Examining drivers of <i>E. coli</i> distribution across urban headwaters using community science

Urban streams and rivers have chronic bacteria contamination in the United States, coming from multiple sources, following a variety of flowpaths to the waterway, and with differing downstream fates. Bacteria from human sewage, estimated through measures of Escherichia coli ( E. coli) , pose the highest risk to human health. We analyzed four years of E. coli monitoring by community science groups to look for spatial and temporal drivers of E. coli densities in watersheds in the urban core of metro Atlanta, GA, with a wide range of racial and economic diversity as well as persistent patterns of segregation and racialized inequality. These watersheds are spaces of environmental injustice, with disproportionate impacts for lower-wealth and predominantly Black communities from flooding, soil contamination, and air pollution. While there were minimal differences in E. coli between watersheds with different Black and white populations, individual sites could be identified as hot and cold spots of contamination. Storm events increased E. coli at most sites, indicating that a combination of runoff and sediment-sorbed E. coli explains about 50% of the temporal variability in E. coli densities. Long-term median E. coli levels were not strongly correlated to land cover or socio-demographic characteristics of the contributing watershed, but temporal E. coli variability was lower in less densely urbanized areas. Temporal and spatial distributions of E. coli are controlled by complex interactions between sources and hydrologic transport that vary across watersheds. While direct correlations to racial demographics were not observed, the interactions between sewage as one environmental harm and the many others (air quality, soil quality, prison-industrial complex, etc) present in minority and low-income urban communities emphasize the oversized burden that environmental justice communities carry.