INVESTIGATING SPATIAL AND TEMPORAL VARIATIONS IN CHLORIDE CONCENTRATIONS AND EXPORT DRIVEN BY DEICING SALT APPLICATION WITH MULTI-YEAR HIGH-FREQUENCY DATASETS

In (sub)urban areas of the United States (US) that receive frozen precipitation, deicing salt use is the primary driver of elevated and increasing chloride concentrations and specific conductance (SC). Elevated chloride concentrations and export result in freshwater salinization with negative effects on aquatic ecosystems and drinking water quality. Awareness of these negative effects is growing across the US with numerous states and other entities working toward improved approaches to deicing salt application. The role of spatial drivers such as urbanization and impervious surface cover in elevated chloride and SC are becoming clearer. For example, based on ~30 million high-frequency (2- to 15-minute) observations from 90 sites in the eastern US, we previously reported that chloride and SC increased with impervious surface cover (IC) and higher latitude. Both chronic and acute chloride criteria were frequently exceeded in sites with greater than 9–10% IC and median annual chloride greater than 30–80 mg/L. Deicer application rates, mean annual temperature, and road density were the strongest predictors of median annual chloride concentrations. In comparison to spatial patterns, the drivers of temporal variations in chloride concentrations and export on an intra-annual or year-to-year basis remain poorly characterized. We will use a subset of our high-frequency dataset along with detailed deicing salt application records to characterize temporal variations in chloride concentrations and export and to understand drivers of those variations. Characterizing variations in chloride concentration is essential for understanding negative effects on aquatic ecosystems while export variations will affect downstream receiving bodies such as drinking water reservoirs. Characterization of the variations in seasonal and annual chloride concentrations and export as well as the interaction between baseflow and stormflow export of chloride will yield valuable insights on the pathways by which chloride moves through watersheds.