Road salt chloride retention in wetland soils and effects on dissolved organic carbon export

Abstract

ABSTRACTDeicing salt runoff is a cause of freshwater salinisation in many regions. Studies in uplands indicate that soil properties affect storage and movement across the landscape of salt and dissolved organic carbon (DOC). Wetlands have unique soil properties, act as buffers between uplands and aquatic ecosystems, and are major sources of DOC to surface waters, yet less is known about these dynamics in wetlands. Soil cores from three wetlands differing in vegetation and soil organic matter (SOM) were flushed with road salt treatments of 0, 2.5, and 5.0 g chloride L−1 followed by no-salt flushes. Leachate was analysed for chloride (Clin), DOC concentration and quality (as specific UV absorbance (SUVA)), and Clin accumulation in soils was measured. Soils retained 3.6–41% of the added Clin, and there was a significant positive relationship between SOM and Clin retention. Salt treatment significantly reduced DOC export from only one of the three soils and had no effect on SUVA. Our findings suggest that the ability of wetland soils to buffer downstream aquatic systems against salt pollution is highly variable and likely limited to low salt concentrations, and that soil Clin accumulation may have negative impacts on wetland flora, fauna and biogeochemistry.