Contaminant Transport in Two Central Missouri Karst Recharge Areas

Karst watersheds with significant losing streams represent a particularly vulnerable setting for ground water contamination because of the direct connection to surface water. Improvement of water quality in this type of karst setting faces many of the same management challenges as typical surface watersheds with regards to implementation of best management practices and responsible development in urbanizing areas. Because of the existing agricultural land-use and future threat of heavy urbanization, two losing stream karst basins were chosen for intensive monitoring in Boone County, MO: Hunters Cave (HC) and Devils Icebox Cave (DI). Both caves were formed in Burlington Limestone and have similar sized recharge areas (33-34 km²) and land uses. However, the DI recharge area has more row crop and less grassland areas than the HC recharge area. Year-round monitoring was initiated in April 1999 and completed in April 2002 with the objective of characterizing the water quality status of the main cave streams relative to herbicide, nutrient, and sediment contamination. Water sampling for contaminants entailed grab samples at regular intervals, and runoff event samples collected using automated sampling equipment. Herbicides or their metabolites were detected in almost 100% of the samples from both cave streams. Total nitrogen and phosphorus concentrations and loads were consistently higher in Devils Icebox watershed, and concentrations of either nutrient correlated to stream discharge and suspended sediment levels. Because of higher concentrations and stream discharge, the DI recharge area had consistently higher loads of herbicides, nutrients, and sediment than the HC recharge area. Prevailing land management has significantly degraded the water quality in both watersheds.