Water Quality in South San Francisco Bay, California: Current Condition and Potential Issues for the South Bay Salt Pond Restoration Project

Abstract

The SBSPRP is an extensive tidal wetland restoration project that is underway at the margin of South San Francisco Bay, California. The Project, which aims to restore former salt ponds to tidal marsh and manage other ponds for water bird support, is taking place in the context of a highly urbanized watershed and an Estuary already impacted by chemical contaminants. There is an intimate relationship between water quality in the watershed, the Bay, and the transitional wetland areas where the Project is located. The Project seeks to restore habitat for endangered and endemic species and to provide recreational opportunities for people. Therefore, water quality and bioaccumulation of contaminants in fish and wildlife is an important concern for the success of the Project. Mercury, PCBs, and PBDEs are the persistent contaminants of greatest concern in the region. All of these contaminants are present at elevated concentrations both in the abiotic environment and in wildlife. Dioxins, pyrethroids, PAHs, and selenium are also problematic. Organochlorine insecticides have historically impacted the Bay, and they remain above thresholds for concern in a small proportion of samples. Emerging contaminants, such as PFCs and non-PBDE flame retardants, are also an important water quality issue. Beyond chemical pollutants, other concerns for water quality in South San Francisco Bay exist, and include biological constituents, especially invasive species, and chemical attributes, such as dissolved oxygen and salinity. Future changes, both from within the Project and from the Bay and watershed, are likely to influence water quality in the region. Project actions to restore wetlands could worsen, improve, or not affect the already impaired water quality in South Bay. Accelerated erosion of buried sediment as a consequence of Project restoration actions is a potentially serious regional threat to South Bay water and sediment quality. Furthermore, the planned restoration of salt ponds to tidal marsh has raised concerns about possible increased net production of methylmercury and its subsequent accumulation in the food web. This concern applies not only to the restored marshes, but also to the South Bay as a whole, which could be affected on a regional scale. The ponds that are converted to tidal marsh will sequester millions of cubic meters of sediment. Sequestration of sediment in marshes could remove contaminated sediment from the active zone of the Bay but could also create marshes with contaminated food webs. Some of the ponds will not be restored to marsh but will be managed for use by water birds. Therefore, the effect of dense avian populations on eutrophication and the introduction of pathogens should be considered. Water quality in the Project also could be affected by external changes, such as human population growth and climate change. To address these many concerns related to water quality, the SBSPRP managers, and others faced with management of wetland restoration at a regional scale, should practice adaptive management...

Seasonal and annual trends in forage fish mercury concentrations, San Francisco Bay

“…These ponds are currently managed for wildlife as part of a long-term restoration project. This project could potentially alter biotic MeHg exposure due to the high sediment MeHg concentrations in some of the salt ponds and the potential for hydrologic modification, including cycles of wetting and drying, to increase MeHg production or release (Grenier and Davis, 2010 elevated silverside concentrations at the Eden Landing site could have resulted from short term exposure to MeHg released from the Eden Landing pond complex, as they transitioned from hydrologically isolated ponds having elevated sediment MeHg production to ponds with a greater hydrological connection to the South Bay (Miles and Ricca, 2010;South Bay Salt Pond Restoration Project, 2006). At Alviso Slough, decreases in fall dissolved oxygen and consequent increases in MeHg production may have caused the increases in silverside Hg from 2005 to 2010, and topsmelt high outlier results in 2009 and 2010.…”

“…An intensive restoration program is underway to restore wetlands surrounding the Bay, including the conversion of thousands of hectares of historic salt ponds and other isolated habitats to wetlands (Goals Project, 1999;Grenier and Davis, 2010). MeHg production can be relatively high in nearshore managed ponds and wetland habitats due to differences in hydrology and redox conditions (Davis et al, 2003;Grenier and Davis, 2010;Heim et al, 2007;Miles and Ricca, 2010). Consequently, Hg monitoring in Bay biota is underway to evaluate potential short and long-term changes in MeHg exposure and bioaccumulation due to habitat restoration.…”

“…Consequently, there are substantial efforts to control specific Hg sources through the U.S. federally mandated Total Maximum Daily Load (TMDL) program (Davis et al, 2012). An intensive restoration program is underway to restore wetlands surrounding the Bay, including the conversion of thousands of hectares of historic salt ponds and other isolated habitats to wetlands (Goals Project, 1999;Grenier and Davis, 2010). MeHg production can be relatively high in nearshore managed ponds and wetland habitats due to differences in hydrology and redox conditions (Davis et al, 2003;Grenier and Davis, 2010;Heim et al, 2007;Miles and Ricca, 2010).…”

Drivers of change in estuarine‐coastal ecosystems: Discoveries from four decades of study in San Francisco Bay

“…A second priority is new contaminants that persist and accumulate in food webs, such as polybrominated diphenyl ethers (PBDEs) (brominated flame retardants). These compounds were undetected in the 1980s, but residues are now common in water, sediments, and biota of South San Francisco Bay where concentrations in harbor seals, bird eggs, and humans are among the highest recorded [ Grenier and Davis , 2010]. The sources and environmental effects of PBDEs are largely unknown, but their presence illustrates the challenge of maintaining the chemical and biological integrity of estuaries when new contaminants emerge faster than our capacity to identify their sources and assess their effects.…”

Reducing methylmercury accumulation in the food webs of San Francisco Bay and its local watersheds

“…One project in the South Bay alone is planning to restore over 15,000 acres of tidal marsh – the largest single tidal wetland restoration project on the Pacific Coast of the USA. This restoration activity is expected to generate a huge net benefit, but carries a potential risk of increasing MeHg in the food web on either a local or regional scale (Grenier and Davis, 2010). Finally, San Francisco Bay is fairly unique in the extent of contaminant monitoring that is performed, due primarily to the Regional Monitoring Program for Water Quality in the San Francisco Estuary (SFEI, 2010a) and long-term monitoring performed since the 1970s by the U.S. Geological Survey.…”