| The hydrogeology and geochemistry of the Upper Lost River drainage basin in south central Indiana were studied in terms of groundwater flow conditions. The study consisted of three parts: part one summarized chemical and isotopic compositions of soil water infiltrating through a thick regolith into the underlying limestone bedrock known as the epikarst zone; pad two used stable isotopes (18O, 2H, and 13C) to separate a typical storm hydrograph at Orangeville Rise into storm water, epikarst water, and phreatic water components. The Orangeville Rise is one of the two major perennial karst springs in the basin with a drainage area of more than 50 mi2. In part three, the chemical and isotopic composition of groundwater along the evolutionary flow path from the recharge area located in the mantled karst portion of the basin to the discharge point at Orangeville Rise was studied using mass balance reaction-path modeling technique.; The study found that the most intensified dissolution of limestone occurred in the epikarst zone where secondary porosity and permeability developed when aggressive soil water encountered bedrock, suggesting that present day chemical weathering is important in the mantled karst portion of the basin. As water flows away from the mantled karst area, its ability to dissolve carbonate rocks diminishes significantly. Depending on the dominant flow condition, discharge at Orangeville Rise was described by either a binary mixing or a trinary mixing process. Using the characteristic chemical and isotopic composition derived from long-term data, the study estimated that the overall discharge at Orangeville Rise consisted of 59% rainwater, 27% epikarst water, and 14% phreatic water.; It was found through reaction-path simulation that the predominant chemical reactions that control chemical and isotopic evolution of groundwater in the Upper Lost River basin were carbonate dissolution/precipitation, gypsum dissolution, oxidation of organic matter, and cation exchange. Mass balance calculation further indicated that the overall mass removal rate through dissolution in the study area was approximately 10,600 kg/day for CaCO3 and about 6,400 kg/day for gypsum although during extremely low flow, CaCO3 saturation was also occurring. |
