USGS

Comparability of Suspended-Sediment Concentration and Total Suspended Solids Data

Water-Resources Investigation Report 00-4191

By John R. Gray, G. Douglas Glysson, Lisa M. Turcios, and Gregory E. Schwarz


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CONTENTS

Abstract

Introduction

Field Techniques and Laboratory Methods

Field Techniques

Laboratory Methods

Suspended-Sediment Concentration Analytical Method

Total Suspended Solids Analytical Method

Differences Between the Suspended-Sediment Concentration and Total Suspended Solids Analytical Methods

Description of Data Used in the Evaluation

Arizona

Hawaii

Illinois

Kentucky

Maryland

Virginia

Washington

Wisconsin

Quality-Control Data

Comparability of Suspended-Sediment Concentration and Total Suspended Solids Data

Natural-Water Data

Quality-Control Data

Conclusions

References Cited

List of Tables:
  1. State in which natural-water samples were collected, collecting organization, collection methods, and devices for obtaining subsamples for suspended-sediment concentration and total suspended solids analyses
  2. Statistical characteristics of paired suspended-sediment concentrations (SSC) and total suspended solids (TSS) data for each of eight States, and for the combined data from all States
List of Figures:
  1. Bar graph showing number of paired suspended-sediment concentration values and total suspended solids values of the 3,235 data pairs for selected suspended-sediment concentration ranges
  2. Scatter plot showing relation between untransformed values of suspended-sediment concentration and total suspended solids for 3,235 data points
  3. Scatter plot showing relation between the base-10 logarithms of suspended-sediment concentration and total suspended solids for 3,235 data pairs in the scattergrams plotted
  4. Scatter plots showing relation between the base-10 logarithms of suspended-sediment concentration and total suspended solids for the data pairs from each State used in the analysis
  5. Scatter plot showing relation between percent sand-size material in the sample analyzed for suspended-sediment concentration and the remainder of suspended-sediment concentration minus total suspended solids
  6. Scatter plot showing relation between total suspended solids and the concentration of suspended sediments finer than 0.062 mm in paired suspended-sediment concentration samples
  7. Graph showing instantaneous water discharges and sediment discharges computed from total suspended solids and suspended-sediment concentration data for a stream in the northeastern United States, 1998
  8. Boxplot showing variability in results of suspended-sediment concentrations and total suspended solids analytical methods in quality-control water samples analyzed by a cooperator laboratory

ABSTRACT

Two laboratory analytical methods — suspended-sediment concentration (SSC) and total suspended solids (TSS) — are predominantly used to quantify concentrations of suspended solid-phase material in surface waters of the United States. The analytical methods differ. SSC data are produced by measuring the dry weight of all the sediment from a known volume of a water-sediment mixture. TSS data are produced by several methods, most of which entail measuring the dry weight of sediment from a known volume of a subsample of the original. An evaluation of 3,235 paired SSC and TSS data, of which 860 SSC values include percentages of sand-size material, shows bias in the relation between SSC and TSS —SSC values tend to increase at a greater rate than their corresponding paired TSS values. As sand-size material in samples exceeds about a quarter of the sediment dry weight, SSC values tend to exceed their corresponding paired TSS values. TSS analyses of three sets of quality-control samples (35 samples) showed unexpectedly small sediment recoveries and relatively large variances in the TSS data. Two quality-control data sets (18 samples) that were analyzed for SSC showed both slightly deficient sediment recoveries, and variances that are characteristic of most other quality-control data compiled as part of the U.S. Geological Survey’s National Sediment Laboratory Quality Assurance Program. The method for determining TSS, which was originally designed for analyses of wastewater samples, is shown to be fundamentally unreliable for the analysis of natural-water samples. In contrast, the method for determining SSC produces relatively reliable results for samples of natural water, regardless of the amount or percentage of sand-size material in the samples. SSC and TSS data collected from natural water are not comparable and should not be used interchangeably. The accuracy and comparability of suspended solid-phase concentrations of the Nation’s natural waters would be greatly enhanced if all these data were produced by the SSC analytical method.



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U.S. Department of the Interior, U.S. Geological Survey
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Last modified: Thursday, September 01 2005, 02:00:48 PM
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