Geology topics

Darell Slotton

Publications and source records attributed to Darell Slotton.

4 recordsLinked to original sources

USGS2023

South San Francisco Bay Salt Pond Restoration Project—A synthesis of Phase-1 mercury studies

The South Bay Salt Pond Restoration Project (SBSPRP) encompasses over 6,000 hectares of former salt production ponds along the south edge of the San Francisco Bay and represents the largest wetland restoration effort on the west coast of North America. A series of studies associated with Phase 1 (2010–2018) restoration activities that are focused on a historically mercury contaminated slough and series of ponds within the restoration area have recently been completed. This report brings together the key findings of these loosely coordinated studies and integrates the results into a more comprehensive and holistic product that informs future restoration activities associated with the SBSPRP and elsewhere. This report documents key findings associated with the breach of pond A6: (1) a short-term spike in slough fish (Mississippi silverside) total mercury concentration in lower Alviso Slough; (2) a short-term spike in surface-water particulate total mercury in lower Alviso Slough; (3) significant sediment scour in Alviso Slough adjacent to and downstream of the breach points; (4) a decrease in surface-sediment methylmercury (as a percentage of total mercury) in lower Alviso Slough; (5) the transport of 70 kilograms per year of sediment-associated total mercury into pond A6 during the first 2 years following the breach but with much of this coming from outside of Alviso Slough, presumably from the nearby shallows, Guadalupe Slough, and the larger southern San Francisco Bay area; and (6) a slowing of bed sediment erosion in lower Alviso Slough 3–5 years after the breaching of pond A6. Although this report is not intended to be prescriptive in terms of the next steps the SBSPRP should or should not take, the totality of the findings presented provide critical process-level information regarding the extent and the duration of spikes in mercury levels in water, sediment, fish, and birds, which appeared to result from the two management actions under study. Thus, these results can be used to anticipate similar ecosystem responses associated with similar management actions that may be considered in the future. We also conclude this report by highlighting unanswered questions associated with mercury dynamics as it relates to the restoration project, and possible future directions for research.

California↗

USGS2011

The effects of wetland restoration on mercury bioaccumulation in the South Bay Salt Pond Restoration Project: Using the biosentinel toolbox to monitor changes across multiple habitats and spatial scales

The project was initiated in April 2010, and to date has included four sampling events of surface water (April, May, June/July, and August 2010) and five sampling events of biota (April, May, June/July, August, and September 2010) and three sampling events for surface sediment (May, June/July, and August 2010). This annual report briefly summarizes our progress to date.

California↗

USGS2008

Ecosystem conceptual model- Mercury

Mercury has been identified as an important contaminant in the Delta, based on elevated concentrations of methylmercury (a toxic, organic form that readily bioaccumulates) in fish and wildlife. There are health risks associated with human exposure to methylmercury by consumption of sport fish, particularly top predators such as bass species. Original mercury sources were upstream tributaries where historical mining of mercury in the Coast Ranges and gold in the Sierra Nevada and Klamath-Trinity Mountains caused contamination of water and sediment on a regional scale. Remediation of abandoned mine sites may reduce local sources in these watersheds, but much of the mercury contamination occurs in sediments stored in the riverbeds, floodplains, and the Bay- Delta, where scouring of Gold-Rush-era sediment represents an ongoing source. Conversion of inorganic mercury to toxic methylmercury occurs in anaerobic environments including some wetlands. Wetland restoration managers must be cognizant of potential effects on mercury cycling so that the problem is not exacerbated. Recent research suggests that wettingdrying cycles can contribute to mercury methylation. For example, high marshes (inundated only during the highest tides for several days per month) tend to have higher methylmercury concentrations in water, sediment, and biota compared with low marshes, which do not dry out completely during the tidal cycle. Seasonally inundated flood plains are another environment experiencing wetting and drying where methylmercury concentrations are typically elevated. Stream restoration efforts using gravel injection or other reworking of coarse sediment in most watersheds of the Central Valley involve tailings from historical gold mining that are likely to contain elevated mercury in associated fines. Habitat restoration projects, particularly those involving wetlands, may cause increases in methylmercury exposure in the watershed. This possibility should be evaluated. The DRERIP mercury conceptual model and its four submodels (1. Methylation, 2. Bioaccumulation, 3. Human Health Effects, and 4. Wildlife Heath Effects) can be used to understand the general relationships among drivers and outcomes associated with mercury cycling in the Delta. Several linkages between important drivers and outcomes have been identified as important but highly uncertain (i.e. poorly understood). For example, there may be significant wildlife health effect of mercury on mammals and reptiles in the Delta, but there is currently very little or no information about it. The characteristics of such linkages are important when prioritizing and funding restoration projects and associated monitoring in the Delta and its tributaries.

Report↗

USGS2004

Summary and Synthesis of Mercury Studies in the Cache Creek Watershed, California, 2000-01

This report summarizes the principal findings of the Cache Creek, California, components of a project funded by the CALFED Bay?Delta Program entitled 'An Assessment of Ecological and Human Health Impacts of Mercury in the Bay?Delta Watershed.' A companion report summarizes the key findings of other components of the project based in the San Francisco Bay and the Delta of the Sacramento and San Joaquin Rivers. These summary documents present the more important findings of the various studies in a format intended for a wide audience. For more in-depth, scientific presentation and discussion of the research, a series of detailed technical reports of the integrated mercury studies is available at the following website: .

Water-Resources Investigations Report↗