ROAD SALT APPLICATIONS AFFECT SOIL PHYSIOCHEMICAL CHARACTERISTICS ACROSS TIME AND SPACE

Since the 1940s, road salts have regularly been used to deice roadways during the winter. The most common road salt is NaCl, which, once dissolved, can be easily transported to and stored in nearby soils, causing degradation of these habitats. While previous studies have explored soil physiochemical changes due to road salting in lab experiments and over short (e.g., winter season only) timescales in the field, to our knowledge, no studies address road salt-induced changes to soils over longer timeframes in field settings. Thus, starting in May 2019, we collected monthly soil samples by a road near Saint Louis, Missouri, where deicing salts were applied in the winter. Soil was collected at six distances from the road (0.25-13 m) and two depths (0-5 cm, 5-15 cm) and processed for Cl^-, Na⁺, and other major ion concentrations, pH, organic matter (OM), and water content. We also measured soil compaction and infiltration during one sampling event. During non-salting months, soil Cl^- was low (<13 mg/kg) at every sampling site but increased rapidly up to 388 mg/kg immediately following deicing applications. Soil Cl^- concentrations were consistently highest near the road during the salting months. The Cl^- added to the soil after salting was flushed quickly. Indeed, we observed up to a 96% concentration decrease only a week after salt application and heavy rain, confirming that Cl^- contamination is mostly transported conservatively by porewater flow. Soil pH near the road significantly (p < 0.05) increased ~0.7 pH units during the road salting season. Farther from the road, soil pH did not vary among sites or seasons. Increased winter soil pH near the road is probably due to salt-derived Na⁺ replacing H⁺ on cation exchange sites, leading to H⁺ leaching. Soil OM, water content, and compaction decreased, while infiltration rates increased, with distance from the road. High OM and water storage potential near the road may enhance the retention of deicers through increased ion exchange capacity and slow porewater movement. Soil cation concentration analyses are ongoing, but, overall, our data show that soils close to roads are most vulnerable to the effects of road salt. Understanding road salt retention and transport in soil is important for ensuring soil health and assessing the role soil plays in transmitting road salt pollution to waterbodies.