Evaluating Relationships Between Total Dissolved Solids (TDS) and Total Suspended Solids (TSS) in a Mining-Influenced Watershed

Measurement of total suspended solids (TSS) and total dissolved solids (TDS) loadings in streams is often used to assess potential impacts from mining on surface water quality within a drainage basin. It has been suggested that TSS could be used as an indicator to estimate TDS loading through the use of a TDS/TSS ratio. The reliability of this approach was tested by examining empirical linear relationships between TSS and TDS loads at three locations within a mining-influenced watershed in Colorado. Predictive accuracy of the relationships was assessed using an independent source of data for the same locations, with comparisons between estimated and observed TDS loads for periods within and outside the years used to develop relationships. Evaluations were conducted over the entire flow regime and for separate periods of low- and high-flow. Improved representation of the data was achieved by incorporation of a regressed average baseflow contribution, indicating the relationship between TDS and TSS loads is not accurately represented by a simple ratio. High variability in data between locations prevents application of a basin scale relationship to all locations within that basin. Local-scale relationships developed under specific flow regimes resulted in more accurate predictions, but results suggest that factors additional to flow may need to be considered to improve predictability. Usefulness of linear empirical relationships to predict TDS load from TSS load will depend on the magnitude of uncertainty that is tolerable for a given situation.