TITLE:
Evaluation of Legacy Hydrochemical Data Using Statistics, Graphical Methods, and Equilibrium Modeling—Platte River Watershed, Nebraska, USA
AUTHORS:
Jon C. Atkinson
KEYWORDS:
Hydrochemical Facies, Surface-Water Quality, NETPATH, Visual MINTEQ, Silicate (Feldspar) Weathering
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.13 No.12,
December
10,
2025
ABSTRACT: The Platte River watershed, the largest river basin in Nebraska (1.06 × 105 km2), crosses the entire state along its W-E course in the approximate N-S center of Nebraska. A plethora of historical (1968-1975) hydrochemistry data [major cations and anions, primarily] resulting from collection and analysis by the Nebraska Department of Environment and Energy (NDEE) were statistically and graphically analyzed and subjected to geochemical modeling. Interpretation of this large legacy dataset (31 Platte River systems sampling stations and 34 sampling sites on 22 tributaries) revealed several hydrochemical facies (Ca-HCO3 and three additional ones, encompassing Ca-SO4 and Na-SO4 facies solely in South Platte River discharge), and slight calcite and dolomite supersaturation comprising a line of evidence for the near thermodynamic equilibrium of the studied surface waters. Scatter plots of selected cations versus anions reveal the impact of silicate minerals (e.g., feldspars) weathering on the aqueous hydrochemistry throughout the watershed. Relatively high concentrations of sulfate (up to 1100 mg/L) in numerous samples from the South Platte River are probably sourced by agricultural fertilizer, irrigation water, and dissolution of gypsum/anhydrite. NETPATH geochemical modeling identified 10 plausible models to simulate the significant decrease in SO4 levels downstream along the South Platte River.