PRBO Conservation Science
Quarterly Journal of PRBO Conservation Science, Number 139, Winter 2005: PRBO's New Environment: Northern San Francisco Bay


If restoration is successful, tidal wetlands may increase to over 32,000 acres by the end of the 21st century.

The Changing Wetland Landscape of San Pablo Bay

Diana Stralberg

Introducing This Issue
Restoring Petaluma River Marsh
Executive Director's Column
The Changing Face of San Pablo Bay
Monitoring North Bay Restoration
Sonoma Baylands Preservation
A Presence on San Francisco Bay
Oak Woodlands and Vineyards
California All-Bird Workshop
Anticipating PRBO's New Center
PRBO's Volunteer Program
Bird Bio: Mute Swan
Birding PRBO's New Back Yard
Lasting Legacy Campaign

Click for larger view. Top to Bottom: San Pablo Bay shoreline habitat past, present, and future. Black areas signify the changing expanse of tidal marsh; light red areas are intertidal mudflat habitats. On the center figure: the symbol with the flag is the location of PRBO's new headquarters; the large quadrangle is Baylands conservation area; the small quadrangle is Petaluma River Marsh. Sources SFEI EcoAtlas, Stuart Siegel..

The shore of San Pablo Bay has undergone drastic transformation in the past two centuries, especially in the extent of tidal marsh. The figure above shows the region 200 years ago (A), today (B), and in the future (C) as envisioned by present restoration planning.

(A) For the last 5,000 years, until the mid-19th century, the deposition of new sediments largely kept pace with sea level rise caused by melting glaciers, resulting in a fairly stable wetland landscape. Historic maps suggest that, prior to European settlement, San Pablo Bay had approximately 59,000 acres (24,000 hectares) of "ancient" tidal marsh and 18,500 acres of intertidal mudflats.

(B) Beginning in the mid 1800s, large areas of tidal wetland in San Pablo Bay were diked for agricultural purposes (primarily grazing and cattle fodder due to high salinity soils), resulting in a dramatic loss of tidal habitats. As tidal wetlands were being lost to diking, increased sedimentation from Gold Rush-era hydraulic mining practices in the Sierra Nevada (1855-1884) created many new wetland areas (now referred to as "centennial marsh"). Nevertheless, by the late 20th century, dredging, filling, and urban development had reduced the area of tidal wetlands in San Pablo Bay by almost 80%, to approximately 17,000 acres of tidal and muted (restricted tidal flow) marsh and 11,000 acres of intertidal mudflats.

(C) Due to increasing awareness about the ecosystem services and wildlife habitat values provided by tidal wetlands, future landscape change in San Pablo Bay promises to be almost equally dramatic as historic landscape change, but in a positive direction. Over 1,500 acres of tidal wetlands have already been restored, and at least 15,000 more acres of restoration are planned. If wetland restoration is successful, tidal wetlands may increase to over 32,000 acres by the end of the 21st century. However, soil compaction, land subsidence, and a reduced supply of alluvial sediments from the Central Valley pose significant challenges to restoration efforts. Additional research and monitoring of restoration projects and outcomes will be needed to maximize the human and wildlife benefits of wetland restoration.


Atwater, B.F. 1979. Ancient processes at the site of southern San Francisco Bay: movement of the crust and changes in sea level. In T. J. Conomos, ed. San Francisco Bay: the urbanized estuary. AAAS, San Francisco.

Goals Project. 1999. Baylands ecosystem habitat goals. A report of habitat recommendations prepared by the San Francisco Bay Area Wetlands Ecosystems Goals Project. Joint publication of the US EPA, San Francisco, and SF Bay Regional Water Quality Control Board, Oakland, CA.

Josselyn, M. 1983. The ecology of San Francisco Bay tidal marshes: a community profile. USFWS, Division of Biological Services, FWS/OBS-83/23. Washington D.C.

SFEI. 1998. EcoAtlas version 1.5b4. San Francisco Estuary Institute, Oakland, CA.

Siegel, Stuart. 2002. Wetland restoration and enhancement projects. Completed and planned projects in the North Bay, San Francisco Estuary. Wetlands and Water Resources, San Rafael, CA.

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