TOTAL SUSPENDED SEDIMENT AND PHOSPHORUS TRANSPORT IN RESPONSE TO STORM EVENTS IN AN AGRICULTURALLY DOMINATED WATERSHED

Increased sediment introduction and transport in streams negatively impact water quality. Deleterious effects include reservoir filling, water pollution and ecological impairment. Sediment introduction and transport typically takes place during storm events. Phosphorus introduction, generally from loss of agricultural runoff and soil erosion also typically takes place during storm events. When phosphorus is applied for agricultural uses it is preferentially retained by smaller sediments. During storm events, these phosphorus rich sediments are more likely to enter the stream system. A small number of large storms can account for a large percentage of sediment and total phosphorus (TP) introduction, leading to elevated levels in waterways. Increased phosphorus introduction into waterways is a main driver of algal blooms and hypoxic conditions such as the dead zone that forms in Lake Erie.

The goal of this study is to determine if turbidity (NTU), total suspended sediments (TSS) and TP exhibit similar transport behaviors in an agricultural watershed. Three years of data are available at the Six Mile Creek watershed located in McLean County Illinois. Analysis of TSS, NTU, and TP data show that both TSS and NTU display a correlation ranging from weakly to strongly positive with TP and an R-value ranging from 0.402 to 0.857. When broken down by phase TSS and particulate phosphorus (PP) and NTU and PP display a moderately positive correlation with an R-value of .606 and .732, respectively. However, TSS and dissolved reactive phosphorus (DRP) and NTU and DRP display a correlation ranging from weakly positive to no association with an R value of .472 and .052, respectively. Ongoing hysteresis analysis is being conducted to elucidate the similarities in transport mechanisms between TSS, NTU and TP. Evaluation of hysteresis patterns allows for further breakdown on an annual, seasonal, or event-based scale. Farmers and agricultural managers may be able to better develop sustainable land management practices if there is a consideration of the correlations between NTU, TSS and TP. This could ultimately mitigate the excessive amount of TSS, and TP introduced into surface waters.