Chemical Cocktails from Coast to Coast: Is there a Universal Water Quality Signature of Urbanization in Streams

In urban systems, a wide variety of processes, including increasing impervious surface cover, road salt application, sewage leaks, and weathering of the built environment, contribute to novel chemical cocktails that are comprised of metals, salts, nutrients, and organic matter. Due to heterogeneous land use and a myriad of pollution sources, water quality is highly variable as streams flow through urban areas. National sensor data sets reveal that water quality in many U.S. streams in different metropolitan areas is influenced by the urban environment; however, these datasets lack concurrent measurements of multiple contaminants over local spatial scales. To investigate if urban streams in different U.S. cities have similar water quality characteristics, we conducted synoptic-style sampling campaigns for nine rivers in five major metropolitan areas (i.e., Baltimore, Maryland; Washington, DC; Cincinnati, Ohio; Denver, Colorado; and Portland, Oregon). We collected 10-65 samples along the flowpath of each stream as the water flows through progressively more urban areas and analyzed for base cation, trace element, carbon, and nitrogen concentrations and organic matter optical properties. Results demonstrate an urban water quality signal in many of the sampled streams where salts/weathering ions, such as Ca2+, Mg2+, Na+, Sr, and K+, increased along rural to urban flowpaths. These ions are often significantly correlated to one another and drive much of the overall dataset variability. Some streams with wide riparian buffer zones and stream restorations did not demonstrate these systematic increases in salt ions, suggesting that green spaces may disrupt this urban signal.      

Impact/Purpose

Urbanization is a major threat to freshwater quality and human health. Multiple stressors such as road salts, heavy metals, sewage leaks, wastewater discharges, and fertilizer application lead to increases pollutant loads and increasing impervious surfaces enhances flashiness of pollutant delivery. Historically, these novel contaminant combinations, known as chemical cocktails, have been difficult to track and manage because most monitoring strategies have been limited spatially and temporally and most management strategies have focused on small reach scales.  Here, we expanded monitoring spatially and increase sampling temporally to better view of transport processes across entire flowpaths in urban streams, thereby revealing a more comprehensive examination of pollutants and loads.  We compare urban watersheds coast to coast to seek common patterns across urban ecosystems in effort to improve monitoring and management of the suite of urban chemical cocktails.   

Citation

Shelton, S., S. Kaushal, P. Mayer, Tamara Newcomer Johnson, R. Shatkay, M. Rippy, AND S. Grant. Chemical Cocktails from Coast to Coast: Is there a Universal Water Quality Signature of Urbanization in Streams. UMD Global FEWture Alliance Annual Symposium, College Park, MD, January 19, 2024.