Total suspended sediment concentrations in Wolf Lake, Mississippi: an EPA 319 (h) landscape improvement project

Author(s): Kroger, R.; Brandt, J.; Fleming, J.; Huenemann, T.; Stubbs, T.; Prevost, J.; Littlejohn, K.; Pierce, S.

The Wolf Broad Lake water body (13 km in length) was evaluated as impaired and included on the Mississippi 303(d) list of impaired water bodies. As such, the EPA 319 (h) program, through the Mississippi Department of Environmental Quality selected this water body and its associated watershed for landscape improvement, with the goal of moving towards improving the lakes water quality, meeting associated evaluated total maximum daily loads, and ultimately de-listing the water body for total suspended sediment (TSS) impairment. A study was undertaken for 2 years to evaluate and document appropriate changes to the total suspended sediment loads (mg/L) and overall lake turbidity. These two objectives were analyzed with monthly surface sampling events of turbidity using automated sampling technology (Eureka Manta 2, Automated Data-son) as well as 20 random samples per sampling trip for TSS analysis. Results from a non-parametric Kruskal-Wallis analysis indicate a significant month-by-year effect on turbidity and TSS (Chi-square = 76.08, P = 0.001), but reach (Chi-square = 2.45, P = 0.784) and depth by reach (Chi-square = 2.44, P = 0.784) did not show significant effects on turbidity. There were no significant correlations between TSS and turbidity concentrations and two day, and seven day summed or mean rainfall. Spearman correlation analysis for TSS indicated significant correlations between TSS and mean two day (r2= 0.62, P= 0.002) and seven day (r2= 0.51, P= 0.014) wind speeds. All other variables used in the analysis did not show significant correlation with TSS (P> 0.05). This suggests that wind conditions, rather than rainfall predict the greatest variability in TSS and turbidity in Wolf Lake. These documented correlations between lake water column TSS and turbidity, and wind highlight the difficulties of demonstrating success in a short temporal period between project initiation and completion. Unmanageable environmental conditions (wind speed and direction), and limited temporal monitoring scales (1 years post BMP implementation) limit the possibility of demonstrating success of water quality improvement within Wolf Lake a 303(d) listed water body.

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