Emerging investigator series: interacting effects of environmental factors on Daphnia magna removal of Escherichia coli from wastewater

Abstract

Treatment wetlands can remove a wide range of pollutants from wastewater and stormwater runoff, including microbial pollutants such as Escherichia coli. Filter feeding zooplankton play an important role in improving water quality in treatment wetlands through grazing and subsequent inactivation of E. coli. Understanding how climate change will impact the various processes governing microbial inactivation in treatment wetlands is essential to ensure adequately treated water. We investigated the impact of interacting environmental factors on the E. coli clearance rate of a keystone zooplankton species, Daphnia magna. We utilized a full factorial experimental design to test the impacts of food abundance, food type, and temperature in flow-through mesocosms under environmentally relevant conditions. Temperature and food abundance interactions were significant, which highlights the importance of studying multiple environmental variables when considering the filter feeding contributions of zooplankton. While both food abundance and temperature had a significant impact on clearance rate, daphnids did not exhibit a preference between algae or E. coli, which were the two food sources used in our studies. We observed that at 25 °C, food abundance and type had a larger impact on E. coli clearance rate than at 15 °C, which has important implications when considering resiliency of treatment wetlands in a warming climate. Our findings show that zooplankton filtration behavior will be impacted by environmental conditions that are projected due to climatic changes, but populations can still inactivate E. coli and improve water quality when exposed to these conditions.