Chloride source delineation in an urban‐agricultural watershed: Deicing agents versus agricultural contributions

Abstract

Analyses (n = 525) of chloride (Cl−), bromide (Br−), nitrate as nitrogen (NO3‐N), sodium (Na+), calcium (Ca2+) and potassium (K+) in stream water, tile‐drain water and groundwater were conducted in an urban‐agricultural watershed (10% urban/impervious, 87% agriculture) to explore potential differences in the signature of Cl− originating from an urban source as compared with an agricultural source. Only during winter recharge events did measured Cl− concentrations exceed the 230 mg/L chronic threshold. At base flow, nearly all surface water and tile water samples had Cl− concentrations above the calculated background threshold of 18 mg/L. Mann–Whitney U tests revealed ratios of Cl− to Br− (p = .045), to NO3‐N (p < .0001), to Ca2+ (p < .0001), and to Na+ (p < .0001) to be significantly different between urban and agricultural waters. While Cl− ratios indicate that road salt was the dominant source of Cl− in the watershed, potassium chloride fertilizer contributed as an important secondary source. Deicing in watersheds where urban land use is minimal had a profound impact on Cl− dynamics; however, agricultural practices contributed Cl− year‐round, elevating stream base flow Cl− concentrations above the background level.

Urbanization drives geographically heterogeneous freshwater salinization in the northeastern United States

“…The measurement we used as a proxy for salinity (conductance) characterizes all collective dissolved ions in water and therefore cannot distinguish specific chemicals driving overall salinization in a system. Although road salts are a clear driver of FSS in cold regions, many additional anthropogenic stressors, including wastewater (Bhide et al., 2021), infrastructure weathering (Moore et al., 2017), and agricultural practices such as liming (Oberhelman & Peterson, 2020) and fertilization (Zampella et al., 2007), can simultaneously drive salinization. Furthermore, lotic ecosystems draining watersheds with FSS drivers might also exhibit falling concentrations of certain ions if other environmental stressors, such as atmospheric deposition and acidic precipitation, are ameliorating (Likens & Buso, 2012; Siemion et al., 2018).…”

Salt Dilution and Flushing Dynamics of an Impaired Agricultural–Urban Stream

“…50 While elevated conductivity during winter has been found to be common in watersheds with even small amounts of impervious surface, agricultural watersheds have been found to have significant year-round salinity issues due to fertilizer ACS ES&T Water pubs.acs.org/estwater Article application. 51 In Appalachian streams, urban sites often have increased SC and Cl − concentrations relative to those of forested streams, with elevated Cl − concentrations coming from diverse sources, including municipal sewage releases at some sites, which do not occur in Stroubles Creek. 52 While SC patterns were predictable at seasonal time scales, event-based dynamics were highly variable.…”

“…The highest variability of both SC and Cl – concentrations occurred during winter, which was attributed to flashier (i.e., rapid, short-term changes in streamflow) hydrographs often observed in urban streams . While elevated conductivity during winter has been found to be common in watersheds with even small amounts of impervious surface, agricultural watersheds have been found to have significant year-round salinity issues due to fertilizer application . In Appalachian streams, urban sites often have increased SC and Cl – concentrations relative to those of forested streams, with elevated Cl – concentrations coming from diverse sources, including municipal sewage releases at some sites, which do not occur in Stroubles Creek .…”

“…Furthermore, while additional de-icing takes place throughout developed parts of the watershed (e.g., different amounts of solid salt application on sidewalks and parking lots vs liquid brining applications), data on salt application by businesses and homeowners are not available to support further analyses of variable patterns in conductivity. Agricultural inputs, deteriorating infrastructure, and walkway de-icing add additional layers of complexity to urbanized watershed salt dynamics. The SC hysteresis patterns in unmodified streams are generally less complex and can be sufficiently characterized by single-point monitoring .…”

Relation between Road-Salt Application and Increasing Radium Concentrations in a Low-pH Aquifer, Southern New Jersey

“…High Ra concentrations have also been shown to be related to agricultural activity, where nitrification of ammonia-based fertilizers reduced the pH of groundwater and made conditions more conducive to the mobility of Ra . Agricultural fertilizers derived from natural phosphate rock could also be sources of Ra , while the addition of KCl fertilizer could lead to increased groundwater Cl concentrations. − Additionally, brine waste from salt-based water softeners was found to mobilize Ra downgradient from septic leach fields, but only when the pH was ≤5.3 . A study in Wisconsin revealed increasing Ra concentrations over a 20-year period but did not identify a cause of the increase .…”