The fate of trace organic compounds and their transformation products along specific hyporheic flow paths

Abstract

<p>Trace organic compounds (TrOCs) are frequently detected in surface waters such as rivers. Possible entry pathways into the environment include stormwater runoff, industrial effluents, and wastewater treatment plant (WWTP) effluents. Understanding the behavior of TrOCs and their transformation products (TPs) is important, as they represent a risk to ecosystem and human health. The hyporheic zone of a river shows high turnover rates for nutrients, dissolved organic carbon, metals, pathogens, and TrOCs. Turnover rates are dependent on both, hydrological and biogeochemical conditions. We conducted a high-frequency sampling campaign in the urban lowland River Erpe (Brandenburg, Germany) which receives treated wastewater from the WWTP Muenchehofe. The aim was to study the fate of TrOCs and respective TPs along specific hyporheic flow paths. The basic idea was to enable the sampling of water parcels along specific hyporheic flow paths by forcing the flow path with a pipe (diameter: 8 cm, length: 27 cm, maximum depth: 17 cm) onto a specific path similar to the natural one. Wood on top of the pipe should increase the hyporheic exchange flow through the pipe and mimic the effect of woody debris which is often used in river restorations. Samples from the hyporheic zone and the surface water were taken every 2 hours for 14 hours. The samples were analyzed for oxygen concentrations, redox parameters, nutrients, and TrOCs. We found a clear redox zonation along the flow paths inside the pipes and investigated its impacts on the fate of TrOCs and their TPs. The hyporheic zone proved as an important river compartment for the retention of TrOCs and their TPs.</p>