Understanding the Chloride Regime of a Midwest Mixed-Land-Use Watershed

Abstract:

Short and long-term exposure to elevated chloride (Cl) concentrations in receiving waters can affect mortality of aquatic organisms (e.g. fish, invertebrates) and alter aquatic biological community structure. Unfortunately, there remains a general lack of quantitative information pertaining to Cl regimes under a variety of land-use types and flow conditions. Hinkson Creek, located in Boone County, Missouri, was placed on the Missouri Department of Natural Resources 303(d) list of impaired waters in 1998 due to multiple stressors including Cl. A 4-yr study was initiated in 2010 to better understand the loading and persistence of Cl in Hinkson Creek and related implications for stream restoration. Using a scale-nested experimental watershed study design (n = 5 gauging sites), observed mean and maximum daily Cl was 25.0 and 247.7, 55.7 and 351.4, 78.1 and 1167.8, 74.7 and 1021.8 and 71.0 and 941.4 mg/l at forested, agricultural, suburban, and urban (n=2) gauging sites, respectively. Average daily flow was 0.75, 0.90, 1.40, 1.98, and 3.18 m³/s in forested, agricultural, suburban, and urban gauging sites, respectively. Daily Cl loading estimates were 1620, 4350, 9470, 12800 and 19400 kg/day for forested agricultural, rural, suburban, and urban gauging sites, respectively. Results indicate that current winter deicing practices by municipalities and homeowners in the HCW are contributing to year-round elevated chloride concentrations. This finding holds holding important implications for watershed management, aquatic ecosystem health, and stream restoration in the HCW and other developing mixed-land-use watersheds of the Mississippi River Basin (MRB) and elsewhere.