DETERMINING THE PROVENANCE OF A CONTEMPORARY SEDIMENT LOAD WITHIN THE OTTER CREEK WATERSHED, KENTUCKY

Soil erosion models are important tools for predicting sources and redistribution of sediment. There is an inherent difficulty in predicting erosion from mixed land-use watersheds, but the use of soil and sediment fingerprinting allows predictive tracer models to be developed. We examined the spatial and temporal variability in sediment sources and yields to Otter Creek, which drains Fort Knox’s tracked-vehicle training area’s and adjoining rural areas in Hardin and Meade counties, Kentucky. The Environmental Management and Natural Resource divisions of Fort Knox are restoring the tracked-vehicle training areas located on the west side of the installation. The objectives of our research were to 1) characterize the extent of erosion within the Otter Creek drainage basin and determine sources of sediment within the watershed; 2) assess the impact of restoration efforts on sediment loads from tracked-vehicle training areas; and 3) identify the inherited geochemical composition of the sediment sources. We hypothesized that the greatest loads of sediment were anticipated from Fort Knox’s tracked-vehicle training areas within the watershed. Coulometric analyses indicated that particulate inorganic carbon was undetectable in source samples and was less than 2 ppm in stream sediment, which indicates minor contributions from erosion of limestone in this fluviokarst terrain. Isotopic analysis showed distinctive differences between upland and stream settings and between storm and baseflow sediment, but only minor differences between each of the three sampling sites. The carbon and nitrogen isotopic signatures fluctuated seasonally. Our findings demonstrate the roles of seasonal changes, restoration efforts, and land use in the context of transport of fine particulate organic C and N. In particular, agriculture within the watershed plays a more significant role in erosion than originally anticipated.