HR: 0800h
AN: PP11B-1449    [Abstracts]
TI: Trace elemental and 87Sr/86Sr isotopic compositions as a method for identifying sediment sources in a major coastal estuary
AU: * Malamud-Roam, F P
EM: fmalamud@eps.berkeley.edu
AF: Department of Geography University of California, Berkeley, 501 McCone Building, University of California Berkeley, Berkeley, CA 94720 United States
AU: Ingram, B L
EM: ingram@eps.berkeley.edu
AF: Depts of Geography and Earth and Planetary Sciences, University of California, 301 McCone Building, University of California Berkeley, Berkeley, CA 94720 United States
AU: Malamud-Roam, K P
EM: kmr@ccmvcd.net
AF: Contra Costa Mosquito and Vector Control District, 55 Mason Circle, Concord, CA 94520 United States
AU: Collins, J
EM: josh@sfei.org
AF: San Francisco Estuary Institute, 7770 Pardee Lane, Oakland, CA 94621 United States
AB: Maintenance and health of tidal wetlands depends most fundamentally on adequate sediment supply. In the San Francisco Bay estuary, tidal marshes that once surrounded the estuary providing natural protection from storms, habitat for a variety of plant and animal species and a host of other important ecological functions, are threatened by rising sea level and insufficient sediments. We present results from an ongoing study evaluating the relative sources of sediments that feed the San Francisco Bay tidal marshlands using their geochemical signatures. We have analyzed the concentrations of 21 trace and major elements and 87Sr/86Sr isotopic ratios in the suspended sediments of major tributaries to the Sacramento - San Joaquin Delta and of smaller tributaries surrounding the northern reach of the Bay estuary. We have also analyzed the geochemical compositions of sediments from marsh surface samples and from a series of short (50-100 cm long) sediment cores collected from Novato Creek Marsh, on the western edge of San Pablo bay. Previous results show that the sediments from the three primary end members can be distinguished, and the results presented here will elaborate, using a combination of multivariate analyses and a mixing model to evaluate the likely sources of sediments occupying the marsh surface, both modern and pre- modern (i.e., before large-scale changes to California hydrologic systems). Initial elemental and 87Sr/86Sr isotopic results indicate that a significant share of the suspended sediments in the estuary and on the marsh surfaces may not come from either of the two major river systems, the Sacramento and San Joaquin. The mean 87Sr/86Sr isotopic ratio measured in samples from Sacramento river tributaries is 0. 706380 and the measured mean of samples from the San Joaquin river tributaries is 0.707191. Of the samples collected from local creeks around San Pablo bay that have been analyzed to date, there is a range of Sr isotope values from 0.709243 to 0.707213. The mean of 87Sr/86Sr isotopic ratio measured in surface marsh sediments is 0.709511, suggesting another important end member source. Cores collected from Novato Creek marsh show variability in geochemical compositions with depth, suggesting some changes in sediment sources over time. These changes are likely due in large part to human modifications of the hydrologic system; however, the data can also provide insights into changing spatial precipitation patterns over the estuary's large watershed region.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1065 Major and trace element geochemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005