Urban river systems are impacted by a variety of runoff sources, which contain a diversity of pollutants and whose discharge is impacted by the timing and local intensity of precipitation events. Generally, an evaluation of the impact and health risks associated with urban pollutants is deciphered from a single timepoint collection during post-event sampling even though this approach does not match the dynamic nature of landscape contributions to the river. In an effort to better understand the timing and potential coupling of regulated pollutants, we used high-frequency time-series sampling and microbial community characterization to evaluate the sources and linkages between sediment and fecal pollution in an urban watershed. Samples were collected at a single location for 13 separate events across two years, including 11 precipitations periods and two dry weather periods. High-frequency sampling (<4 hr timescale) revealed that fecal bacterial indicator and total suspended solids concentrations were not tightly coupled across storm hydrographs, which indicates unique pollution source origins. We also characterized the microbial community with 16S rRNA gene sequencing and then partitioned the resulting amplicon sequence variants (ASVs) into source environments for sewage, sediment, and freshwater. These data indicated the microbial community undergoes rapid member displacement over short (2-4 hour) timescales. During heavy rain events, >20% of a community’s identified ASVs could be newly arrived between sampling intervals, and these organisms were generally associated with upstream sediment and downstream urban sewage pollution. Ultimately, categorizing source environments for mixed microbial assemblages revealed uncoupled timing of regulated pollutants and the value of high-frequency sampling for understanding the complex dynamics of aquatic-terrestrial interfaces in urban water systems. 

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  ()