Turbidity, total dissolved solids, sulfate, chloride, water quality standard, watershed management
The West Fork of the White River (WFWR) watershed in northwest Arkansas is a trans-ecoregion watershed and is experiencing land-use changes, especially in the downstream portion of the watershed. The entire 54-km long river has been on the State’s 303(d) list of impaired waterbodies for turbidity, total dissolved solids (TDS), and sulfate for many years. The purpose of this study was to identify which part(s) of the river fail to meet applicable water quality standards (WQS) and to investigate possible sources of pollutants, whether human-caused or naturally occurring. Water samples were collected once or twice a month at 9 sites along the WFWR from June 2014 through June 2018 and analyzed for turbidity, TDS, sulfate, and chloride. Median turbidity values ranged from 1.8 to 10.8 NTU and generally increased from upstream to downstream (p<0.05). TDS, sulfate, and chloride also increased from upstream to downstream (p<0.05), with median concentrations ranging from 40.8 to 151.3 mg/L, 3.5 to 27.9 mg/L, and 3.2 to 5.5 mg/L, respectively. Human development (urban plus pasture land use) also increases in the watershed from upstream (19%) to downstream (39%). The two most downstream sites exceeded the limit for turbidity and TDS in over 40% of the samples collected, thus violating the applicable WQS. Sulfate concentrations exceeded the limit in over 60% of samples collected from the 5 most downstream sites, where the underlying geology becomes more limestone and shale dominant, a potentially important source of sulfate. In addition to analyzing water quality in the WFWR, we looked at a larger dataset of 119 sites in the Boston Mountains and Ozark Highlands ecoregions, compiled from the Arkansas Department of Environmental Quality online database. Turbidity, TDS, sulfate, and chloride concentrations were all significantly greater in the Ozark Highlands than the Boston Mountains ecoregion (p<0.05). Our data suggest that there are likely human and natural sources of elevated constituent concentrations in the WFWR, and water resource managers should consider these variables when reviewing assessment methodologies or targeting areas for remediation activities.
Scott, Erin E.. 2019. Turbidity and Ion Concentrations Vary with Land Use and Underlying Geology at the West Fork of the White River. Arkansas Water Resource Center, Fayetteville, AR. MSC388. 15