Maike Huszarik

• Chemical pollution is a ubiquitous stressor affecting streams and their linkages to riparian forests. Contaminants act by altering the emergence of aquatic insects from streams. Emergent insects can also take up contaminants and transfer them into the terrestrial ecosystem. Emergent insects are an important source of prey for riparian insectivores and changes in the emergence flux or contamination of insects can affect the riparian food web. However, little is knownabout the implications of emerging contaminants such as agricultural pesticides and wastewatereffluent on the terrestrial food web. In this dissertation, I address possible consequences ofagricultural and wastewater stream pollution for riparian insectivores, namely bats and spiders. The contribution of aquatic prey to riparian spider diets has mainly been determined by stableisotope analysis, but DNA metabarcoding, a highly sensitive method of identifying consumedprey using DNA, promises to further detangle changes in these trophic interactions. In Chapter2, we tested a bleaching decontamination protocol to determine the suitability of using metabarcoding on spiders contaminated during sampling. We confirmed the applicability of metabarcoding, but also found that the wolf spiders (Lyocsidae) collected in riparian areas did not appear to rely strongly on aquatic prey. This informed our choice of Tetragnatha montana, which are highly reliant on aquatic prey, for the field study in Chapter 3. We then conducted three field studies. Chapters 3 and 4 evaluate indirect trophic effects of chemical stream pollution on spiders and bats, respectively. Chapter 5 quantifies the accumulation of pesticides from the stream to riparian spiders via emergent insects. We found that riparian bats foraged more and that spiders consumed more Chironomidae at more polluted sites, indicating that there was no overall decrease in emergence due to chemical pollution. We also found that certain pesticides accumulated in emergent insects and riparian spiders. Together, this suggests that chemical stream pollution resulted in an increased dietary exposure of riparian insectivores to contaminants, rather than a decrease in prey availability. These results demonstrate the role of streams and aquatic-terrestrial linkages in propagating stressors across ecosystem boundaries. They also show the benefit of using sensitive methods like DNA metabarcoding to unveil trophic effects of chemical pollution. Future studies should focus on quantifying the risk of contaminant uptake and potential effects for riparian bats, as well as considering how the observed drivers change in different contamination scenarios and ecosystems. This knowledge is important to protect the functionality of the riparian ecosystem and its inhabitants.