Abraham Gonzalez, “Fecal Indicator and Sediment in the Milwaukee River Watershed”
Mentors: Ryan Newton & Jill McClary, Freshwater Sciences
The Milwaukee River watershed is impaired by fecal bacteria and sediment pollutants, which can be hazardous to human and ecosystem health. New regulations will require local municipalities to control the levels of both fecal bacteria and sediment in their storm water discharge. To mitigate these pollutants, it is important to know if sediment and fecal bacteria are connected and how they are transported through the watershed. Our goal was to quantify the abundance of common sewer bacteria and determine the extent to which they are particle-associated versus free-floating (planktonic) in discharge released to the Milwaukee River and Estuary. Samples were collected weekly for 6 months from three sites: the Milwaukee River, Milwaukee inner harbor, and nearshore Lake Michigan. Each sample was divided into two subsamples: one subsample was filtered through a 3-μm filter to remove particles and particle-attached bacteria and the other subsample was left unaltered. Each subsample was then processed to quantify fecal indicator bacteria (fecal coliform, enterococci, and Escherichia coli) using standard membrane filtration on appropriate differential media. After the plates were incubated, colony-forming units were recorded and used to quantify the fraction of each fecal indicator that was particle-associated. On average, the majority of fecal bacteria were not particle-attached, and the fraction of particle-attached fecal bacteria was slightly higher in Lake Michigan (51%) than the river or harbor (32%). The fraction of particle-attached bacteria also varied widely, from 0% to 93% for E. coli. This variation was not driven by precipitation, as there was no relationship (R2 = 0.0005, p > 0.05) between rainfall and the percent of planktonic bacteria. Our work suggests that FIB in the Milwaukee river watershed are largely planktonic and expected to have different transport than sediment in the system.
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