Climate change scenarios predict lower flow rates during summer that may lead to higher proportions of wastewater in small and medium sized streams. Moreover, micropollutants (e.g. pharmaceuticals and other contaminants) continuously enter aquatic environments via treated wastewater. However, there is a paucity of knowledge, whether extended exposure to secondary treated wastewater disrupts important ecosystem functions, e.g. leaf breakdown. Therefore, the amphipod shredder Gammarus fossarum was exposed to natural stream water (n=34) and secondary treated wastewater (n=32) for four weeks in a semi-static test system under laboratory conditions. G. fossarum exposed to wastewater showed significant reductions in feeding rate (25%), absolute consumption (35%), food assimilation (50%), dry weight (18%) and lipid content (22%). Thus, high proportions of wastewater in the stream flow may affect both the breakdown rates of leaf material and thus the availability of energy for the aquatic food web as well as the energy budget of G. fossarum.
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