Sediment grain-size and loss-on-ignition analyses from 2002 Englebright Lake coring and sampling campaigns

This report presents sedimentologic data from three 2002 sampling campaigns conducted in Englebright Lake on the Yuba River in northern California. This work was done to assess the properties of the material deposited in the reservoir between completion of Englebright Dam in 1940 and 2002, as part of the Upper Yuba River Studies Program. Included are the results of grain-size-distribution and loss-on-ignition analyses for 561 samples, as well as an error analysis based on replicate pairs of subsamples

Methylmercury degradation and exposure pathways in streams and wetlands impacted by historical mining

The authors acknowledge financial support from the National Science Foundation: EAR-1226741 (to M.B.S.) and EAR-1225630 (to J.D.B.).Monomethyl mercury (MMHg) and total mercury (THg) concentrations and Hg stable isotope ratios (δ202Hg and Δ199Hg) were measured in sediment and aquatic organisms from Cache Creek (California Coast Range) and Yolo Bypass (Sacramento Valley). Cache Creek sediment had a large range in THg (87 to 3870 ng/g) and δ202Hg (− 1.69 to − 0.20‰) reflecting the heterogeneity of Hg mining sources in sediment. The δ202Hg of Yolo Bypass wetland sediment suggests a mixture of high and low THg sediment sources. Relationships between %MMHg (the percent ratio of MMHg to THg) and Hg isotope values (δ202Hg and Δ199Hg) in fish and macroinvertebrates were used to identify and estimate the isotopic composition of MMHg. Deviation from linear relationships was found between %MMHg and Hg isotope values, which is indicative of the bioaccumulation of isotopically distinct pools of MMHg. The isotopic composition of pre-photodegraded MMHg (i.e., subtracting fractionation from photochemical reactions) was estimated and contrasting relationships were observed between the estimated δ202Hg of pre-photodegraded MMHg and sediment IHg. Cache Creek had mass dependent fractionation (MDF; δ202Hg) of at least − 0.4‰ whereas Yolo Bypass had MDF of + 0.2 to + 0.5‰. This result supports the hypothesis that Hg isotope fractionation between IHg and MMHg observed in rivers (− MDF) is unique compared to + MDF observed in non-flowing water environments such as wetlands, lakes, and the coastal ocean.PostprintPeer reviewe

Sacramento-San Joaquin Delta Regional Ecosystem Restoration Implementation Plan

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

Geochemical Data for Mercury, Methylmercury, and Other Constituents in Sediments from Englebright Lake, California, 2002

This report presents geochemical data from two 2002 sampling campaigns conducted in Englebright Lake on the Yuba River in northern California. A deep coring campaign was done in May–June 2002 and a shallow sampling campaign was completed in October 2002. This work assessed the chemical composition of material deposited in the reservoir between 1940, the year Englebright Dam was completed, and 2002 as part of the Upper Yuba River Studies Program, an effort designed to evaluate the feasibility of introducing anadromous fish, including steelhead and spring-run Chinook salmon, upstream from Englebright Dam. Results of analyses of total mercury (HgT) in 444 subsamples, methylmercury (MeHg) in 243 subsamples, and other trace and major elements in 202 subsamples are presented. Data quality was evaluated on the basis of analyses of replicate pairs of subsamples, standardreference materials, blanks, and spike additions. Deep coring penetrated the full thickness of material deposited after 1940 at six locations in the reservoir; the cores reached a maximum depth of 32.8 meters below the reservoir floor. At the three deep coring sites closest to Englebright Dam, concentrations of HgT (dry basis) were consistently in the range of 100 to 500 ng/g (nanogram per gram), in sediment dominantly of silt size (median grain size of 0.004 to 0.063 mm [millimeter]). At the deep coring sites located farther upstream, the upper parts of the profile had lower concentrations of HgT, generally ranging from 2 to 100 ng/g, in sediment dominantly of sand size (median grain size from 0.063 to 2 mm). The lower part of the vertical profiles at three upstream coring sites had higher concentrations of HgT than the upper and middle parts of these profiles, and had finer median grain size. The highest median concentration of MeHg (1.1 ng/g) was in the top 2 cm (centimeter) of the shallow box cores. This vertical interval also had the highest value of the ratio of MeHg to HgT, 0.41 percent. Median concentrations of MeHg and median values of MeHg/HgT decreased systematically with depth from 0–4 to 4–8 to 8–12 cm in the shallow cores. However, similar systematic decreases were not observed at the meter scale in the deep cores of the MEM (MEthylMercury) series. The overall median of the ratio MeHg/HgT in the deep cores was 0.25 percent, not much less than the overall median value for the shallow cores (0.33 percent). Mercury-203 radiotracer divalent inorganic mercury (203Hg(II)) was used to determine microbial mercury-methylation potential rates for 11 samples collected from three reservoir locations and various depths in the sediment profile. For the five shallow mercury-methylation subsamples, ancillary geochemical parameters were assayed, including microbial sulfate reduction rates, sulfur speciation (sediment acid volatile sulfide, total reduced sulfur, and pore-water sulfate), iron speciation (sediment acid extractable iron(II), amorphous iron(III), crystalline iron(III) and pore-water iron(II)), porewater chloride and dissolved organic carbon, and pH, oxidation- reduction potential (Eh) and whole-sediment organic content. The highest potential rates of microbial mercury methylation were measured in shallow (0 to 8 cm depth) sediments (5 to 30 nanograms of mercury per gram dry sediment per day), whereas potential rates for subsamples collected from depths greater than 500 cm were consistently below the detection limit of the radiotracer method (\u3c 0.02 nanogram of mercury per gram dry sediment per day). Chemical analyses of trace and major elements in bed sediment are presented for 202 samples from deep cores from five locations in Englebright Lake. The mean values and standard deviations for selected trace elements were as follows (in micrograms per gram): antimony, 2.4 ± 1.6; arsenic, 69 ± 48; chromium, 134 ± 23; lead, 33 ± 25; and nickel, 87 ± 24. Concentrated samples of heavy-mineral grains, prepared using nine large-volume composite samples from deep cores, were examined using optical and scanning-electron microscopy. Estimated gold concentrations in the composite sediment samples ranged from 38 to 840 milligrams per cubic meter. Grains of gold-mercury amalgam and grains of electrum (native gold), with and without mercury staining, were observed in the heavy-mineral concentrates. Results of this study will be used to evaluate potential effects on fish habitat and trace-element transport in relation to various scenarios regarding efforts to improve fish passage at Englebright Lake. The scenarios include dredging or release of sediments to downstream environments in association withdam modification or removal

Kinetics of Homogeneous and Surface-Catalyzed Mercury(II) Reduction by Iron(II)

Production of elemental mercury, Hg(0), via Hg­(II) reduction is an important pathway that should be considered when studying Hg fate in environment. We conducted a kinetic study of abiotic homogeneous and surface-catalyzed Hg(0) production by Fe­(II) under dark anoxic conditions. Hg(0) production rate, from initial 50 pM Hg­(II) concentration, increased with increasing pH (5.5–8.1) and aqueous Fe­(II) concentration (0.1–1 mM). The homogeneous rate was best described by the expression, <i>r</i>_<i>hom</i> = <i>k</i>_<i>hom</i> [FeOH⁺] [Hg­(OH)₂]; <i>k</i>_<i>hom</i> = 7.19 × 10⁺³ L (mol min)⁻¹. Compared to the homogeneous case, goethite (α-FeOOH) and hematite (α-Fe₂O₃) increased and γ-alumina (γ-Al₂O₃) decreased the Hg(0) production rate. Heterogeneous Hg(0) production rates were well described by a model incorporating equilibrium Fe­(II) adsorption, rate-limited Hg­(II) reduction by dissolved and adsorbed Fe­(II), and rate-limited Hg­(II) adsorption. Equilibrium Fe­(II) adsorption was described using a surface complexation model calibrated with previously published experimental data. The Hg(0) production rate was well described by the expression <i>r</i>_<i>het</i> = <i>k</i>_<i>het</i> [>SOFe^(II)] [Hg­(OH)₂], where >SOFe^(II) is the total adsorbed Fe­(II) concentration; <i>k</i>_<i>het</i> values were 5.36 × 10⁺³, 4.69 × 10⁺³, and 1.08 × 10⁺² L (mol min)⁻¹ for hematite, goethite, and γ-alumina, respectively. Hg(0) production coupled to reduction by Fe­(II) may be an important process to consider in ecosystem Hg studies

Environmental Factors Affecting Mercury in Camp Far West Reservoir, California, 2001–03

This report documents water quality in Camp Far West Reservoir from October 2001 through August 2003. The reservoir, located at approximately 300 feet above sea level in the foothills of the northwestern Sierra Nevada, California, is a monomictic lake characterized by extreme drawdown in the late summer and fall. Thermal stratification in summer and fall is coupled with anoxic conditions in the hypolimnion. Water-quality sampling was done at approximately 3-month intervals on eight occasions at several stations in the reservoir, including a group of three stations along a flow path in the reservoir: an upstream station in the Bear River arm (principal tributary), a mid-reservoir station in the thalweg (pre-reservoir river channel), and a station in the deepest part of the reservoir, in the thalweg near Camp Far West Dam. Stations in other tributary arms of the reservoir included those in the Rock Creek arm of the reservoir, a relatively low-flow tributary, and the Dairy Farm arm, a small tributary that receives acidic, metal-rich drainage seasonally from the inactive Dairy Farm Mine, which produced copper, zinc, and gold from underground workings and a surface pit. Several water-quality constituents varied significantly by season at all sampling stations, including major cations and anions, total mercury (filtered and unfiltered samples), nitrogen (ammonia plus organic), and total phosphorus. A strong seasonal signal also was observed for the sulfur-isotope composition of aqueous sulfate from filtered water. Although there were some spatial differences in water quality, the seasonal variations were more profound. Concentrations of total mercury (filtered and unfiltered water) were highest during fall and winter; these concentrations decreased at most stations during spring and summer. Anoxic conditions developed in deep parts of the reservoir during summer and fall in association with thermal stratification. The highest concentrations of methylmercury in unfiltered water were observed in samples collected during summer from deep-water stations in the anoxic hypolimnion. In the shallow (less than 14 meters depth) oxic epilimnion, concentrations of methylmercury in unfiltered water were highest during the spring and lowest during the fall. The ratio of methylmercury to total mercury (MeHg/HgT) increased systematically from winter to spring to summer, largely in response to the progressive seasonal decrease in total mercury concentrations, but also to some extent because of increases in MeHg concentrations during summer. Water-quality data for Camp Far West Reservoir are used in conjunction with data from linked studies of sediment and biota to develop and refine a conceptual model for mercury methylation and bioaccumulation in the reservoir and the lower Bear River watershed. It is hypothesized that MeHg is produced by sulfate-reducing bacteria in the anoxic parts of the water column and in shallow bed sediment. Conditions were optimal for this process during late summer and fall. Previous work has indicated that Camp Far West Reservoir is a phosphate-limited system—molar ratios of inorganic nitrogen to inorganic phosphorus in filtered water were consistently greater than 16 (the Redfield ratio), sometimes by orders of magnitude. Therefore, concentrations of orthophosphate were expectedly very low or below detection at all stations during all seasons. It is further hypothesized that iron-reducing bacteria facilitate release of phosphorus from iron-rich sediments during summer and early fall, stimulating phytoplankton growth in the fall and winter, and that the MeHg produced in the hypolimnion and metalimnion is released to the entire water column in the late fall during reservoir destratification (vertical mixing). Mercury bioaccumulation factors (BAF) were computed using data from linked studies of biota spanning a range of trophic position: zooplankton, midge larvae, mayfly nymphs, crayfish, threadfin shad, bluegill, and spotted bass. Significant increases in total mercury in tissue with increasing organism size were observed for all three fish species and for crayfish. The BAF values were computed using the average methylmercury concentration (wet) in biota divided by the arithmetic mean concentration of methylmercury in filtered water (0.04 nanograms per liter). As expected, the BAF values increased systematically with increasing trophic position. Values of BAF were 190,000 for zooplankton; 470,000 to 930,000 for three taxa of invertebrates; 2.7 million for threadfin shad (whole body); 4.2 million for bluegill (fillet); and 10 million for spotted bass (fillet). The BAF values are high compared with those for biota in other reservoirs in northern California and elsewhere, indicating relatively efficient biomagnification of mercury in Camp Far West Reservoir

Spatial and Seasonal Variability of Dissolved Methylmercury in Two Stream Basins in the Eastern United States

We assessed methylmercury (MeHg) concentrations across multiple ecological scales in the Edisto (South Carolina) and Upper Hudson (New York) River basins. Out-of-channel wetland/floodplain environments were primary sources of filtered MeHg (F-MeHg) to the stream habitat in both systems. Shallow, open-water areas in both basins exhibited low F-MeHg concentrations and decreasing F-MeHg mass flux. Downstream increases in out-of-channel wetlands/floodplains and the absence of impoundments result in high MeHg throughout the Edisto. Despite substantial wetlands coverage and elevated F-MeHg concentrations at the headwater margins, numerous impoundments on primary stream channels favor spatial variability and lower F-MeHg concentrations in the Upper Hudson. The results indicated that, even in geographically, climatically, and ecologically diverse streams, production in wetland/floodplain areas, hydrologic transport to the stream aquatic environment, and conservative/nonconservative attenuation processes in open water areas are fundamental controls on dissolved MeHg concentrations and, by extension, MeHg availability for potential biotic uptake