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.

Surface water–groundwater interaction within a karstic system enhances contaminant transport, making karst aquifers susceptible to anthropogenic practices. Contaminated waters related to agricultural and animal husbandry in northwestern Illinois (USA) prompted this investigation. Six streams and five springs were sampled for 16 parameters to assess anthropogenic influences. Statistical analyses revealed differences in 13 of 16 parameters between the stream and spring waters. Rock–water interaction was identified as the dominant mechanism defining the chemistry for both waters, which were classified as Ca-Mg HCO3. Elevated nitrate as nitrogen (NO3-N), chloride (Cl−), sodium, and potassium concentrations indicate that human activities have influenced the quality of both water types. All streams and springs had NO3-N concentration exceeding background levels, with concentrations ranging from 2.9 to 14.5 mg/L and 2.9 to 30.1 mg/L, respectively. NO3-N/Cl relationships at individual locations showed elevated concentrations of NO3-N due to fertilizers, while the spring waters were influenced by manure, septic effluent, or mixed sources. The presence of coliform supports the likelihood of animal or human waste influences on waters. Dissimilarities within their chemical fingerprints can be traced to aid in differentiating sources within the waters.

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Manual and high-frequency observations (n = 525) of chloride (Cl-), bromide (Br-), nitrate (NO3-N), sodium (Na +), calcium (Ca 2+), and potassium (K +) in stream and tile-drain waters were conducted in an urban-agricultural watershed (10% urban/impervious, 87% agriculture) to investigate the importance of stormflow to Cltransport and to explore potential differences in the signature of Cloriginating from an urban source as compared to an agricultural source. The study was undertaken in Evergreen Lake Watershed (ELW) located in central Illinois. Samples were collected on a weekly interval from February 2018 to February 2019 at three station along Six Mile Creek (SMC), the main drainage of ELW. All storm events were sampled at high-frequency at the most downstream station while select storm events were sampled at an upstream station to compare how export changes along the stream. Mann-Whitney U test show ratios of Clto Br-(p = 0.045), NO3-N (p < 0.0001), Ca 2+ (p < 0.0001), and Na + (p < 0.0001) to be statistically significantly different between urban and agricultural waters. Clratios indicate that road salt is the dominant source of Clin ELW while KCl fertilizer is a secondary source. Total Clexport during the study period was 7.77x10 5 kg. Storm events are vital to Clexport in ELW, accounting for 57.5% of total Clload during only 19% of the study period. The importance of storm events varies seasonally with winter and spring storms accounting for nearly half of total Clexport, while summer and fall storm event account for only 10% of total export. Results imply two periods of Clflushing in ELW. The first is associated with flushing of road salt from impervious surfaces following the cold season and second is associated with flushing salt build up after the dry season. When road salt is present on watershed surfaces increased discharge always corresponds with increased Clexport. During storm events when road salt is not present on watershed surfaces increased in discharge corresponds with increased Clexport for lower discharges (Q < 4 m 3 /s). At higher discharges the relationship between discharge and Clexport reaches an asymptote (~ 0.2 Kg/s) where further increases in discharge do not correspond with increased Clexport. Overall, urban, tile, and stream waters exhibit some degree of salinization in ELW with respect to Clas almost all sample concentrations were elevated above calculated background threshold concentration of 18 mg/l. These results highlight the dramatic influence that deicing operations on only a small portion of a watershed can have on the Cldynamics of the entire system. Road salt appears to be able to salinize the dominantly agricultural ELW raising Clconcentrations to levels hazardous to ecosystems and water supplies (>100 mg/l), although the exact extent of salinization in ELW remains unknown and is likely confined to surface and ground water in areas where deicing operations occur and that receive road salt runoff. Fertilizer inputs should also not be ignored as this work and others show th...