Ecosystem Function

With South San Francisco Bay in the background, the vegetated habitat to the left of the levee represents healthy tidal marsh. To the right is a former salt pond. Photo credit: Mark C. Marvin-DiPasquale, USGS Image Gallery

Historic tidal sloughs, such as the one above, are still visible in the surface of the former salt ponds. One management goal is to reinstate tidal flushing to these hydrologically disconnected areas and to restore healthy marsh function, without increasing methylmercury production. Photo credit: Mark C. Marvin-DiPasquale, USGS Image Gallery

The San Francisco Bay (SFB) in California (USA) is contaminated with mercury as a result of historic mining practices in the region; one of the largest point sources being the New Almaden mercury mining district, which drains into the South SFB through Alviso Slough. The State of California recently purchased over 16,000 acres of former salt production ponds for the purpose of wetland habitat restoration, with a majority of these ponds being in South SFB. Research in this area includes: a) the current status of mercury cycling by microbial processes in former salt ponds, Alviso Slough and South SFB reference sites, b) the interaction of wetland plants and the microbial mercury cycle, c) toxic methylmercury production by bacteria, and its incorporation into the local food web, d) trophic transfer of methylmercury and effects on avian reproduction, and e) proposed wetland restoration scenarios and their impact on mobilizing mercury buried in sediment, as well their affect on the status of mercury cycling and bioaccumulation in this region. 

Related Link:

South Bay Salt Pond Restoration Project

Publication:

Marvin-DiPasquale, M., and Cox, M.H., 2007, Legacy Mercury in Alviso Slough, South San Francisco Bay, California: Concentration, Speciation and Mobility U.S. Geological Survey Open-File Report number 2007-1240, p 98. (online open-file report)

For more information contact Mark C. Marvin-DiPasquale, Menlo Park Regional Office; Lisamarie Windham-Myers, Menlo Park Regional Office; Josh T. Ackerman, Western Ecological Research Center; and Collin A. Eagles-Smith, Western Ecological Research Center.

See also Geomicrobiology: Mercury >>

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At the foot of San Francisco’s historic Presidio, Crissy Marsh consists of a mix of subtidal, intertidal and upland habitats. Photo Credit: Lisamarie Windham-Myers, USGS

Water sampling the Crissy Marsh inlet to the San Francisco Bay, with Alcatraz Island seen in the background. The inlet is subject to periodic closure events, resulting from longshore sand migration and a muted tidal prism. Photo Credit: Hillary Harms, USGS

As part of the Golden Gate National Recreation Area, Crissy Field is a popular recreational destination in San Francisco, California, for both residents and tourists. The restoration of 18-acres of historic tidal marsh at this site has had great success in terms of public outreach and visibility, but less success in terms of revegetated marsh sustainability. Native cordgrass (Spartina foliosa) has experienced dieback and has failed to recolonize following extended flooding events resulting from periodic closures of the inlet channel, which inhibits daily tidal flushing. These inlet closure events are attributed to the marsh’s small tidal prism and to sand deposition near the inlet mouth. The National Park Service (NPS) currently manages the marsh by dredging the inlet channel to reinstate tidal flow approximately once per year during the spring (at the beginning of the active growing season). The joint USGS-NPS Water Quality Monitoring Program is sponsoring ecosystem-level research at the Crissy Field marsh to help advise NPS wetland managers as to the impacts of these closure events on marsh sustainability, both in terms of plant stress (e.g. fermentative respiration) and the microbial cycling of sulfur and mercury. Specifically we are investigating to what extent closure events are associated with a) increased reduced sulfur concentrations (generated by microbial sulfate reduction) in sediment and pore water, which might be toxic to juvenile or newly recolonized plants, and b) increased toxic methylmercury production by microbes in the sub-tidal and intertidal zones. This research, and that of collaborators in USGS Coastal and Marine Geology, is providing a scientific basis for determining how rapidly and how often to dredge the tidal channel after a closure event, and to inform habitat enhancement projects including a current design to daylight a perennial creek that drains into the marsh and to expand transitional wetland habitats.

Related Links:

• Coastal Evolution: Process-based Multi-scale Modeling
• National Park Service / US Geological Survey - Water Quality Partnership
• Crissy Field - National Park Service: Golden Gate National Recreation Area

For more information contact Lisamarie Windham-Myers, Menlo Park Regional Office, Mark C. Marvin-DiPasquale, Menlo Park Regional Office, and Kristen Ward, NPS Golden Gate National Recreation Area (NPS-GGNRA).

See also Geomicrobiology: Mercury >>
See also Microbial Ecology: Plant-Microbe Interactions >>

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