PS 48-227 - Sources and Consequences of Stream Salinization along an Urbanization Gradient in the Lake Champlain Basin, Vermont USA

Abstract: Salinization of surface and groundwaters is a global issue that promotes infrastructure corrosion, threatens drinking water, and compromises ecosystem health. Sodium levels in Lake Champlain have tripled since 1960, and many basin streams show increasing chloride and high specific conductivity. This project seeks to fill critical gaps in our understanding of the source(s), degree, and consequences of stream salinization within the Lake Champlain Basin (LCB) streams. Eight independent headwater stream study sites in/near Burlington, VT were selected based on having similar drainage areas (2-10 km²), representing an urban land use (ULU) gradient (0-89% of drainage area), and having safe public access points. To focus primarily on urban salinization, the eight stream sites had low (< 30%) agricultural land cover. Specific conductance, temperature, and dissolved oxygen were measured in-stream at each site at weekly or biweekly intervals beginning in July 2022. Grab water samples were collected on each visit for laboratory analysis of total and dissolved metals, cations, anions, and dissolved organic carbon. Twice annually, stream macroinvertebrates were collected (fall and spring) from riffle habitats in each stream using Serber samplers. Benthic macroinvertebrates were identified to the lowest practical taxa (usually genus), counted, and prepared for elemental analysis.

Specific conductance (SPC) and Chloride were strongly correlated to ULU%. Streams representing watersheds with < 17% ULU had SPC and Cl- ranging 20-463 µS/cm and 1-83 mg/L, respectively. In contrast, SPC and Cl- in more urban streams ( >50% ULU) ranged 590-8174 µS/cm, and 79-1385 mg/L, routinely exceeding the EPA and Vermont State impaired water criterion of 230 mg/L for Cl-, even in summer, suggesting salinized groundwater is an important source of stream salinization. Na:Cl ratios of ~1 in all seasons suggest the dominant source of salinization is halite (NaCl, road salt). Macroinvertebrate richness decreased with ULU%, and beta diversity calculations revealed increasing dissimilarity from the 0% ULU reference site as ULU% increased. Urban stream communities were defined by a lack of salt-sensitive taxa, such as mayflies and stoneflies, and instead dominated by salt-tolerant organisms such as hydropsychid caddsiflies, chironomids, and crustaceans. These results support the hypothesis that salt pollution defines biotic community composition in urban streams in areas subject to heavy winter road salt use.