San Pablo Bay

INTRODUCTION

Audubon California and the San Pablo Bay National Wildlife Refuge plan to enhance or restore 757 acres of tidal marsh, sub-tidal, and marsh-upland transition environments on the Refuge. Specifically, we will conduct restoration of 89 acres and enhancement of an additional 668 acres of tidal marsh and associated environments. Our goals are to support the re-establishment of native vegetation, improve estuarine-dependent wildlife habitats, and reduce or eliminate future mosquito population management issues. These benefits are expected through improvement of hydrological flow and tidal flushing, re-establish connections between marsh areas, and restoration of native plants along the marsh-upland transition zone. Internal levees and sills, which form barriers to tidal flow and circulation, will be breached or removed and new channels that re-connect marsh areas to existing drainages will be excavated. These actions will return tidal circulation to the site, resulting in development of a functioning tidal marsh/tidal slough complex, enlarged area of shallow channel habitat, and increased tidal prism and deep channels. To measure the effectiveness of project actions, surveys will be conducted before and after construction. Control sites will also be surveyed to allow for comparisons among similar landscape types (e.g., tidal marsh plain, muted tidal marsh, interior marsh ponds) before and after construction.

Project Area

The Refuge lies along the northern border of San Pablo Bay and was established in 1970 for the purpose of protecting and providing habitat for migratory birds and species listed as endangered or threatened. The project area encompasses the Lower Tubbs Island and Tolay Creek units of the Refuge. The Lower Tubbs Island unit of the Refuge is 249-acres in size and was transferred to the Refuge from the Nature Conservancy in 1978 (Figure 1). The Refuge acquired this unit to provide habitat for endangered species and other estuarine-dependent wildlife. Hydrology of Lower Tubbs Island is characterized as muted tidal and exchanges tidal water with San Pablo Bay and adjacent marsh units through a series of perimeter channels and culverts. The unit contains several interior man-made levees, culverts and waterways that functioned to improve duck habitat when the site was a hunting club prior to the 1970’s. The vegetation is dominated by native tidal marsh-adapted species such as pickleweed (Sarcocornia pacifica), salt grass (Distichlis spicata), Pacific cordgrass (Spartina foliosa), sedge (Scirpus maritimus) and gumplant (Grindelia stricta). Pepperweed (Lepidium latifolium), an invasive plant species, has colonized the unit but remains at low density levels.
The Tolay Creek unit of the Refuge (435 acres) includes approximately 5.6 kilometers of creek and associated tidal environments south of Highway 37 (Figure 1). The Refuge and the California Department of Fish and Game initiated a restoration project in 1999 to increase tidal flow to upper portions of Tolay Creek. Historically, Tolay Creek received freshwater input from Tolay Lake (north of Highway 37) and intermittent streams in the Sonoma Mountains (via Sonoma Creek). Human activities such as levee construction and conversion to agricultural land have dramatically altered the landscape of Tolay Creek, decreasing the size of the tidal flood plain and associated marsh. The open water and tidal creek channel areas contain little vegetation, except for Spartina foliosa and patches of in the transition zones. In addition, the area provided poor habitat for wildlife. Common plants of Tolay Creek tidal marsh include pickleweed, saltgrass, jaumea (Jaumea carnosa), and alkali heath (Frankenia salina).

Levee vegetation of the Lower Tubbs Island and Tolay Creek units consist largely of native coyote bush (Baccharis pilularis) intermixed with native and non-native perennial plants. Non native species dominate plant cover along levees and include the invasive perennial pepperweed (Lepidium latifolium), yellow star thistle (Centaurea solstitialis), fennel (Foeniculum vulgare), and mustard (Brassica spp.), and non-native grass species (e.g., Bromus diandrus).

Endangered Species and Migratory Birds

The federal and state endangered salt marsh harvest mouse (Reithrodontomys raviventris) and California clapper rail (Rallus longirostris) occur within the project area. The project area also supports several state listed or Species of Concern such as the California black rail (Laterallus jamaicensis), San Pablo song sparrow (Melospiza melodia samuelis), salt marsh common yellowthroat (Geothlypis trichas sinuosa). The presence and distribution of these species is directly related to the quantity and quality of available habitat. Areas where tidal water impoundments occur in conjunction with poor vegetation health are less likely to support these species because of poor habitat conditions. At least 13 species of waterfowl and 30 species of waterbirds use the Tolay Creek and Lower Tubbs Island units during some portion of the year. Intertidal mudflats of the project area are used extensively by shorebirds.

Problem Description
The project area contains historic tidal environments that experience impeded tidal flows from remnant dikes and levees. These conditions have resulted in stagnant pools of water (Figures 1-4) that cause plant mortality or reduce health and encourage above normal mosquito production. Application of pesticides occurs when mosquito numbers exceed established thresholds (by the Marin-Sonoma Mosquito and Vector Control District). These pesticides affect mosquito and other invertebrate species used as food by native wildlife and access for mosquito management causes disturbance to wildlife and plant populations. In addition, tidal mixing between Tolay Creek and Lower Tubbs Island is limited to 2 culverts which require continued maintenance. As climate change events (e.g., frequent intense storms) become more common on the Refuge, these mad-made structures are likely to fail, increasing issues related to tidal impoundment.

Enhancement and restoration of tidal flows at Tubbs Island and Tolay Creek may enlarge the area of shallow channel habitat and tidal marsh interior mudflats. Increased tidal prism would also enlarge existing deep channels to the benefit of fish and diving ducks. Increasing the area of healthy tidal marsh would expand habitat for endangered tidal marsh species such as the California Clapper Rail and the salt marsh harvest mouse. Enhancing existing tidal environments would also benefit several rare plants and birds such as the San Pablo Bay song sparrow and saltmarsh common yellowthroat that depend on the marsh and upland transition zone. Expansion of marsh interior mudflats within the project area would provide important high tide roosting and foraging environments for migratory and wintering shorebirds and waterfowl.

Volunteering

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