Road salt intrusion dynamics in a Midwestern prairie-wetland complex

Abstract:

Inland freshwater wetlands throughout the northern U.S. and Canada are experiencing an increase in salinity due to road salt runoff during winter months. Freshwater salinization affects soil texture, contaminant transport, microbial activity, and plant growth in wetlands. Therefore, there is a pressing need to understand the dynamics of road salt intrusion in these ecosystems. This study uses a distributed high-resolution sensing network to evaluate these dynamics in a prairie-wetland complex, Gensburg Markham Prairie (GMP). The network consists of in situ sensors measuring electrical conductivity (EC), surface and groundwater level, precipitation, water temperature, and air temperature at 30-minute intervals. Also, water samples were collected monthly from 13 shallow groundwater wells and eight surface water locations and analyzed for Cl^-, Mg²⁺, Na⁺, Ca²⁺, and K⁺. Two-years of continuous EC data show a sharp increase during winter months, generally by an order-of-magnitude, due to road salt applications in nearby roads. Traditional water quality sampling methods would likely have missed these abrupt changes in EC levels caused by unanticipated snowmelt runoff events. The spatial distributions of EC and Cl^- reveal higher levels at the periphery of GMP near roadways, and in a preferential groundwater flow path in the interior of the prairie. Spectral analysis of EC time-series in ditches suggests that there is no correlation between salinity dynamics at super-annual timescales, indicating that the dynamics are not event-driven, and the introduced solutes are rapidly exported from the site. This research supports development of improved de-icing strategies by local agencies and informs site-specific management of wetland ecosystems under anthropogenic stressors.