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Results for “Anaerobe”

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At least 145 records · Page 8Linked to original sources

USGS1987

Rapid assay for microbially reducible ferric iron in aquatic sediments

The availability of ferric iron for microbial reduction as directly determined by the activity of iron-reducing organisms was compared with its availability as determined by a newly developed chemical assay for microbially reducible iron. The chemical assay was based on the reduction of poorly crystalline ferric iron by hydroxylamine under acidic conditions. There was a strong correlation between the extent to which hydroxylamine could reduce various synthetic ferric iron forms and the susceptibility of the iron to microbial reduction in an enrichment culture of iron-reducing organisms. When sediments that contained hydroxylamine-reducible ferric iron were incubated under anaerobic conditions, ferrous iron accumulated as the concentration of hydroxylamine-reducible ferric iron declined over time. Ferrous iron production stopped as soon as the hydroxylamine-reducible ferric iron was depleted. In anaerobic incubations of reduced sediments that did not contain hydroxylamine-reducible ferric iron, there was no microbial iron reduction, even though the sediments contained high concentrations of oxalate-extractable ferric iron. A correspondence between the presence of hydroxylamine-reducible ferric iron and the extent of ferric iron reduction in anaerobic incubations was observed in sediments from an aquifer and in fresh- and brackish-water sediments from the Potomac River estuary. The assay is a significant improvement over previously described procedures for the determination of hydroxylamine-reducible ferric iron because it provides a correction for the high concentrations of solid ferrous iron which may also be extracted from sediments with acid. This is a rapid, simple technique to determine whether ferric iron is available for microbial reduction.

Potomac River estuary↗

USGS1991

Methylmercury decomposition in sediments and bacterial cultures: Involvement of methanogens and sulfate reducers in oxidative demethylation

Demethylation of monomethylmercury in freshwater and estuarine sediments and in bacterial cultures was investigated with 14 CH 3 HgI. Under anaerobiosis, results with inhibitors indicated partial involvement of both sulfate reducers and methanogens, the former dominating estuarine sediments, while both were active in freshwaters. Aerobes were the most significant demethylators in estuarine sediments, but were unimportant in freshwater sediments. Products of anaerobic demethylation were mainly 14 CO 2 as well as lesser amounts of 14 CH 4 . Acetogenic activity resulted in fixation of some 14 CO 2 produced from 14 CH 3 HgI into acetate. Aerobic demethylation in estuarine sediments produced only 14 CH 4 , while aerobic demethylation in freshwater sediments produced small amounts of both 14 CH 4 and 14 CO 2 . Two species of Desulfovibrio produced only traces of 14 CH 4 from 14 CH 3 HgI, while a culture of a methylotrophic methanogen formed traces of 14 CO 2 and 14 CH 4 when grown on trimethylamine in the presence of the 14 CH 3 HgI. These results indicate that both aerobes and anaerobes demethylate mercury in sediments, but that either group may dominate in a particular sediment type. Aerobic demethylation in the estuarine sediments appeared to proceed by the previously characterized organomercurial-lyase pathway, because methane was the sole product. However, aerobic demethylation in freshwater sediments as well as anaerobic demethylation in all sediments studied produced primarily carbon dioxide. This indicates the presence of an oxidative pathway, possibly one in which methylmercury serves as an analog of one-carbon substrates.

California↗

USGS1992

A hydrogen-oxidizing, Fe(III)-reducing microorganism from the Great Bay estuary, New Hampshire

A dissimilatory Fe(III)- and Mn(IV)-reducing bacterium was isolated from bottom sediments of the Great Bay estuary, New Hampshire. The isolate was a facultatively anaerobic gram-negative rod which did not appear to fit into any previously described genus. It was temporarily designated strain BrY. BrY grew anaerobically in a defined medium with hydrogen or lactate as the electron donor and Fe(III) as the electron acceptor. BrY required citrate, fumarate, or malate as a carbon source for growth on H 2 and Fe(III). With Fe(III) as the sole electron acceptor, BrY metabolized hydrogen to a minimum threshold at least 60-fold lower than the threshold reported for pure cultures of sulfate reducers. This finding supports the hypothesis that when Fe(III) is available, Fe(III) reducers can outcompete sulfate reducers for electron donors. Lactate was incompletely oxidized to acetate and carbon dioxide with Fe(III) as the electron acceptor. Lactate oxidation was also coupled to the reduction of Mn(IV), U(VI), fumarate, thiosulfate, or trimethylamine n -oxide under anaerobic conditions. BrY provides a model for how enzymatic metal reduction by respiratory metal-reducing microorganisms has the potential to contribute to the mobilization of iron and trace metals and to the immobilization of uranium in sediments of Great Bay Estuary.

New Hampshire↗

USGS1994

Spatial variability in biodegradation rates as evidenced by methane production from an aquifer

Accurate predictions of carbon and energy cycling rates in the environment depend on sampling frequencies and on the spatial variability associated with biological activities. We examined the variability associated with anaerobic biodegradation rates at two sites in an alluvial sand aquifer polluted by municipal landfill leachate. In situ rates of methane production were measured for almost a year, using anaerobic wells installed at two sites. Methane production ranged from 0 to 560 μmol · m -2 · day -1 at one site (A), while a range of 0 to 120,000 μmol · m -2 · day -1 was measured at site B. The mean and standard deviations associated with methane production at site A were 17 and 57 μmol · m -2 · day -1 , respectively. The comparable summary statistics for site B were 2,000 and 9,900 μmol · m -2 · day -1 . The coefficients of variation at sites A and B were 340 and 490%, respectively. Despite these differences, the two sites had similar seasonal trends, with the maximal rate of methane production occurring in summer. However, the relative variability associated with the seasonal rates changed very little. Our results suggest that (i) two spatially distinct sites exist in the aquifer, (ii) methanogenesis is a highly variable process, (iii) the coefficient of variation varied little with the rate of methane production, and (iv) in situ anaerobic biodegradation rates are lognormally distributed.

Applied and Environmental Microbiology↗

USGS1995

Benzene oxidation coupled to sulfate reduction

Highly reduced sediments from San Diego Bay, Calif., that were incubated under strictly anaerobic conditions metabolized benzene within 55 days when they were exposed initially to I μ M benzene. The rate of benzene metabolism increased as benzene was added back to the benzene-adapted sediments. When a [ 14 C]benzene tracer was included with the benzene added to benzene-adapted sediments, 92% of the added radioactivity was recovered as 14 CO 2 . Molybdate, an inhibitor of sulfate reduction, inhibited benzene uptake and production of 14 CO 2 from [ 14 C]benzene. Benzene metabolism stopped when the sediments became sulfate depleted, and benzene uptake resumed when sulfate was added again. The stoichiometry of benzene uptake and sulfate reduction was consistent with the hypothesis that sulfate was the principal electron acceptor for benzene oxidation. Isotope trapping experiments performed with [ 14 C]benzene revealed that there was no production of such potential extracellular intermediates of benzene oxidation as phenol, benzoate, p -hydroxybenzoate, cyclohexane, catechol, and acetate. The results demonstrate that benzene can be oxidized in the absence of O 2 , with sulfate serving as the electron acceptor, and suggest that some sulfate reducers are capable of completely oxidizing benzene to carbon dioxide without the production of extracellular intermediates. Although anaerobic benzene oxidation coupled to chelated Fe(III) has been documented previously, the study reported here provides the first example of a natural sediment compound that can serve as an electron acceptor for anaerobic benzene oxidation.

California↗

USGS1995

Assessment of intrinsic bioremediation of jet fuel contamination in a shallow aquifer, Beaufort, South Carolina

Field and laboratory studies show that microorganisms indigenous to the ground-water system underlying Tank Farm C, Marine Corps Air Station Beaufort, S.C., degrade petroleum hydrocarbons under aerobic and anaerobic conditions. Under aerobic conditions, sediments from the shallow aquifer underlying the site mineralized radiolabeled (14C) toluene to 14CO2 with first-order rate constants of about -0.29 per day. Sediments incubated under anaerobic conditions mineralized radiolabeled toluene more slowly, with first-order rate constants of -0.001 per day. Although anaerobic rates of biodegradation are low, they are significant in the hydrologic and geochemical context of the site. Because of low hydraulic conductivities (1.9-9.1 feet per day) and low hydraulic gradients (about 0.004 feet per feet), ground water flows slowly (approximately 20 feet per year) at this site. Furthermore, aquifer sediments contain organic-rich peat that has a high sorptive capacity. Under these conditions, hydrocarbon contaminants have moved no further than 10 feet downgradient of the jet fuel free product. Digital solute-transport simulations, using the range of model parameters measured at the site, show that dissolved contaminants will be completely degraded before they are discharged from the aquifer into adjacent surface-water bodies. These results show that natural attenuation processes are containing the migration of soluble hydrocarbons, and that intrinsic bioremediation is a potentially effective remedial strategy at this site.

South Carolina↗

USGS2000

Biodegradation of chlorinated ethenes at a karst site in middle Tennessee

This report presents results of field and laboratory investigations examining the biodegradation of chlorinated ethenes in a karst aquifer contaminated with trichloroethylene (TCE). The study site, located in Middle Tennessee, was selected because of the presence of TCE degradation byproducts in the karst aquifer and available site hydrologic and chlorinated-ethene information. Additional chemical, biological, and hydrologic data were gathered to evaluate whether the occurrence of TCE degradation byproducts in the karst aquifer was the result of biodegradation within the aquifer or simply transport into the aquifer. Geochemical analysis established that sulfate-reducing conditions, essential for reductive dechlorination of chlorinated solvents, existed in parts of the contaminated karst aquifer. Other areas of the aquifer fluctuated between anaerobic and aerobic conditions and contained compounds associated with cometabolism, such as ethane, methane, ammonia, and dissolved oxygen. A large, diverse bacteria population inhabits the contaminated aquifer. Bacteria known to biodegrade TCE and other chlorinated solvents, such as sulfate-reducers, methanotrophs, and ammonia-oxidizers, were identified from karst-aquifer water using the RNA-hybridization technique. Results from microcosms using raw karst-aquifer water found that aerobic cometabolism and anaerobic reductive-dechlorination degradation processes were possible when appropriate conditions were established in the microcosms. These chemical and biological results provide circumstantial evidence that several biodegradation processes are active in the aquifer. Additional site hydrologic information was developed to determine if appropriate conditions persist long enough in the karst aquifer for these biodegradation processes to be significant. Continuous monitoring devices placed in four wells during the spring of 1998 indicated that pH, specific conductance, dissolved oxygen, and oxidation-reduction potentials changed very little in areas isolated from active ground-water flow paths. These stable areas in the karst aquifer had geochemical conditions and bacteria conducive to reductive dechlorination of chlorinated ethenes. Other areas of the karst aquifer were associated with active ground-water flow paths and fluctuated between anaerobic and aerobic conditions in response to rain events. Associated with this dynamic environment were bacteria and geochemical conditions conducive to cometabolism. In summary, multiple lines of evidence developed from chemical, biological, and hydrologic data demonstrate that a variety of biodegradation processes are active in this karst aquifer.

Tennessee↗

USGS1975

Chemical quality and temperature of water in Flaming Gorge Reservoir, Wyoming and Utah, and the effect of the reservoir on the Green River

The major tributaries to Flaming Gorge Reservoir contribute an average of about 97 percent of the total streamflow and 82 percent of the total load of dissolved solids. The Green River is the largest tributary, and for the 1957-72 water years it contributed 81 percent of the total streamflow and 70 percent of the total load of dissolved solids. The principal constituents in the tributary streamflow are calcium and sulfate during periods of lowest flow and calcium and bicarbonate during periods of highest flow. Flaming Gorge Dam was closed in November 1962, and the most significant load changes of chemical constituents due to the net effect of inflow, outflow, leaching, and chemical precipitation in the reservoir have been load changes of sulfate and bicarbonate. The average increase of dissolved load of sulfate in the reservoir for the 1969-72 water years was 110,000 tons (99,790 t) per year, which was 40,000 tons (36,287 t) per year less than for the 1963-66 water years. The average decrease of dissolved load of bicarbonate in the reservoir for 1969-72 was 40,000 tons (36,287 t) per year, which was the same as the decrease for 1963-66. Anaerobic conditions were observed in the deep, uncirculated part of the reservoir near the dam during the 1971 and 1972 water years, and anaerobic or near-anaerobic conditions were observed near the confluence of the Blacks Fork and Green River during the summers of 1971 and 1972. The water in Flaming Gorge Reservoir is in three distinct layers, and the upper two layers (the epilimnion and the metalimnion) mixed twice during each of the 1971-72 water years. The two circulation periods were in the spring and fall. The water in the deepest layer (the hypolimnion) did not mix with the waters of the upper zones because the density difference was too great and because the deep, narrow shape of the basin probably inhibits mixing. The depletion of flow in the Green River downstream from Flaming Gorge Dam between closure of the dam and the end of the 1972 water year was 4,500,000 acre-feet (5,550.8 hm 3 ). Of this total, water stored in the reservoir accounted for 3,500,000 acre-feet (4,317.2 hm 3 ), evaporation consumed 700,000 acre-feet (863.4 hm 3 ), and 300,000 acre-feet (370.0 hm 3 ) went into bank storage. The net load of dissolved solids added to the river system during the 1963-72 water years, due to leaching and chemical precipitation, was 1,730,000 tons (1,569,421 t). The leaching rate was 200,000 tons (181,436 t) per year for 1963-68,115,000 tons (104,326 t) per year for 1969-70 and 150,000 tons (136,077 t) per year for 1971-72. It appears that the leaching rates should decrease in the future since the reservoir level in 1972 was near maximum pool level. The most significant increase in concentration of the chemical constituents in the water below the reservoir involved the sulfate ion, which increased from about 115 milligrams per litre (42 percent of the anions) in 1957 to about 200 milligrams per litre (54 percent), in 1972. But the highest concentration, about 290 milligrams per litre (58 percent), occurred in 1963, immediately after closure of the dam. Prior to closure of the dam, the average monthly temperature of the Green River below the damsite ranged from 0 ° C to 19.5 ° C as compared to 3.5 ° C to 10.0 ° C after closure.

Utah↗

USGS2003

Inorganic nitrogen transformations in the bed of the Shingobee River, Minnesota: Integrating hydrologic and biological processes using sediment perfusion cores

Inorganic N transformations were examined in streambed sediments from the Shingobee River using sediment perfusion cores. The experimental design simulated groundwater-stream water mixing within sediment cores, which provided a well-defined one-dimensional representation of in situ hydrologic conditions. Two distinct hydrologic and chemical settings were preserved in the sediment cores: the lowermost sediments, perfused with groundwater, remained anaerobic during the incubations, whereas the uppermost sediments, perfused with oxic water pumped from the overlying water column, simulated stream water penetration into the bed. The maintenance of oxic and anoxic zones formed a biologically active aerobic-anaerobic interface. Ammonium (NH4+) dissolved in groundwater was transported conservatively through the lower core zone but was removed as it mixed with aerated recycle water. Concurrently, a small quantity of nitrate (NO3-) equaling ???25% of the NH4+ loss was produced in the upper sediments. The NH4+ and NO3- profiles in the uppermost sediments resulted from coupled nitrification-denitrification, because assimilation and sorption were negligible. We hypothesize that anaerobic microsites within the aerated upper sediments supported denitrification. Rates of nitrification and denitrification in the perfusion cores ranged 42-209 and 53-160 mg N m-2 day-1, respectively. The use of modified perfusion cores permitted the identification and quantification of N transformations and verified process control by surface water exchange into the shallow hyporheic zone of the Shingobee River.

Minnesota↗

USGS2000

Redox conditions and the efficiency of chlorinated ethene biodegradation: Laboratory studies

The potential for biodegradation of highly reduced groundwater contaminants is greatest under aerobic conditions and least under CO2-reducing (methanogenic) conditions. Laboratory studies conducted using [1,2-14C] vinyl chloride (VC) indicate the same pattern applies to the anaerobic oxidation of relatively reduced chloroethylenes. Recent studies, showing that CH4 can be a significant product of microbial degradation of VC under methanogenic conditions, clarified mechanisms underlying anaerobic VC mineralization and emphasized the redox dependence of this process. A microcosm study conducted with stream bed sediments demonstrated rapid degradation of [1,2-14C] VC and simultaneous production of 14CO2 and 14CH4. The results of acetate mineralization studies indicated that these sediments contained active acetotrophic methanogens. VC degradation involved an initial transformation to acetate via oxidative acetogenesis followed by acetotrophic methanogenesis to yield CO2 and CH4 as final products. Based on these recent results, a conceptual model for anaerobic microbial degradation of VC to non-chlorinated products can be proposed.

Conference Paper↗

USGS2015

Soil greenhouse gas emissions and carbon budgeting in a short-hydroperiod floodplain wetland

Understanding the controls on floodplain carbon (C) cycling is important for assessing greenhouse gas emissions and the potential for C sequestration in river-floodplain ecosystems. We hypothesized that greater hydrologic connectivity would increase C inputs to floodplains that would not only stimulate soil C gas emissions but also sequester more C in soils. In an urban Piedmont river (151 km 2 watershed) with a floodplain that is dry most of the year, we quantified soil CO 2 , CH 4 , and N 2 O net emissions along gradients of floodplain hydrologic connectivity, identified controls on soil aerobic and anaerobic respiration, and developed a floodplain soil C budget. Sites were chosen along a longitudinal river gradient and across lateral floodplain geomorphic units (levee, backswamp, and toe slope). CO 2 emissions decreased downstream in backswamps and toe slopes and were high on the levees. CH 4 and N 2 O fluxes were near zero; however, CH 4 emissions were highest in the backswamp. Annual CO 2 emissions correlated negatively with soil water-filled pore space and positively with variables related to drier, coarser soil. Conversely, annual CH 4 emissions had the opposite pattern of CO 2 . Spatial variation in aerobic and anaerobic respiration was thus controlled by oxygen availability but was not related to C inputs from sedimentation or vegetation. The annual mean soil CO 2 emission rate was 1091 g C m −2  yr −1 , the net sedimentation rate was 111 g C m −2  yr −1 , and the vegetation production rate was 240 g C m −2  yr −1 , with a soil C balance (loss) of −338 g C m −2  yr −1 . This floodplain is losing C likely due to long-term drying from watershed urbanization.

Virginia↗

USGS2016

Intertidal salt marshes as an important source of inorganic carbon to the coastal ocean

Dynamic tidal export of dissolved inorganic carbon (DIC) to the coastal ocean from highly productive intertidal marshes and its effects on seawater carbonate chemistry are thoroughly evaluated. The study uses a comprehensive approach by combining tidal water sampling of CO 2 parameters across seasons, continuous in situ measurements of biogeochemically-relevant parameters and water fluxes, with high-resolution modeling in an intertidal salt marsh of the U.S. northeast region. Salt marshes can acidify and alkalize tidal water by injecting CO 2 (DIC) and total alkalinity (TA). DIC and TA generation may also be decoupled due to differential effects of marsh aerobic and anaerobic respiration on DIC and TA. As marsh DIC is added to tidal water, the buffering capacity first decreases to a minimum and then increases quickly. Large additions of marsh DIC can result in higher buffering capacity in ebbing tide than incoming tide. Alkalization of tidal water, which mostly occurs in the summer due to anaerobic respiration, can further modify buffering capacity. Marsh exports of DIC and alkalinity may have complex implications for the future, more acidified ocean. Marsh DIC export exhibits high variability over tidal and seasonal cycles, which is modulated by both marsh DIC generation and by water fluxes. The marsh DIC export of 414 g C m −2 yr −1 , based on high-resolution measurements and modeling, is more than twice the previous estimates. It is a major term in the marsh carbon budget and translates to one of the largest carbon fluxes along the U.S. East Coast.

Massachusetts↗

USGS2002

Alkylcyclohexanes in environmental geochemistry

The n-alkylated cyclohexanes (CHs) are a homologous series of hydrocarbon compounds that are commonly present in crude oil and refinery products such as diesel fuel. These compounds exhibit specific distribution patterns for different fuel types, providing useful fingerprints for characterizing petroleum products, especially after degradation of n-alkanes has occurred. However, there are no published data to show how these compounds are altered in the environment after long-term spillage of petroleum products. This paper presents two case studies of oil spills that demonstrate the changing distribution patterns resulting from long-term anaerobic microbial degradation. These spills are the 1979 crude-oil spill in Bemidji, Minnesota, and a chronic diesel-fuel spillage from 1953-1991 at Mandan, North Dakota. The alkyl CHs in both spilled oil products are affected by similar biodegradative processes in which the compounds undergo a consistent pattern of loss from the high molecular weight end of the homolog distribution. Degradation results in a measurable increase in the concentrations of the homologs in the lower molecular weight range, a gradual lowering in carbon number of the homolog maximum, and a gradual decrease of the total homolog range from the high molecular weight end. This pattern is the opposite of low-end loss expected with weathering and aerobic biodegradation. The enhancement of the low molecular mass alkyl CH homologs, if not recognized as a degradative pathway of diesel fuel in an anaerobic environment, can potentially be misinterpreted in fuel-oil fingerprinting as deriving from lower distillation-range fuels or admixture of diesel with other fuels.

Environmental Forensics↗

USGS2017

Bacteria versus selenium: A view from the inside out

Bacteria and selenium (Se) are closely interlinked as the element serves both essential nutrient requirements and energy generation functions. However, Se can also behave as a powerful toxicant for bacterial homeostasis. Conversely, bacteria play a tremendous role in the cycling of Se between different environmental compartments, and bacterial metabolism has been shown to participate to all valence state transformations undergone by Se in nature. Bacteria possess an extensive molecular repertoire for Se metabolism. At the end of the 1980s, a novel mode of anaerobic respiration based on Se oxyanions was experimentally documented for the first time. Following this discovery, specific enzymes capable of reducing Se oxyanions and harvesting energy were found in a number of anaerobic bacteria. The genes involved in the expression of these enzymes have later been identified and cloned. This iterative approach undertaken outside-in led to the understanding of the molecular mechanisms of Se transformations in bacteria. Based on the extensive knowledge accumulated over the years, we now have a full(er) view from the inside out , from DNA-encoding genes to enzymes and thermodynamics. Bacterial transformations of Se for assimilatory purposes have been the object of numerous studies predating the investigation of Se respiration. Remarkable contributions related to the understating of the molecular picture underlying seleno-amino acid biosynthesis are reviewed herein. Under certain circumstances, Se is a toxicant for bacterial metabolism and bacteria have evolved strategies to counteract this toxicity, most notably by the formation of elemental Se (nano)particles. Several biotechnological applications, such as the production of functional materials and the biofortification of crop species using Se-utilizing bacteria, are presented in this chapter.

Book chapter↗

USGS1988

Acetylene as a substrate in the development of primordial bacterial communities

The fermentation of atmospheric acetylene by anaerobic bacteria is proposed as the basis of a primordial heterotrophic food chain. The accumulation of fermentation products (acetaldehyde, ethanol, acetate and hydrogen) would create niches for sulfate-respiring bacteria as well as methanogens. Formation of acetylene-free environments in soils and sediments would also alter the function of nitrogenase from detoxification to nitrogen-fixation. The possibility of an acetylene-based anaerobic food chain in Jovian-type atmospheres is discussed. ?? 1988 Kluwer Academic Publishers.

Origins of Life and Evolution of the Biosphere↗

USGS1998

Bacillus arsenicoselenatis, sp. nov., and Bacillus selenitireducens, sp. nov.: Two haloalkaliphiles from Mono Lake, California that respire oxyanions of selenium and arsenic

Two gram-positive anaerobic bacteria (strains E1H and MLS10) were isolated from the anoxic muds of Mono Lake, California, an alkaline, hypersaline, arsenic-rich water body. Both grew by dissimilatory reduction of As(V) to As(III) with the concomitant oxidation of lactate to acetate plus CO2. Bacillus arsenicoselenatis (strain E1H) is a spore-forming rod that also grew by dissimilatory reduction of Se(VI) to Se(IV). Bacillus selenitireducens (strain MLS 10) is a short, non-spore-forming rod that grew by dissimilatory reduction of Se(IV) to Se(0). When the two isolates were cocultured, a complete reduction of Se(VI) to Se(0) was achieved. Both isolates are alkaliphiles and had optimal specific growth rates in the pH range of 8.5-10. Strain E1H had a salinity optimum at 60 g 1-1 NaCl, while strain MLS10 had optimal growth at lower salinities (24-60 g 1-1 NaCl). Both strains have limited abilities to grow with electron donors and acceptors other than those given above. Strain MLS10 demonstrated weak growth as a microaerophile and was also capable of fermentative growth on glucose, while strain E1H is a strict anaerobe. Comparative 16S rRNA gene sequence analysis placed the two isolates with other Bacillus spp. in the low G+C gram-positive group of bacteria.

Archives of Microbiology↗

USGS1998

Assessment of natural attenuation of aromatic hydrocarbons in groundwater near a former manufactured-gas plant, South Carolina, USA

Shallow, anaerobic groundwater near a former manufactured-gas plant (MGP) in Charleston, South Carolina, USA, contains mono- and polycyclic aromatic hydrocarbons (MAHs and PAHs, respectively). Between 1994 and 1997, a combination of field, laboratory, and numerical-flow and transport-model investigations were made to assess natural attenuation processes affecting MAH and PAH distributions. This assessment included determination of adsorption coefficients (K(ad)) and first-order biodegradation rate constants (K(bio)) using aquifer material from the MGP site and adjacent properties. Naphthalene adsorption (K(ad) = 1.35 x 10-7 m3/mg) to aquifer sediments was higher than toluene adsorption (K(ad) = 9.34 x 10-10 m3/mg), suggesting preferential toluene transport relative to naphthalene. However, toluene and benzene distributions measured in January 1994 were smaller than the naphthalene distribution. This scenario can be explained, in part, by the differences between biodegradation rates of the compounds. Aerobic first-order rate constants of 14C-toluene, 14C-benzene, and 14C-naphthalene degradation were similar (-0.84, -0.03, and 0.88 day-1, respectively), but anaerobic rate constants were higher for toluene and benzene (-0.002 and -0.00014 day-1, respectively) than for naphthalene (-0.000046 day-1). Both areal and cross-sectional numerical simulations were used to test the hypothesis suggested by these rate differences that MAH compounds will be contained relative to PAHs. Predictive simulations indicated that the distributions of toluene and benzene reach steady-state conditions before groundwater flow lines discharge to an adjacent surface-water body, but do discharge low concentrations of naphthalene. Numerical predictions were 'audited' by measuring concentrations of naphthalene, toluene, and benzene at the site in early 1997. Measured naphthalene and toluene concentrations were substantially reduced and the areal extent of contamination smaller than was both observed in January 1994 and predicted for 1997. Measured 1997 benzene concentrations and distribution were shown to be relatively unchanged from those measured in 1994, and similar to predictions for 1997.The natural attenuation processes affecting mono- and polycyclic aromatic hydrocarbons (MAHs and PAHs, respectively) distributions in groundwater near a former manufactured-gas plant in South Carolina, USA was evaluated. This assessment included determination of adsorption coefficients and first-order biodegradation rate constants. Detailed results obtained in the study are presented.

South Carolina↗

USGS1989

Organic geochemistry and brine composition in Great Salt, Mono, and Walker Lakes

Samples of Recent sediments, representing up to 1000 years of accumulation, were collected from three closed basin lakes (Mono Lake, CA, Walker Lake, NV, and Great Salt Lake, UT) to assess the effects of brine composition on the accumulation of total organic carbon, the concentration of dissolved organic carbon, humic acid structure and diagenesis, and trace metal complexation. The Great Salt Lake water column is a stratified Na-Mg-Cl-SO 4 brine with low alkalinity. Algal debris is entrained in the high density (1.132–1.190 g/cc) bottom brines, and in this region maximum organic matter decomposition occurs by anaerobic processes, with sulfate ion as the terminal electron acceptor. Organic matter, below 5 cm of the sediment-water interface, degrades at a very slow rate in spite of very high pore-fluid sulfate levels. The organic carbon concentration stabilizes at 1.1 wt%. Mono Lake is an alkaline (Na-CO 3 -Cl-SO 4 ) system. The water column is stratified, but the bottom brines are of lower density relative to the Great Salt Lake, and sedimentation of algal debris is rapid. Depletion of pore-fluid sulfate, near l m of core, results in a much higher accumulation of organic carbon, approximately 6 wt%. Walker Lake is also an alkaline system. The water column is not stratified, and decomposition of organic matter occurs by aerobic processes at the sediment-water interface and by anaerobic processes below. Total organic carbon and dissolved organic carbon concentrations in Walker Lake sediments vary with location and depth due to changes in input and pore-fluid sulfate concentrations. Nuclear magnetic resonance studies ( 13 C) of humic substances and dissolved organic carbon provide information on the source of the Recent sedimentary organic carbon (aquatic vs. terrestrial), its relative state of decomposition, and its chemical structure. The spectra suggest an algal origin with little terrestrial signature at all three lakes. This is indicated by the ratio of aliphatic to aromatic carbon and the absence of chemical structures indicative of the lignin of vascular plants. The dissolved organic carbon of the Mono Lake pore fluids is structurally related to humic acid and is also related to carbohydrate metabolism. The alkaline pore fluids, due to high pH, solubilize high molecular weight organic matter from the sediments. This hydrophilic material is a metal complexing agent. Despite very high algal productivities, organic carbon accumulation can be low in stratified lakes if the anoxic bottom waters are hypersaline with high concentrations of sulfate ion. Labile organic matter is recycled to the water column and the sedimentary organic matter is relatively nonsusceptible to bacterial metabolism. As a result, pore-fluid dissolved organic carbon and metal-organic complexation are low.

Geochimica et Cosmochimica Acta↗