Project Number: 6408-13000-018-17
Project Type: Reimbursable

Start Date: Jul 15, 2005
End Date: Jun 30, 2008

Objective:
To determine rates and volumes of fine-sediment transport to Lake Tahoe from distributed and stream-channel sources.

Approach:
Radionuclides (137Cs, 210Pb) and stable isotopes (13N and 15C) will be used to fingerprint fine-grained sediment sources. Suspended sediment will be sampled at three watersheds during the snowmelt runoff season (May to June). The upland sources of sediment will be investigated before and after stream sampling and may include, but not be limited to, construction sites, dirt roads, fields, pasture, forest, channel bed and banks, and floodplains. Sampling of upland sediment sources will occur in late summer. Cesium-137 can also be used to inventory upland erosion rates using a mass budget approach. Samples for the erosion mass budget will be collected during the upland-source sampling period. All sediment collected for fingerprinting analyses will have the sand removed (> 0.63 mm). Radionuclides will be analyzed at the USDA-ARS, Beltsville Agricultural Research Center, MD, Hydrology and Remote Sensing Lab facilities under the direction of Jerry Ritchie, Soil Scientist. Stable isotopes will be analyzed at the U.S. Geological Survey Stable Isotope Lab in Reston, VA under the supervision of Ty Coplen, Research Hydrologist. When all data have been analyzed by appropriate laboratories, discriminant analysis will be used to determine if the fingerprints are capable of discriminating between sources. A multivariate mixing model will subsequently be used to estimate the relative contributions of each source. The mixing model developed for the Chesapeake Bay Sediment Studies by Jurate Landwehr, U.S. Geological Survey National Research Program, Research Stochastic Hydrologist, will be used. Erosion yields from the Cesium mass budget analysis will be quantified using existing models. Research in fine-grained sediment tracking will be led by Dr. Allen Gellis, USGS, Maryland District, working in cooperation with the ARS, NSL. Using the methodology described above in combination with fine-grained sediment loadings data, the ARS will provide estimates of the contribution of total and fine suspended sediment resulting from in-stream erosional processes for the three watersheds. These watersheds include: Upper Truckee River, Blackwood Creek, and Third Creek.