Geology topics

David P. Krabbenhoft

Publications and source records attributed to David P. Krabbenhoft.

At least 91 records · Page 5Linked to original sources

USGS2014

Mercury concentrations and distribution in soil, water, mine waste leachates, and air in and around mercury mines in the Big Bend region, Texas, USA

Samples of soil, water, mine waste leachates, soil gas, and air were collected from areas mined for mercury (Hg) and baseline sites in the Big Bend area, Texas, to evaluate potential Hg contamination in the region. Soil samples collected within 300 m of an inactive Hg mine contained elevated Hg concentrations (3.8–11 µg/g), which were considerably higher than Hg in soil collected from baseline sites (0.03–0.05 µg/g) distal (as much as 24 km) from mines. Only three soil samples collected within 300 m of the mine exceeded the probable effect concentration for Hg of 1.06 µg/g, above which harmful effects are likely to be observed in sediment-dwelling organisms. Concentrations of Hg in mine water runoff (7.9–14 ng/L) were generally higher than those found in springs and wells (0.05–3.1 ng/L), baseline streams (1.1–9.7 ng/L), and sources of drinking water (0.63–9.1 ng/L) collected in the Big Bend region. Concentrations of Hg in all water samples collected in this study were considerably below the 2,000 ng/L drinking water Hg guideline and the 770 ng/L guideline recommended by the U.S. Environmental Protection Agency (USEPA) to protect aquatic wildlife from chronic effects of Hg. Concentrations of Hg in water leachates obtained from leaching of mine wastes varied widely from <0.001 to 760 µg of Hg in leachate/g of sample leached, but only one leachate exceeded the USEPA Hg industrial soil screening level of 31 µg/g. Concentrations of Hg in soil gas collected at mined sites (690–82,000 ng/m 3 ) were highly elevated compared to soil gas collected from baseline sites (1.2–77 ng/m 3 ). However, air collected from mined areas at a height of 2 m above the ground surface contained concentrations of Hg (4.9–64 ng/m 3 ) that were considerably lower than Hg in soil gas from the mined areas. Although concentrations of Hg emitted from mine-contaminated soils and mine wastes were elevated, persistent wind in southwest Texas disperses Hg in the air within a few meters of the ground surface.

Texas↗

USGS2014

Lacustrine responses to decreasing wet mercury deposition rates: results from a case study in northern Minnesota

We present a case study comparing metrics of methylmercury (MeHg) contamination for four undeveloped lakes in Voyageurs National Park to wet atmospheric deposition of mercury (Hg), sulfate (SO 4 –2 ), and hydrogen ion (H + ) in northern Minnesota. Annual wet Hg, SO 4 –2 , and H + deposition rates at two nearby precipitation monitoring sites indicate considerable decreases from 1998 to 2012 (mean decreases of 32, 48, and 66%, respectively). Consistent with decreases in the atmospheric pollutants, epilimnetic aqueous methylmercury (MeHg aq ) and mercury in small yellow perch (Hg fish ) decreased in two of four lakes (mean decreases of 46.5% and 34.5%, respectively, between 2001 and 2012). Counter to decreases in the atmospheric pollutants, MeHg aq increased by 85% in a third lake, whereas Hg fish increased by 80%. The fourth lake had two disturbances in its watershed during the study period (forest fire; changes in shoreline inundation due to beaver activity); this lake lacked overall trends in MeHg aq and Hg fish . The diverging responses among the study lakes exemplify the complexity of ecosystem responses to decreased loads of atmospheric pollutants.

Minnesota↗

USGS2014

Spatial distribution of mercury in southeastern Alaskan streams influenced by glaciers, wetlands, and salmon

Southeastern Alaska is a remote coastal-maritime ecosystem that is experiencing increased deposition of mercury (Hg) as well as rapid glacier loss. Here we present the results of the first reported survey of total and methyl Hg (MeHg) concentrations in regional streams and biota. Overall, streams draining large wetland areas had higher Hg concentrations in water, mayflies, and juvenile salmon than those from glacially-influenced or recently deglaciated watersheds. Filtered MeHg was positively correlated with wetland abundance. Aqueous Hg occurred predominantly in the particulate fraction of glacier streams but in the filtered fraction of wetland-rich streams. Colonization by anadromous salmon in both glacier and wetland-rich streams may be contributing additional marine-derived Hg. The spatial distribution of Hg in the range of streams presented here shows that watersheds are variably, yet fairly predictably, sensitive to atmospheric and marine inputs of Hg.

Alaska↗

USGS2014

Effects of urbanization on mercury deposition and accumulation in New England

We compare total mercury (HgT) loading and methylmercury (MeHg) accumulation in streams and lakes from an urbanized area (Boston, Massachusetts) to rural regions of southern New Hampshire and Maine. The maximum HgT loading, as indicated by HgT atmospheric deposition, HgT emissions, and sediment HgT concentrations, did not coincide with maximum MeHg concentrations in fish. Urbanized ecosystems were areas of high HgT loading but had low MeHg concentrations in fish. Controls on MeHg production and accumulation appeared to be related primarily to HgT loading in undeveloped areas, while ecosystem sensitivity to MeHg formation appeared to be more important in regulating accumulation of MeHg in the urban area.

Connecticut, Maine, Massachusetts, New Hampshire, ↗

USGS2014

Mercury in the nation's streams - Levels, trends, and implications

Mercury is a potent neurotoxin that accumulates in fish to levels of concern for human health and the health of fish-eating wildlife. Mercury contamination of fish is the primary reason for issuing fish consumption advisories, which exist in every State in the Nation. Much of the mercury originates from combustion of coal and can travel long distances in the atmosphere before being deposited. This can result in mercury-contaminated fish in areas with no obvious source of mercury pollution. Three key factors determine the level of mercury contamination in fish - the amount of inorganic mercury available to an ecosystem, the conversion of inorganic mercury to methylmercury, and the bioaccumulation of methylmercury through the food web. Inorganic mercury originates from both natural sources (such as volcanoes, geologic deposits of mercury, geothermal springs, and volatilization from the ocean) and anthropogenic sources (such as coal combustion, mining, and use of mercury in products and industrial processes). Humans have doubled the amount of inorganic mercury in the global atmosphere since pre-industrial times, with substantially greater increases occurring at locations closer to major urban areas. In aquatic ecosystems, some inorganic mercury is converted to methylmercury, the form that ultimately accumulates in fish. The rate of mercury methylation, thus the amount of methylmercury produced, varies greatly in time and space, and depends on numerous environmental factors, including temperature and the amounts of oxygen, organic matter, and sulfate that are present. Methylmercury enters aquatic food webs when it is taken up from water by algae and other microorganisms. Methylmercury concentrations increase with successively higher trophic levels in the food web—a process known as bioaccumulation. In general, fish at the top of the food web consume other fish and tend to accumulate the highest methylmercury concentrations. This report summarizes selected stream studies conducted by the U.S. Geological Survey (USGS) since the late 1990s, while also drawing on scientific literature and datasets from other sources. Previous national mercury assessments by other agencies have focused largely on lakes. Although numerous studies of mercury in streams have been conducted at local and regional scales, recent USGS studies provide the most comprehensive, multimedia assessment of streams across the United States, and yield insights about the importance of watershed characteristics relative to mercury inputs. Information from other environments (lakes, wetlands, soil, atmosphere, glacial ice) also is summarized to help understand how mercury varies in space and time.

Circular↗

USGS2013

Mercury and methylmercury dynamics in the hyporheic zone of an Oregon stream

The role of the hyporheic zone in mercury (Hg) cycling has received limited attention despite the biogeochemically active nature of this zone and, thus, its potential to influence Hg behavior in streams. An assessment of Hg geochemistry in the hyporheic zone of a coarse-grained island in the Coast Fork Willamette River in Oregon, USA, illustrates the spatially dynamic nature of this region of the stream channel for Hg mobilization and attenuation. Hyporheic flow through the island was evident from the water-table geometry and supported by hyporheic-zone chemistry distinct from that of the bounding groundwater system. Redox-indicator species changed abruptly along a transect through the hyporheic zone, indicating a biogeochemically reactive stream/hyporheic-zone continuum. Dissolved organic carbon (DOC), total Hg, and methylmercury (MeHg) concentrations increased in the upgradient portion of the hyporheic zone and decreased in the downgradient region. Total Hg (collected in 2002 and 2003) and MeHg (collected in 2003) were correlated with DOC in hyporheic-zone samples: r 2 =0.63 (total Hg-DOC, 2002), 0.73 (total Hg-DOC, 2003), and 0.94 (MeHg-DOC, 2003). Weaker Hg/DOC association in late summer 2002 than in early summer 2003 may reflect seasonal differences in DOC reactivity. Observed correlations between DOC and both total Hg and MeHg reflect the importance of DOC for Hg mobilization, transport, and fate in this hyporheic zone. Correlations with DOC provide a framework for conceptualizing and quantifying Hg and MeHg dynamics in this region of the stream channel, and provide a refined conceptual model of the role hyporheic zones may play in aquatic ecosystems.

Water, Air, & Soil Pollution↗

USGS2013

U.S. Geological Survey environmental health science strategy — Providing environmental health science for a changing world

Executive Summary America has an abundance of natural resources. We have bountiful clean water, fertile soil, and unrivaled national parks, wildlife refuges, and public lands. These resources enrich our lives and preserve our health and wellbeing. These resources have been maintained because of our history of respect for their value and an enduring commitment to their vigilant protection. Awareness of the social, economic, and personal value of the health of our environment is increasing. The emergence of environmentally driven diseases caused by exposure to contaminants and pathogens is a growing concern worldwide. New health threats and patterns of established threats are affected by both natural and anthropogenic changes to the environment. Human activities are key drivers of emerging (new and re-emerging) health threats. Societal demands for land and natural resources, quality of life, and economic prosperity lead to environmental change. Natural earth processes, climate trends, and related climatic events will compound the environmental impact of human activities. These environmental drivers will influence exposure to disease agents, including viral, bacterial, prion, and fungal pathogens, parasites, synthetic chemicals and substances, natural earth materials, toxins, and other biogenic compounds. The U.S. Geological Survey (USGS) defines environmental health science broadly as the interdisciplinary study of relations among the quality of the physical environment, the health of the living environment, and human health. The interactions among these three spheres are driven by human activities, ecological processes, and natural earth processes; the interactions affect exposure to contaminants and pathogens and the severity of environmentally driven diseases in animals and people. This definition provides USGS with a framework for synthesizing natural science information from across the Bureau and providing it to environmental, natural resource, agricultural, and public health managers. USGS specializes in science at the environment-health interface, by characterizing the processes that affect the interaction among the physical environment, the living environment, and people, and the resulting factors that affect ecological and human exposure to disease agents. The USGS is a Federal science agency with a broad range of natural science expertise relevant to environmental health. USGS provides scientific information and tools as a scientific basis for management and policy decisionmaking. This report describes a 10-year strategy that encompasses the portfolio of USGS environmental health science. It summarizes national environmental health priorities that USGS is best suited to address, and will serve as a strategic framework for USGS environmental health science goals, actions, and outcomes for the next decade. Implementation of this strategy is intended to aid coordination of USGS environmental health activities and to provide a focal point for disseminating information to stakeholders. The “One Health” paradigm advocated by the World Health Organization (WHO; World Health Organization, 2011), and the American Veterinary Medical Association (AVMA; American Veterinary Medical Association, 2008), among others, is based on a general recognition that the health of humans, animals, and the environment are inextricably linked. Thus, successful efforts to protect that health will require increased interdisciplinary research and increased communication and collaboration among the broader scientific and health community. This strategy is built upon that paradigm.

Circular↗

USGS2013

Global change and mercury

More than 140 nations recently agreed to a legally binding treaty on reductions in human uses and releases of mercury that will be signed in October of this year. This follows the 2011 rule in the United States that for the first time regulates mercury emissions from electricity-generating utilities. Several decades of scientific research preceded these important regulations. However, the impacts of global change on environmental mercury concentrations and human exposures remain a major uncertainty affecting the potential effectiveness of regulatory activities.

Science↗

USGS2012

Methylation of Hg downstream from the Bonanza Hg mine, Oregon

Speciation of Hg and conversion to methyl-Hg were evaluated in stream sediment, stream water, and aquatic snails collected downstream from the Bonanza Hg mine, Oregon. Total production from the Bonanza mine was >1360t of Hg, during mining from the late 1800s to 1960, ranking it as an intermediate sized Hg mine on an international scale. The primary objective of this study was to evaluate the distribution, transport, and methylation of Hg downstream from a Hg mine in a coastal temperate climatic zone. Data shown here for methyl-Hg, a neurotoxin hazardous to humans, are the first reported for sediment and water from this area. Stream sediment collected from Foster Creek flowing downstream from the Bonanza mine contained elevated Hg concentrations that ranged from 590 to 71,000ng/g, all of which (except the most distal sample) exceeded the probable effect concentration (PEC) of 1060ng/g, the Hg concentration above which harmful effects are likely to be observed in sediment-dwelling organisms. Concentrations of methyl-Hg in stream sediment collected from Foster Creek varied from 11 to 62ng/g and were highly elevated compared to regional baseline concentrations (0.11-0.82ng/g) established in this study. Methyl-Hg concentrations in stream sediment collected in this study showed a significant correlation with total organic C (TOC, R 2 =0.62), generally indicating increased methyl-Hg formation with increasing TOC in sediment. Isotopic-tracer methods indicated that several samples of Foster Creek sediment exhibited high rates of Hg-methylation. Concentrations of Hg in water collected downstream from the mine varied from 17 to 270ng/L and were also elevated compared to baselines, but all were below the 770ng/L Hg standard recommended by the USEPA to protect against chronic effects to aquatic wildlife. Concentrations of methyl-Hg in the water collected from Foster Creek ranged from 0.17 to 1.8ng/L, which were elevated compared to regional baseline sites upstream and downstream from the mine that varied from <0.02 to 0.22ng/L. Aquatic snails collected downstream from the mine were elevated in Hg indicating significant bioavailability and uptake of Hg by these snails. Results for sediment and water indicated significant methyl-Hg formation in the ecosystem downstream from the Bonanza mine, which is enhanced by the temperate climate, high precipitation in the area, and high organic matter.

Oregon↗

USGS2012

Litterfall mercury dry deposition in the eastern USA

Mercury (Hg) in autumn litterfall from predominately deciduous forests was measured in 3 years of samples from 23 Mercury Deposition Network sites in 15 states across the eastern USA. Annual litterfall Hg dry deposition was significantly higher (median 12.3 micrograms per square meter (μg/m 2 ), range 3.5–23.4 μg/m 2 ) than annual Hg wet deposition (median 9.6 μg/m 2 , range 4.4–19.7 μg/m 2 ). The mean ratio of dry to wet Hg deposition was 1.3–1. The sum of dry and wet Hg deposition averaged 21 μg/m 2 per year and 55% was litterfall dry deposition. Methylmercury was a median 0.8% of Hg in litterfall and ranged from 0.6 to 1.5%. Annual litterfall Hg and wet Hg deposition rates differed significantly and were weakly correlated. Litterfall Hg dry deposition differed among forest-cover types. This study demonstrated how annual litterfall Hg dry deposition rates approximate the lower bound of annual Hg dry fluxes.

Environmental Pollution↗

USGS2012

USGS Environmental health science strategy: providing environmental health science for a changing world: Public review release

America has an abundance of natural resources. We have bountiful clean water, fertile soil, and unrivaled national parks, wildlife refuges, and public lands. These resources enrich our lives and preserve our health and wellbeing. These resources have been maintained because of our history of respect for their value and an enduring commitment to their vigilant protection. Awareness of the social, economic, and personal value of the health of our environment is increasing. The emergence of environmentally driven diseases caused by environmental exposure to contaminants and pathogens is a growing concern worldwide. New health threats and patterns of established threats are affected by both natural and anthropogenic changes to the environment. Human activities are key drivers of emerging (new and re-emerging) health threats. Societal demands for land and natural resources, a better quality of life, improved economic prosperity, and the environmental impacts associated with these demands will continue to increase. Natural earth processes, climate trends, and related climatic events will add to the environmental impact of human activities. These environmental drivers will influence exposure to disease agents, including viral, bacterial, prion, and fungal pathogens, parasites, natural earth materials, toxins and other biogenic compounds, and synthetic chemicals and substances. The U.S. Geological Survey (USGS) defines environmental health science broadly as the interdisciplinary study of relations among the quality of the physical environment, the health of the living environment, and human health. The interactions among these three spheres are driven by human activities, ecological processes, and natural earth processes; the interactions affect exposure to contaminants and pathogens and the severity of environmentally driven diseases in animals and people. This definition provides USGS with a framework for synthesizing natural science information from across the Bureau and providing it to environmental, natural resource, agricultural, and public-health managers. The USGS is a Federal science agency with a broad range of natural science expertise relevant to environmental health. USGS provides scientific information and tools as a scientific basis for management and policy decision making. USGS specializes in science at the environment-health interface, by characterizing the processes that affect the interaction among the physical environment, the living environment, and people, and the resulting factors that affect ecological and human exposure to disease agents. This report describes a 10-year strategy that encompasses the portfolio of USGS environmental health science. It summarizes national environmental health priorities that USGS is best suited to address, and will serve as a strategic framework for USGS environmental health science goals, actions, and outcomes for the next decade. Implementation of this strategy is intended to aid coordination of USGS environmental health activities and to provide a focal point for disseminating information to stakeholders. The "One Health" paradigm advocated by the World Health Organization (WHO, 2011), and the American Veterinary Medicine Association (AVMA, 2008), among others, is based on a general recognition that the health of humans, animals, and the environment are inextricably linked. Thus, successful efforts to protect that health will require increased interdisciplinary research and increased communication and collaboration among the broader scientific and health community. This strategy is built upon that paradigm. The vision, mission, and five cornerstone goals of the USGS Environmental Health Science Strategy were developed with significant input from a wide range of stakeholders. Vision - The USGS is a premier source of the environmental health science needed to safeguard the health of the environment, fish, wildlife, and people. Mission - The mission of USGS in environmental health science is to contribute scientific information to environmental, natural resource, agricultural, and public-health managers, who use that science to support sound decision making. USGS provides the science to: - Goal 1: Identify, prioritize, and detect contaminants and pathogens of emerging environmental concern. - Goal 2: Reduce the impact of contaminants on the environment, fish, wildlife, and people. - Goal 3: Reduce the impact of pathogens on the environment, fish, wildlife, and people. - Goal 4: Discover the complex interactions and combined effects of exposure to contaminants and pathogens. - Goal 5: Prepare for and respond to environmental impacts and related health threats of natural and anthropogenic disasters. Goals 1 through 4 are intended to provide science to address environmental health threats in a logical order, from informing prevention and preparedness, to supporting systematic management response to environmental health issues. Goal 4 addresses the interaction among contaminants and pathogens, an issue of emerging concern in environmental health science. Goal 5 acknowledges the fact that natural and anthropogenic disasters can cause immediate and prolonged adverse environmental health threats. This strategy proposes that USGS take the following strategic science actions to achieve each of the five goals of this strategy: Goal 1: Identify, prioritize, and detect contaminants and pathogens of emerging environmental concern. - Strategic Science Action 1. - Prioritize contaminants and pathogens of emerging concern to guide research, detection, and management activities. - Strategic Science Action 2. - Conduct surveillance and monitoring to provide early warning of emerging health threats. - Strategic Science Action 3. - Develop approaches and tools that identify vulnerable environmental settings, ecosystems, and species. Goal 2: Reduce the impact of contaminants on the environment, fish, wildlife, and people. - Strategic Science Action 1. - Systematically characterize the sources, occurrence, transport and fate of environmental contaminants to guide efforts to manage and mitigate contamination. - Strategic Science Action 2. - Evaluate the threats of contamination on the health of the environment, fish, wildlife, and people, and inform the associated management and protection efforts. - Strategic Science Action 3. - Characterize potential human exposure to support establishment of health-based standards or guidelines and contamination-reduction efforts. Goal 3: Reduce the impact of pathogens on the environment, fish, wildlife, and people. - Strategic Science Action 1. - Determine the biotic and abiotic factors that control the ecology of infectious diseases affecting natural populations of aquatic and terrestrial species and potential transmission to other animals and humans. - Strategic Science Action 2. - Establish how natural and anthropogenic environmental changes affect the distribution and severity of infectious diseases in natural populations of aquatic and terrestrial species and potential transmission to other animals and humans. - Strategic Science Action 3. - Develop surveillance systems to identify changing patterns of disease activity in priority geographic areas. Goal 4: Discover the complex interactions and combined effects of exposure to contaminants and pathogens. - Strategic Science Action 1. - Identify how exposure to one class of disease agents (contaminants or pathogens) can make an organism more susceptible to effects from exposure to the other class of disease agents. - Strategic Science Action 2. - Implement interdisciplinary studies that characterize the effects of combined exposure to pathogens and contaminants. Goal 5: Prepare for and respond to the environmental impacts and related health threats of natural and anthropogenic disasters. - Strategic Science Action 1. - Establish a formal interdisciplinary science capability to rapidly assess the environmental health risks associated with disasters. - Strategic Science Action 2. - Enhance methods to anticipate, prepare for, and identify environmental, ecological, and related health impacts of future disasters. This strategy is one of seven USGS science strategies developed concurrently: - Climate and Land Use Change - Core Science Systems - Ecosystems - Energy and Mineral Resources - Environmental Health - Natural Hazards - Water. This strategy describes how USGS will address the highest priority environmental health issues facing the Nation. The ultimate intended outcome of this science strategy is prevention and reduction of adverse impacts to the quality of the environment, the health of our living resources, and human health. Communication with, and receiving input from, partners and stakeholders regarding their science needs is essential for successful implementation of this strategy. It is incumbent on USGS to reach out to all stakeholders to ensure that USGS efforts are focused on the highest priority environmental health issues and that products are provided in the most timely and usable form to all those who can use them. USGS must reach out to the scientific community, internally and externally, to ensure that our efforts are integrated with and take full advantage of the activities of others.

Open-File Report↗

USGS2011

Mercury export from the Yukon River Basin and potential response to a changing climate

We measured mercury (Hg) concentrations and calculated export and yield from the Yukon River Basin (YRB) to quantify Hg flux from a large, permafrost-dominated, high-latitude watershed. Exports of Hg averaged 4400 kg Hg yr -1 . The average annual yield for the YRB during the study period was 5.17 μg m -2 yr -1 , which is 3–32 times more than Hg yields reported for 8 other major northern hemisphere river basins. The vast majority (90%) of Hg export is associated with particulates. Half of the annual export of Hg occurred during the spring with about 80% of 34 samples exceeding the U.S. EPA Hg standard for adverse chronic effects to biota. Dissolved and particulate organic carbon exports explained 81% and 50%, respectively, of the variance in Hg exports, and both were significantly ( p < 0.001) correlated with water discharge. Recent measurements indicate that permafrost contains a substantial reservoir of Hg. Consequently, climate warming will likely accelerate the mobilization of Hg from thawing permafrost increasing the export of organic carbon associated Hg and thus potentially exacerbating the production of bioavailable methylmercury from permafrost-dominated northern river basins.

Alaska↗

USGS2011

Mercury distribution and lipid oxidation in fish muscle: Effects of washing and isoelectric protein precipitation

Nearly all the mercury (Hg) in whole muscle from whitefish ( Coregonus clupeaformis ) and walleye ( Sander vitreus ) was present as methyl mercury (MeHg). The Hg content in whole muscle from whitefish and walleye was 0.04–0.09 and 0.14–0.81 ppm, respectively. The myofibril fraction contained approximately three-fourths of the Hg in whitefish and walleye whole muscle. The sarcoplasmic protein fraction (e.g., press juice) was the next most abundant source of Hg. Isolated myosin, triacylglycerols, and cellular membranes contained the least Hg. Protein isolates prepared by pH shifting in the presence of citric acid did not decrease Hg levels. Addition of cysteine during washing decreased the Hg content in washed muscle probably through the interaction of the sulfhydryl group in cysteine with MeHg. Primary and secondary lipid oxidation products were lower during 2 °C storage in isolates prepared by pH shifting compared to those of washed or unwashed mince from whole muscle. This was attributed to removing some of the cellular membranes by pH shifting. Washing the mince accelerated lipid peroxide formation but decreased secondary lipid oxidation products compared to that of the unwashed mince. This suggested that there was a lipid hydroperoxide generating system that was active upon dilution of aqueous antioxidants and pro-oxidants.

Journal of Agricultural and Food Chemistry↗

USGS2011

Removal of inorganic mercury and methylmercury from surface waters following coagulation of dissolved organic matter with metal-based salts

The presence of inorganic mercury (IHg) and methylmercury (MeHg) in surface waters is a health concern worldwide. This study assessed the removal potential use of metal-based coagulants as a means to remove both dissolved IHg and MeHg from natural waters and provides information regarding the importance of Hg associations with the dissolved organic matter (DOM) fraction and metal hydroxides. Previous research indicated coagulants were not effective at removing Hg from solution; however these studies used high concentrations of Hg and did not reflect naturally occurring concentrations of Hg. In this study, water collected from an agricultural drain in the Sacramento-San Joaquin Delta was filtered to isolate the dissolved organic matter (DOM) fraction. The DOM was then treated with a range of coagulant doses to determine the efficacy of removing all forms of Hg from solution. Three industrial-grade coagulants were tested: ferric chloride, ferric sulfate, and polyaluminum chloride. Coagulation removed up to 85% of DOM from solution. In the absence of DOM, all three coagulants released IHg into solution, however in the presence of DOM the coagulants removed up to 97% of IHg and 80% of MeHg. Results suggest that the removal of Hg is mediated by DOM-coagulant interactions. There was a preferential association of IHg with the more aromatic, higher molecular weight fraction of DOM but no such relationship was found for MeHg. This study offers new fundamental insights regarding large-scale removal of Hg at environmentally relevant regarding large-scale removal of Hg at environmentally relevant concentrations.

Science of the Total Environment↗

USGS2011

Source apportionment of atmospheric trace gases and particulate matter--Comparison of log-ratio and traditional approaches

No abstract available.

Conference Paper↗

USGS2010

Comparison of atmospheric mercury speciation and deposition at nine sites across central and eastern North America

This study presents >5 cumulative years of tropospheric mercury (Hg) speciation measurements, over the period of 2003–2009, for eight sites in the central and eastern United States and one site in coastal Puerto Rico. The purpose of this research was to identify local and regional processes that impact Hg speciation and deposition (wet + dry) across a large swath of North America. Sites sampled were selected to represent both a wide range of mercury exposure and environmental conditions. Seasonal mean concentrations of elemental Hg (1.27 ± 0.31 to 2.94 ± 1.57 ng m−3; x ± s), reactive gaseous mercury (RGM; 1.5 ± 1.6 to 63.3 ± 529 pg m−3), and fine particulate Hg (1.2 ± 1.4 to 37.9 ± 492 pg m−3) were greatest at sites impacted by Hg point sources. Diel bin plots of Hgo and RGM suggest control by a variety of local/regional processes including impacts from Hg point sources and boundary layer/free tropospheric interactions as well as from larger‐scale processes affecting Hg speciation (i.e., input of the global Hg pool, RGM formed from oxidation of Hgo by photochemical compounds at coastal sites, and elemental Hg depletion during periods of dew formation). Comparison of wet Hg deposition (measured), RGM and fine particulate Hg dry deposition (calculated using a multiple resistance model), and anthropogenic point source emissions varied significantly between sites. Significant correlation between emission sources and dry deposition was observed but was highly dependant upon inclusion of data from two sites with exceptionally high deposition. Findings from this study highlight the importance of environmental setting on atmospheric Hg cycling and deposition rates.

Journal of Geophysical Research↗

USGS2010

The role of groundwater transport in aquatic mercury cycling

Mercury, which is transported globally by atmospheric pathways to remote aquatic environments, is a ubiquitous contaminant at very low (nanograms Hg per liter) aqueous concentrations. Until recently, however, analytical and sampling techniques were not available for freshwater systems to quantify the actual levels of mercury concentrations without introducing significant contamination artifacts. Four different sampling strategies were used to evaluate ground water flow as a mercury source and transport mechanism within aquatic systems. The sampling strategies employ ultraclean techniques to determine mercury concentrations in groundwater and pore water near Pallette Lake, Wisconsin. Ambient groundwater concentrations are about 2–4 ng Hg L −1 , whereas pore waters near the sediment/water interface average about 12 ng Hg L −1 , emphasizing the importance of biogeochemical processes near the interface. Overall, the groundwater system removes about twice as much mercury (1.5 g yr −1 ) as it contributes (0.7 g yr −1 ) to Pallette Lake. About three fourths of the groundwater mercury load is recycled, thought to be derived from the water column.

Wisconsin↗

USGS2010

Transient hydrogeological controls on the chemistry of a seepage lake

A solute mass balance method was used to estimate groundwater inflow and outflow rates for Nevins Lake, Michigan, a seepage lake in the upper peninsula that historically has shown extremely variable water chemistry compared with most other seepage lakes. A 4-year study (1989–1992) of the hydrology and geochemistry of Nevins Lake and its contiguous groundwater system revealed that changes in the mass of dissolved solutes are the result of annual hydraulic gradient reversals. A pronounced acidification of Nevins Lake from 1986 to 1988 was likely caused by drought-induced diminished groundwater inflow rates. In this study, dissolved calcium (the major cation in water of Nevins Lake, groundwater, and precipitation) was used for estimating mass flow rates. During the 1989–1992 period, Nevins Lake showed a reproducible annual cycle in calcium mass. Immediately following spring snowmelt and the resulting hydraulic gradient reversal, the mass of dissolved calcium in the lake increases rapidly, and then it decreases steadily throughout the summer and early fall, at which time the lake becomes hydraulically mounded and receives no groundwater inflow. Groundwater flow rates estimated by the solute mass balance method are sensitive to assumed solute concentrations in discharging groundwater. Pore water samples from the lake bed are shown to be more representative of water discharging to the lake than are samples from piezometers near the lake shore, but spatial and temporal variability in pore water chemistry must be considered. Stable isotope analyses ( 18 O and 2 H) of lake water, groundwater, and pore water samples show that water discharging to Nevins Lake in the spring is entirely recycled lake water, and no groundwater derived from terrestrial recharge reaches the lake. The conceptual model formulated during this study linking lake chemistry and the contiguous groundwater system and general groundwater flow patterns surrounding highly transient lake systems are likely transferable to other similar systems.

Michigan↗