Stormwater Best Management Practices: Experimental Evaluation of Chemical Cocktails Mobilized by Freshwater Salinization Syndrome
Citation:
Galella, J., S. Kaushal, P. Mayer, C. Maas, R. Shatkay, AND R. Stutzke. Stormwater Best Management Practices: Experimental Evaluation of Chemical Cocktails Mobilized by Freshwater Salinization Syndrome. Frontiers in Environmental Science. Frontiers, Lausanne, Switzerland, 11:1020914, (2023). https://doi.org/10.3389/fenvs.2023.1020914
Impact/Purpose:
Our study addresses the phenomenon of freshwater salinization syndrome (FSS) where salts, especially NaCl from road salts, can exacerbate the mobilization of heavy metals, ions, and nutrients into combinations of chemical pollutants that we term “chemical cocktails”. We describe how these chemical cocktails form under controlled lab mesocosm experiments where sediments from stormwater management features were dosed with various types of salts and incubated under simulated conditions to determine which types of salts are most effective at mobilizing metals and other pollutants. Our results show differential effects of salt types on various heavy metals including copper and lead and that salinization from road salts and other sources may cause exceedances of drinking water pollutants. Our results are intended to help guide watershed and drinking water managers anticipate pollutant pulses during periods of freshwater salinization and identify threshold applications of road salts.
Description:
Freshwater Salinization Syndrome (FSS) refers to the suite of physical, biological, and chemical impacts of salt ions on the degradation of natural, engineered, and social systems. Impacts of FSS on mobilization of chemical cocktails has been documented in streams and groundwater, but little research has focused on the effects of FSS on stormwater best management practices (BMPs) such as: constructed wetlands, bioswales, ponds, and bioretention. However emerging research suggests that stormwater BMPs may be both sources and sinks of contaminants, shifting seasonally with road salt applications. We conducted lab experiments to investigate this premise; replicate water and soil samples were collected from four distinct stormwater feature types (bioretention, bioswale, constructed wetlands and retention ponds) and were used in salt incubation experiments conducted under six different salinities with three different salts (NaCl, CaCl2, and MgCl2). Increased salt concentrations had profound effects on major and trace element mobilization, with all three salts showing significant positive relationships across nearly all elements analyzed. Across all sites, mean salt retention was 34%, 28%, and 26% for Na+, Mg2+ and Ca2+ respectively, and there were significant differences among stormwater BMPs. Salt type showed preferential mobilization of certain elements. NaCl mobilized Cu, a potent toxicant to aquatic biota, at rates over an order of magnitude greater than both CaCl2 and MgCl2. Stormwater BMP type also had a significant effect on elemental mobilization, with ponds mobilizing significantly more Mn than other sites. However, salt concentration and salt type consistently had significant effects on mean concentrations of elements mobilized across all stormwater BMPs (p < 0.05), suggesting that processes such as ion exchange mobilize metals mobilize metals and salt ions regardless of BMP type. Our results suggest that decisions regarding the amounts and types of salts used as deicers can have significant effects on reducing contaminant mobilization to freshwater ecosystems.
URLs/Downloads:
DOI: Stormwater Best Management Practices: Experimental Evaluation of Chemical Cocktails Mobilized by Freshwater Salinization Syndrome