management strategies to protect stream ecosystem integrity