Simultaneous Attenuation of Trace Organic Compounds and Dissolved Organic Matter in a River and its Hyporheic Zone?

Abstract:

Trace organic compounds (TrOCs) occur widespread in the environment and threaten the quality of drinking water resources. These substances reach the environment with the effluents of treated waste water, which also contain high loads of dissolved organic matter (DOM). While some previous studies concluded microbial co-metabolism of TrOCs and DOM, the results of other studies indicated that TrOC attenuation is inhibited under high DOM concentrations. Therefore, we conducted a field sampling campaign within the framework of the Worldwide Hydrobiogeochemistry Observation Network for Dynamic River Systems (WHONDRS) in order to examine the concurrence of the attenuation of TrOCs and DOM compound classes. At a side channel of the River Erpe, Berlin, Germany, which receives treated waste water, samples were taken from surface water and the hyporheic zone in 25 cm sediment depth every 3 hours for 48 hours. Additional surface water samples were taken 850 m upstream of the main sampling site. The surface water stretch and the hyporheic flow path were compared in their capability to attenuate TrOCs and DOM as well as in the occurrence of concurrent attenuation of TrOCs and DOM compound classes. Mean attenuation of TrOCs was higher in the hyporheic zone (49.4 %) compared to the surface water stretch (11.7 %). Similarly, turnover of DOM was also stronger in the hyporheic zone. TrOCs concentrations correlated positively with the relative proportions of easily bioavailable DOM compound classes and negatively with poorly bioavailable DOM compound classes. In this context, more and stronger correlations were found in the hyporheic zone compared to surface water. In conclusion, the attenuation of easily bioavailable DOM compounds and TrOCs is likely linked through microbial co-metabolism. TrOC attenuation and DOM turnover mainly take place in the hyporheic zone making it an efficient natural bioreactor.