Date of Award
Master of Science (MS)
Eric EWP Peterson
Long-term increase in chloride (Cl-) concentration in surface water and groundwater from anthropogenic sources, including deicing salts, agriculture, septic effluents, and wastewater treatment plants is a growing cause for concern all over the world. In rural midwestern US with predominant agricultural land usage and less impervious surface cover, agriculture may serve as a potential source for Cl- in surface and groundwater systems. A saturated riparian buffer (SRB) installed adjacent to a central Illinois stream to reduce nutrient losses was used to identify populations of Cl-, substantiate agricultural influence, and identify spatial and temporal Cl- variations within the SRB. 2297 water samples collected from 35 wells, a diversion box and stream over a 7-year period within the SRB were analyzed for major anions, with major cations analyzed for 155 samples from four sampling runs. Based upon well depth and locations within the SRB, sample locations were delineated into diamicton groundwater (DW), downgradient shallow groundwater (DGSW), upgradient shallow groundwater (UGSW), diversion box (DB), and stream (ST). Seasons were divided to correspond with agricultural practices: spring/planting, summer/growing, fall/harvest, and winter/fallow. Cumulative probability curve and two-way ANOVA results identified three similar populations of Cl-: [(1) UGSW; (2) DB, DGSW, DW; and (3) ST]. Background chloride concentration was established in the waters of the UGSW at 3.9 mg/L. Elevated concentrations above background and Principal Component Analysis (PCA) classifications suggest agricultural contributions (KCl fertilizer or nitrification inhibitors) from tile-drainage waters within the diversion box (9.8 mg/L) were a source of chloride. The two-way ANOVA analysis also indicated temporal variability between the waters of the diversion box (due to agricultural runoff) and UGSW in spring; and between the DGSW (due to mixing between agricultural runoff and groundwater) and UGSW in spring. Chloride concentrations observed in the study were up to the levels that could potentially alter microbial communities and inhibit denitrification, thereby, decreasing the efficiency of the SRB to reduce nitrate transport to the stream. KEYWORDS: ANOVA; Chloride; Groundwater; Principal component analysis; Saturated riparian buffer; Stream.
Commander, Okiemute, "Assessment of Spatial and Temporal Variations in Chloride Concentration in an Agricultural Tile-Drained Area in Central Illinois" (2023). Theses and Dissertations. 1727.