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Chloride source delineation in an urban‐agricultural watershed: Deicing agents versus agricultural contributions
Author(s) -
Oberhelman Andrew,
Peterson Eric W.
Publication year - 2020
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/hyp.13861
Subject(s) - impervious surface , watershed , tile drainage , environmental science , nitrate , potassium , chloride , groundwater , hydrology (agriculture) , surface water , environmental chemistry , fertilizer , chemistry , base flow , soil water , environmental engineering , drainage basin , ecology , geography , soil science , geology , biology , cartography , organic chemistry , geotechnical engineering , machine learning , computer science
Analyses ( n = 525) of chloride (Cl − ), bromide (Br − ), nitrate as nitrogen (NO 3 ‐N), sodium (Na + ), calcium (Ca 2+ ) 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 NO 3 ‐N ( p < .0001), to Ca 2+ ( 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.