Indiana Geological and Water Survey

Abstract The evolution of porosity in shales with increasing maturity was examined in a suite of five New Albany Shale samples spanning a maturity range from immature (vitrinite reflectance, Ro 0.35%) to postmature (Ro 1.41%). Devonian to lower Mississippian New Albany Shale samples from the Illinois Basin used in this study contain marine type II kerogen having total organic carbon contents from 1.2 to 13.0 wt. %. Organic petrology, CO2 and N2 low-pressure adsorption, and mercury intrusion capillary pressure techniques were used to quantify pore volumes, pore sizes, and pore-size distributions. Increasing maturity of the New Albany Shale is paralleled by many changes in the characteristics of porosity. The total porosity of 9.1 vol. % in immature New Albany Shale decreases to 1.5 vol. % in the late mature sample, whereas total pore volumes decrease from 0.0365 to 0.0059 cm3/g in the same sequence. Reversing the trend at even higher maturity, the postmature New Albany Shale exhibits higher porosity and larger total pore volumes compared to the late mature sample. With increasing maturity, changes in total porosity and total pore volumes are accompanied by changes in pore-size distributions and relative proportions of micropores, mesopores, and macropores. Porosity-related variances are directly related to differences in the amount and character of the organic matter and mineralogical composition, but maturity exerts the dominant control upon these characteristics. We conclude that organic matter transformation due to hydrocarbon generation and migration is a pivotal cause of the observed porosity differences.

Two Pennsylvanian coal samples (Spr326 and Spr879-IN1) and two Upper Devonian-Mississippian shale samples (MM1 and MM3) from the Illinois Basin were studied with regard to their porosity and pore accessibility. Shale samples are early mature stage as indicated by vitrinite reflectance (Ro) values of 0.55% for MM1 and 0.62% for MM3. The coal samples studied are of comparable maturity to the shale samples, having vitrinite reflectance of 0.52% (Spr326) and 0.62% (Spr879-IN1). Gas (N2 and CO2) adsorption and small-angle and ultrasmall-angle neutron scattering techniques (SANS/USANS) were used to understand differences in the porosity characteristics of the samples. The results demonstrate that there is a major difference in mesopore (2–50 nm) size distribution between the coal and shale samples, while there was a close similarity in micropore (<2 nm) size distribution. Micropore and mesopore volumes correlate with organic matter content in the samples. Accessibility of pores in coal is pore-size specific and can vary significantly between coal samples; also, higher accessibility corresponds to higher adsorption capacity. Accessibility of pores in shale samples is low.

Abstract An integrated nomenclature scheme is proposed to capture the inherent heterogeneity of fine-grained sedimentary rocks at the 102 to 10−3 mm scale and to assist the evaluation of these rocks as sinks of organic carbon, barriers to fluid flows, and reservoirs of oil and gas. This scheme incorporates previous knowledge and the latest field, petrographic, and laboratory observations. We propose to name fine-grained sedimentary rocks using a root term based on their texture (grain size), which is modified by description of bedding, composition, and grain origin. Regarding texture, we suggest the use of “mudstone” as a class name for the entire spectrum of fine-grained sedimentary rocks. We define mudstone as a rock in which more than fifty percent of its grains are mud (clay and silt) size (< 62.5 µm). Similar to the approach used for the description of sandstone texture, mudstone texture can be refined by a “coarse,” “medium,” or “fine” size-range term. Regarding bedding, we follow Campbell's (1967) genetic approach to define laminae, laminasets, and beds, and describe lamina geometry, continuity, and shape. Regarding composition, we propose terms such as “siliceous,” “calcareous,” “argillaceous,” and “carbonaceous” to capture differences in rock composition. The name of a mudstone can be further modified by additional attributes that detail the form and origin of the rock components. Application of this approach to the Cretaceous Eagle Ford Shale illustrates the variability typically present in mudstone successions and demonstrates how our detailed characterization can be used to decipher and predict rock properties of economic interest.

Microbial methane accumulations have been discovered in multiple coal-bearing basins over the past two decades. Such discoveries were originally based on unique biogenic signatures in the stable isotopic composition of methane and carbon dioxide. Basins with microbial methane contain either low-maturity coals with predominantly microbial methane gas or uplifted coals containing older, thermogenic gas mixed with more recently produced microbial methane. Recent advances in genomics have allowed further evaluation of the source of microbial methane, through the use of high-throughput phylogenetic sequencing and fluorescent in situ hybridization, to describe the diversity and abundance of bacteria and methanogenic archaea in these subsurface formations. However, the anaerobic metabolism of the bacteria breaking coal down to methanogenic substrates, the likely rate-limiting step in biogenic gas production, is not fully understood. Coal molecules are more recalcitrant to biodegradation with increasing thermal maturity, and progress has been made in identifying some of the enzymes involved in the anaerobic degradation of these recalcitrant organic molecules using metagenomic studies and culture enrichments. In recent years, researchers have attempted lab and subsurface stimulation of the naturally slow process of methanogenic degradation of coal.

This paper describes a soil moisture data set from the 82,000 km 2 Murrumbidgee River Catchment in southern New South Wales, Australia. Data have been archived from the Murrumbidgee Soil Moisture Monitoring Network (MSMMN) since its inception in September 2001. The Murrumbidgee Catchment represents a range of conditions typical of much of temperate Australia, with climate ranging from semiarid to humid and land use including dry land and irrigated agriculture, remnant native vegetation, and urban areas. There are a total of 38 soil moisture‐monitoring sites across the Murrumbidgee Catchment, with a concentration of sites in three subareas. The data set is composed of 0–5 (or 0–8), 0–30, 30–60, and 60–90 cm average soil moisture, soil temperature, precipitation, and other land surface model forcing at all sites, together with other ancillary data. These data are available on the World Wide Web at http://www.oznet.org.au .

Fourier transform infrared spectroscopy (FTIR) can provide crucial information on the molecular structure of organic and inorganic components and has been used extensively for chemical characterization of geological samples in the past few decades. In this paper, recent applications of FTIR in the geological sciences are reviewed. Particularly, its use in the characterization of geochemistry and thermal maturation of organic matter in coal and shale is addressed. These investigations demonstrate that the employment of high-resolution micro-FTIR imaging enables visualization and mapping of the distributions of organic matter and minerals on a micrometer scale in geological samples, and promotes an advanced understanding of heterogeneity of organic rich coal and shale. Additionally, micro-FTIR is particularly suitable for in situ, non-destructive characterization of minute microfossils, small fluid and melt inclusions within crystals, and volatiles in glasses and minerals. This technique can also assist in the chemotaxonomic classification of macrofossils such as plant fossils. These features, barely accessible with other analytical techniques, may provide fundamental information on paleoclimate, depositional environment, and the evolution of geological (e.g., volcanic and magmatic) systems.

Abstract A review of the literature indicates that numerous microorganisms can reduce ferric iron during the metabolism of organic matter. In most cases, the reduction of ferric iron appears to be enzymatically catalyzed and, in some instances, may be coupled to an electron transport chain that could generate ATP. However, the physiology and biochemistry of ferric iron reduction are poorly understood. In pure culture, ferric iron‐reducing organisms metabolize fermentable substrates, such as glucose, primarily to typical fermentation products, and transfer only a minor portion of the electron equivalents in the fermentable substrates to ferric iron. However, fermentation products, especially hydrogen and acetate, may be important electron donors for ferric iron reduction in natural environments. The ability of some organisms to couple the oxidation of fermentation products to the reduction of ferric iron means that it is possible for a food chain of iron‐reducing organisms to completely mineralize nonrecalcitrant organic matter with ferric iron as the sole electron acceptor. The rate and extent of ferric iron reduction depend on the forms of ferric iron that are available. Most of the ferric iron in sediments is resistant to microbial reduction. Ferric iron‐reducing organisms can exclude sulfate reduction and methane production from the zone of ferric iron reduction in sediments by outcompeting sulfate‐reducing and methanogenic food chains for organic matter when ferric iron is available as amorphic ferric oxyhydroxide. There are few quantitative estimates of the rates of ferric iron reduction in natural environments, but there is evidence that ferric iron reduction can be an important pathway for organic matter decomposition in some environments. There is a strong need for further study on all aspects of microbial reduction of ferric iron.

This paper presents a method, mostly empirical, of deriving synthetic unit‐graphs. It is of assistance in the study and analysis of runoff‐characteristics of drainage‐areas of from 10 to 10,000 square miles for which stream‐flow records may or may not be available. No attempt has been made to eliminate the use or need of judgment and experience in such studies. The “lag” or time from center of mass of rainfall to peak of runoff is the principal drainage‐basin characteristic used in deriving the synthetic unit‐graphs. An approximate method of determining the “lag” is given for use on areas with no stage‐records available. The peak‐rate of the unit‐graph is expressed as a function of the “lag”.

Dissimilatory metal reduction has the potential to be a helpful mechanism for both intrinsic and engineered bioremediation of contaminated environments. Dissimilatory Fe(III) reduction is an important intrinsic process for removing organic contaminants from aquifers contaminated with petroleum or landfill leachate. Stimulation of microbial Fe(III) reduction can enhance the degradation of organic contaminants in ground water. Dissimilatory reduction of uranium, selenium, chromium, technetium, and possibly other metals, can convert soluble metal species to insoluble forms that can readily be removed from contaminated waters or waste streams. Reduction of mercury can volatilize mercury from waters and soils. Despite its potential, there has as yet been limited applied research into the use of dissimilatory metal reduction as a bioremediation tool.

Changes in the D/H ratio of sedimentary organic matter (SOM) during thermal maturation have been difficult to interpret because the effects of hydrogen exchange and kinetic fractionations are confounded in natural samples. Recent analytical developments have significantly improved our understanding of the responsible mechanisms. In this paper, we review experimental and field data that document a progressive increase in the D/H ratio of most organic hydrogen at the bulk and molecular levels, and suggest that the transfer of hydrogen from water to organic matter is the most important mechanism leading to those changes. SOM and water in natural petroleum systems approach a pseudoequilibrium D/H fractionation of about −80 to −110‰. D/H ratios of organic hydrogen can preserve quantitative information about paleoclimate throughout diagenesis, and some qualitative information through catagenesis.

Abstract This study involved analyses of kerogen petrography, gas desorption, geochemistry, microporosity, and mesoporosity of the New Albany Shale (Devonian–Mississippian) in the eastern part of the Illinois Basin. Specifically, detailed core analysis from two locations, one in Owen County, Indiana, and one in Pike County, Indiana, has been conducted. The gas content in the locations studied was primarily dependent on total organic carbon content and the micropore volume of the shales. Gas origin was assessed using stable isotope geochemistry. Measured and modeled vitrinite reflectance values were compared. Depth of burial and formation water salinity dictated different dominant origins of the gas in place in the two locations studied in detail. The shallower Owen County location (415–433 m [1362–1421 ft] deep) contained significant additions of microbial methane, whereas the Pike County location (832–860 m [2730–2822 ft] deep) was characterized exclusively by thermogenic gas. Despite differences in the gas origin, the total gas in both locations was similar, reaching up to 2.1 cm3/g (66 scf/ton). Lower thermogenic gas content in the shallower location (lower maturity and higher loss of gas related to uplift and leakage via relaxed fractures) was compensated for by the additional generation of microbial methane, which was stimulated by an influx of glacial melt water, inducing brine dilution and microbial inoculation. The characteristics of the shale of the Maquoketa Group (Ordovician) in the Pike County location are briefly discussed to provide a comparison to the New Albany Shale.

A series of molecular and geochemical studies were performed to study microbial, coal bed methane formation in the eastern Illinois Basin. Results suggest that organic matter is biodegraded to simple molecules, such as H(2) and CO(2), which fuel methanogenesis and the generation of large coal bed methane reserves. Small-subunit rRNA analysis of both the in situ microbial community and highly purified, methanogenic enrichments indicated that Methanocorpusculum is the dominant genus. Additionally, we characterized this methanogenic microorganism using scanning electron microscopy and distribution of intact polar cell membrane lipids. Phylogenetic studies of coal water samples helped us develop a model of methanogenic biodegradation of macromolecular coal and coal-derived oil by a complex microbial community. Based on enrichments, phylogenetic analyses, and calculated free energies at in situ subsurface conditions for relevant metabolisms (H(2)-utilizing methanogenesis, acetoclastic methanogenesis, and homoacetogenesis), H(2)-utilizing methanogenesis appears to be the dominant terminal process of biodegradation of coal organic matter at this location.

Environmental context Neonicotinoids are under increased scrutiny because they have been implicated in pollinator declines and, more recently, as potential aquatic toxicants. Nevertheless, there is currently little information on concentrations of multiple neonicotinoids in surface water. This paper presents a summary of concentrations of six neonicotinoids in streams from across the United States in both urban and agricultural areas. These environmental data are important in determining the potential risk of neonicotinoids to non-target aquatic and terrestrial organisms. Abstract To better understand the fate and transport of neonicotinoid insecticides, water samples were collected from streams across the United States. In a nationwide study, at least one neonicotinoid was detected in 53 % of the samples collected, with imidacloprid detected most frequently (37 %), followed by clothianidin (24 %), thiamethoxam (21 %), dinotefuran (13 %), acetamiprid (3 %) and thiacloprid (0 %). Clothianidin and thiamethoxam concentrations were positively related to the percentage of the land use in cultivated crop production and imidacloprid concentrations were positively related to the percentage of urban area within the basin. Additional sampling was also conducted in targeted research areas to complement these national-scale results, including determining: (1) neonicotinoid concentrations during elevated flow conditions in an intensely agricultural region; (2) temporal patterns of neonicotinoids in heavily urbanised basins; (3) neonicotinoid concentrations in agricultural basins in a nationally important ecosystem; and (4) in-stream transport of neonicotinoids near a wastewater treatment plant. Across all study areas, at least one neonicotinoid was detected in 63 % of the 48 streams sampled.

Abstract Deleterious effects of urban stormwater are widely recognized. In several countries, regulations have been put into place to improve the conditions of receiving water bodies, but planning and engineering of stormwater control is typically carried out at smaller scales. Quantifying cumulative effectiveness of many stormwater control measures on a watershed scale is critical to understanding how small‐scale practices translate to urban river health. We review 100 empirical and modelling studies of stormwater management effectiveness at the watershed scale in diverse physiographic settings. Effects of networks with stormwater control measures (SCMs) that promote infiltration and harvest have been more intensively studied than have detention‐based SCM networks. Studies of peak flows and flow volumes are common, whereas baseflow, groundwater recharge, and evapotranspiration have received comparatively little attention. Export of nutrients and suspended sediments have been the primary water quality focus in the United States, whereas metals, particularly those associated with sediments, have received greater attention in Europe and Australia. Often, quantifying cumulative effects of stormwater management is complicated by needing to separate its signal from the signal of urbanization itself, innate watershed characteristics that lead to a range of hydrologic and water quality responses, and the varying functions of multiple types of SCMs. Biases in geographic distribution of study areas, and size and impervious surface cover of watersheds studied also limit our understanding of responses. We propose hysteretic trajectories for how watershed function responds to increasing imperviousness and stormwater management. Even where impervious area is treated with SCMs, watershed function may not be restored to its predevelopment condition because of the lack of treatment of all stormwater generated from impervious surfaces; non‐additive effects of individual SCMs; and persistence of urban effects beyond impervious surfaces. In most cases, pollutant load decreases largely result from run‐off reductions rather than lowered solute or particulate concentrations. Understanding interactions between natural and built landscapes, including stormwater management strategies, is critical for successfully managing detrimental impacts of stormwater at the watershed scale.

Research Article| May 01, 2013 Geochemical controls on shale microstructure John J. Valenza, II; John J. Valenza, II 1Schlumberger-Doll Research, 1 Hampshire Street, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar Nicholas Drenzek; Nicholas Drenzek 1Schlumberger-Doll Research, 1 Hampshire Street, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar Flora Marques; Flora Marques 1Schlumberger-Doll Research, 1 Hampshire Street, Cambridge, Massachusetts 02139, USA Search for other works by this author on: GSW Google Scholar Markus Pagels; Markus Pagels 2Schlumberger Innovation Center at TerraTek, 1935 Fremont Drive, Salt Lake City, Utah 84104, USA Search for other works by this author on: GSW Google Scholar Maria Mastalerz Maria Mastalerz 3Indiana Geological Survey, Indiana University, 611 N. Walnut Grove Avenue, Bloomington, Indiana 47405-2208, USA Search for other works by this author on: GSW Google Scholar Author and Article Information John J. Valenza, II 1Schlumberger-Doll Research, 1 Hampshire Street, Cambridge, Massachusetts 02139, USA Nicholas Drenzek 1Schlumberger-Doll Research, 1 Hampshire Street, Cambridge, Massachusetts 02139, USA Flora Marques 1Schlumberger-Doll Research, 1 Hampshire Street, Cambridge, Massachusetts 02139, USA Markus Pagels 2Schlumberger Innovation Center at TerraTek, 1935 Fremont Drive, Salt Lake City, Utah 84104, USA Maria Mastalerz 3Indiana Geological Survey, Indiana University, 611 N. Walnut Grove Avenue, Bloomington, Indiana 47405-2208, USA Publisher: Geological Society of America Received: 17 May 2012 Revision Received: 12 Dec 2012 Accepted: 22 Dec 2012 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2013 Geological Society of America Geology (2013) 41 (5): 611–614. https://doi.org/10.1130/G33639.1 Article history Received: 17 May 2012 Revision Received: 12 Dec 2012 Accepted: 22 Dec 2012 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation John J. Valenza, Nicholas Drenzek, Flora Marques, Markus Pagels, Maria Mastalerz; Geochemical controls on shale microstructure. Geology 2013;; 41 (5): 611–614. doi: https://doi.org/10.1130/G33639.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The uptick in hydrocarbon production from shale in the United States has generated interest in metrics of unconventional reservoir quality, like permeability. We use conventional gas sorption to characterize shale microstructure, which provides insight on the features that govern mass transport. The gas sorption data are analyzed to determine the surface area, AS (m2/g), and pore volume, VP (cm3/g) of 30 samples from basins across North America. With this information, we quantify the effect of composition and thermal maturity on shale microstructure. In particular, we find that the specific surface area of the organic component evolves from ∼50 m2/g total organic carbon (TOC) in immature shale to ∼500 m2/g TOC for regions that produce dry gas. The increase in AS is accompanied by an increase in VP and concomitant decline in average pore size (e.g., rH = 4VP/AS). We contend that the latter is due to the development of nanometer-sized pores in kerogen as it is converted to mobile hydrocarbon which is ultimately expelled. This hypothesis is supported by similar measurements on companion samples after bitumen extraction or combustion, which underscore the intimate spatial association of petroleum and kerogen. Coupled with information on accessibility to the porosity garnered by varying the particle size, these results establish a clear link between organic matter, thermal maturity, and reservoir quality in unconventional shale systems. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

River deltas all over the world are sinking beneath sea-level rise, causing significant threats to natural and social systems. This is due to the combined effects of anthropogenic changes to sediment supply and river flow, subsidence, and sea-level rise, posing an immediate threat to the 500–1,000 million residents, many in megacities that live on deltaic coasts. The Mississippi River Deltaic Plain (MRDP) provides examples for many of the functions and feedbacks, regarding how human river management has impacted source-sink processes in coastal deltaic basins, resulting in human settlements more at risk to coastal storms. The survival of human settlement on the MRDP is arguably coupled to a shifting mass balance between a deltaic landscape occupied by either land built by the Mississippi River or water occupied by the Gulf of Mexico. We developed an approach to compare 50 % L:W isopleths (L:W is ratio of land to water) across the Atchafalaya and Terrebonne Basins to test landscape behavior over the last six decades to measure delta instability in coastal deltaic basins as a function of reduced sediment supply from river flooding. The Atchafalaya Basin, with continued sediment delivery, compared to Terrebonne Basin, with reduced river inputs, allow us to test assumptions of how coastal deltaic basins respond to river management over the last 75 years by analyzing landward migration rate of 50 % L:W isopleths between 1932 and 2010. The average landward migration for Terrebonne Basin was nearly 17,000 m (17 km) compared to only 22 m in Atchafalaya Basin over the last 78 years (p < 0.001), resulting in migration rates of 218 m/year (0.22 km/year) and <0.5 m/year, respectively. In addition, freshwater vegetation expanded in Atchafalaya Basin since 1949 compared to migration of intermediate and brackish marshes landward in the Terrebonne Basin. Changes in salt marsh vegetation patterns were very distinct in these two basins with gain of 25 % in the Terrebonne Basin compared to 90 % decrease in the Atchafalaya Basin since 1949. These shifts in vegetation types as L:W ratio decreases with reduced sediment input and increase in salinity also coincide with an increase in wind fetch in Terrebonne Bay. In the upper Terrebonne Bay, where the largest landward migration of the 50 % L:W ratio isopleth occurred, we estimate that the wave power has increased by 50–100 % from 1932 to 2010, as the bathymetric and topographic conditions changed, and increase in maximum storm-surge height also increased owing to the landward migration of the L:W ratio isopleth. We argue that this balance of land relative to water in this delta provides a much clearer understanding of increased flood risk from tropical cyclones rather than just estimates of areal land loss. We describe how coastal deltaic basins of the MRDP can be used as experimental landscapes to provide insights into how varying degrees of sediment delivery to coastal deltaic floodplains change flooding risks of a sinking delta using landward migrations of 50 % L:W isopleths. The nonlinear response of migrating L:W isopleths as wind fetch increases is a critical feedback effect that should influence human river-management decisions in deltaic coast. Changes in land area alone do not capture how corresponding landscape degradation and increased water area can lead to exponential increase in flood risk to human populations in low-lying coastal regions. Reduced land formation in coastal deltaic basins (measured by changes in the land:water ratio) can contribute significantly to increasing flood risks by removing the negative feedback of wetlands on wave and storm-surge that occur during extreme weather events. Increased flood risks will promote population migration as human risks associated with living in a deltaic landscape increase, as land is submerged and coastal inundation threats rise. These system linkages in dynamic deltaic coasts define a balance of river management and human settlement dependent on a certain level of land area within coastal deltaic basins (L).

Abstract A series of M b 3.8–5.5 induced seismic events in the midcontinent region, United States , resulted from injection of fluid either into a basal sedimentary reservoir with no underlying confining unit or directly into the underlying crystalline basement complex. The earthquakes probably occurred along faults that were likely critically stressed within the crystalline basement. These faults were located at a considerable distance (up to 10 km) from the injection wells and head increases at the hypocenters were likely relatively small (∼70–150 m). We present a suite of simulations that use a simple hydrogeologic‐geomechanical model to assess what hydrogeologic conditions promote or deter induced seismic events within the crystalline basement across the midcontinent. The presence of a confining unit beneath the injection reservoir horizon had the single largest effect in preventing induced seismicity within the underlying crystalline basement. For a crystalline basement having a permeability of 2 × 10 −17 m 2 and specific storage coefficient of 10 −7 /m, injection at a rate of 5455 m 3 /d into the basal aquifer with no underlying basal seal over 10 years resulted in probable brittle failure to depths of about 0.6 km below the injection reservoir. Including a permeable ( k z = 10 −13 m 2 ) Precambrian normal fault, located 20 m from the injection well, increased the depth of the failure region below the reservoir to 3 km. For a large permeability contrast between a Precambrian thrust fault (10 −12 m 2 ) and the surrounding crystalline basement (10 −18 m 2 ), the failure region can extend laterally 10 km away from the injection well.

Abstract Characterizing the impacts of climatic change on hydrologic processes is critical for managing freshwater systems. Specifically, there is a need to evaluate how the two major components of streamflow, baseflow and stormflow, have responded to recent trends in climate. We derive baseflow and stormflow for 674 sites throughout the United States from 1980 to 2010 to examine their associations with precipitation, potential evapotranspiration, and maximum/minimum temperature. The northeastern (NE) and southwestern (SW) United States display consistent trends in baseflow and stormflow: increasing during fall and winter in the NE and decreasing during all seasons in the SW. Trends elsewhere and at other times of the year are more variable but still associated with changes in climate. Counter to expectations, baseflow and stormflow trends throughout the United States tend to change concurrently. These trends are primarily associated with precipitation trends, but increases in PET are influential and likely to become important in the future.

The flux of dissolved organic carbon (DOC) from mangrove swamps accounts for 10% of the global terrestrial flux of DOC to coastal oceans. Recent findings of high concentrations of mercury (Hg) and methylmercury (MeHg) in mangroves, in conjunction with the common co-occurrence of DOC and Hg species, have raised concerns that mercury fluxes may also be large. We used a novel approach to estimate export of DOC, Hg, and MeHg to coastal waters from a mangrove-dominated estuary in Everglades National Park (Florida, USA). Using in situ measurements of fluorescent dissolved organic matter as a proxy for DOC, filtered total Hg, and filtered MeHg, we estimated the DOC yield to be 180 (±12.6) g C m(-2) yr(-1), which is in the range of previously reported values. Although Hg and MeHg yields from tidal mangrove swamps have not been previously measured, our estimated yields of Hg species (28 ± 4.5 μg total Hg m(-2) yr(-1) and 3.1 ± 0.4 μg methyl Hg m(-2) yr(-1)) were five times greater than is typically reported for terrestrial wetlands. These results indicate that in addition to the well documented contributions of DOC, tidally driven export from mangroves represents a significant potential source of Hg and MeHg to nearby coastal waters.

The carbon isotope effects associated with synthesis of methane from acetate have been determined for Methanosarcina barkeri 227 and for methanogenic archaea in sediments of Wintergreen Lake, Michigan. At 37 degrees C, the 13C isotope effect for the reaction acetate (methyl carbon) --> methane, as measured in replicate experiments with M. barkeri, was - 21.3% +/- 0.3%. The isotope effect at the carboxyl portion of acetate was essentially equal, indicating participation of both positions in the rate-determining step, as expected for reactions catalyzed by carbon monoxide dehydrogenase. A similar isotope effect, - 19.2% +/- 0.3% was found for this reaction in the natural community (temperature = 20 degrees C). Given these observations, it has been possible to model the flow of carbon to methane within lake sediment communities and to account for carbon isotope compositions of evolving methane. Extension of the model allows interpretation of seasonal fluctuations in 13C contents of methane in other systems.