Tracking anthropogenic salt signatures in urban streams
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Along urban streams and rivers, various processes, including road salt application, sewage leaks, and weathering of the built environment, contribute to novel chemical cocktails made up of metals, salts, nutrients, and organic matter. More work is needed to fully understand how sources of multiple contaminants vary along rural-to-urban flowpaths through different U.S. cities and how these contaminants can be exported from or retained within urban watersheds. To track the impacts of urbanization, we conducted longitudinal stream synoptic (LSS) monitoring in nine watersheds in five major metropolitan areas of the U.S. as well as routine monitoring at intensive Washington, DC and Baltimore, MD sites. Results demonstrated that salt-derived ions (Ca, Mg, Na, and K) and commonly correlated elements (e.g. Sr, N, Cu) formed salty chemical cocktails that increased along rural to urban flowpaths across U.S. cities. Streams flowing through restored reaches and wide riparian buffer zones in parks did not show longitudinal increases in salty chemical cocktails along flowpaths. The flux data revealed the relative importance of uptake processes and dilution, signifying there is attenuation within these conservation and restoration areas. Temporally, road salt related pulses in salinity, primarily of Na, contribute to a large portion of salt fluxes from urban systems. Our results suggest that salty chemical cocktails may be a common water quality signature of urbanization, elevated salinity can be exported to receiving waters, and urbanization-related salinity can be prevented by or retained within conservation and restoration areas.