Effects of anthropogenic pollution and hydrological variation on macroinvertebrates in Mediterranean rivers: A case-study in the upper Tagus river basin (Spain)
Résumé
Seasonal hydrological variation and chemical pollution represent two main drivers of freshwater biodiversity change in Mediterranean rivers. We investigated to what extent low !ow conditions can modify the effects of chemical pollution on macroinvertebrate communities. To that purpose, we selected twelve sampling sites in the upper Tagus river basin (central Spain) having different sources of chemical pollution and levels of seasonal hydrological variation. The sites were classi"ed as natural (high !ow variation, low chemical impact), agricultural (high !ow variation, high agricultural chemical inputs) and urban (limited !ow variation, high urban chemical inputs). In these sites, we measured daily water discharge, nutrients, and contaminant concentrations, and we sampled benthic macroinvertebrates, in spring, summer and autumn. Signi"cant differences related to toxic pres- sure and nutrient concentrations were observed between the three groups of sites. Seasonal patterns were found for some water quality parameters (e.g. nitrites, ammonia, suspended solids, metal toxicity), particularly in agri- cultural sites. Taxonomic and functional richness were slightly lower in the polluted sites (agricultural and urban), particularly during low !ow periods (summer and early autumn). Functional diversity was signi"cantly lower in sites with seasonal !ow variation (agricultural sites) as compared to the more constant ones (urban sites). The frequency of traits such as large size, asexual reproduction, aquatic passive dispersion and the produc- tion of cocoons increased in response to pollution during low !ow periods. This study shows that the impacts of anthropogenic chemical pollution on taxonomic and functional characteristics of macroinvertebrate communi- ties seem to be larger during low !ow periods. Therefore, further studies and monitoring campaigns assessing the effects of chemical pollution within these periods are recommended.
