KARST SUSCEPTIBILITY TO ANTHROPOGENIC INFLUENCES IN THE DRIFTLESS AREA OF NORTHWEST ILLINOIS

In karst, the water chemistry of spring waters reveals the interactions between surface water and groundwater. Concerns about anthropogenic influences on the waters in northwest Illinois prompted an investigation examining the water chemistry of local springs and streams. For a year, six streams and six springs were sampled monthly for concentrations of major ions, pH, temperature, specific conductance, dissolved oxygen, biological oxygen demand, turbidity, and total coliform. Qualitative and quantitative analyses, including principal component analysis (PCA), were conducted to assess the influences of surface conditions on the karst waters. When plotted on a Piper Diagram, both waters displayed similar hydrochemical facies: Ca-Mg HCO₃. PCA confirmed the importance of water-rock interaction on the water chemistry, but highlighted differences among the parameters controlling the anthropogenic chemical signatures of the waters. These anthropogenic impacts observed in both waters include nitrate as nitrogen (NO₃-N) and total coliform. NO₃-N concentrations ranged from 2.9 to 14.6 mg/L for the streams and from 0.3 to 30.1 mg/L for the springs; reported background concentrations are 2.5 mg/L. Total coliform was detected in both waters, with more frequent and higher counts in the stream water. The pH (6.5±0.15:mean±standard deviation) and the calcite saturation index values (-0.60±0.21) of the spring waters imply short residence times within the karst system, limiting any remedial mechanism in the subsurface. Overall, the chemical fingerprints of the stream and spring waters display differences; however, both streams and springs are susceptible to anthropogenic practices.