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Structural and functional assessment of multi-stressed lowland waters

Water bodies in densely populated lowland areas are commonly affected by pollution from agricultural activities and wastewater treatment plant (WWTP) discharges, yet the selection of appropriate water quality assessment methods for these water bodies is under debate. Therefore, we aimed to 1) compare the ability of structural and functional metrics to detect adverse effects of anthropogenic stress on aquatic ecosystems and 2) assess the ability of trait-based metrics to diagnose the potential causes of the observed adverse effects in water quality assessment. Specifically, we compared the responses of several structural (both taxonomic and trait-based) and functional (i.e., based on ecological processes) metrics across a series of stressors in 20 lowland water bodies affected to varying degrees by agricultural activities and WWTP discharges. The measured stressors included nutrients, dissolved oxygen saturation, water temperature, and proxies for pesticides, pharmaceuticals, and personal care products. Taxa evenness and the trait-based SPEcies At Risk organic (SPEARorganic) and pesticide (SPEARpesticide) metrics were negatively correlated with the proxy for organic toxicants. Microbial decomposition and invertebrate consumption showed opposite and more complex relationships with the stressors. These findings suggest that functional metrics may detect patterns of anthropogenic stress that are not evident from structural metrics alone. In terms of diagnostic value, our results indicated that both SPEAR metrics may be used to diagnose the combined presence of organic toxicants from agricultural activities and WWTP discharges, although the SPEAR approach may need to be combined with other methods. We conclude that structural (both taxonomic and trait-based) and functional metrics may provide complementary information that, when integrated, allows for more thorough water quality assessment strategies.