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The REPEAT Project:

Rates and Evolution of Peat Accretion Through Time in the Sacramento-San Joaquin Delta of California

Repeat project coring crew: Dr. Judith Drexler, Jacob Fleck, and Christian de Fontaine

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

Drexler, J.Z., de Fontaine, C.S. and Knifong, D. 2007. Age determination of the remaining peat in the Sacramento-San Joaquin Delta, CA. U.S. Geological Survey Open File Report, 2007-1303

Deverel, S.J., Drexler, J.Z., Ingrum, T., and Hart, C. 2008. Simulated Holocene, recent, and future accretion in channel marsh islands and impounded marshes for subsidence mitigation, Sacramento-San Joaquin Delta, California, USA. REPEAT Project Final Report to the CALFED Science Program of the Resources Agency of California, 60 pp.

Drexler, J.Z., de Fontaine, C.S., and Deverel, S.J. 2009. The legacy of wetland drainage on the peat resource in the Sacramento San Joaquin Delta, CA, USA. Wetlands, 29(1): 372-386.

Drexler, J.Z., de Fontaine, C.S., and Thomas A. Brown. 2009. Peat accretion histories during the past 6,000 years in marshes of the Sacramento-San Joaquin Delta of California, USA. Estuaries and Coasts 32: 871-892.

Drexler, J.Z. 2011. Peat formation processes through the millennia in tidal marshes of the Sacramento-San Joaquin Delta, California, USA. Estuaries and Coasts DOI 10.1007/s12237-011-9393-7

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, Sr, U, and Mg/Ca will be used to obtain a qualitative measure of the variability of salinity through time. 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]
REPEATmap


Project Chief: Dr. Judith Drexler
Phone: 916-278-3057
Email: jdrexler@usgs.gov

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