306-1 Impact of Land Use/Land Cover Practices and Configuration on Freshwater Salinization Syndrome Solute and Nutrient Export in Two Suburban Headwater Streams

Abstract:

In winter 2024-2025, Pennsylvania applied over 600,000 tons of road salt to state roads alone. Upon application, road salt is transported to nearby freshwater systems through surface runoff and groundwater via baseflow. Excess sodium in road salt-impacted runoff can lead to reverse cation exchange in nearby soils, causing increased cation and trace metal exports to waterways through a process known as the Freshwater Salinization Syndrome (FSS). Additionally, excess sodium can degrade soils, thereby enhancing the mobilization of organic matter and nitrogen into waterways, where they can affect downstream ecosystems and water supplies. While the FSS has many recognized negative impacts, little is known about how land use/land cover practices and configuration can affect the timing and delivery of FSS ions and nutrients (ex. dissolved organic carbon [DOC] and nitrate [NO₃^-]) to suburban watersheds. We hypothesized that (1) FSS-related solutes will decrease as % forest cover increases longitudinally in the downstream direction reflecting dilution, and increase as % impervious surface cover (ISC) remains stable longitudinally reflecting a cumulative effect; (2) there will be a temporal lag between Cl^- and NO₃^-/DOC pulses, and the relative time differences will differ as a function of sub-watershed area with larger watersheds experiencing greater lag times; and (3) DOC and NO₃^- pulses will be the highest following a winter storm event. To address these research questions, we performed weekly synoptic sampling over the 2026 water year for nine subwatersheds in the greater Philadelphia, Pennsylvania area that comprise the two larger watersheds of the Mill Creek and East Branch of the Indian Creek, which vary in ISC in their upstream area. Samples were analyzed for major cations (Na⁺, K⁺, Mg²⁺, Ca²⁺), anions (Cl^-, Br^-, NO₃^-, PO₄^3-, SO₄^2-), and DOC. GIS analysis was conducted to determine relative ISC and forest cover in each subwatershed. A spatial analysis of FSS solute concentrations was also performed to assess responses to the relative amount of ISC and forest cover in the upstream area. Likewise, a temporal analysis of Cl^- and DOC/NO₃^- was performed at a subwatershed scale to determine the relative lag time of solutes following a winter storm event. The study results contribute to the understanding of FSS solute and nutrient transport in suburban watersheds, particularly those in road salt-affected regions.

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.