The combined use of metrics of biological quality and biomarkers to detect the effects of reclaimed water on macroinvertebrate assemblages in the lower part of a polluted Mediterranean river (Llobregat River, NE Spain)

The main purpose of this paper is to evaluate whether introducing reclaimed water to the lower part of the Llobregat River has an effect on the macroinvertebrate community assemblage and the biomarker responses of the caddisfly larvae Hydropsyche exocellata. Therefore, a before-and-after experiment was carried out at two locations, upstream and downstream of the discharge effluent. At both of the stations, quantitative benthic samples were taken using a Surber net. Several biological metrics were calculated to evaluate the biological quality. For the biomarker study, the population condition of the caddisfly H. exocellata was analysed. In both sites, as a result of physicochemical water conditions, the macroinvertebrate communities are dominated by taxa that are tolerant to pollution, and the ecological status of both sites is always poor. The discharge of the reclaimed water did not affect the composition and abundance of the dominant taxa, but the few intolerant species that were found upstream before the experiment disappeared downstream. Consequently, most of the metrics indicating the level of biological impairment had slightly lower values after the introduction of the treated water, even though the ecological status was always poor. Nevertheless, significant and specific toxic effects on the collected H. exocellata larvae were observed using biomarkers. The effects included oxidative stress-related responses, such as decreased antioxidant enzyme activities and increased levels of lipid peroxidation. Therefore, indications of additional stress to the populations of the caddisfly H. exocellata were found using several biomarkers, which can indicate a potential further deterioration of the ecological status of the river. In polluted rivers, such as the Llobregat, structural indicators are unable to indicate further impairment and biomarkers may be used as an useful tool to detect then the environmental impoverishment. The combination of both kinds of indicators is necessary for the establishment of the ecological status of a system, following the indications of the Water Framework Directive (WFD). (C) 2012 Elsevier Ltd. All rights reserved.