HIGH-FREQUENCY SAMPLING ACROSS PRECIPITATION EVENTS REVEALS “HIDDEN” DYNAMICS IN MICROBIAL POLLUTANT LOADING TO AN URBAN RIVER

Many urban rivers have impaired designations and restrictions on recreational uses because of pollutants entering from the surrounding landscape. Precipitation events drive much of this yearly pollutant loading, but discharge regulations are often determined from limited within event sample collection. The Milwaukee River in Milwaukee, WI USA has discharge regulations for water clarity and fecal contamination that are evaluated by total maximum daily load (TMDL) criteria for total suspended solids (TSS) and fecal indicator bacteria (FIB). To better understand the source, timing, and loading of these pollutants, we used high-frequency time-series sampling (2-hour composites) to collect river water for 13 events. During heavy rains, we found that the microbial community could undergo rapid member displacement by rain-driven microbial immigrants. This rapid flux from the landscape included heavy loading of fecal-associated bacteria, but this loading was uncoupled from changes in sediment loading, indicating the pollutants originate from different sources. For regulatory purposes, our results revealed large FIB loading early in precipitation events that far exceeded later event-driven loads. This within-event variability had not been accounted for fully in previous regulatory estimates, which we believe has resulted in TMDL estimates that are >100-fold below current yearly loading conditions. We contend, microbial time-series can reveal the hidden-present for rapidly changing systems as well as serve as indicators of longer-term ecosystem change.

Primary Presenter: Ryan Newton, University of Wisconsin-Milwaukee (newtonr@uwm.edu)

Authors:

Ryan Newton, University of Wisconsin-Milwaukee  (newtonr@uwm.edu)

Jill McClary-Gutierrez, University of Wisconsin-Milwaukee  (mcclary@uwm.edu)