Trace organic compounds in wastewater-loaded lowland River Erpe – Key findings from 12 years of research

Increasing concentrations of trace organic compounds (TrOCs) in water bodies worldwide are of great concern. In addition to a general load reduction and a better understanding of the ecotoxicological effects of TrOC cocktails, it is important to better understand the pathways and fate of this large group of compounds in the environment. The lowland River Erpe (Berlin/Brandenburg, Germany), which receives treated wastewater from an urban wastewater treatment plant, is an excellent site for such research, as TrOC concentrations are exceptionally high compared to other German rivers, allowing reliable process studies without much analytical effort such as prior enrichment steps of water samples. In addition, the river system offers a variety of reaches that differ in hydrology and streambed morphology, allowing for different types of investigations. Over the past 12 years, more than 100 researchers have been involved in several large and numerous smaller studies on the River Erpe. Topics have included the role of hyporheic zones in the self-purification capacity of streams with respect to TrOCs, seasonal changes, interactions between easily degradable organic matter and TrOC attenuation, the importance of identifying flow paths for understanding biogeochemical processes, the effects of management actions such as macrophyte removal on the fate of TrOCs, the effects of losing conditions on TrOC input to aquifers and bank filtration systems, the effects of discharge of treated effluent from a large new industrial site on river water composition, and the identification of microbial key players associated with TrOC removal, and much more. Ongoing research includes topics such as bioremediation, the effects of migrating bedforms on the fate of TrOCs, and the effects of droughts on water quality at bathing sites in the receiving River Spree. Research highlights and future directions are presented.