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.
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
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.
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.
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.
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.
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.
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.
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.
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