Road-Salt Induced Salinization of Urban Lakes and Wetlands: Implications for Monitoring

Road-salt-induced salinization can alter the biogeochemical properties of urban freshwaters, which are also vulnerable to multiple contemporary stressors (e.g., eutrophication, acidification). Therefore, it is important to characterize the degree of salinization and the relationship between chloride and other environmental parameters. Here, we investigate the salinization of urban lakes and wetlands in Halifax Regional Municipality, Nova Scotia, Canada, a lake-dense region that has experienced significant increases in chloride concentrations over the last few decades. We characterize recent lake salinization based on 2022-2024 monitoring data of 72 lakes and provide the first appraisal of wetland salinization in the region. Mixed effects models were used to determine the influence of (a) sampling location and timing on lake chloride concentrations, and (b) run-off input type, distance, and sample depth on wetland soil salinity. Overall, lakes and wetlands were found to be highly salinized. Chloride concentrations were significantly related to other salt constituents and metals, including Ba, Cu, Mn, and Sr. Chloride concentrations were significantly higher in lake deep-water samples than respective outlet samples (p < 0.001), and higher in spring than summer (p < 0.001), and this difference was more pronounced in high Cl^- lakes. Measures of salinity were elevated in the deeper (10-20 cm) soil profile compared to the upper (0-10 cm) layer, suggesting possible downward movement of Na. Our research provides a better understanding of spatial and temporal trends in salinization, which helps inform monitoring strategies. Further research is needed to understand drivers of salinity in urban wetlands and the ecological impacts of chloride in highly salinized urban lakes.