Simultaneous attenuation of trace organics and change in organic matter composition in the hyporheic zone of urban streams

Anke Putschew,Hanna Schulz,Joerg Lewandowski,Robert E Danczak,Birgit M Mueller

doi:10.1038/s41598-021-83750-8

Abstract

Trace organic compounds (TrOCs) enter rivers with discharge of treated wastewater. These effluents can contain high loads of dissolved organic matter (DOM). In a 48 h field study, we investigated changes in molecular composition of seven DOM compound classes (FTICR-MS) and attenuation of 17 polar TrOCs in a small urban stream receiving treated wastewater. Correlations between TrOCs and DOM were used to identify simultaneous changes in surface water and the hyporheic zone. Changes in TrOC concentrations in surface water ranged between a decrease of 29.2% for methylbenzotriazole and an increase of 152.2% for the transformation product gabapentin-lactam. In the hyporheic zone, only decreasing TrOC concentrations were observed, ranging from 4.9% for primidone to 93.8% for venlafaxine . TrOC attenuation coincided with a decline of molecular diversity of easily biodegradable DOM compound classes while molecular diversity of poorly biodegradable DOM compound classes increased. This concurrence indicates similar or linked attenuation pathways for biodegradable DOM and TrOCs. Strong correlations between TrOCs and DOM compound classes as well as high attenuation of TrOCs primarily occurred in the hyporheic zone. This suggests high potential for DOM turnover and TrOC mitigation in rivers if hyporheic exchange is sufficient.

Highlights

Trace organic compounds (TrOCs) enter rivers with discharge of treated wastewater
Our hypotheses are: (1) In urban streams with elevated nutrient loads, TrOC attenuation coincides with changes in dissolved organic matter (DOM) molecular diversity, especially for DOM compound classes with high bioavailability, along a surface water flow path and a flow path into the hyporheic zone
wastewater treatment plants (WWTP)-induced fluctuations of discharge and electrical conductivity (EC) in surface water (SW) were observed at our two sampling sites (Supplementary Figure S 2) which were both downstream of the WWTP

Summary

Introduction

Trace organic compounds (TrOCs) enter rivers with discharge of treated wastewater. These effluents can contain high loads of dissolved organic matter (DOM). TrOC attenuation coincided with a decline of molecular diversity of biodegradable DOM compound classes while molecular diversity of poorly biodegradable DOM compound classes increased This concurrence indicates similar or linked attenuation pathways for biodegradable DOM and TrOCs. Strong correlations between TrOCs and DOM compound classes as well as high attenuation of TrOCs primarily occurred in the hyporheic zone. A variety of laboratory studies found differing impacts of organic matter on the attenuation of T rOCs9–12, knowledge on potential simultaneous turnover of these compounds in a real river and its hyporheic zone is still lacking. It was observed that the attenuation of 9 out of 14 TrOCs25 or hydrophilic neutral T rOCs23 was independent of the BDOC concentration

Methods

Results

Conclusion