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.
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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.