PART VIA. Wetlands: what are they and why should we care?

San Francisco Bay consists of Bay water, sediments at the Bay bottom, and marshy areas around the edges of the Bay. These areas are wet during much of the year and are appropriately named "wetlands". Around the Bay, wetlands consist mostly of salt marshes, and mudflats that lie bayward of the marshes. As the water level fluctuates daily with the tides, these areas are periodically inundated with Bay water. They are also susceptible to flooding when winter rains send fresh water to streams that feed into the Bay through the wetland areas.

Wetlands have been recognized as one of the estuary's most important assets because of the following values and functions:

• Biological Diversity. Wetlands provide important habitat for diverse communities of plants and animals, including over 50 percent of the federally listed threatened or endangered species.
• Waterfowl Habitat.Wetlands provide the principal habitat for migratory waterfowl. California provides critical wintering habitat for millions of waterfowl migrating along the Pacific Flyway, which extends from Canada to Mexico.
• Fisheries.Wetlands provide direct spawning and rearing habitats and food supply that supports both freshwater and marine fisheries.
• Flood Control. Wetlands detain flood flows, reducing the size and destructiveness of floods.
• Water Quality. Wetlands absorb and filter pollutants that could otherwise degrade ground water or the water quality of rivers, lakes, and estuaries.
• Ground Water Recharge. Some wetlands recharge aquifers that provide urban and agricultural water supplies.
• Recreation. Wetlands support a multi-million-dollar fishing, hunting, and outdoor recreation industry nationwide.

Natural wetland areas along San Francisco Bay are uncommon sights, as human development during the past 150 years or so has removed more than 90% of wetland areas from their original state. When wetlands are destroyed, the Bay loses much of its ability to support life and to maintain good health (see benefits above). The Bay's wetlands consist primarily of salt marshes and intertidal mudflats.

Click here to go to the web site for the San Francisco Estuary Institute (SFEI). On this page you will find the San Francisco EcoAtlas. The map on the left shows a historic view of wetland areas around the bay. The map on the left shows a modern view of the bay, where wetland areas have been destroyed primarily by diking and filling for various uses, including agriculture and to produce salt.

1. Compare the maps. Where along the edge of the bay are wetlands (tidal marshes) best preserved today?

2. Where along the bay are most of the salt ponds (used to evaporate salt from Bay water for commercial uses)? most of the developed farmlands? (Note that some farmland areas are being converted to urban developments)

3. The intertidal flat area appears to have expanded between 1800 and present. Considering what you learned about sediment accumulation in Part VB., how would you explain this expansion? (The intertidal flats are the upper parts of shallow mud flats, the part that is alternately exposed and covered by water during the daily tidal cycle.)

Return to Estuaries Home Page