Daniel Obrist

Daniel Obrist
University of Massachusetts Lowell | UML · Department of Environmental, Earth and Atmospheric Sciences

PhD

About

145
Publications
22,257
Reads
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4,875
Citations
Introduction
My research combines atmospheric chemistry and surface-atmospheric exchange processes with terrestrial biogeochemistry to understand the fate of persistent pollutants in the biosphere. I am particularly interested in the cycling of mercury and organic pollutants in ecosystems ranging from the arctic tundra to temperature forests and desert shrub steppes. I am a Professor and Chairman of the Department of Environmental, Earth and Atmospheric Sciences at UMass Lowell.
Additional affiliations
January 2007 - present
University of Nevada, Reno
Position
  • Faculty Member

Publications

Publications (145)
Poster
Behavior and transport of mercury in the soil profiles
Conference Paper
The fate of mercury in soils and litter during carbon decomposition: relationships between Hg0 and CO2 emissions in the laboratory and field and a litter mass balance study
Poster
Assessing the Fate of Litter Mercury during Decomposition under Controlled Laboratory Conditions
Conference Paper
Elemental Mercury Depletion in Soils: An Unaccounted Mercury Sink?
Article
Full-text available
Anthropogenic mercury (Hg) emissions have driven marked increases in Arctic Hg levels, which are now being impacted by regional warming, with uncertain ecological consequences. This Review presents a comprehensive assessment of the present-day total Hg mass balance in the Arctic. Over 98% of atmospheric Hg is emitted outside the region and is trans...
Chapter
Mercury, emitted by both natural and anthropogenic sources, is a toxic chemical that cycles throughout the cryosphere. Given its long residence time in the atmosphere, mercury can travel long distances making it a global pollutant. Long-term measurements of atmospheric mercury around polar regions demonstrate, for the most part, decreasing concentr...
Article
Salt marsh estuaries serve as sources and sinks for nutrients and elements to and from estuarine water, which enhances and alleviates watershed fluxes to the coastal ocean. We assessed sources and sinks of mercury in the intertidal Plum Island Sound estuary in Massachusetts, the largest salt marsh estuary of New England, using 25-km spatial water s...
Article
Mercury (Hg) is an environmental toxicant dangerous to human health and the environment. Its anthropogenic emissions are regulated by global, regional, and local policies. Here, we investigate Hg sources in the coastal city of Boston, the third largest metropolitan area in the Northeastern United States. With a median of 1.37 ng m-3, atmospheric Hg...
Article
Full-text available
Significance Direct measurements of atmospheric deposition of gaseous elemental mercury (GEM) over a temperate forest showed a pronounced annual deposition of 25.1 µg ⋅ m ⁻² , which dominated as a source of mercury. GEM deposition was five times greater than wet deposition and three times greater than litterfall deposition, which has been used as a...
Article
Mercury (Hg) is a global pollutant that emits in large quantities to the atmosphere (>6,000–8,000 Mg Hg per year) through anthropogenic activities, biomass burning, geogenic degassing and legacy emissions from land and oceans. Up to two-thirds of terrestrial Hg emissions are deposited back onto land, predominantly through vegetation uptake of Hg. I...
Article
Atmospheric deposition is an important source of trace metals to surface environments, but knowledge about plant bioavailability of recently deposited metals and their fate in the soil-plant system is limited. We performed a fully factorial soil and atmosphere exposure experiment with three vegetables (radish, lettuce, and soybean). Treatments incl...
Article
Redox reactions are important for cycling of carbon (C) in soils frequently subject to fluctuations in redox conditions, such as wetland soils, which contribute around one third of the global terrestrial C reservoir. Priming effects (PE), induction of changes in C mineralization due to additions of energy-rich organic carbon (OC) substrates, have b...
Article
Full-text available
Understanding the processes that influence and control carbon cycling in Arctic tundra ecosystems is essential for making accurate predictions about what role these ecosystems will play in potential future climate change scenarios. Particularly, air–surface fluxes of methane and carbon dioxide are of interest as recent observations suggest that the...
Article
Full-text available
Measurements of land-air mercury (Hg) exchanges over vegetated surfaces are needed to further constrain Hg fluxes over vegetated terrestrial surfaces. Yet, knowledge of land-air Hg dynamics in alpine grasslands remains poor. Hg fluxes over an alpine meadow were measured throughout a full vegetation period in the central Tibetan Plateau (TP). This T...
Preprint
Full-text available
Understanding the processes that influence and control carbon cycling in Arctic tundra ecosystems is essential for making accurate predictions about what role these ecosystems will play in potential future climate change scenarios. Particularly, air–surface fluxes of methane and carbon dioxide are of interest as recent observations suggest that the...
Article
Full-text available
The tundra plays a pivotal role in the Arctic mercury (Hg) cycle by storing atmospheric Hg deposition and shuttling it to the Arctic Ocean. A recent study revealed that 70 % of the atmospheric Hg deposition to the tundra occurs through gaseous elemental mercury (GEM or Hg(0)) uptake by vegetation and soils. Processes controlling land–atmosphere exc...
Article
Full-text available
To simulate global mercury (Hg) dynamics in chemical transport models (CTMs), surface-atmosphere exchange of gaseous elemental mercury, Hg0, is often parameterized based on resistance-based dry deposition schemes coupled with a...
Article
Bromine atoms play a central role in atmospheric reactive halogen chemistry, depleting ozone and elemental mercury, thereby enhancing deposition of toxic mercury, particularly in the Arctic near-surface troposphere. However, direct bromine atom measurements have been missing to date, due to the lack of analytical capability with sufficient sensitiv...
Article
Full-text available
The tundra plays a pivotal role in the Arctic mercury (Hg) cycling by storing atmospheric Hg deposition and shuttling it to the Arctic Ocean. A recent study revealed that 70 % of the atmospheric Hg deposition to the tundra occurs by gaseous elemental mercury (GEM or Hg(0)) uptake by vegetation and soils. Processes controlling land – atmosphere exch...
Article
Full-text available
A total of 1360 weeks of mercury (Hg) wet deposition data were collected by the state of Alaska Department of Environmental Conservation and the U.S. National Park Service across five stations spanning up to 8 years. Here, we analyze concentration patterns, source regions, and seasonal and annual Hg deposition loadings across these five sites in Al...
Article
Vegetation uptake of atmospheric mercury (Hg) is an important mechanism enhancing atmospheric Hg deposition via litterfall and senescence. We here report Hg concentrations and pool sizes of different plant functional groups and plant species across nine tundra sites in northern Alaska. Significant spatial differences were observed in bulk vegetatio...
Article
Full-text available
A total of 1,360 weeks of mercury (Hg) wet deposition data were collected by the State of Alaska Department of Environmental Conservation and the U.S. National Park Service, across five stations covering up to eight years. Here, we analyze concentration patterns, source regions, and seasonal and annual deposition loadings across these five sites in...
Article
Mercury is a global pollutant that has been emitted and released into the environment from numerous human activities including coal combustion, artisanal gold mining, mining of other metals, and chemical production, resulting in the elevated exposure of humans and wildlife throughout the world. Mercury contamination has been recognized by the inter...
Article
Tundra soils serve as major sources of mercury (Hg) input to the Arctic Ocean via river runoff and coastal erosion; yet little information is available on tundra soil Hg concentrations, pool sizes, origins, and dynamics. We present a detailed investigation of Hg in the active layer (upper ~100 cm subject to seasonal thaw) of tundra soils across 11...
Article
Full-text available
In the Arctic, the snowpack forms the major interface between atmospheric and terrestrial cycling of mercury (Hg), a global pollutant. We investigated Hg dynamics in an interior Arctic tundra snowpack in northern Alaska during two winter seasons. Using a snow tower system to monitor Hg trace gas exchange, we observed consistent concentration declin...
Article
Full-text available
Anthropogenic mercury emissions are transported through the atmosphere as gaseous elemental mercury (Hg(0)) before they are deposited to Earth’s surface. Strong seasonality in atmospheric Hg(0) concentrations in the Northern Hemisphere has been explained by two factors: anthropogenic Hg(0) emissions are thought to peak in winter due to higher energ...
Article
Full-text available
We review recent progress in our understanding of the global cycling of mercury (Hg), including best estimates of Hg concentrations and pool sizes in major environmental compartments and exchange processes within and between these reservoirs. Recent advances include the availability of new global datasets covering areas of the world where environme...
Article
Full-text available
In the Arctic, the snowpack forms the major interface between atmospheric and terrestrial mercury (Hg) cycling, a global pollutant. In this study, we investigated Hg dynamics in an interior arctic tundra snowpack in northern Alaska during two snow seasons. Using a snow tower system and soil wells to monitor trace gas exchange of Hg, we observed con...
Poster
Full-text available
This experiment was to investigate Hg, carbon, and trace element mobility in frozen permafrost tundra soils using cores obtained from the northern Alaskan slope during the summer of 2016. The goal was to measure the amount of Hg leachate from mineral-rich, transitional and permanent permafrost soils, and asses the relevant factors related to mobili...
Article
Anthropogenic activities have led to large-scale mercury (Hg) pollution in the Arctic. It has been suggested that sea-salt-induced chemical cycling of Hg (through ‘atmospheric mercury depletion events’, or AMDEs) and wet deposition via precipitation are sources of Hg to the Arctic in its oxidized form (Hg(ii)). However, there is little evidence for...
Article
The reduction of emissions of mercury is a declared aim of the Minamata Convention, a UN treaty designed to protect human health and the environment from adverse effects of mercury. To assess the effectiveness of the convention in the future, better constraints about the current mercury emissions is a premise. In our study, we applied a top-down ap...
Article
The behavior of iron (Fe)-bound organic carbon (OC) under anoxic conditions in natural soils and sediments represents a critical knowledge gap for understanding the biogeochemical cycles of OC and Fe. In this study, we investigated the dynamics of Fe and OC in four forest soils in the presence of the dissimilatory Fe-reducing bacterium, Shewanella...
Poster
Full-text available
Adequate parameterization of atmosphere-surface exchange processes of gaseous elemental mercury (Hg0) is an essential component of chemical transport models (CTMs) to better simulate and understand the global biogeochemical cycling of mercury (Hg). In CTMs such as GEOS-Chem, the existing atmosphere-surface exchange parameterization of Hg0 has large...
Article
Forest biomass and soils represent some of the largest reservoirs of actively cycling mercury (Hg) on Earth, but many uncertainties exist regarding the source and fate of Hg in forest ecosystems. We systematically characterized stable isotope compositions of Hg in foliage, litter, and mineral soil horizons across 10 forest sites in the contiguous U...
Article
Full-text available
Iron oxide minerals play an important role in stabilizing organic carbon (OC) and regulating the biogeochemical cycles of OC on the earth surface. To predict the fate of OC, it is essential to understand the amount, spatial variability, and characteristics of Fe-bound OC in natural soils. In this study, we investigated the concentrations and charac...
Article
Full-text available
Western NorthAmerica is a region defined by extreme gradients in geomorphology and climate,which support a diverse array of ecological communities and natural resources. The region also has extreme gradients in mercury (Hg) contamination due to a broad distribution of inorganic Hg sources. These diverse Hg sources and a varied landscape create a un...
Article
Full-text available
Understanding the emissions of mercury (Hg) from wildfires is important for quantifying the global atmospheric Hg sources. Emissions of Hg from soils resulting from wildfires in the Western United States was estimated for the 2000 to 2013 period, and the potential emission of Hg from forest soils was assessed as a function of forest type and soil-h...
Article
Full-text available
Iron oxide minerals play an important role in stabilizing organic carbon (OC) and regulating the biogeochemical cycles of OC on the earth surface. To predict the fate of OC, it is essential to completely understand the amount, spatial variability and characteristics of Fe-bound OC in natural soils. In this study, we investigated the concentrations...
Article
Despite 30 years of study, gaseous elemental mercury (Hg(0)) exchanges between terrestrial surfaces and the atmosphere still remain uncertain. We compiled data from 132 studies, including 1,290 reported fluxes from more than 200,000 individual measurements, into a database to statistically examine flux magnitudes and controls. We found that fluxes...
Article
Mercury is an important environmental pollutant that can enter the food chain, can pose threats to ecosystems and human health, and is globally distributed via atmospheric transport. In the atmosphere, reactive forms of mercury (Hg(II) species can be produced by oxidation of the dominant atmospheric species (gaseous elemental mercury (GEM)). This o...
Article
Full-text available
Biweekly snowpack core samples were collected at seven sites along two elevation gradients in the Tahoe Basin during two consecutive snow years to evaluate total wintertime snowpack accumulation of nutrients and pollutants in a high-elevation watershed of the Sierra Nevada. Additional sampling of wet deposition and detailed snow pit profiles were c...
Article
Centuries of anthropogenic releases have resulted in a global legacy of mercury (Hg) contamination. Here we use a global model to quantify the impact of uncertainty in Hg atmospheric emissions and cycling on anthropogenic enrichment and discuss implications for future Hg levels. The plausibility of sensitivity simulations is evaluated against multi...
Article
Full-text available
Atmospheric mercury (Hg) measurements using the Tekran® analytical system from five high-elevation sites (1400–3200 m elevation), one in Asia and four in the western US, were compiled over multiple seasons and years, and these data were compared with the GEOS-Chem global model. Mercury data consisted of gaseous elemental Hg (GEM) and "reactive Hg"...
Article
A newly developed pulsed cavity ring-down spectroscopy (CRDS) system for measuring atmospheric gaseous elemental mercury (GEM) concentrations at high temporal resolution (25 Hz) was used to successfully conduct the first eddy covariance (EC) flux measurements of GEM. GEM is the main gaseous atmospheric form, and quantification of bidirectional exch...
Article
Full-text available
Bi-weekly snowpack core samples were collected at seven sites along two elevation gradients in the Tahoe Basin during two consecutive snow years to evaluate total wintertime snowpack accumulation of nutrients and pollutants in a high elevation watershed of the Sierra Nevada. Additional sampling of wet deposition and detailed snow pit profiles was c...
Conference Paper
The surface-atmosphere exchange of mercury (Hg) is temporally and spatially dynamic and soils can serve as large reservoirs for atmospheric deposition of Hg. However, due to semi-volatile behavior of elemental Hg (Hg0) and reduction processes, Hg0 can re-emit to the atmosphere, undergoing a bi-directional flux. These processes, particularly re-emis...
Conference Paper
The surface-atmosphere exchange of mercury (Hg) is temporally and spatially dynamic and soils can serve as large reservoirs for atmospheric deposition of Hg. However, due to semi-volatile behavior of elemental Hg (Hg0) and reduction processes, Hg0 can re-emit to the atmosphere, undergoing a bi-directional flux. These processes, particularly re-emis...