103 research outputs found
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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 equilÃbrio 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
Estudo da alimentação dos peixes no rio Grande à jusante da usina hidrelétrica de Itutinga, Minas Gerais, Brasil
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The relative influence of catchment and site variables on fish and macroinvertebrate richness in cerrado biome streams
Landscape and site-scale data analyses aid
the interpretation of biological data and thereby help
us develop more cost-effective natural resource management
strategies. Our study focused on environmental
influences on stream assemblages and we
evaluated how three classes of environmental variables
(geophysical landscape, land use and cover, and
site habitat), influence fish and macroinvertebrate
assemblage richness in the Brazilian Cerrado biome.
We analyzed our data through use of multiple linear
regression (MLR) models using the three classes of
predictor variables alone and in combination. The four MLR models explained dissimilar amounts of benthic
macroinvertebrate taxa richness (geophysical landscape
R² ≈ 35%, land use and cover R² ≈ 28%,
site habitat R² ≈ 36%, and combined R² ≈ 51%).
For fish assemblages, geophysical landscape, land use
and cover, site habitat, and combined models
explained R² ≈ 28%, R² ≈ 10%, R² ≈ 31%,
and R² ≈ 47% of the variability in fish species
richness, respectively. We conclude that (1) environmental
variables differed in the degree to which they
explain assemblage richness, (2) the amounts of
variance in assemblage richness explained by geophysical
landscape and site habitat were similar, (3)
the variables explained more variability in macroinvertebrate
taxa richness than in fish species richness,
and (4) all three classes of environmental variables studied were useful for explaining assemblage richness
in Cerrado headwater streams. These results help
us to understand the drivers of assemblage patterns at
regional scales in tropical areas.Keywords: Anthropogenic pressures, Biological diversity, Multiple linear regression models, Brazil, Savanna, Physical habitat structure, Streams, Landscape ecology, Partition of varianceKeywords: Anthropogenic pressures, Biological diversity, Multiple linear regression models, Brazil, Savanna, Physical habitat structure, Streams, Landscape ecology, Partition of varianc
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AFS Position Paper and Policy on Mining and Fossil Fuel Extraction
Following a four-year period of writing, member comment, and multiple revisions, the AFS Position Paper and Policy on Mining and Fossil Fuel Extraction was approved unanimously by the membership at the Society's annual business meeting August 19, 2015, in Portland, Oregon. The entire document can be read at fisheries.org/policy_statements; a brief summary follows
Fish and macroinvertebrate assemblages reveal extensive degradation of the world's rivers
Rivers suffer from multiple stressors acting simultaneously on their biota, but the consequences are poorly quantified at the global scale. We evaluated the biological condition of rivers globally, including the largest proportion of countries from the Global South published to date. We gathered macroinvertebrate- and fish-based assessments from 72,275 and 37,676 sites, respectively, from 64 study regions across six continents and 45 nations. Because assessments were based on differing methods, different systems were consolidated into a 3-class system: Good, Impaired, or Severely Impaired, following common guidelines. The proportion of sites in each class by study area was calculated and each region was assigned a Köppen-Geiger climate type, Human Footprint score (addressing landscape alterations), Human Development Index (HDI) score (addressing social welfare), % rivers with good ambient water quality, % protected freshwater key biodiversity areas; and % of forest area net change rate. We found that 50% of macroinvertebrate sites and 42% of fish sites were in Good condition, whereas 21% and 29% were Severely Impaired, respectively. The poorest biological conditions occurred in Arid and Equatorial climates and the best conditions occurred in Snow climates. Severely Impaired conditions were associated (Pearson correlation coefficient) with higher HDI scores, poorer physico-chemical water quality, and lower proportions of protected freshwater areas. Good biological conditions were associated with good water quality and increased forested areas. It is essential to implement statutory bioassessment programs in Asian, African, and South American countries, and continue them in Oceania, Europe, and North America. There is a need to invest in assessments based on fish, as there is less information globally and fish were strong indicators of degradation. Our study highlights a need to increase the extent and number of protected river catchments, preserve and restore natural forested areas in the catchments, treat wastewater discharges, and improve river connectivity
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