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Abstract:
A longitudinal study of water chemistry in Pettyjohns Cave, Georgia, reveals a wide range of major ion water chemistry at different sampling points within the cave, and pronounced seasonal water-chemistry variations at some locations. The cave occurs in the Mississippian Bangor Limestone on the east side of Pigeon Mountain in the Appalachian Plateaus physiographic province of northwest Georgia, USA. Four sampling points within the cave were monitored at approximately 2- to 3-month intervals for 22 months: a major conduit stream; a small conduit tributary; water dripping into the cave through a small fracture; and water dripping from active speleothems. Other waters, including surface water, were sampled as available. Samples were analyzed for temperature, pH, specific conductance, alkalinity, and major ions. Most spatial water chemistry trends within the cave appear to be the result of rock-water interaction along distinct subsurface flowpaths. Temporal variations, most pronounced in conduit streams, result primarily from mixing of distinct waters in varying ratios, although seasonal changes in CO2 partial pressure may account for some variation. Results illustrate the inherent spatial and temporal variability of water chemistry in karst aquifers and point to the need to design sampling programs carefully.