Distribution of Escherichia coli and Enterococci in water, sediments, and bank soils along North Shore Channel between Bridge Street and Wilson Avenue, Metropolitan Water Reclamation District of Greater Chicago

Abstract

The Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) wished to know the distribution and potential sources of fecal indicator bacteria, E. coli and enterococci, in water, sediments, and upland soils along an upstream and downstream portion of the North Shore Channel (NSC) that is the receiving stream for the District’s North Side Water Reclamation Plant (NSWRP) outfall. Biweekly water and sediment samples were collected between August and October 2008 and included the following locations upstream of the outfall: Bridge Street (UPS-1), Oakton Street (UPS-2), the NSWRP outfall (OF), and downstream: Foster Avenue (DNS-1), and Wilson Avenue (DNS-2). E. coli and enterococci were consistently found in water and sediments at all sampling locations, with bacterial densities in water increasing below the NSWRP outfall; bacterial densities in sediment were more variable. On a relative measurement basis (i.e., 100 ml=100 g), both E. coli and enterococci densities were significantly higher in sediments than water. E. coli and enterococci were consistently recovered from bank soil along wooded, grassy, erosional, and depositional areas at two recreational parks, as well as other riparian areas along the river. Thus, soils along the river basin are likely sources of these bacteria to the NSC channel, introduced through runoff or other physical processes. Tributaries, such as the North Branch of the Chicago River (NBCR) that flow into NSC near Albany Ave, may provide a constant source of E. coli and enterococci to the NSC. Additionally, storm sewer outfalls may increase E. coli loadings to NSC during wet weather conditions. Our findings suggest that the abundance of nonpoint sources contributing to the overall fecal indicator bacteria (FIB) load in the NSC channel may complicate bacteria source determination and remediation efforts to protect the stream water quality.