Estimating Suspended Solids from Turbidity in the Robeson Creek,NC Watershed

The purpose of this project was to assess the effect of estimating total suspended solids (TSS) concentrations from turbidity on TSS loads for streams in the Robeson Creek watershed. Discharge was monitored continuously and base‐flow grab and storm event composite samples were collected and analyzed for TSS and turbidity from five sites during five years of monitoring. For base‐flow samples, the TSS‐turbidity relationship for all five sites was poor indicating that TSS concentrations in base flow cannot be estimated from a TSS‐turbidity relationship. To test the effect of analyzing fewer samples, TSS from every third and the first 20 samples collected from each site was used to develop TSS‐turbidity relationships. In addition, the TSS‐turbidity relationship developed from the most downstream site was used to estimate TSS concentrations from turbidity measured at the other four sites. For four of the five sites, analyzing every third sample for TSS and using the TSS‐turbidity relationship to estimate the missing TSS concentrations would result in mean TSS loads that were not significantly different from the observed. Using the TSS‐turbidity relationship from the outlet to estimate TSS from turbidity measured at the other four sites resulted in significantly different mean TSS loads at three of the four sites. These results indicate that estimating TSS concentrations from turbidity using a TSS‐turbidity relationship developed from a subset of the overall dataset should be done with great caution.