Multivariate analyses of the effect of an urban wastewater treatment plant on spatial and temporal variation of water quality and nutrient distribution of a tropical mid-order river.

Freshwater resources are increasingly scarce due to human activities, and the understanding of water quality variations at different spatial and temporal scales is necessary for adequate management. Here, we analyze the hypotheses that (1) the presence of a wastewater treatment plant (WWTP) and (2) a polluted tributary that drains downstream from the WWTP change the spatial patterns of physicochemical variables (pH, turbidity, dissolved oxygen, and electrical conductivity) and nutrient concentrations (reactive soluble phosphorus, total phosphorus, nitrogen series, total nitrogen, and total dissolved carbon) along a mid-order river in SE Brazil and that these effects depend on rainfall regime. Six study sites were sampled along almost 4 years to evaluate the impacts of human activities, including sites upstream (1-3) and downstream (5-6) from the WWTP. The impacts were observed presenting an increasing trend from the source (site 1) towards Água Quente stream (site 4, the polluted tributary), with signs of attenuation at site 5 (downstream from both WWTP and site 4) and the river mouth (site 6). Input of nutrients by rural and urban runoff was observed mainly at sites 2 and 3, respectively. At sites 4 and 5, the inputs of both untreated and treated wastewaters increased nutrient concentrations and changed physicochemical variables, with significant impacts to Monjolinho River. Seasonal variations in the measured values were also observed, in agreement with the pluviometric indexes of the region. Univariate analyses suggested no effect of the WWTP for most variables, with continued impacts at sites downstream, but non-parametric multivariate analysis indicated that these sites were recovering to chemical characteristics similar to upstream sites, apparently due to autodepuration. Therefore, multivariate methods that allow rigorous tests of multifactor hypotheses can greatly contribute to determine effects of both point and non-point sources in river systems, thus contributing to freshwater monitoring and management.

Recolonization of experimental gaps by the mussels Brachidontes darwinianus and B. solisianus in a subtropical rocky shore

Mexilhões são importantes dominantes do espaço na região entremarés de costões rochosos. Diversos fatores influenciam a distribuição de espécies coexistentes, tais como diferenças de tolerância fisiológica, histórias de vida e uso de recursos distribuídos irregularmente no espaço e tempo. Neste estudo, a velocidade de recolonização dos mexilhões Brachidontes darwinianus e B. solisianus foi comparada para avaliar suas respostas a clareiras abertas por perturbações. B. darwinianus foi muito mais rápido que B. solisianus, fechando rapidamente clareiras abertas no banco de mexilhões. Este resultado sugere que quando estas espécies co-ocorrem, sua distribuição está relacionada não só a tolerâncias fisiológicas distintas, mas também a diferentes respostas a perturbações. B. darwinianus é mais tolerante a baixas salinidades, dominando zonas estuarinas, além de geralmente ocorrer na região mais baixa do mediolitoral. As características morfológicas e ecológicas destas espécies que influenciam este padrão são discutidas.