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Tidal Mudflats
Tidal mudflats are intertidal areas covered twice a day by the Bay's high tides. These expanses of mud support an extensive community of shellfish, snails and other invertebrates, as well as algae and eelgrass. During high tide, fish feed in the shallow waters covering the mudflats, and during low tide when the mudflats are exposed shorebirds come to feed. Tidal flats are extremely important for wintering waterfowl and shorebirds. Given the South Bayís large acreage of mudflats, many biologists consider it to be one of the regionsí most important areas for shorebirds.
Tidal Marshes
Tidal marshes are found in the intertidal zone along the Bay edge between mean tide level (MTL) and just above mean higher high water (MHHW). They consist primarily of areas completely open to tidal influence including tidal channels. They also include areas of muted tidal marsh, which are areas where culverts or other obstructions reduce the range of tides but still allow frequent inundation. Salt marshes develop along the shores of protected estuarine bays and river mouths, as well as in more marine-dominated bays and lagoons. Most of California's coastal wetlands are estuarine salt marshes with associated tidal channels and mudflats.
Tidal marshes are at a higher elevation than the tidal zone in tidal mudflats. The tidal marshes are vegetated wetlands that regularly receive some tidal action, though unlike the tidal mudflats they are not completed inundated by the tides. Pacific cordgrass and common pickleweed as well as other specialized plants that can tolerate tidal saltwater, grow in the tidal marshes.
High quality tidal marshes contain intricate networks of channels through which the tides move in and out of the marsh complex. During very high tides shallow depressions called salt pannes hold water within the marsh for weeks. Tidal marshes provide critical habitat for an array of species including young salmon and steelhead trout, shorebirds and ducks that forage in the salt pannes, and mammals like the endangered salt marsh harvest mouse.
Muted Tidal / Managed Ponds
Both muted tidal ponds and managed ponds are wetlands that are diked. Muted tidal ponds may have limited tidal exchange through culverts or small channels. The water exchange through the culverts and pipelines is limited, so that the change in water level in the ponds is small (usually a few inches) compared to the range of tidal change in other marsh areas (several feet). Managed ponds are shallow open water habitat with no tidal flow. These wetlands contain water all year long and can have various salinities, from low salinity (similar to seawater) to high salinity (3 times or more seawater salinity). The ponds can vary in depth from very shallow (less than 12 inches) to deep (more than 3 feet). Muted tidal marshes exhibit many of the same features as fully tidal marshes, but they often lack the plant diversity due to the limited tidal range.
Muted tidal and managed ponds provide feeding and roosting (resting) areas for waterfowl. Under the right conditions (water depth and salinity) muted tidal ponds provide feeding areas for large populations of waterfowl. The water depth and salinity affect the types of vegetation, insects, and other invertebrates that live in the ponds. The specific types of waterfowl feeding in a pond depend on the specific conditions in the pond; for example, shore birds like shallow ponds, and certain other birds like to feed on brine shrimp, which only live in higher salinity ponds.
Saltwater Evaporation Ponds (Salt Ponds)
Currently, most of the project area is composed of saltwater evaporation ponds. These ponds are a habitat for a variety of microorganisms, insects, and crustaceans that are foodstuff for small fish and waterfowl. The salinity of the ponds varies, and has a major influence on the type of organisms that live in individual ponds. By absorbing and releasing heat energy more slowly than adjacent land areas, the ponds also help to moderate climatic conditions in the area. The extensive levee systems surrounding the ponds provide roosting and nesting areas for a variety of birds, including the least tern (an endangered species), snowy plover (a "species of special concern"), and numerous waterfowl.
Seasonal Wetlands
Most seasonal wetlands in the project area are former tidal marshes that have been closed off from the Bay's tidal action by the construction of dikes and levees. With each year's winter rains, these low-lying areas fill with fresh water, and then slowly dry out after the rainy season ends. Salt grass, bulrush, and cattails near the Bay are species typically found in seasonal wetlands. Other depressions in the upland area where saline soils support marsh species may also be seasonal wetlands. Seasonal ponds and marshes create a habitat bonanza for Bay Area wildlife. Ducks, shorebirds, egrets and herons feed and rest here; hawks, owls, coyotes and fox hunt the small mammals of the marshes; black-tailed deer feed on the soft marsh plants.
Riparian Corridors and Freshwater Marshes
Along streams and rivers flowing into the Bay are riparian corridors and freshwater marsh. Riparian wetlands, which occur on the edge of steams, rivers, and lakes, commonly feature woody vegetation such as red alder, wax myrtle, and willow. Riparian habitats are characterized by lush vegetation and a rich diversity of species. Elderberries, wild rose, and blackberries grow beneath willow, oak, laurel, sycamore and cottonwood trees. Songbirds, woodpeckers, hawks, owls, frogs, snakes, skunks, raccoon, coyote and deer thrive here. Healthy riparian corridors are critical habitat for local spawning salmon, steelhead trout and other anadromous fish.
Freshwater marshes occur in freshwater ponds, low lying areas that accumulate runoff, and slow-moving segments of streams. They are vegetated mostly with herbaceous plants, predominantly cattails, sedges, and rushes. Freshwater marshes have mineral soils that are less fertile than those of salt marshes, and exhibit a greater variety of plant species than do salt marshes.
References Used
- Baylands Ecosystem Habitat Goals, SF Bay Area Wetlands Ecosystem Goals Project
- Feasibility Analysis: South Bay Salt Pond Restoration, Siegel and Bachand
- Turning Salt into Environmental Gold, Save the Bay
- Wetland Overview, EPA fact sheet 843-F-01-002a
- Types of Wetlands, EPA fact sheet 843-F-01-002b
- Restoring the Estuary: An Implementation Strategy for the San Francisco Bay Joint Venture. January 2001
- Shaw, Samuel P. and C. Gordon Fredine 1956. Wetlands of the United States - their extent and their value to waterfowl and other wildlife. U.S. Department of the Interior, Washington, D.C. Circular 39. Northern Prairie Wildlife Research Center Home Page.
http://ceres.ca.gov/ceres/calweb/coastal/wetlands.html
- http://www.npwrc.usgs.gov/resource/1998/uswetlan/uswetlan.htm (Version 05JAN99).
http://www.watres.com/topics/tp-wetlands.html
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