RELATIONSHIPS BETWEEN LAND USE AND WATER QUALITY OF THE KARST AQUIFER BENEATH BOWLING GREEN, KENTUCKY

Karst regions are dominated by extensive dissolution of bedrock resulting in complex aquifers that typically have high permeability, heterogeneity and groundwater flow velocities. Groundwater within such subsurface drainage systems can be extremely vulnerable to contamination from land use. The Lost River Groundwater Basin, a well developed karst drainage system developed within the St. Louis and Ste. Genevieve Limestones of south central Kentucky’s Mississippian Plateau, offers an excellent setting to study relationships between land use and karst ground water quality, with a well delineated recharge area and subsurface flow paths, and distinct areas of urban and agricultural land use.

Following a previous, extensive program of groundwater flow mapping using fluorescent dyes and potentiometric surface mapping, a program of quarterly water quality monitoring was conducted from 2005-2012 at three surface and six groundwater locations in and near the Lost River Basin. At the various locations these waters represented a range of both urban and agricultural land use across a region with otherwise homogenous karst hydrogeology and climate. These samples were analyzed for five field and 20 laboratory parameters.

Results of the analyses illustrate the trends in contaminant levels over the past eight years. Atrazine levels are trending downward, possibly due to increase in residential development in the county on formerly agricultural land. Over the whole study, 60% of 144 groundwater samples and 63% of 72 surface water samples were positive for atrazine, though only one sample exceeded the EPA’s Maximum Contaminant Level of 3 ppb. Urban land use resulted in higher fecal bacteria levels than agriculture, and levels were generally higher in groundwater than surface water. Fluoride levels in groundwater subcatchments may help identify city water system leaks. Concentrations of several different urban contaminants decreased through the study period, coincident with the city’s efforts to increase public education about karst groundwater contamination. This suggests that proactive efforts to raise public awareness of relationship between land use and groundwater quality may be a useful tool to ameliorate negative impacts on water quality in karst landscapes.