The Effect of Road Salt on Wetland Soils

• Mukta Kantak, Environmental Science, University of Texas at Austin

• Shreeram Inamdar, College of Agriculture and Natural Resources, Plant and Soil Sciences, University of Delaware

Road salt (typically sodium chloride, NaCl) has been widely used since the 1970s for deicing roads, particularly in North America. The increasing use of road salts for de-icing in urban and suburban areas poses a significant threat to water and soil quality and biogeochemical cycles of nutrients, particularly nitrogen (N) dynamics. This study investigates the impacts of road salt salinization on soil quality relating to the alterations in N cycles in roadside wetlands. We sampled 13 wetlands in Delaware, USA, including 3 unimpacted and 10 impacted sites with varying levels of road salt. Soil and water parameters that were measured included Na+, Cl–, conductivity, nitrate-N, ammonium-N, total N, total organic carbon, and living microbial biomass. 

Our results suggest that elevated Na+ and Cl– levels in wetland soils due to road salt application can interfere with nitrogen cycling. Some sites with higher concentrations of Na+ and Cl– showed higher concentrations of ammonium and nitrate in ponded surface water, compared to levels of ammonium and nitrate in the soils, while other sites showed different trends possibly due to other external factors. This elevated nitrogen concentration, particularly in the form of ammonium in surface water, could be because sodium displaces ammonium nitrogen sorbed on soil surfaces through cation exchange mechanism. Excess ammonium can cause eutrophication, a process of algal bloom that deteriorates surface water quality by reducing dissolved oxygen levels, subsequently killing aquatic organisms. We hypothesized that more Na+ and Cl– levels would lead to lower levels of biomass and higher conductivity levels, but these trends were not as apparent in our data. Na+ concentrations measured in soils ranged from 19.5 to as much as 735 ppm, while the electrical conductivity of the sampled soil ranged from 0.035 to 11.67 mmhos/cm, showing large amounts of variability across the 13 sites.

Overall, our research indicates that road salt salinization disrupts nitrogen cycles in roadside wetlands, resulting in varied surface water nitrogen levels.  These disruptions can trigger broader ecological and water quality challenges, and negatively impact overall soil productivity and biodiversity, emphasizing the importance of implementing management and mitigation measures in human-influenced areas to safeguard surface and groundwater resources.