104-6 Strong long-term relationship between chloride and dissolved organic carbon export in road salt-affected exurban and suburban watersheds

Session: A Showcase of Undergraduate Research in Hydrogeology (Posters)

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Abstract:

Road salts and salt-impacted runoff are often transported to the side of the road, where sodium (Na⁺) and chloride (Cl^-) can infiltrate the soil, leach into groundwater, and slowly be released into streams over time, leading to a long-term increase in waterways. However, the deposition of Na⁺ in roadside soils can also alter the soil's composition, causing the displacement of calcium and magnesium, which leads to a decrease in soil aggregate stability and the release of organic matter. While lab and limited field studies suggest an influx of road salt to roadside soils can lead to pulses of dissolved organic carbon (DOC) delivery from soils and groundwater to streams, few to no studies have examined the long-term relationship of these parameters in road salt-affected watersheds. To address these knowledge gaps, we utilize a 20-year dataset (1998-2020) of monthly streamwater quality data, combined with daily streamflow data, for six exurban and suburban watersheds in southeastern Pennsylvania to assess the co-relationship between flow-normalized Cl^- and DOC concentrations. The relationship between long-term land management practices (e.g., LULC change, road salt/brine inputs, etc.) and DOC concentrations and loads is also explored. Similar patterns were observed in the study watersheds, with flow-normalized Cl^- and DOC initially increasing, reaching an inflection point in DOC, and then subsequently decreasing. Over the last 10 years of the study period, a strong, statistically significant negative relationship (r²> 0.89; p < 0.01) was observed between flow-normalized Cl^- and DOC concentrations, suggesting a decrease in organic matter over time in upstream roadside soils.  Furthermore, the subsequent decrease in flow-normalized DOC concentrations was not statistically associated with any LULC changes during the study period. These findings have important implications for watershed management. For example, road salt-driven increases in streamwater DOC concentrations can increase the potential for disinfection byproducts during the water treatment process. Conversely, a subsequent decrease in DOC concentrations can negatively impact microbial processes and freshwater food webs.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8353

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