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U.S. Geological Survey USGS Open-File Report 76–389

Distribution of Seed Plants with Respect to Tide Levels and Water Salinity in the Natural Tidal Marshes of the Northern San Francisco Bay Estuary, California

By Brian F. Atwater and Charles W. Hedel

Thumbnail of and link to report PDF (25 MB)Abstract

Shoaling of subtidal and intertidal mud flats has permitted tidal marshes to spread across large marginal areas of the San Francisco Bay estuary during the past several thousand years. By 1850 A.D. the tidal marshes of the estuary, including those of the Sacramento–San Joaquin Delta, covered an area nearly twice as large as the area of open water. Nearly 95 percent of these marshes have been diked or filled during the past 125 years.

Species distributions along leveled transects at six tidal marshes indicate that elevation and water salinity are the principal ecological factors that control the distribution of seed plants in the remaining natural tidal marshes of the northern San Francisco Bay estuary. Marsh surfaces situated near mean tide level are populated by robust monocotyledons (e.g., Spartina foliosa, Scirpus californicus), whereas surfaces situated near high-tide levels support dicotyledons and a few small monocotyledonous species (e.g., Salicornia virginica, Distichlis spicata). Marshes near the seaward end of the estuary are typically occupied by 10-15 salt-tolerant species (e.g., Spartina foliosa, Salicornia virginica), whereas marshes at the riverward end of the estuary are inhabited by as many as 30 species, most of which are known to tolerate moderate or small amounts of salt (e.g., Scirpus spp., Phragmites communis, Typha latifolia).

Last modified May 22, 2012
First posted October 30, 2010

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Suggested citation:

Atwater, B.F., and Hedel, C.W., 1976, Distribution of seed plants with respect to tide levels and water salinity in the natural tidal marshes of the northern San Francisco Bay estuary, California: U.S. Geological Survey Open-File Report 76–389, 41 p., 8 plates. (Available at




Methods of Study

Historical and environmental setting of the tidal marshes



eight plates

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