RESUMO
Abstract For mitigation of environmental problems generated by bad water resource management, the first step is to develop methods for effective diagnosis. The potential bioindicator, mainly in the benthic community, in the evaluation of water quality is the structure of the community, associated with magnitude of environmental impact. The aim of the present study was to evaluate the effectiveness of abundance biomass curves (ABC) as tools to estimate ecological quality in reservoirs in the Brazilian semi-arid region. Two reservoirs, Epitácio Pessoa and Argemiro de Figueiredo were selected. These reservoirs are located in the watershed of the Paraíba River, in Northeast Brazil. Sampling was done at 40 sites in the littoral region of each reservoir, during the periods of higher and lower water volume in the reservoirs. ABC for semi-arid region reservoirs showed disparate results for biological and environmental indicators, because they had a better relationship with momentary variables (physical and chemical parameters). This may be related to the high occurrence of exotic species, principally Corbicula largillierti, which has a high biomass, in association with a severe drought period. ABC must thus be used with parsimony and combined with other indicators, for an accurate and coherent characterization.
Resumo Para mitigação de problemas ambientais gerados pela má gestão de recursos hídricos, o primeiro passo é o desenvolvimento metodologias de diagnósticos eficientes. O potencial bioindicador, principalmente da comunidade bentônica, na avaliação da qualidade da água deve-se aos aspectos estruturais dessa comunidade, associado com a magnitude de impactos ambientais. O objetivo do presente estudo foi avaliar a eficiência das curvas de biomassa e abundância (ABC) como ferramentas para estimar a qualidade ecológica em reservatórios na região do semi-árido brasileiro. Dois reservatórios, Epitácio Pessoa e Argemiro de Figueiredo foram selecionados. Estes reservatórios estão localizados na bacia do rio Paraíba, no nordeste do Brasil. As coletas foram realizadas em 40 locais na região litorânea de cada reservatório, durante os períodos de maior e menor volume de hídrico. As curvas ABC, quando plotadas em reservatórios do semiárido, apresentaram resultados diferentes aos indicadores biológicos e ambientais, tendo uma relação melhor com as variáveis momentâneas (parâmetros físicos e químicos). Isso pode estar relacionado à alta ocorrência de espécies exóticas, principalmente Corbicula largillierti, o que reflete uma elevada biomassa, combinada com um período severo de seca. O método ABC devem ser utilizadas com parcimônia e associada a outros indicadores, para uma caraterização coerente e precisa.
RESUMO
Turnover (i.e., species substitution) and nestedness (i.e., subsets of species from more diverse locations), the two main mechanisms used to explain the beta diversity of biological communities, have different implications for biodiversity conservation. To better understand how these mechanisms contribute to beta diversity, we tested the following hypotheses: (i) greater dissimilarity in community composition occurs between estuarine zones than other hierarchical level studied; (ii) beta diversity in these communities develops by turnover in estuaries with a lower degree of anthropogenic impact, but by nestedness in estuaries with a greater degree of anthropogenic impact; and (iii) the structuring mechanism is independent of season. We studied two tropical estuaries (dry and wet seasons) that vary in terms of land-use of the drainage basins. Subtidal benthic macroinvertebrates were sampled along the estuarine gradient in each of the two estuaries. The additive partitioning approach to species diversity was used to determine the hierarchical scale with the greatest dissimilarity in community composition. General beta diversity was measured using the Sorensen dissimilarity index, partitioning the turnover and nestedness components. The greatest dissimilarity in the composition of the communities occurred between the zones along the estuarine gradient in both seasons (dry = 58.6%; wet = 46.3%). In the estuary with a lower degree of anthropogenic influence, benthic macroinvertebrate diversity was generated by turnover regardless of the season. In the estuary with a greater degree of anthropogenic impact, beta diversity was structured by turnover during the dry season and a combination of both mechanisms during the wet season. We conclude that turnover is the principal mechanism responsible for beta diversity in benthic macroinvertebrate communities in tropical estuaries.
