COMPARING CONTROLS ON WATER QUALITY IN TWO KARST BASINS, INNER BLUEGRASS REGION, KENTUCKY

We are investigating the processes controlling anion concentrations (F^-, Cl^-, SO₄^2-, and NO₃^-) and field parameters (pH, temperature, specific conductance [SC], and dissolved oxygen [DO]) in two karst basins in central Kentucky. Samples were collected weekly beginning 9 June 2021 from Royal Spring (RS), the outlet of a 58-km² groundwater basin containing both urban and agricultural land use, and Camden Creek (CC), which drains a 771-ha agricultural watershed. RS results were compared against discharge (Q) data from a co-located USGS gauge, whereas CC results were compared against precipitation data from the Lexington Airport, located 14 km ESE.

F^-, Cl^-, and SO₄^2- concentrations were higher at RS and NO₃^- was higher at CC. NO₃^- concentrations did not tend to vary with Q at RS, while NO₃^- at CC fluctuated and appeared to increase following days with > 5 cm of rainfall. Values of pH and DO were higher at CC than at RS, whereas values of SC tended to be higher and were more variable at RS than at CC. Differences between the two sites appear to reflect differences in land use/land cover and possibly in basin size and flow paths. SO₄^2- increased with Cl^- at RS, suggestive of anthropogenic sources of salinity. Higher F^- concentrations at RS suggest leakage from municipal water mains. Elevated SC at RS may also reflect greater water-rock interaction during longer residence times in the larger basin. Elevated NO₃^- at CC may indicate greater NO₃^- flushing from soils or less NO₃^- attenuation along flow paths. Temperature varied over a narrower range at RS, consistent with thermal equilibration along subsurface flow paths. Elevated pH and DO at CC could reflect photosynthesis by instream vegetation. The study will continue through the winter and spring to examine seasonal variability in anion concentrations and field parameters.