356-11 Contrasting Road Salt Fate in Two Urban Watersheds in Omaha, NE

Abstract:

Salinization of surface waters due to winter road salt addition is a pervasive problem across the globe. Previous work has shown that all trophic levels are affected by intensive road salt usage in freshwater ecosystems, though often at sublethal levels, nevertheless impacting ecosystem function. We explore the impact of road salt on two urban watersheds in Omaha, Nebraska: Elmwood Creek that feeds into Little Papillion Creek and Heron Haven, a springfed wetland flowing into Big Papillion Creek. Both watersheds include first-order streams each with a natural drainage area of ~1.5 km² and are extensively impacted by stormwater infrastructure significantly increasing drainage area and potential anthropogenic additions. We present high-resolution conductivity data from inlets and outlets of both watersheds between October 2025 and March 2026, as well as chloride spot samples during the same period. Omaha Public Works utilizes sodium chloride salt/brine, calcium chloride brine, and sand to maintain winter roads, depending on temperature and severity of storm events.

At Elmwood Creek, peaks in conductivity at both upstream and downstream sites follow snow events. The upstream site peaks at over 6000μS/cm and consistently falls over ~14 days back to background levels at ~900μS/cm. The downstream site also peaks following snowfall events but reaches peaks of ~3000μS/cm before returning to background levels. The lower conductivity noted at the downstream site is likely related to dilution as its watershed includes residential neighborhoods that are not as aggressively salted as well as green infrastructure designed to increase infiltration.

In contrast Heron Haven shows retention and/or dilution of road salt within the wetland. The groundwater retains consistently low conductivity (~900μS/cm). The anthropogenically impacted inlet, which drains a residential area and major roadway through stormwater infrastructure, does not respond directly to snowfall events. Instead, following an initial pulse where conductivity reached over 15,000μS/cm, values slowly decreased through time with a noted freshening during a mid-January rain event. Over the same period, the wetland outlet never exceeded ~1000μS/cm, though there is a noted increase in conductivity concurrent with the high conductivity at the anthropogenic inlet. These data indicate that the salt is retained within the wetland and future work will focus on where the salt is partitioned in the ecosystem.

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