The REPEAT Project:
Rates and Evolution of Peat Accretion Through Time in the Sacramento-San Joaquin Delta of California
Dr. Judith Drexler, right, with scientists Jacob Fleck, center, and Christian de Fontaine, collecting a peat core on the Tip of Mandeville Tip, a marsh island in the Delta. |
During the Holocene, a 1,400 km2 tidal marsh region formed in the Sacramento-San Joaquin Delta, which is situated at the landward end of the San Francisco Bay Estuary.
Over 90 percent of this region was drained for agriculture during the past 100 to 150 years. Nevertheless, small relict marshes remain, which constitute an archive of information on peat formation processes, geomorphological change, carbon storage, and anthropogenic disturbance.
The purpose of the REPEAT project is to use this peat archive to study marsh formation processes in order to inform current wetland restoration efforts in the Delta. In addition, our research is shedding light on environmental contamination and environmental change in the Delta through the millennia.
During the summer of 2005, we collected peat cores from four pairs of islands (drained farmed islands and relatively undisturbed, marsh islands) in the Delta in order to discern the differences between them. Peat cores were sectioned and analyzed for bulk density, percentage of organic matter, percentage of organic carbon, and a suite of major and trace elements. Achenes (fruiting bodies of bulrushes), charcoal, and plant fragments other than roots were analyzed for radiocarbon content.
So far, we have determined:
- Peat accretion histories for the entire lifetimes of 3 marshes
- How inorganic vs. organic constituents of peat vary over the millennia
- How peat on drained farmed islands differs from undisturbed peat
- The contaminant history of lead and mercury in the Delta
- Predicted time frames for bringing elevations of subsided islands back to sea level by using wetland restoration to re-build peat soils
Project Chief: Dr. Judith Drexler, U.S. Geological Survey, California Water Science Center (CWSC), Sacramento, CA
Co-Principal Investigators: Dr. Charles Alpers, CWSC; Dr. Steven Deverel, Hydrofocus, Inc., Davis, CA; Dr. Kenneth Verosub, University of California, Davis, Department of Geology (UCD); and Dr. Irina Delusina (UCD)
A Primer on the Livingstone Corer
View a series of videos on the Livingstone corer.Reports and Publications
What's next
The second phase of the REPEAT project began in the summer of 2009. This phase of the project is concerned with characterizing the paleosalinity of the Delta. Concentrations of Na and Sr will be used to obtain a qualitative measure of the variability of salinity through time. Strontium and uranium isotopes in peat, vegetation, ocean water, and river water will be used to form a mixing model of salinity in the San Francisco Bay Estuary. This model will be used to quantify the salinity regime in the Delta during the past ~6,800 years.
Map of Delta and coring sites
(click the image for a larger jpg version) or PDF[552k]
Project Chief: Dr. Judith Drexler
Phone: 916-278-3057
Email: jdrexler@usgs.gov
Adobe Reader or similar software is required to view PDF documents. Download the latest version of Adobe Reader, free of charge.
