Seasonal and stormflow chloride loads in an urban–agricultural watershed in central Illinois, USA

High-Frequency Data Provides Insight into Chloride Transport Pathways and Exceedances of Chronic Chloride Guidelines for the Protection of Aquatic Life in Streams Impacted by Deicers

“…The extent and severity of Cl exposure to aquatic life are dependent on the [Cl] dynamics within freshwater bodies, which are influenced by the transport pathways of Cl from its various sources. Deicers applied to roads and parking lots will dissolve in rain or meltwater and be transported from areas of application and snow storage to surface waters via assorted pathways, predominantly: (i) direct input (e.g., spray or drainage from bridges); (ii) overland flow from impervious areas adjacent to the receiving water; (iii) piped flow via storm sewer systems; and (iv) infiltration and subsequent subsurface flow (interflow and/or groundwater flow). − The first three pathways are rapid, occurring over hours or days, whereas subsurface transit times can reach weeks to months (interflow and shallow riparian groundwaters), or years to decades (longer or deeper groundwater paths). , Annual watershed Cl retention can range from 40 to 90% of total deicer application, driving high [Cl] in groundwater discharge for months to years. − Elevated [Cl] during stream inter-event flow conditions in the non-salting season (i.e., including late spring, summer, and early fall, depending on latitude) has been attributed to groundwater contributions of Cl. ,,,,,− Surface water [Cl] dynamics are controlled by the relative contributions of these rapid and slow transport pathways during and following precipitation and melt events, and across seasons. , …”

Lakes protect downstream riverine habitats from chloride toxicity

“…In freshwater environments, toxicity guidelines are often set for acute exposure limits (the ability of organisms to withstand short duration exposures to high concentrations) and chronic toxicity limits (long‐term exposure; US Environmental Protection Agency [EPA] 1988). Recognizing that salinity and ion concentrations in freshwater environments are impacted in part by stormflow and hydrologic connectivity (Liu and Bao 2020; Oberhelman and Peterson 2021), it is important to understand the drivers of spatiotemporal variability that may cause concentrations to exceed ecotoxicity thresholds. A useful method to examine variability in water chemistry is by examining concentration–discharge relationships, or export regimes (Diamond and Cohen 2018; Zimmer et al 2019), which Botter et al (2020) describe as a “fundamental descriptor of the spatiotemporal interaction between hydrological, geochemical, and biogeochemical processes in the catchment.” Export regimes can differ over seasonal and hydrological scales (Minaudo et al 2019; Knapp et al 2020) in addition to being influenced by watershed characteristics, especially land use, which can establish and modify hydrological behavior and solute loading (Musolff et al 2015; Minaudo et al 2019).…”

“…Land use has demonstrated ability to alter solute loads and yields, that is, load per area (Li and Bush 2015). Understanding spatiotemporal variation of salt yield within a watershed can help determine high risk areas for toxicity and influences that individual, smaller areas have on overall watershed water quality (Mooney et al 2020; Dugan et al 2023; Oberhelman and Peterson 2021). In our study, we use concentration–discharge theory to examine SpC–discharge (cQ) relationships in streams across space and time to investigate seasonal patterns, land use drivers, and the influence of connectivity on the salinization of a freshwater watershed.…”