Salty chemical cocktails as water quality signatures: longitudinal trends and breakpoints along different U.S. streams
Citation:
Shelton, S., S. Kaushal, P. Mayer, R. Shatkay, M. Rippy, S. Grant, AND Tamara Newcomer Johnson. Salty chemical cocktails as water quality signatures: longitudinal trends and breakpoints along different U.S. streams. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 930:172777, (2024). https://doi.org/10.1016/j.scitotenv.2024.172777
Impact/Purpose:
This study examined chemical mixtures of salt and related elements in streams across sites at 4 US cities to establish whether these salty chemical cocktails varied distinctively along urban flowpaths. We found that salt concentrations increased along rural to urban flowpaths suggesting that such cocktails could be used as indicators of urbanization and pollution sources and sink. We found that salty chemical cocktails decreased as streams flowed through parks and restorations suggesting such areas may be zones of remediation for salt and related pollutants. We developed improved methods to identify chemical patterns that can be used to track sources, fate, and transport of pollution.
Description:
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. Due to heterogeneous land use and a myriad of pollution sources, water quality is highly variable as streams flow through urban areas. It is currently unknown how sources of multiple contaminants vary along rural-to-urban flowpaths through different U.S. cities. 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. During each LSS monitoring campaign, 10-53 sites were sampled along the flowpath of each stream, as they flowed through progressively more urbanized areas. Results demonstrated that salt 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. Salty chemical cocktails explained 46.1% of the overall variability in geochemistry among streams and showed distinct typologies, trends, and transitions (e.g., increasing, plateaus, pulses) along flowpaths through metropolitan regions. Pollution sources in streams across cities could be classified based on salty chemical cocktails. Streams flowing through restored reaches and wide riparian buffer zones in parks did not show longitudinal increases in salty chemical cocktails along flowpaths, suggesting that there could be attenuation via conservation and restoration. Our results suggest that salty chemical cocktails may be a common water quality signature of urbanization, and there may be potential to use salty chemical cocktails to track nonpoint and point sources of pollution.
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DOI: Salty chemical cocktails as water quality signatures: longitudinal trends and breakpoints along different U.S. streams