What is Wetland Restoration?
Restoration is the return of a degraded wetland or former wetland to its preexisting, naturally functioning condition, or a condition as close to that as possible. Restoration projects require planning, implementation, monitoring and management, using a team with expertise in ecology, hydrology, engineering and environmental planning.
Why Restore Wetlands?
Restoring lost and degraded wetlands is essential to ensure the health of our watersheds. Over the past 200 years, wetlands have vanished at an alarming rate; in the Bay Area, it is estimated that 95% of the Bay’s historic tidal wetlands have been destroyed. Such losses hamper wetland functions, such as water quality protection, habitat for fish and other wildlife, and flood protection.
Restoration Goals of the South Bay Salt Pond Restoration Project
The goal of South Bay Salt Pond Restoration Project is to improve the physical, biological, and chemical health of the San Francisco Estuary by restoring over 15,000 acres of Cargill salt ponds to wetlands. The restoration planning effort will integrate restoration with flood management, while also providing for public access, recreation, and education opportunities. Ultimately, the area will be a combination of tidal marsh and managed ponds, with channels and corridors of similar habitat connecting these areas.
Wetlands Restoration in the San Francisco Bay Area
Wetlands restoration is a relatively “young” science. Wetland restoration efforts have been underway in the Bay Area since the late 1960’s, and much has been learned from the successes and failures of these projects. Selecting suitable sites and relying on natural processes emerge as key factors for successful restoration.
Considerations for the South Bay Restoration Project
Salt production in the San Francisco Bay Estuary has been going on since the 1860’s. The current network of South Bay salt production ponds have been in operation for the last 50 years. These salt ponds have altered the South Bay ecosystem in two ways. These shallow ponds have changed the Bay’s natural hydrology and degraded water quality; at the same time, these salt ponds have been providing valuable waterfowl habitat. While salt pond restoration will benefit some species, other species may be negatively impacted by the loss of salt pond habitat. Restoration must balance these habitat needs.
Physical Conditions and Hydrology
There are several physical conditions that will affect the feasibility of restoring salt ponds to tidal marshes: presence of channels, availability of material for levees, pond subsidence, potential for flooding, and infrastructure impediments (railroad crossings, bridges, underground pipes, etc.). Groundwater pumping has caused significant subsidence in some of the ponds, making revegetation difficult. Also, in order to restore natural tidal flow to marshes, the proximity to tidal waters, the existence of channels and other factors must be considered. It will also be important to integrate the need for flood control levees with the levees required for wetland restoration.
Restoration may provide new habitat for invasive non-native species. Invasive species are non-native species that displace native species by either out-competing them for available habitat, by predation, or by introducing diseases. Invasive species are extremely harmful to native species. In the South Bay, smooth cordgrass, Norway rat and red fox are the non-native species of concern. Newly restored wetlands are particularly vulnerable to invasion by smooth cordgrass (Spartina alterniflora), and no satisfactory control measure has yet been identified. The non-native Norway rat and red fox prey on the eggs of nesting birds, so restoration must find ways to limit access to nesting areas.
Not all of the 15,000 acres will be restored to tidal marshes. Factors that will be considered are the wildlife habitat needs and the existing conditions of the salt ponds. In some pond areas there are conditions that exist which make tidal marsh restoration extremely difficult ñ need for flood control levees, severe pond subsidence, infrastructure that interferes with tidal movement, residual high salinity. These areas may be used for other types of habitat, such as managed ponds (shallow open water habitats) and salt pannes (flat, unvegetated hypersaline areas with seasonal ponds). Water depths in managed ponds can range in depth from a few inches (preferred by shore birds) to deeper than 3 feet (required for diving ducks). Salinities in managed ponds may also vary.
Restoration of wetlands is a dynamic process ñ natural conditions and the wildlife use of the ponds vary from year to year. The timing of the restoration activities will be important not only to avoid disturbing wildlife species but also to ensure that earlier phases of the restoration have been successful before altering other habitat. It will be necessary to carefully monitor conditions as the restoration proceeds, and adapt the restoration plans to ensure overall project goals are achieved.
Baylands Ecosystem Habitat Goals, SF Bay Area Wetlands Ecosystem Goals Project