A Geochemical Approach for Investigating Watershed Sediment Sources

Nationally, sediment is of considerable concern as related to several important issues including water quality, health of aquatic organisms, and reservoir-storage capacity. For decades, millions of dollars have been spent annually in an attempt to reduce the amount of sediment that enters streams. This expenditure has occurred despite the fact that a fundamental question remains unanswered for most of the United States; that is, does the majority of the sediment in streams originate from surface soils or channel banks? In this study, sediment sources were investigated for Perry Lake, a large Federal reservoir with a 2,900 km2 watershed on the Delaware River in northeast Kansas. The objective was to determine, through a comparison of the composition of reservoir sediments and source materials, if the majority of the deposited sediment originated from surface soils or channel banks within the Perry Lake watershed. Within the watershed, a nested approach was used in which five representative subwatersheds were selected for sampling. The subwatersheds ranged in size from 20 to 50 km2. A small reservoir marked the downstream extent for each of three subwatersheds. In each subwatershed, multiple surface-soil sites (i.e., cropland and grassland) and channel-bank sites were sampled to a depth of 2 to 3 cm. Recently deposited reservoir bottom sediments were sampled to a depth of 2 to 3 cm for Perry Lake and for the three small reservoirs using a box corer. The reservoir bottom sediments provided an integrated sample of the sediment received from each of the contributing watersheds. Also, the banks of the main-stem Delaware River were sampled. All samples were sieved to isolate the <0.063-mm-size fraction for analyses. The samples were analyzed for carbon, nitrogen, phosphorus, several trace elements, and cesium-137. In this presentation, methods are described, problems are identified, and preliminary results are discussed in the context of previous sediment-sourcing studies.

Juracek, K.E., and Ziegler, A.C., 2005, A geochemical approach for investigating watershed sediment sources [abs], in Program Summaries for AGU Fall Meeting, December 5-9, San Francisco, California: EOS Transactions of American Geophysical Union, v. 86, no. 52, Fall Meeting Supplement, Abstract H51E-0409, 1 p.