ASSESSING STORMWATER IMPACTS AND HYDROGEOLOGICAL INFUENCES ON WATER QUALITY IN AN URBAN KARST LAKE

Urban karst lakes, often created by subsidence and sinkhole activity, are understudied with respect to the role they play in urban karst hydrology and the water quality implactions from their existence in the landscape. It is well documented that stormwater runoff influences various parameters (heavy metals, oil and grease, salts, etc.) and that other urban impacts (septic runoff, detergents, and organic waste) all can negatively impact groundwater systems, which include the expression of the water table where is intersects karst lakes. Additionally, these lakes can serve as accumulators of sediment and waste that is directed into the system. Here, we present data from Limestone Lake, a large karst lake in the urbanized area of Bowling Green, Kentucky, regarding the extent of impacts to its water quality and the lake’s role in the heavily modified urban karst system. Ten-minute resolution data was collected for water depth, pH, conductivity, turbidity, and temperature within a four-month time span. Weekly water samples were collected for oil and grease, biological oxygen demand, alkalinity, chemical Oxygen demand, anions, cations, total organic carbon, total fecal coliform, and E. coli. The results indicate that the lake is responsive to stormwater pollution with a lag time. Changes in the water geochemistry values, water level, and parameters, such as nitrates and E.coli, resulted from storm events. High resolution monitoring displayed daily as well as seasonal fluctions. Seasonal and daily data indicate that the lake is not as contaminated as nearby groundwater sample sites and may function more as a surface water body in the karst system. The downstream spring to which the lake discharges also has varying water quality levels, partially driven by storm events, but also consistently higher than the lake itself. This indicates the potential for additional inputs into the system downstream of the lake. In conclusion, the importance of karst lakes and their role in urban karst hydrology merits further research and this case study proves that additional site-specific knowledge is still needed.