Indication of pesticide effects and recolonization in streams.

The agricultural use of pesticides leads to environmentally relevant pesticide concentrations that cause adverse effects on stream ecosystems. These effects on invertebrate community composition can be identified by the bio-indicator SPEAR. However, refuge areas have been found to partly confound the indicator. On the basis of three monitoring campaigns of 41 sites in Central Germany, we identified 11 refuge taxa. The refuge taxa, mainly characterized by dispersal-based resilience, were observed only nearby uncontaminated stream sections and independent of the level of pesticide pressure. Through incorporation of this information into the revised SPEAR indicator, the community structure specifically identified the toxic pressure and no longer depended on the presence of refuge areas. With regard to ecosystem functions, leaf litter degradation was predicted by the revised SPEAR and the median water temperature at a site (R = 0.38, P = 0.003). Furthermore, we designed the bio-indicator SPEAR to quantify the magnitude of general recolonization at a given stream site. We conclude that the taxonomic composition of aquatic invertebrate communities enables a specific indication of anthropogenic stressors and resilience of ecosystems.