By Terry Tillman and Tim Dodson
The San Francisco Bay Delta is unmistakably one of the largest estuaries on the Pacific Coast. This region includes the San Francisco Bay – a vast inlet where the Pacific Ocean ultimately joins freshwater in-flows originating in the Sierra Nevada Mountains, creating the dynamic mixing zone we refer to as the Delta.
While being an epicenter of commerce and recreation for millions of Californians, the San Francisco Bay Delta is also an essential habitat to a host of plants and animals. Where salt water and fresh water occur together in the mixing area or brackish zone, a unique and crucial environment has evolved over time. The State Wildlife Action Plan (SWAP) 2015 Update has identified this area as the greater San Francisco Bay Delta (SFBD) Conservation Unit.
The SFBD Conservation Unit offers diverse tidally influenced habitat types such as open deep water, shallow water, tidal wetlands, salt marsh, freshwater wetlands, riparian, managed wetlands, grasslands, and cultivated lands. It is home to over 130 species of fish and a retreat for over one million migrating birds who find sanctuary in its open waters, sloughs, rivers, marshes and tidelands as they traverse the Pacific Flyway. A broad spectrum of wildlife, including marine mammals, invertebrates, and shellfish, as well as plants inhabit this estuarine ecosystem. In addition to supporting a critical food web and rearing grounds for many species, the Bay and Delta also provides important aesthetic, economic, and recreational benefits for neighboring communities.
One of the most important habitat types found in the SFBD Conservation Unit is salt marsh habitat. Salt marsh habitat occurs as a narrow band of vegetation around the bay and delta where fresh and salt waters mix in areas that are generally at or below 6.5 feet in elevation. Salt marsh habitat is important because it provides rearing, foraging, and nesting habitats for numerous species, many of which are protected under the state and/or federal endangered species acts.
Species such as the salt-marsh harvest mouse, clapper rail, and Suisun thistle depend on healthy salt marsh habitats for survival. The salt marsh also provides ecosystem services including pollution amelioration, nutrient cycling, water storage and aquifer recharge, carbon sequestration, flood protection and shore line protection.
The interaction of past, present, and future land uses, combined with changing and uncertain climatic conditions, shapes the future ecological landscape in the SFBD. Besides climate change impacts such as higher annual temperatures, less snow pack and snow period, and sea level rise, other stresses believed to be affecting salt marsh habitats are sediment erosion, pollution, extreme events and flooding, changes in groundwater levels, and invasive species. Human activities likely impacting salt marsh habitat are housing and commercial development, incompatible livestock grazing and farming pracitces, roads and railroads, illegal activities, and water management among others.
The SWAP update has developed conservation strategies intended to be implemented over the next decade. Several of these address restoring, protecting, and enhancing salt marsh habitat. Strategic actions also include conducting research and monitoring. Some of the interests under this strategy are to decipher population trends of sensitive species that occur in the area, and to provide a regional framework to better integrate and share data with conservation collaborators. One key strategy considers educational programs to better inform the public about the impacts affecting salt marsh habitats, its importance, and the role it plays within the sphere of the entire SFBD Conservation Unit.
Other strategic actions will include the identification, management, and control of invasive species as well as advocacy for laws and policies that will protect existing habitats and streamline restoration projects. These conservation strategies are meant to benefit the habitat, species, and the ecosystem services that salt marsh offers. They are interrelated and incorporated within a high-level program that focuses on integrated resource management and joint advocacy partnerships.