INVESTIGATING HYSTERESIS EFFECTS IN SUSPENDED SEDIMENTS AND TURBIDITY IN FIVE NORTHWEST ARKANSAS RIVERS

The relationships between total suspended sediments (TSS) and turbidity with discharge in streams are expected to vary based on where they occur on the hydrograph. We compiled and analyzed thirteen years of data, collected by the Arkansas Department of Environmental Quality and the United States Geological Survey, at sites on five Northwest Arkansas Rivers to investigate these hysteresis effects. When data are separated based on whether they fall on the rising or receding limb of the hydrograph, slope and r² values for both TSS and turbidity are lower on the receding limbs than on the rising limbs for four of the five rivers. This indicates that there is likely a stronger correlation with discharge on the rising limbs. This supports the hypothesis of hysteresis. A statistically significant difference (p<0.05) in the means of the log-transformed TSS data exists in only two rivers, Kings and Buffalo. The log-transformed turbidity data for two rivers, Kings and War Eagle Creek, also show a statistically significant difference in the means. It is likely that the expected differences in means are not being recognized fully in the other rivers as a result of sampling methods (most samples were taken on the receding limbs) or because multiple samples were not collected during single flow events.