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RESUMO As atividades humanas afetam a disponibilidade e a qualidade da água em muitos ecossistemas aquáticos. A Barragem Santa Bárbara é um importante manancial de abastecimento público do município de Pelotas, Rio Grande do Sul, Brasil, que vem sofrendo um processo de eutrofização acelerado, tornando importante o uso de monitoramentos ambientais como ferramenta de controle desses mananciais. O objetivo deste estudo foi avaliar a comunidade de macroinvertebrados bentônicos presentes nas raízes de macrófitas aquáticas flutuantes e suas relações com a qualidade da água na bacia de acumulação da Barragem Santa Bárbara. Em 2018, foram realizadas quatro amostragens em dois ambientes desse ecossistema. As análises físico-químicas foram realizadas para correlacionar com as análises biológicas. Os macroinvertebrados bentônicos retirados das raízes das macrófitas aquáticas flutuantes foram triados e identificados ao menor nível taxonômico possível. Para análise de dados, foram utilizadas análises de regressão múltipla, análise de variância (ANOVA) e Análise de Componentes Principais. Os macroinvertebrados bentônicos foram analisados também quanto à ocorrência de frequência, riqueza e abundância, e ao índice de diversidade de Shannon-Wiener. Foi possível registrar 13.154 espécimes de macroinvertebrados bentônicos associados a 100 g de peso seco de macrófitas aquáticas flutuantes, divididos em 35 táxons e distribuídos em nove ordens e 27 famílias. Os grupos mais abundantes foram Amphipoda, Chironomidae e Oligochaeta. O índice de diversidade apresentou média de H' = 1,67, classificando o ecossistema aquático como moderadamente poluído. As ferramentas utilizadas neste estudo são úteis para ações de gerenciamento e preservação de mananciais, principalmente os utilizados para abastecimento público.
ABSTRACT Human activities affect the availability and quality of water in many aquatic ecosystems. The Santa Bárbara Dam is an important source of public water supply in the city of Pelotas, Rio Grande do Sul, Brazil, which has been undergoing an accelerated eutrophication process, thus making it important to use environmental monitoring as a control tool for these sources. The aim of this study was to evaluate the community of benthic macroinvertebrates in the roots of floating aquatic macrophytes and their connection with water quality in the Santa Bárbara Dam accumulation basin. Four samples were taken in 2018, in two environments of this ecosystem. Physical-chemical analyses were conducted to correlate with biological analyses. Benthic macroinvertebrates taken from the roots of floating aquatic macrophytes were screened and identified at the lowest possible taxonomic level. For data analysis, multiple regression analysis, ANOVA, and Principal Component Analysis were used. Benthic macroinvertebrates were also analyzed for frequency, richness and abundance, and the Shannon-Wiener diversity index. It was possible to register 13.154 specimens of benthic macroinvertebrates associated with 100 g of dry weight of floating aquatic macrophytes, divided into 35 taxa, and distributed in 09 orders and 27 families. The most abundant groups were Amphipoda, Chironomidae, and Oligochaeta. The diversity index showed an average of H '= 1.67, classifying the aquatic ecosystem as moderately polluted. The tools used in this study are useful for managing and preservation of water sources, especially those used for public supply.
RESUMO
Temporary wetlands are short-term alternative ecosystems formed by flooding for irrigation of areas used for rice farming. The goal of this study is to describe the development cycle of rice fields as temporary wetlands in southern Brazil, evaluating how this process affect the gas production (CH4 and CO2) in soil with difference % carbon and organic matter content. Two areas adjacent to Lake Mangueira in southern Brazil were used during a rice-farming cycle. One area had soil containing 1.1% carbon and 2.4% organic matter, and the second area had soil with 2.4% carbon and 4.4% organic matter. The mean rates of gas production were 0.04 ± 0.02 mg CH4 m(-2) d(-1) and 1.18 ± 0.30 mg CO2 m(-2) d(-1) in the soil area with the lower carbon content, and 0.02 ± 0.03 mg CH4 m(-2) d(-1) and 1.38 ± 0.41 mg CO2 m(-2) d(-1) in the soil area with higher carbon content. Our results showed that mean rates of CO2 production were higher than those of CH4 in both areas. No statistically significant difference was observed for production of CH4 considering different periods and sites. For carbon dioxide (CO2), however, a Two-Way ANOVA showed statistically significant difference (p = 0.05) considering sampling time, but no difference between areas. The results obtained suggest that the carbon and organic matter contents in the soil of irrigated rice cultivation areas may have been used in different ways by soil microorganisms, leading to variations in CH4 and CO2 production.
