ORIGINAL ARTICLE Stream chloride concentrations as a function of land use: a comparison of an agricultural watershed to an urban agricultural watershed Samanta Manon Lax 1 • Eric Wade Peterson 2 • Stephen J. Van der Hoven 3 Received: 29 November 2016 / Accepted: 16 October 2017 Ó Springer-Verlag GmbH Germany 2017 Abstract The concentration of chloride (Cl - ) in streams in northern regions has increased as a result of applications of deicers. This study focused on quantifying the relationship between land use and stream Cl - concentrations. The study area comprises two adjacent watersheds in central Illinois, with similar geology and climate but different land uses (agricultural and urban). GIS analysis delineated watershed land use and calculated road surface areas. Stream water samples were collected and analyzed for anionic compo- sition. During the winter months, streams dominated with urban land use experienced a 20-fold increase in Cl - concentrations (range between 36 and 1350 mg L -1 ); Cl - concentrations in agricultural dominated streams also increased, but the increase was smaller (3X) and concen- trations remained low (between 11 and 58 mg L -1 ). As road salts are not the sole source of Cl - in a stream, Cl - and bromide (Br - ) mass ratios (Cl/Br) and Cl - and sodium (Na) molar ratios ([Cl]/[Na]) were used to identify poten- tial sources of Cl - . The ratios indicate urbanized water- sheds were impacted by road salts; agricultural watersheds ratios indicate other anthropogenic sources. A nonlinear relationship between urban land use and stream Cl - con- centrations indicates urban land use as low as 23% results in elevated Cl - concentrations (greater than 150 mg L -1 ) in stream waters. Keywords GIS Á Land use Á Road salts Á Chloride Á Deicers Introduction Chloride (Cl - ) is highly soluble and does not biodegrade, volatilize, precipitate, or significantly absorb onto mineral surfaces (Environment Canada 2001; Meriano et al. 2009). Thus, Cl - is mobile and easily transported within surface water or infiltrated into the subsurface. Natural sources of Cl - include atmospheric deposition, rock weathering, and basin brines (Gardner and Royer 2010; Kelly et al. 2008; Panno et al. 2006); the contribution of these sources is a function of geologic materials and geographic location. Humans have altered the natural cycle of Cl - in systems through changes associated with urbanization (Kelly et al. 2008; Ramakrishna and Viraraghavan 2005; Schlesinger 2004) and agriculture (Gardner and Royer 2010; Kelly 2008). During winter months in northern latitudes, deicers, primarily sodium chloride (NaCl) or potassium chloride (KCl), are often applied to impervious surfaces such as roads, walkways, and parking lots to keep these areas clear of snow and ice (Environment Canada 2001; Locat and Ge ´linas 1989; Marsalek 2003). In watersheds where deicers have been employed, natural inputs contribute less than 1% to the total Cl - load (Meriano et al. 2009; Novotny et al. 2009; Paja ˛k et al. 2015). In rural watersheds, Cl - inputs from agriculture and septic sewer systems only contribute an additional 1–3% to the total Cl - load (David et al. 2016; Kelly et al. 2008). The remaining load is attributed to deicers, which as a non- point source of Cl - accounts for 87–97% of the Cl - entering a system (Kelly et al. 2008; Meriano et al. 2009). In urban watersheds, wastewater treatment plants contribute more Cl - than road salts, but roads salts still contribute over 35% (Novotny et al. 2009). & Eric Wade Peterson ewpeter@ilstu.edu 1 Layne Christensen, 320 W. 8th Street, Suite 201, Bloomington, IN 47404, USA 2 Department of Geography-Geology, Illinois State University, Normal, IL 61790, USA 3 Genesis Engineering & Redevelopment, Inc., Lodi, CA 95240, USA 123 Environ Earth Sci (2017)76:708 DOI 10.1007/s12665-017-7059-x