Mercury inputs to Great Salt Lake, Utah: Reconnaissance-Phase results

In response to increasing public concern regarding mercury (Hg) cycling in Great Salt Lake (GSL) ecosystem, a series of studies were initiated to differentiate between the mass of Hg from riverine versus atmospheric sources to GSL. Cumulative riverine Hg load to GSL during a 1 year time period (April 1, 2007 to March 31, 2008) was 6 kg, with almost 50% of the cumulative Hg load contributed by outflow from Farmington Bay. Comparison of cumulative annual atmospheric Hg deposition (32 kg) to annual riverine deposition (6 kg) indicates that atmospheric deposition is the dominant input source to GSL. A sediment core collected from the southern arm of GSL was used to reconstruct annual Hg deposition rates over the past ~ 100 years. Unlike most freshwater lakes, small changes in water level in GSL significantly changes the lake surface area available for direct deposition of atmospheric Hg. There is good agreement between lake elevation (and corresponding lake surface area) and Hg deposition rates estimated from the sediment core. Higher lake levels, combined with sediment focusing processes, result in an increase in Hg accumulation rates observed in the sediment core. These same combination of processes are responsible for the lower Hg accumulation rates observed in the sediment core during historic low stands of GSL

Sex differences in contaminant concentrations of fish: a synthesis

Abstract A comparison of whole-fish polychlorinated biphenyl (PCB) and total mercury (Hg) concentrations in mature males with those in mature females may provide insights into sex differences in behavior, metabolism, and other physiological processes. In eight species of fish, we observed that males exceeded females in whole-fish PCB concentration by 17 to 43 %. Based on results from hypothesis testing, we concluded that these sex differences were most likely primarily driven by a higher rate of energy expenditure, stemming from higher resting metabolic rate (or standard metabolic rate (SMR)) and higher swimming activity, in males compared with females. A higher rate of energy expenditure led to a higher rate of food consumption, which, in turn, resulted in a higher rate of PCB accumulation. For two fish species, the growth dilution effect also made a substantial contribution to the sex difference in PCB concentrations, although the higher energy expenditure rate for males was still the primary driver. Hg concentration data were available for five of the eight species. For four of these five species, the ratio of PCB concentration in males to PCB concentration in females was substantially greater than the ratio of Hg concentration in males to Hg concentration in females. In sea lamprey (Petromyzon marinus), a very primitive fish, the two ratios were nearly identical. The most plausible explanation for this pattern was that certain androgens, such as testosterone and 11-ketotestosterone, enhanced Hg-elimination rate in males. In contrast, long-term elimination of PCBs is negligible for both sexes. According to this explanation, males not only ingest Hg at a higher rate than females but also eliminate Hg at a higher rate than females, in fish species other than sea lamprey. Male sea lamprey do not possess either of the above-specified androgens. These apparent sex differences in SMRs, activities, and Hg-elimination rates in teleost fishes may also apply, to some degree, to higher vertebrates including humans. Our synthesis findings will be useful in (1) developing sex-specific bioenergetics models for fish, (2) developing sex-specific risk assessment models for exposure of humans and wildlife to contaminants, and (3) refining Hg mass balance models for fish and higher vertebrates.http://deepblue.lib.umich.edu/bitstream/2027.42/134637/1/13293_2016_Article_90.pd

Atmospheric mercury and fine particulate matter in coastal New England : implications for mercury and trace element sources in the northeastern United States

This paper is not subject to U.S. copyright. The definitive version was published in Atmospheric Environment 79 (2013): 760–768, doi:10.1016/j.atmosenv.2013.07.031.Intensive sampling of ambient atmospheric fine particulate matter was conducted at Woods Hole, Massachusetts over a four-month period from 3 April to 29 July, 2008, in conjunction with year-long deployment of the USGS Mobile Mercury Lab. Results were obtained for trace elements in fine particulate matter concurrently with determination of ambient atmospheric mercury speciation and concentrations of ancillary gasses (SO2, NOx, and O3). For particulate matter, trace element enrichment factors greater than 10 relative to crustal background values were found for As, Bi, Cd, Cu, Hg, Pb, Sb, V, and Zn, indicating contribution of these elements by anthropogenic sources. For other elements, enrichments are consistent with natural marine (Na, Ca, Mg, Sr) or crustal (Ba, Ce, Co, Cs, Fe, Ga, La, Rb, Sc, Th, Ti, U, Y) sources, respectively. Positive matrix factorization was used together with concentration weighted air-mass back trajectories to better define element sources and their locations. Our analysis, based on events exhibiting the 10% highest PM2.5 contributions for each source category, identifies coal-fired power stations concentrated in the U.S. Ohio Valley, metal smelting in eastern Canada, and marine and crustal sources showing surprisingly similar back trajectories, at times each sampling Atlantic coastal airsheds. This pattern is consistent with contribution of Saharan dust by a summer maximum at the latitude of Florida and northward transport up the Atlantic Coast by clockwise circulation of the summer Bermuda High. Results for mercury speciation show diurnal production of RGM by photochemical oxidation of Hg° in a marine environment, and periodic traverse of the study area by correlated RGM-SO2(NOx) plumes, indicative of coal combustion sources.We acknowledge support of the USGS Toxic Substances Hydrology Program, the USGS Energy Resources Program, the National Science Foundation Small Grants for Exploratory Research Program, and for initial support, the USGS Mendenhall Postdoctoral Program

The effect of natural organic matter on mercury methylation by Desulfobulbus propionicus 1pr3

Methylation of tracer and ambient mercury (200Hg and 202Hg, respectively) equilibrated with four different natural organic matter (NOM) isolates was investigated in vivo using the Hg-methylating sulfate-reducing bacterium Desulfobulbus propionicus 1pr3. Desulfobulbus cultures grown fermentatively with environmentally representative concentrations of dissolved NOM isolates, Hg[II], and HS− were assayed for absolute methylmercury (MeHg) concentration and conversion of Hg(II) to MeHg relative to total unfiltered Hg(II). Results showed the 200Hg tracer was methylated more efficiently in the presence of hydrophobic NOM isolates than in the presence of transphilic NOM, or in the absence of NOM. Different NOM isolates were associated with variable methylation efficiencies for either the 202Hg tracer or ambient 200Hg. One hydrophobic NOM, F1 HpoA derived from dissolved organic matter from the Florida Everglades, was equilibrated for different times with Hg tracer, which resulted in different methylation rates. A 5 day equilibration with F1 HpoA resulted in more MeHg production than either the 4 h or 30 day equilibration periods, suggesting a time dependence for NOM-enhanced Hg bioavailability for methylation

Sediment-Water Interactions Affecting Dissolved-Mercury Distributions in Camp Far West Reservoir, California

Field and laboratory studies were conducted in April and November 2002 to provide the first direct measurements of the benthic flux of dissolved (0.2-micrometer filtered) mercury species (total and methylated forms) between the bottom sediment and water column at three sampling locations within Camp Far West Reservoir, California: one near the Bear River inlet to the reservoir, a second at a mid-reservoir site of comparable depth to the inlet site, and the third at the deepest position in the reservoir near the dam (herein referred to as the inlet, midreservoir and near-dam sites, respectively; Background, Fig. 1). Because of interest in the effects of historic hydraulic mining and ore processing in the Sierra Nevada foothills just upstream of the reservoir, dissolved-mercury species and predominant ligands that often control the mercury speciation (represented by dissolved organic carbon, and sulfides) were the solutes of primary interest. Benthic flux, sometimes referred to as internal recycling, represents the transport of dissolved chemical species between the water column and the underlying sediment. Because of the affinity of mercury to adsorb onto particle surfaces and to form insoluble precipitates (particularly with sulfides), the mass transport of mercury in mining-affected watersheds is typically particle dominated. As these enriched particles accumulate at depositional sites such as reservoirs, benthic processes facilitate the repartitioning, transformation, and transport of mercury in dissolved, biologically reactive forms (dissolved methylmercury being the most bioavailable for trophic transfer). These are the forms of mercury examined in this study. In contrast to typical scientific manuscripts, this report is formatted in a pyramid-like structure to serve the needs of diverse groups who may be interested in reviewing or acquiring information at various levels of technical detail (Appendix 1). The report enables quick transitions between the initial summary information (figuratively at the top of the pyramid) and the later details of methods or results (figuratively towards the base of the pyramid) using hyperlinks to supporting figures and tables, and an electronically linked Table of Contents. During two sampling events, two replicate sediment cores (Coring methods; Fig. 2) from each of three reservoir locations (Fig. 1) were used in incubation experiments to provide flux estimates and benthic biological characterizations. Incubation of these cores provided “snapshots” of solute flux across the sediment-water interface in the reservoir, under benthic, environmental conditions representative of the time and place of collection. Ancillary data, including nutrient and ligand fluxes, were gathered to provide a water-quality framework from which to compare the results for mercury

Managing for RADical ecosystem change: applying the Resist-Accept- Direct (RAD) framework

Ecosystem transformation involves the emergence of persistent ecological or social–ecological systems that diverge, dramatically and irreversibly, from prior ecosystem structure and function. Such transformations are occurring at increasing rates across the planet in response to changes in climate, land use, and other factors. Consequently, a dynamic view of ecosystem processes that accommodates rapid, irreversible change will be critical for effectively conserving fish, wildlife, and other natural resources, and maintaining ecosystem services. However, managing ecosystems toward states with novel structure and function is an inherently unpredictable and difficult task. Managers navigating ecosystem transformation can benefit from considering broader objectives, beyond a traditional focus on resisting ecosystem change, by also considering whether accepting inevitable change or directing it along some desirable pathway is more feasible (that is, practical and appropriate) under some circumstances (the RAD framework). By explicitly acknowledging transformation and implementing an iterative RAD approach, natural resource managers can be deliberate and strategic in addressing profound ecosystem change

Gaseous mercury flux from salt marshes is mediated by solar radiation and temperature

Salt marshes are ecologically sensitive ecosystems where mercury (Hg) methylation and biomagnification can occur. Understanding the mechanisms controlling gaseous Hg flux from salt marshes is important to predict the retention of Hg in coastal wetlands and project the impact of environmental change on the global Hg cycle. We monitored Hg flux from a remote salt marsh over 9 days which included three cloudless days and a 4 mm rainfall event. We observed a cyclical diel relationship between Hg flux and solar radiation. When measurements at the same irradiance intensity are considered, Hg flux was greater in the evening when the sediment was warm than in the morning when the sediment was cool. This is evidence to suggest that both solar radiation and sediment temperature directly influence the rate of Hg(II) photoreduction in salt marshes. Hg flux could be predicted from solar radiation and sediment temperature in sub-datasets collected during cloudless days (R2 = 0.99), and before (R2 = 0.97) and after (R2 = 0.95) the rainfall event, but the combined dataset could not account for the lower Hg flux observed after the rainfall event that is in contrast to greater Hg flux from soils after rainfall events

Hydrologic and geochemical controls of freshwater ferromanganese deposit formation at Trout Lake, Vilas County, Wisconsin

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