San Francisco Estuarine Wetlands

The San Francisco Estuarine system is a complex of interconnected embayments, sloughs, marshes, channels, and rivers.  The system is comprised of the Delta Area (north), receiving the waters of the Sacramento and San Joaquin river systems and the San Francisco Bay proper (south), into which the Delta waters flow.  Geographically and hydrodynamically the estuary can be divided into the northern bay, which passes south, and westward from the Delta through Suisun and San Pablo bays, and the south bay, which extends southeastward toward San Jose.  They join in the central bay near the Golden Gate, the connection with the Pacific Ocean.

The waters of the San Francisco Bay are a mixture of the salt water flowing in from the Pacific Ocean and the fresh water flowing from rivers that feed into the bay.  The water in the bay is neither salty nor fresh, but brackish.  This entire system is known as an estuary.  The San Francisco estuarine system is made up of three bays:  San Francisco in the south and the San Pablo and Suisun Bays in the north.  There is only one outlet to the Pacific Ocean for all 3 bays, a small opening underneath the Golden Gate Bridge (connecting San Francisco and Marin).  The force of tides (caused by gravitational attraction of the Moon and Sun) causes water to move into and out of the bay.  The influence of this mass movement caused by the tides flushes the estuarine system. 

The San Francisco estuarine system is a very productive area.  It is important to the entire ecosystem of the western United States.  Many organisms depend on the bay for food, safety and shelter.  Migrating birds need to rest here on their trips to warmer climates and nest during breeding seasons.  The animals in the estuarine system are varied.  Mammals, birds, reptiles, amphibians, invertebrates, protozoa, and fish are all components of this system.  The system has many parts to it because of the need of the larger animals to feed on the smaller animals.  This process is called the food chain and it gives us clues to why animals eat and live where they do.

The bays today are very shallow, 85% of the water is less than 30 feet deep.  There are deep, narrow channels that cut the bottom of the bay, the Golden Gate (about 400 feet deep) and the Carquinez Strait (about 100 feet deep).  Circulation of the bays is dependent mainly on the strong tidal action, especially in the south bay and river inflow, especially in the north bays.  Winds, storms and bottom topography change these patterns locally. 

Salt marshes of the San Francisco Bay area are highly productive and extremely valuable to the bay's ecology.  Salt marshes contain a variety of plants, but there are only a few common to all California salt marshes.  The plant groups occur in four distinct zones due mainly to the amount of salt in the soil, texture of soil, rates of sediment deposition, and the length of submergence.  The specific location of each zone changes in response to time of the year and environmental conditions, but their relative positions remain the same.

San Francisco Bay Area is rich in human history that used our wetlands.  The Native Americans needed wetlands for food source,  building materials,  and transportation.  The Spaniards also used the wetlands especially for food and transportation.  Unlike the Native Americans they used wood and adobe as their preferred building material. The Mexican Rancheros who owned much of the land prior to the California Gold Rush in the 1850’s  used the wetlands for their farming and ranching lifestyle.  Farmers on the 1900’s learned how to control the wetlands for their agricultural and ranching lifestyles.  They also learned how to use wells to draw water from the wetlands for their everyday life.  Today we use water for every facet of our lives from manufacturing to drinking.  Without water the San Francisco Bay Area would not be what it is today.    

Habitats of the San Francisco Estuarine area

The San Francisco Bay Area has many diverse habitats ranging from open water to grassland to high saline environments.  This is a brief look at the characteristics of the different habitats.

The Tidal Flat is an area that is affected by daily tidal action.  During high tide many fish species use the area to forage for food.  Once the tide has gone out the water birds begin to feast on those unfortunate enough to get stuck on the flat.  Most of the vegetation consists of algae, sea lettuce and eel grass.  Invertebrates include worms, diatoms and shellfish. This is considered one of the most important areas for shorebirds such as the American Avocet.

The Tidal Marsh is also effected by tidal action but it contains some amount of water all day (usually around 6-12” at low tide) and vascular vegetation suitable for the brackish to saline environment.  The vegetation can vary widely depending on the area of the bay you are working in due to the interaction of fresh water and bay water, the amount of sediment, erosion and the type of soil available for the vegetation to grow. 

A brackish tidal marsh would contain cattails, tules,   and alkali bulrush in the lower tidal portions.  Around mid marsh species such as spike rush, Baltic rush, silverweed and salt grass begin to emerge.  Towards the more upland areas common pickleweed, salt grass, gumplant, and alkali-heath are found.

A tidal salt marsh contains plants such as Pacific cordgrass and pickleweed.  The higher salt content than the brackish marsh and therefore the plants must be able to remove the salt from the water in order to produce any form of food.

Diked Wetland are historic tidal marsh areas that have been blocked form the tides in an effort to “reclaim” the land usually for agriculture.  The water found in this type of wetland can vary drastically due to the local influences of other waters and how long it goes before receiving any new water. These areas are usually full of more upland plants along with many non-native species.  Some native species found in this area includes common pickleweed, saltgrass, alkali bulrush tules and cattail.

Managed Marsh is a diked wetland that is maintained for wildlife habitat.  Depending on the wildlife you wish to encourage the type of plants and animals along with water salinity will vary. 

 Other examples of diked Baylands include salt ponds and storage/treatment ponds.  The salt ponds are usually maintained for the production of salt for manufacture.  As times are more stringent on the process of solar salt crystallizing more of these ponds are being restored and need to be watched carefully so that many of the species that utilize these ponds do not disappear.  The storage/treatment ponds are areas where local city governments and or industry store or treat runoff so that it does not flow into the natural waterways.  This way many of the contaminants do not flow directly into the bay, after they all settle out the area is dredged and recycled elsewhere.

 A Riparian Forest is the area that separates a creek or river from the surrounding vegetation.  These areas can be steep or gradual, wide or narrow depending on the body of water they are surrounding.  The amount of light and moisture available also plays a part in the type of habitat that surrounds the area.  Common trees include the California bay laurel, western sycamore, cottonwood, box elder, willows and oaks.  Some of the understory can consist of elderberry, wild rose, and California blackberry.  This is thought to be the most densely populated area for wildlife because it can be the habitat for animals such as the California newt, Pacific treefrog, ring necked snake, ornate shrew, broad-footed mole, deer mouse, opossum, striped skunk, raccoon, black-tailed deer, a variety of birds which include: scrub jay, song sparrows, woodpeckers, great horned owl, and tree swallows.  This is creekside vegetation that usually is the majority of restoration projects.

 The Willow Grove is an area of willows that seem to come out of nowhere.  These willows tend to grow where there is groundwater surfacing in intermittent ponds, springs, or where creeks go back into the ground.  They act as a riparian habitat usually much smaller than the forest and provide the necessary shelter for a variety of amphibians and other birds that prey on the amphibians.

 Grasslands are areas that are usually flat and were once used for cattle grazing or farming purposes.  Historically they were covered with native grasses and sages, but with the increase in agriculture around the bay these habitats were filled with more appropriate grasses for cattle from other parts of the world.  This is the area for many of the small mammals that inhabit the area along with the burrowing owl, kestrels, hawks, various reptiles and some amphibians.

 Oak woodland is usually found on the hillsides surrounding the bay.  The habitat includes oak trees and provides the necessary shelter and nesting habitat for wildlife.  This is the area where plants such as madrone, manzanita, coffeeberry, pink flowering current, poison oak, creeping snowberry, California blackberry, and cream bush make their residence.   Wildlife can include southern alligator lizard, gopher snake, red-tailed hawk, California quail, woodpeckers, scrub jays, California ground squirrel, black tailed deer and others.