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Salinization is increasingly affecting many watersheds, significantly impacting drinking water resources and infrastructure, reducing stability and resilience of aquatic ecosystems, and potentially hindering stream and river restoration efforts. Salinization is related to deicer use on roadways with additional contributions from accelerated weathering of impervious surfaces, water softeners, and sewage. The concentrations of chloride observed in many urban streams in Maryland now exceed the limit of 250 mg/L established by the U.S. EPA for chronic toxicity to freshwater life. These observed ranges and extreme fluctuations in salinity can mobilize nitrogen, phosphorus, base cations, and toxic metals from sediments to streams due to enhanced ion exchange and solubility. The objectives of this study are to: (1) assess the effects of freshwater salinization from different common salt ions on mobilization of nutrients and metals in urban streams surrounded by differing land use and geomorphic setting; and (2) characterize changes in concentrations and fluxes of salts, nutrients, and metals in urban streams following winter deicing events to better inform development of total maximum daily loads
(TMDLs). The effects of salinization on mobilizing nutrients and metals will be characterized in 3 ways: (1) controlled laboratory incubations with soils and sediments exposed to varying levels of NaCl, KCl, CaCl2, and MgCl2 concentrations; (2) short-term salinization experiments in urban streams before winter snow events; (3) monitoring of ambient water quality following winter deicing events in urban streams. The proposed project will provide an estimate of different salt concentrations and thresholds of mobilization of nutrients and metals across a broad range of streams in the Baltimore, MD and Washington DC metropolitan regions. In addition to publishing scientific papers, we will also develop facts sheets for the U.S. EPA, University of Maryland Extension, and Maryland Sea Grant on the levels and types of contaminants mobilized by different salt ions.