TRACING SUSPENDED SEDIMENT IN AN ANTHROPOGENICALLY INFLUENCED WATERSHED WITH NUMEROUS CHANGES TO LAND USAGE AND STREAM MORPHOLOGY

Nutrient loading in rivers in the Upper Sangamon River Basin (USRB) has led to concentrations of nitrate that exceeds EPA water quality standards and concentrations of phosphorous which promote algal growth. These nutrients are primarily introduced by fertilizers and transported via adsorption to suspended sediments. This study focuses on the Wildcat Slough, a river in the USRB with a 61.3km² watershed primarily used for agriculture, but includes five other land types within it. We estimate the relative contribution of each land surface type to the suspended sediment load of the Wildcat Slough using a sediment fingerprinting technique. We use a statistically verified suite of tracers including trace metals and stable isotopes of carbon and nitrogen, which show significant variances between the different land types within the Wildcat’s watershed. A mixing model uses the concentrations of these tracers from samples collected in suspension and from the different land types to estimate the amount of sediment each source contributes. Initial results are promising, showing that a dozen tracers are capable of distinguishing between the land types on their own.

We evaluate the influence of landforms in controlling sediment sources within the Wildcat Slough basin. The Wildcat Slough undergoes morphological changes as it approaches the confluence with the Sangamon River. The upper reaches of the Wildcat Slough are retained within a deep, channelized ditch with a complex network of drainage tiles emptying into it as it flows through the farm fields. Closer to the confluence, however, it freely meanders through forest, pasture, and prairies and has established point bars and outer banks. The correspondence between land use and channel morphology allows us to track the contributions to suspended load as a function of channel character.