South Bay Salt Pond Restoration Project
The South Bay Salt Pond (SBSP) Restoration Project is the largest tidal restoration project on the West Coast, and will transform 15,100 acres to a mosaic of tidal wetlands and managed pond habitats. The restored tidal wetland system will provide a critical natural buffer against the effects of climate change such as sea level rise, coastal flooding, and erosion.
Salt production has occurred in San Francisco Bay since the 1800s, and a large percentage of wetland loss in the south bay was due to tidal lands levied for salt ponds. In 2003, under the leadership of Senator Dianne Feinstein, Cargill, Inc. sold approximately 16,500 acres of salt ponds (15,100 acres in South Bay and 1,400 acres in North Bay) back to the State of California. Federal and state resource agencies and several private foundations provided funding for the purchase. Following the salt pond acquisition, the Center for Collaborative Policy began working with the US Fish and Wildlife Service (USFWS), the California Department of Fish and Game (CDFG), and the California Coastal Conservancy (CCC) to design a restoration plan. The final SBSP Restoration Plan was adopted in 2008 with three primary goals: (1) restoring and enhancing the wetlands to historic tidal marsh conditions, (2) providing recreational opportunities, and (3) improving flood protection.
The six project objectives of the SBSP Restoration Plan include:
- Create, restore, or enhance habitats;
- Maintain or improve existing levels of flood protection;
- Provide public access and recreational opportunities;
- Protect or improve existing levels of water and sediment quality;
- Implement measures to improve current levels of vector management and manage the spread of invasive species; and
- Protect the services provided by existing infrastructure.
The SBSP Restoration Project evaluated three long-term alternatives to restoring salt ponds in South San Francisco Bay: (A) no action; (B) managed pond emphasis (50:50 tidal habitat: managed ponds by area); and (C) tidal emphasis (90:10 tidal habitat: managed ponds by area). Alternative B, when fully implemented, would provide approximately 7,500 acres of tidal habitat and 7,500 acres of managed salt pond habitat. Alternative B designates approximately 20% of the managed pond habitat to be intensely managed for birds (e.g., waterfowl, shorebirds), provides a cohesive line of flood protection along the landward edge of the former salt ponds, and provides public access and recreation features. Alternative C, when fully implemented, would provide approximately 13,400 acres of tidal habitat and 1,600 acres of managed salt ponds. Alternative C designates all managed pond habitats to be intensely managed for birds, and provides similar flood protection and recreation features to Alternative B. The optimal configuration of tidal habitat and managed salt ponds that achieves project objectives while avoiding adverse impacts was unable to be determined due to moderate to high levels of uncertainty, so the project team decided to implement an adaptive management plan.
The basic approach of the SBSP Adaptive Management Plan is to implement restoration efforts in multiple phases. Lessons learned from each phase of the project inform future phases and determine the final habitat configuration. The final outcome is likely to fall between the 50:50 and 90:10 scenarios, and would achieve the maximum amount of tidal restoration possible without causing adverse effects on ecosystem services and/or resources. Each restoration target is associated with specific management triggers (e.g., indications that targets are not being met), applied studies, and potential management actions. For example, restoration activities aim to avoid the introduction of invasive algae species into San Francisco Bay, so the observation of invasives would trigger an investigation into if the pond configuration influences algal composition and abundance and may lead to an altered approach.
Outcomes and Conclusions
Phase 1 of the SBSP Restoration Project (2008–2016) aimed to provide immediate ecosystem services as well as to address key uncertainties (e.g., mercury contamination) surrounding the SBSP project. For example, 53 water systems were installed throughout several ponds with the aim of slowly adding water back into the salt pond system and lowering the salinity before reintroducing the water into the bay. The project team uses monitoring and a tracking scorecard to indicate if progress on restoration activities are meeting expectations or not. For example, targeted Phase 1 studies found that restoration activities successfully led to the return of several marsh species (e.g., salt marsh harvest mice), migratory waterbirds, and native fish species.
Phase 2 projects (2016–present) include creating 294 acres of new tidal marsh, enhancing 37 acres of pond habitats, and constructing a new hiking trail in the Don Edwards San Francisco Bay National Wildlife Refuge. The goal is that the completion of Phase 2 activities will result in the 50:50 tidal marsh:pond configuration.
Challenges that have arisen during the project include the potential for restoration activities to lead to mercury mobilization, threats to new and novel species, and a higher risk of invasive species expansion. During the gold rush, South San Francisco Bay had one of the largest mercury mines, which led to dormant and isolated mercury contamination in the salt ponds. Restoring tidal action or permanent flooding could cause the mercury to be mobilized. Over the last 100–150 years, new suites of species have adapted to the high salinity and utilize the salt pond habitat. In addition, some high salinity ponds were observed to serve as habitat for a disproportionate number of certain avian species. Thus, restoration strategies were required to incorporate both habitats (i.e. salt ponds and tidal wetlands) rather than simply restoring all habitats to tidal wetlands. Finally, the restoration of tidal wetlands will create new habitats that invasive species (e.g., non-native and hybrid Spartina) may colonize.
In addition to several of the challenges currently faced by the SBSP Restoration Project, sea level rise is predicted to impact sediment supply and accretion. A main goal of restoration efforts therefore is to act with a sense of urgency (i.e. building marshes back up as soon as possible), thereby increasing ecosystem resilience and keeping up with sea level rise. All of these challenges are being addressed through directed studies by teams of researchers as part of the adaptive management strategy.
Kershner, J. (2021). South Bay Salt Pond Restoration Project [Case study on a project of the California Coastal Conservancy]. Version 2.0. Product of EcoAdapt’s State of Adaptation Program. Retrieved from CAKE: https://www.cakex.org/case-studies/south-bay-salt-pond-restoration-project (Last updated August 2021)