Sommerfield, C.K., 2016. Qualities and limitations of fluvial suspended sediment data published by the United States Geological Survey.
Fluvial suspended sediment concentration (SSC) data published by the United States Geological Survey (USGS) are frequently used to address questions of sediment delivery to estuaries and coasts. Despite the availability of USGS reports detailing methods of sample collection and data processing, many end users remain misinformed about the characteristics and limitations of these data. Two types of USGS-SSC data are available for stream gauging stations: (1) discrete samples and (2) daily record. Discrete samples are laboratory measurements of SSC from water collected at a stream gauging station. In contrast, daily-record data are interpolations of SSC from a smaller number of discrete samples available for a station. A potential source of confusion arises because both types of USGS-SSC data are given the identical description (suspended sediment concentration, mg/L) and parameter code (80154) in the national database. Although the daily-record series for a station is derived from actual samples, discrete and daily SSC values for the same date of record are not always strongly correlated because of factors related to sampling and data processing. As shown in this paper, discrete-sample SSC data series for some stations are inhomogeneous and biased because of changes in USGS sampling practices over the decades, thereby limiting the possible end uses of the data. Ultimately it is up to users to determine which type of SSC data are best suited for a particular application and whether the statistical properties of a data set are conducive to applications such as trend analysis.