G. Douglas Glysson

Adjustment of total suspended solids data for use in sediment studies

The U.S. Environmental Protection Agency identifies fluvial sediment as the single most widespread pollutant in the Nations rivers and streams, affecting aquatic habitat, drinking water treatment processes, and recreational uses of rivers, lakes, and estuaries. A significant amount of suspended-sediment data has been produced using the total suspended solids (TSS) laboratory analysis method. An evaluation of data collected and analyzed by the U.S. Geological Survey and others has shown that the variation in TSS analytical results is considerably larger than that for traditional suspended-sediment concentration analyses (SSC) and that the TSS data show a negative bias when compared to SSC data. This paper presents the initial results of a continuing investigation into the differences between TSS and SSC results. It explores possible relations between these differences and other hydrologic data collected at the same stations. A general equation was developed to relate TSS data to SSC data. However, this general equation is not applicable for data from individual stations. Based on these analyses, there appears to be no simple, straightforward way to relate TSS and SSC data unless pairs of TSS and SSC results are available for a station.

Proceedings of the Federal Interagency Workshop on Turbidity and Other Sediment Surrogates, April 30-May 2, 2002, Reno, Nevada

As part of the Subcommittee on Sedimentation’s “Turbidity and Other Sediment Surrogates Workshop,” April 30-May 2, 2002, a questionnaire on uses of turbidity was submitted to water-quality coordinators for all State and some Tribal agencies. The questionnaire was designed to address key issues related to turbidity, including water-quality standards, technology, ranges observed, water bodies, seasonal variability, calibration and sampling protocols, and use of other measures of fluvial and suspended sediment. All but 5 of the 40 agencies that responded indicated having established either narrative or numeric standards for turbidity under their jurisdictions. In addition to water-quality standards, several agencies are using either turbidity or TSS to identify sediment-impaired streams or stream reaches with application to developing sediment TMDLs. Water clarity was identified by the agencies as the parameter of primary interest when measuring turbidity. Several agencies have correlated either turbidity or TSS with habitat or aquatic life. Several agencies indicated having noticed a seasonal variability in turbidity that is possibly related to an increase in plankton in the water column and not runoff. Reported ranges in turbidity vary widely, ranging from below detection limits to over 10,000 NTU. The large majority of agencies use instruments operating on the bulk optical properties of watersediment mixtures, including turbidimeters, optical backscatter meters (OBS), and optical transmissometers to infer turbidity, and analyses of grab samples to provide the comparative SSC or TSS data. Some agencies are using flow-integrated sampling techniques depending upon the project objectives. The majority of the agencies that measure turbidity use formazin as a calibration standard and USEPA Method 180.1 for analysis (U.S. Environmental Protection Agency, 1999). The majority of the agencies used either Oracle, STORET, or a “local” database or spreadsheet for data storage and analysis. The agencies identified several technical needs related to turbidity, including improving the relation between turbidity, TSS, SSC, channel stability, and biological impairment; establishing reference fluvial sediment conditions and means of measuring significant departure from reference conditions; improving depthintegrated isokinetic samplers; and developing a consistent procedure and less expensive probes that can be rapidly deployed and are stable in the field. In addition, most agencies agreed that additional longterm, stream-discharge, suspended and bedload data are needed, and that the USEPA should revise Method 180.1 on turbidity (U.S. Environmental Protection Agency, 1999) to include state-of-the-art instrumentation capable of measuring higher concentrations of turbidity without making sample dilutions.