GEOCHEMISTRY OF URBAN WATERSHEDS: A HEAVY METAL AND LAND USE ANALYSIS

This study investigates relationships between land use and heavy metal pollutants in the water of urban streams in Rock Island, IL, and Davenport, IA. 50 sites were tested during the summer of 2021 for pH and specific conductance in urban, suburban, and rural locations. Samples were gathered from each site for ICP-MS analysis of Zn, Se, As, Pb, and Hg, and one site was identified for sequential hourly samples during a rain event to compare heavy metal concentrations during baseflow and peak flow conditions. SPC and pH data were compared to metal concentrations in an effort to test for relationships, while metal concentrations were compared to EPA Freshwater Aquatic Life Criteria standards to determine the health of the watershed ecosystem and potential risks. Generally, samples from more rural and agricultural sites yielded metal concentrations that could be of concern. This can possibly be attributed to increased use of pesticides and fertilizers used in farming practices. Lab analysis found little to no Hg at all sites, with no obvious relationship with specific land uses. Ultimately, Pb concentrations trended higher at sites categorized by commercial or more developed land in highly urbanized areas such as shopping centers. Zn trended higher in multiple land use categories, including agriculture, commercial/developed, and urban residential areas. Concentrations of Se and As showed only a slight tendency to be higher in residential areas, both urban and rural. We found that overall metal concentrations tended to be higher in rural areas, both agricultural and residential, as well as in urban recreational spaces such as parks. However, many high concentrations were found in urban land use areas. We found a correlation between only SPC and Se and As. Additional analyses of storm samples are pending but do not have pH and SPC data. This preliminary study has created a better overall understanding of the geochemistry of local watersheds and should be used to guide future research regarding metal pollutants, their potential sources (nearby or upstream), and threats.