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References

Various Reports

Methylmercury Cycling, Bioaccumulation, and Export from Rice Fields and Wetlands in the Yolo Bypass
This study evaluated methylmercury in water, fish, and aquatic invertebrates in seasonal and permanent wetlands and in flooded rice fields. The research was conducted by the US Geological Survey and Department of Fish and Game Moss Landing Marine Laboratories and funded by Propositions 40 and 50.

Assessment of Methylmercury Contributions from Sacramento-San Joaquin Delta Farmed Islands
This study was conducted by researchers at the Moss Landing Marine Laboratories and HydroFocus and funded by the Central Valley Water Board. The purpose of the study was to answer the following key questions: 1) Are Delta farmed islands net producers or sinks of methylmercury? and, 2) If farmed islands are producers, what are the methylmercury loads contributed to Delta channels?

Sacramento-San Joaquin Delta Methylmercury TMDL
In addition to the above two reports, a list of other reports are listed on Sacramento-San Joaquin Delta Methylmercury TMDL page.

Sacramento-San Joaquin Delta Regional Ecosystem Restoration Implementation Plan
Mercury has been identified as a contaminant of concern or chemical stressor in the Sacramento– San Joaquin Delta ecosystem. Sources of mercury include historic mercury and gold mines as well as ongoing atmospheric deposition from regional and global sources. The conceptual model presented here is comprised of the main model and four submodels: 1) Mercury Methylation, which includes both a) formation of reactive (inorganic) mercury and b) microbial transformation of reactive (inorganic) mercury to (organic) methylmercury; 2) Methylmercury Bioaccumulation; 3) Human Health Effects; and 4) Wildlife Health Effects. Principal intermediate outcomes are methylmercury concentrations in water and sediment (Submodel 1) and methylmercury concentrations in biota (Submodel 2). The final model outcomes are export of mercury and methylmercury out of the Delta, effects on human health, and effects on wildlife health. In the following narrative, we provide a brief description of each submodel in relation to its drivers, linkages, and outcomes, and the interactions with other conceptual models constructed as part of the Delta Regional Ecosystem Restoration Implementation Plan (DRERIP) for the CALFED Bay-Delta Program. We also discuss the limitations of the overall mercury conceptual model and its submodels, and provide some recommendations for application of the model in resource management.

2008 CALFED Mercury Reports

Methylmercury Concentrations and Loads in the Central Valley and Freshwater Delta
The purpose of this study is threefold. First, identify the major sources of methyl mercury in the Sacramento and San Joaquin Basins and determine the magnitude of the loads exported to the Delta. Second, determine the efficiency with which methyl mercury is transported from Central Valley sources to the Delta. Finally, construct a methyl mercury mass balance box model for the Delta in collaboration with other Researchers in this project.

Mercury and Suspended Sediment Concentrations and Loads in the Central Valley and Freshwater Delta
The purpose of this study is two-fold. The first aim was to determine the primary sources of mercury and suspended sediment in the Sacramento and San Joaquin Basins. The second was to determine whether the Delta is a source or sink for mercury and suspended sediment.

Atmospheric Mercury Deposition Studies
Work conducted under this task involved two major components: (1) Collection of atmospheric mercury wet deposition samples and (2) Determination of the dry deposition of mercury based on modeling of measurements of atmospheric mercury species (total gaseous mercury, TGM, reactive gaseous mercury, RGM; and particulate mercury, HgP).

Total Mercury and Methylmercury in Surface Sediments of Different Delta Ecosystems
For this task the major effort is to conduct studies of spatial and temporal distribution of methylmercury (MMHg) and total mercury (Hgt) in sediment and water to determine the role of habitat and season in controlling concentrations. This information will be used to identify habitat types and locations of 'hot spots' in the Delta and will be a framework for future mercury monitoring projects. Two approaches were used in this monitoring effort: (1) study many sites a few times per year and; (2) study a subset of four sites monthly over multiple years.

Monomethylmercury Sediment-Water Exchange
The major effort for this task is to conduct studies of the sediment-water exchange of mercury to determine the relative role of sediments as sources of mercury and monomethylmercury (MMHg) to the water column. This information will be used to assess the significance of sediment-water exchange in comparison to other sources into the Delta using a mass balance approach. Two basic methods were used to determine sediment-water exchange: (1) a direct assessment using deployment of benthic flux chambers and; (2) modeling the sediment-water exchange from measurements of interstitial pore water concentration gradients.

Monomethylmercury Photodegredation Studies
Solar radiation entering the water column can play an important role in MMHg cycling. Recent studies have shown that photo-degradation of MMHg by sunlight can occur in surface waters of lakes. The lake studies show that photo-degradation is influenced by aqueous MMHg concentration and light intensity. The seawater study shows MMHg being degraded by sunlight (>280 nm), ultraviolet light A (320-400 nm), and ultraviolet light B (280-320 nm). This study hypothesized that photo-degradation is a significant sink for MMHg in the surface waters of the Delta. Photo-degradation was investigated at several locations to fill in data gaps in conceptual understanding of sources, sinks, and cycling of MMHg in the Delta. This work is part of a larger study to investigate the transport, cycling, and fate of mercury and monomethylmercury in the San Francisco Delta and its tributaries. Portions of this larger study as they relate to photo-degradation will be discussed here.

Monomethylmercury Loading Studies in Delta Wetlands – Twitchell Island
The State of California currently has goals to increase the acreage of marsh habitat in the Delta. It is critical the new marshes be designed or modified to not increase the amount of MMHg in the Delta. The goal of this study is to investigate the affect of marsh habitat design on mercury cycling and MMHg production. This study may inform managers and marsh engineers about designs that could minimize MMHg flux from marsh habitat. The following Hypotheses were investigated using two experimental wetlands located at Twitchell Island, in the Delta: (1) MMHg concentrations and loads differ with marsh type; (2) Concentrations and flux of MMHg out of marsh habitat varies seasonally; (3) concentrations of total mercury in marsh sediment is uniform and; (4) MMHg is generated within marsh habitat in sediments.

Monomethylmercury Loading Studies in Delta Wetlands – Sycamore Slough and Suisun Marsh
The goal of this task is to determine if MMHg loads from current wetlands represent a significant threat to the Delta ecosystem. The primary objective of this is task is to determine MMHg loads from different types of wetland habitats and to compare the loads from these wetlands to loads from Delta tributaries, atmospheric deposition, and Delta sediment. We used a whole ecosystem sampling approach in Calfed Mercury Project, Task 5.3a Sycamore Slough and Suisun Marsh Page 2 of 12 which we monitor concentrations of MMHg over complete tidal cycles to quantify the amount of MMHg moving into and out of the marshes studied.

Monomethylmercury Loading Studies in Delta Wetlands – Grizzly Island
The goal of this task is to determine if MMHg loads from current wetlands represent a significant threat to the Delta ecosystem. The primary objective of this is task is to determine MMHg loads from different types of wetland habitats and to compare the loads from these wetlands to loads from Delta tributaries, atmospheric deposition, and Delta sediment. We used a whole ecosystem sampling approach in Calfed Mercury Project, Task 5.3a Sycamore Slough and Suisun Marsh Page 2 of 12 which we monitor concentrations of MMHg over complete tidal cycles to quantify the amount of MMHg moving into and out of the marshes studied. Both, tidal (This Report, Task 4.2 Report, & Task 5.3a Browns Island Report) and non tidal wetlands (Task 5.3a Twitchell & 5.3a Grizzly Island Reports) were studied.

Mononmethylmercury Loading Studies in Delta Wetlands – Brown’s Island
The approach of the study is to 1) to expand the current work of the USGS on chemical composition of DOM from different sources within the Delta to include parameters related to mercury solubilization, binding, and partitioning; and 2) to expand current measurement of tidal fluxes of DOM to include mercury species by identifying correlates measured in situ to predict real time fluxes of mercury and methylmercury in the complex hydrodynamic exchange of the tidal wetland environment.

Monomethylmercury Loss in the Delta Through Particulate Deposition
Ongoing methylmercury (MMHg) mass balance estimates for the Sacramento San Joaquin Delta (Delta) suggest that it is a net MMHg sink (Foe, 2003; Foe et al., 2008). Two processes have been identified that could explain much of the loss of MMHg in the Delta. The first is photodemethylation (Gill, 2008) and the second is sedimentation, the subject of this report.

Sediment Biogeochemistry Studies in Delta Wetlands
This task is designed to investigate the relationship between major biogeochemical processes in sediments and the production of MMHg. The field work for this task involves: (1) measurements of mercury and MMHg in interstitial pore waters using the whole-core squeezing technique and also high resolution near-surface profiles of oxygen, sulfide, and other parameters in interstitial pore waters using a microelectrode profiler system (Unisense); (2) measurements of MMHg in sediments; (3) measurements of mercury, MMHg, and ancillary parameters (e.g. iron, manganese, and dissolved oxygen) in the water column collected by an in situ water sampler during tidal flushing of water on and off a marsh.