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Results for “Biodegradation”

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USGS2008

Potential for 4- n -nonylphenol biodegradation in stream sediments

The potential for in situ biodegradation of 4-nonylphenol (4-NP) was investigated in three hydrologically distinct streams impacted by wastewater treatment plants (WWTPs) in the United States. Microcosms were prepared with sediments from each site and amended with [U-ring- 14 C]4- n -nonylphenol (4- n -NP) as a model test substrate. Microcosms prepared with sediment collected upstream of the WWTP outfalls and incubated under oxic conditions showed rapid and complete mineralization of [U-ring- 14 C]4- n -NP to 14 CO 2 in all three systems. In contrast, no mineralization of [U-ring- 14 C]4- n -NP was observed in these sediments under anoxic (methanogenic) conditions. The initial linear rate of [U-ring-14C]4-n-NP mineralization in sediments from upstream and downstream of the respective WWTP outfalls was inversely correlated with the biochemical oxygen demand (BOD) of the streambed sediments. These results suggest that the net supply of dissolved oxygen to streambed sediments is a key determinant of the rate and extent of 4-NP biodegradation in stream systems. In the stream systems considered by the present study, dissolved oxygen concentrations in the overlying water column (8–10 mg/L) and in the bed sediment pore water (1–3 mg/L at a depth of 10 cm below the sediment–water interface) were consistent with active in situ 4-NP biodegradation. These results suggest WWTP procedures that maximize the delivery of dissolved oxygen while minimizing the release of BOD to stream receptors favor efficient biodegradation of 4-NP contaminants in wastewater-impacted stream environments.

Colorado, Iowa↗

USGS2002

Simulated transport and biodegradation of chlorinated ethenes in a fractured dolomite aquifer near Niagara Falls, New York

Leakage of trichloroethene (TCE) from a neutralization pond at a former manufacturing facility near Niagara Falls, N.Y. during 1950-87 into the Guelph Formation of the Lockport Group, a fractured dolomite aquifer, created a plume of TCE and its metabolites that, by 1990, extended about 4,300 feet south of the facility. A smaller plume of dense, nonaqueous-phase liquids (DNAPL) probably serves as a continuing source of TCE. The presence of the TCE metabolites cis-1,2-dichloroethene (DCE), vinyl chloride (VC), and ethene in the plume, and the results of previous laboratory microcosm studies, indicate that the TCE is being degraded by naturally occurring microorganisms. Biodegradation rates of TCE and its metabolites were estimated through simulation with BIOMOC, a solute-transport model that represents multispecies reactions through Monod kinetics. A fracture zone in the Guelph Formation was represented as a porous medium containing an extensive, 3-foot thick layer with several interconnected fractures; this layer is bounded above and below by subhorizontal stratigraphic contacts. The Monod reaction constants were estimated through nonlinear regression to minimize the difference between computed concentrations of TCE and its metabolites, and the concentrations measured before and during 5 years of pump-and-treat remediation. Transport simulations indicated that, by April 1998, the chlorinated ethene plume had reached a dynamic equilibrium between the rate of TCE dissolution and the rate of removal through pumping and biodegradation. Biodegradation of chlorinated ethenes at the site can be simulated as first-order reactions because the concentrations are generally less than the half-saturation constants estimated for Monod kinetics (320 mg/L for TCE, 10 mg/L for DCE, and 1 mg/L for VC). Computed degradation rates are proportional to the estimated ground-water velocity, which could vary by more than an order magnitude at the site, as indicated by the estimated range of fracture porosity--3 to 0.3 percent. Half-lives corresponding to first-order rate constants estimated for the lower velocity (5 to 15 feet per day) ranged from 21 to 25 days for TCE, 170 to 230 days for DCE, and 18 to 23 days for VC. Chlorinated ethene concentrations of April 1998 were better reproduced when the TCE source was represented as a constant concentration than as a constant flux, because the latter predicted that the plume would dissipate after 5 years of pump-and-treat remediation. This result indicates that the rate of TCE dissolution is not limited by the mass of TCE in the DNAPL plume. Simulation of diffusion by the transport model MOC3D indicated that concentrations of these contaminants within the rock matrix surrounding the fracture zone were relatively unchanged after 5 years of pump-and-treat remediation. The principal sources of uncertainty in the prediction of biodegradation rates and of the fate of chlorinated ethenes at the site are the fracture porosity and DNAPL mass in the aquifer.

New York↗

USGS2015

Aerobic biodegradation potential of endocrine disrupting chemicals in surface-water sediment at Rocky Mountains National Park, USA

Endocrine disrupting chemicals (EDC) in surface water and bed sediment threaten the structure and function of aquatic ecosystems. In natural, remote, and protected surface-water environments where contaminant releases are sporadic, contaminant biodegradation is a fundamental driver of exposure concentration, timing, duration, and, thus, EDC ecological risk. Anthropogenic contaminants, including known and suspected EDC, were detected in surface water and sediment collected from 2 streams and 2 lakes in Rocky Mountains National Park (ROMO). The potential for aerobic EDC biodegradation was assessed in collected sediments using 6 14 C-radiolabeled model compounds. Aerobic microbial mineralization of natural (estrone and 17β-estradiol) and synthetic (17α-ethinylestradiol) estrogen was significant at all sites. ROMO bed sediment microbial communities also effectively degraded the xenoestrogens, bisphenol-A and 4-nonylphenol. The same sediment samples exhibited little potential for aerobic biodegradation of triclocarban, however, illustrating the need to assess a wider range of contaminant compounds. The current results support recent concerns over the widespread environmental occurrence of carbanalide antibacterials, like triclocarban and triclosan, and suggest that backcountry use of products containing these compounds should be discouraged.

Rocky Mountain National Park↗

USGS2014

Greenhouse gases generated from the anaerobic biodegradation of natural offshore asphalt seepages in southern California

Significant offshore asphaltic deposits with active seepage occur in the Santa Barbara Channel offshore southern California. The composition and isotopic signatures of gases sampled from the oil and gas seeps reveal that the coexisting oil in the shallow subsurface is anaerobically biodegraded, generating CO 2 with secondary CH 4 production. Biomineralization can result in the consumption of as much as 60% by weight of the original oil, with 13 C enrichment of CO 2 . Analyses of gas emitted from asphaltic accumulations or seeps on the seafloor indicate up to 11% CO 2 with 13 C enrichment reaching +24.8‰. Methane concentrations range from less than 30% up to 98% with isotopic compositions of –34.9 to –66.1‰. Higher molecular weight hydrocarbon gases are present in strongly varying concentrations reflecting both oil-associated gas and biodegradation; propane is preferentially biodegraded, resulting in an enriched 13 C isotopic composition as enriched as –19.5‰. Assuming the 132 million barrels of asphaltic residues on the seafloor represent ~40% of the original oil volume and mass, the estimated gas generated is 5.0×1010 kg (~76×109 m 3 ) CH 4 and/or 1.4×1011 kg CO 2 over the lifetime of seepage needed to produce the volume of these deposits. Geologic relationships and oil weathering inferences suggest the deposits are of early Holocene age or even younger. Assuming an age of ~1,000 years, annual fluxes are on the order of 5.0×107 kg (~76×106 m 3 ) and/or 1.4×108 kg for CH 4 and CO 2 , respectively. The daily volumetric emission rate (2.1×105 m 3 ) is comparable to current CH 4 emission from Coal Oil Point seeps (1.5×105 m 3 /day), and may be a significant source of both CH 4 and CO 2 to the atmosphere provided that the gas can be transported through the water column.

California↗

USGS2006

Biodegradation of organic chemicals in soil/water microcosms system: Model development

The chemical interactions of hydrophobic organic contaminants with soils and sediments may result in strong binding and slow subsequent release rates that significantly affect remediation rates and endpoints. In order to illustrate the recalcitrance of chemical to degradation on sites, a sorption mechanism of intraparticle sequestration was postulated to operate on chemical remediation sites. Pseudo-first order sequestration kinetics is used in the study with the hypothesis that sequestration is an irreversibly surface-mediated process. A mathematical model based on mass balance equations was developed to describe the fate of chemical degradation in soil/water microcosm systems. In the model, diffusion was represented by Fick's second law, local sorption-desorption by a linear isotherm, irreversible sequestration by a pseudo-first order kinetics and biodegradation by Monod kinetics. Solutions were obtained to provide estimates of chemical concentrations. The mathematical model was applied to a benzene biodegradation batch test and simulated model responses correlated well compared to measurements of biodegradation of benzene in the batch soil/water microcosm system. A sensitivity analysis was performed to assess the effects of several parameters on model behavior. Overall chemical removal rate decreased and sequestration increased quickly with an increase in the sorption partition coefficient. When soil particle radius, a, was greater than 1 mm, an increase in radius produced a significant decrease in overall chemical removal rate as well as an increase in sequestration. However, when soil particle radius was less than 0.1 mm, an increase in radius resulted in small changes in the removal rate and sequestration. As pseudo-first order sequestration rate increased, both chemical removal rate and sequestration increased slightly. Model simulation results showed that desorption resistance played an important role in the bioavailability of organic chemicals in porous media. Complete biostabilization of chemicals on remediation sites can be achieved when the concentration of the reversibly sorbed chemical reduces to zero (i.e., undetectable), with a certain amount of irreversibly sequestrated chemical left inside the soil particle solid phase. ?? 2006 Springer Science + Business Media B.V.

Water, Air, & Soil Pollution↗

USGS1995

Screening tests for assessing the anaerobic biodegradation of pollutant chemicals in subsurface environments

Screening methods were developed to assess the susceptibility of ground water contaminants to anaerobic biodegradation. One method was an extrapolation of a procedure previously used to measure biodegradation activity in dilute sewage sludge. Aquifer solids and ground water with no additional nutritive media were incubated anaerobically in 160-ml serum bottles containing 250 mg·l −1 carbon of the substrate of interest. This method relied on the detection of gas pressure or methane production in substrateamended microcosms relative to background controls. Other screening procedures involved the consumption of stoichiometrically required amounts of sulfate or nitrate from the same type of incubations. Close agreement was obtained between the measured and calculated amounts of substrate bioconversion based on the measured biogas pressure in methanogenic microcosms. Storage of the microcosms for up to 6 months did not adversely influence the onset or rate of benzoic acid mineralization. The lower detection limits of the methanogenic assay were found to be a function of the size of the microcosm headspace, the mean oxidation state of the substrate carbon, and the method used to correct for background temperature fluctuations. Using these simple screening procedures, biodegradation information of regulatory interest could be generated, including, (i) the length of the adaptation period, (ii) the rate of substrate decay and (iii) the completeness of the bioconversion.

Journal of Microbiological Methods↗

USGS2010

Organic intermediates in the anaerobic biodegradation of coal to methane under laboratory conditions

Organic intermediates in coal fluids produced by anaerobic biodegradation of geopolymers in coal play a key role in the production of methane in natural gas reservoirs. Laboratory biodegradation experiments on sub-bituminous coal from Texas, USA, were conducted using bioreactors to examine the organic intermediates relevant to methane production. Production of methane in the bioreactors was linked to acetate accumulation in bioreactor fluid. Long chain fatty acids, alkanes (C 19 –C 36 ) and various low molecular weight aromatics, including phenols, also accumulated in the bioreactor fluid and appear to be the primary intermediates in the biodegradation pathway from coal-derived geopolymers to acetate and methane.

Texas↗

USGS1998

Field and laboratory evidence for intrinsic biodegradation of vinyl chloride contamination in a Fe(III)-reducing aquifer

Intrinsic bioremediation of chlorinated ethenes in anaerobic aquifers previously has not been considered feasible, due, in large part, to 1) the production of vinyl chloride during microbial reductive dechlorination of higher chlorinated contaminants and 2) the apparent poor biodegradability of vinyl chloride under anaerobic conditions. In this study, a combination of field geochemical analyses and laboratory radiotracer ([1,2-14C] vinyl chloride) experiments was utilized to assess the potential for intrinsic biodegradation of vinyl chloride contamination in an Fe(III)-reducing, anaerobic aquifer. Microcosm experiments conducted under Fe(III)-reducing conditions with material from the Fe(III)-reducing, chlorinated-ethene contaminated aquifer demonstrated significant oxidation of [1,2-14C] vinyl chloride to 14CO2 with no detectable production of ethene or other reductive dehalogenation products. Rates of degradation derived from the microcosm experiments (0.9-1.3% d-1) were consistent with field-estimated rates (0.03-0.2% d-1) of apparent vinyl chloride degradation. Field estimates of apparent vinyl chloride biodegradation were calculated using two distinct approaches; 1) a solute dispersion model and 2) a mass balance assessment. These findings demonstrate that degradation under Fe(III) reducing conditions can be an environmentally significant mechanism for intrinsic bioremediation of vinyl chloride in anaerobic ground-water systems.

Journal of Contaminant Hydrology↗

USGS1999

Quantification of aerobic biodegradation and volatilization rates of gasoline hydrocarbons near the water table under natural attenuation conditions

Aerobic biodegradation and volatilization near the water table constitute a coupled pathway that contributes significantly to the natural attenuation of hydrocarbons at gasoline spill sites. Rates of hydrocarbon biodegradation and volatilization were quantified by analyzing vapor transport in the unsaturated zone at a gasoline spill site in Beaufort, South Carolina. Aerobic biodgradation rates decreased with distance above the water table, ranging from 0.20 to 1.5 g m −3 d −1 for toluene, from 0.24 to 0.38 g m −3 d −1 for xylene, from 0.09 to 0.24 g m −3 d −1 for cyclohexene, from 0.05 to 0.22 g m −3 d −1 for ethylbenzene, and from 0.02 to 0.08 g m −3 d −1 for benzene. Rates were highest in the capillary zone, where 68% of the total hydrocarbon mass that volatilized from the water table was estimated to have been biodegraded. Hydrocarbons were nearly completely degraded within 1m above the water table. This large loss underscores the importance of aerobic biodradation in limiting the transport of hydrocarbon vapors in the unsaturated zone and implies that vapor‐plume migration to basements and other points of contact may only be significant if a source of free product is present. Furthermore, because transport of the hydrocarbon in the unsaturated zone can be limited relative to that of oxygen and carbon dioxide, soil‐gas surveys conducted at hydrocarbon‐spill sites would benefit by the inclusion of oxygen‐ and carbon‐dioxide‐gas concentration measurements. Aerobic degradation kinetics in the unsaturated zone were approximately first‐order. First‐order rate constants near the water table were highest for cyclohexene (0.21–0.65 d −1 ) and nearly equivalent for ethylbenzene (0.11–0.31 d −1 ), xylenes (0.10–0.31 d −1 ), toluene (0.09–0.30 d −1 ), and benzene (0.07–0.31 d −1 ). Hydrocarbon mass loss rates at the water table resulting from the coupled aerobic biodgradation and volatilization process were determined by extrapolating gas transport rates through the capillary zone. Mass loss rates from groundwater were highest for toluene (0.20–0.84 g m −2 d −1 ), followed by xylenes (0.12–0.69 g m −2 d −1 ), cyclohexene (0.05–0.15 g m −2 d −1 ), ethylbenzene (0.02–0.12 g m −2 d −1 ), and benzene (0.01–0.04 g m −2 d −1 ). These rates exceed predicted rates of solubilization to groundwater, demonstrating the effectiveness of aerobic biodgradation and volatilization as a combined natural attenuation pathway.

Water Resources Research↗

USGS2012

Biodegradability of dissolved organic carbon in the Yukon River and its tributaries: Seasonality and importance of inorganic nitrogen

Northern high-latitude rivers transport large amounts of terrestrially derived dissolved organic matter (DOM) from boreal and arctic ecosystems to coastal areas and oceans. Current knowledge of the biodegradability of DOM in these rivers is limited, particularly for large rivers discharging to the Arctic Ocean. We conducted a seasonally comprehensive study of biodegradable dissolved organic carbon (BDOC) dynamics in the Yukon River and two of its tributaries in Alaska, USA. Distinct seasonal patterns of BDOC, consistent across a wide range of watershed size, indicate BDOC is transported year-round. Relative biodegradability (%BDOC) was greatest during winter, and decreased into spring and summer. Due to large seasonal differences in DOC concentration, the greatest concentrations of BDOC (mg C L −1 ) occurred during spring freshet, followed by winter and summer. While chemical composition of DOM was an important driver of BDOC, the overriding control of BDOC was mineral nutrient availability due to wide shifts in carbon (C) and nitrogen (N) stoichiometry across seasons. We calculated seasonal and annual loads of BDOC exported by the Yukon River by applying measured BDOC concentrations to daily water discharge values, and also by applying an empirical correlation between %BDOC and the ratio of DOC to dissolved inorganic N (DIN) to total DOC loads. The Yukon River exports &sim;0.2 Tg C yr −1 as BDOC that is decomposable within 28 days. This corresponds to 12–18% of the total annual DOC export. Furthermore, we calculate that the six largest arctic rivers, including the Yukon River, collectively export &sim;2.3 Tg C yr −1 as BDOC to the Arctic Ocean.

Global Biogeochemical Cycles↗

USGS2009

Fractionation of stable isotopes in perchlorate and nitrate during in situ biodegradation in a sandy aquifer

An in situ experiment was performed in a shallow alluvial aquifer in Maryland to quantify the fractionation of stable isotopes in perchlorate (Cl and O) and nitrate (N and O) during biodegradation. An emulsified soybean oil substrate that was previously injected into this aquifer provided the electron donor necessary for biological perchlorate reduction and denitrification. During the field experiment, groundwater extracted from an upgradient well was pumped into an injection well located within the in situ oil barrier, and then groundwater samples were withdrawn for the next 30 h. After correction for dilution (using Br– as a conservative tracer of the injectate), perchlorate concentrations decreased by 78% and nitrate concentrations decreased by 82% during the initial 8.6 h after the injection. The observed ratio of fractionation effects of O and Cl isotopes in perchlorate (e18O/e37Cl) was 2.6, which is similar to that observed in the laboratory using pure cultures (2.5). Denitrification by indigenous bacteria fractionated O and N isotopes in nitrate at a ratio of ~0.8 (e18O/e15N), which is within the range of values reported previously for denitrification. However, the magnitudes of the individual apparent in situ isotope fractionation effects for perchlorate and nitrate were appreciably smaller than those reported in homogeneous closed systems (0.2 to 0.6 times), even after adjustment for dilution. These results indicate that (1) isotope fractionation factor ratios (e18O/e37Cl, e18O/e15N) derived from homogeneous laboratory systems (e.g. pure culture studies) can be used qualitatively to confirm the occurrence of in situ biodegradation of both perchlorate and nitrate, but (2) the magnitudes of the individual apparent e values cannot be used quantitatively to estimate the in situ extent of biodegradation of either anion.

Environmental Chemistry↗

USGS2005

Biodegradation of N-nitrosodimethylamine in soil from a water reclamation facility

The potential introduction of N -nitrosodimethylamine (NDMA) into groundwater during water reclamation activities poses a significant risk to groundwater drinking supplies. Greater than 54% biodegradation of N -[methyl- 14 C]NDMA to 14 CO 2 or to 14 CO 2 and 14 CH 4 was observed in soil from a water reclamation facility under oxic or anoxic conditions, respectively. Likewise, biodegradation was significant in microcosms containing soil with no history of NDMA contamination. These results indicate that aerobic and anaerobic biodegradation of NDMA may be an effective component of NDMA attenuation in water reclamation facility soils.

Bioremediation Journal↗

USGS2005

Measuring rates of biodegradation in a contaminated aquifer using field and laboratory methods

Rates of biodegradation were measured in a petroleum hydrocarbon-contaminated aquifer using a combination of field and laboratory methods. These methods are based on tracking concentration changes of substrates (both electron donors and acceptors) or final products of microbial metabolism over time. Ground water at the study site (Hanahan, South Carolina) is anoxic, and sulfate reduction is the predominant terminal electron accepting process. Laboratory studies conducted with sediment cored from the site showed that 14 C-toluene was mineralized to 14 CO 2 with a first-order degradation rate constant (k tol ) of -0.01 d −1 under sulfate-reducing conditions. Under nitrate-amended, Fe(III)-amended, or nonamended (methanogenic) conditions, toluene was not significantly mineralized. 14 C-Benzene was degraded at low but measurable rates (k ben = -0.003 d −1 ) under sulfate-reducing conditions whereas degradation under methanogenic conditions was negligible. These results illustrate the extreme sensitivity of laboratory-measured biodegradation rates to terminal electron-accepting conditions, and show the necessity of carefully matching experimental conditions to in situ conditions. Concentration decreases of toluene along aquifer flowpaths, when the uncertainty of ground-water flow velocities was considered, indicated k tol values ranging from -0.0075 to -0.03 d −1 . Concentration decreases of sulfate and concentration increases of dissolved inorganic carbon (DIC), when normalized for assumed stoichiometric oxidation of toluene coupled to sulfate reduction, yielded a k so4 range of -0.005 to -0.02 d −1 , and a k DIC value range of +0.00075 to +0.003 d −1 . Because both laboratory and field methods have numerous sources of uncertainty, a combination of these methods is the most appropriate procedure for evaluating biodegradation rate constants in contaminated ground-water systems.

Groundwater↗

USGS1991

Aerobic biodegradation potential of subsurface microorganisms from a jet fuel-contaminated aquifer

In 1975, a leak of 83,000 gallons (314,189 liters) of jet fuel (JP-4) contaminated a shallow water-table aquifer near North Charleston, S.C. Laboratory experiments were conducted with contaminated sediments to assess the aerobic biodegradation potential of the in situ microbial community. Sediments were incubated with 14 C-labeled organic compounds, and the evolution of 14 CO 2 was measured over time. Gas chromatographic analyses were used to monitor CO 2 production and O 2 consumption under aerobic conditions. Results indicated that the microbes from contaminated sediments remained active despite the potentially toxic effects of JP-4. 14 CO 2 was measured from [ 14 C]glucose respiration in unamended and nitrate-amended samples after 1 day of incubation. Total [ 14 C]glucose metabolism was greater in 1 mM nitrate-amended than in unamended samples because of increased cellular incorporation of 14 C label. [ 14 C]benzene and [ 14 C]toluene were not significantly respired after 3 months of incubation. With the addition of 1 mM NO 3 , CO 2 production measured by gas chromatographic analysis increased linearly during 2 months of incubation at a rate of 0.099 μ mol g -1 (dry weight) day -1 while oxygen concentration decreased at a rate of 0.124 μ mol g -1 (dry weight) day -1 . With no added nitrate, CO 2 production was not different from that in metabolically inhibited control vials. From the examination of selected components of JP-4, the n -alkane hexane appeared to be degraded as opposed to the branched alkanes of similar molecular weight. The results suggest that the in situ microbial community is active despite the JP-4 jet fuel contamination and that biodegradation may be compound specific. Also, the community is strongly nitrogen limited, and nitrogen additions may be required to significantly enhance hydrocarbon biodegradation.

South Carolina↗

USGS2003

Preliminary assessment of microbial communities and biodegradation of chlorinated volatile organic compounds in wetlands at Cluster 13, Lauderick Creek area, Aberdeen Proving Ground, Maryland

A preliminary assessment of the microbial communities and biodegradation processes for chlorinated volatile organic compounds was con-ducted by the U.S. Geological Survey in wetlands at the Cluster 13, Lauderick Creek area at Aberdeen Proving Ground, Maryland. The U.S. Geological Survey collected wetland sediment samples from 11 sites in the Lauderick Creek area for microbial analyses, and used existing data to evaluate biodegradation processes and rates. The bacterial and methanogen communities in the Lauderick Creek wetland sediments were similar to those observed in a previous U.S. Geological Survey study at the West Branch Canal Creek wet-land area, Aberdeen Proving Ground. Evaluation of the degradation rate of 1,1,2,2-tetrachloroethane and the daughter compounds produced also showed similar results for the two wetlands. How-ever, a vertical profile of contaminant concentra-tions in the wetlands was available at only one site in the Lauderick Creek area, and flow velocities in the wetland sediment are unknown. To better evaluate natural attenuation processes and rates in the wetland sediments at Lauderick Creek, chemi-cal and hydrologic measurements are needed along ground-water flowpaths in the wetland at additional sites and during different seasons. Nat-ural attenuation in the wetlands, enhanced biore-mediation, and constructed wetlands could be feasible remediation methods for the chlorinated volatile organic compounds discharging in the Lauderick Creek area. The similarities in the microbial communities and biodegradation pro-cesses at the Lauderick Creek and West Branch Canal Creek areas indicate that enhanced bioreme-diation techniques currently being developed for the West Branch Canal Creek wetland area would be transferable to this area.

Maryland↗

USGS2015

Biodegradability of dissolved organic carbon in permafrost soils and aquatic systems: a meta-analysis

As Arctic regions warm and frozen soils thaw, the large organic carbon pool stored in permafrost becomes increasingly vulnerable to decomposition or transport. The transfer of newly mobilized carbon to the atmosphere and its potential influence upon climate change will largely depend on the degradability of carbon delivered to aquatic ecosystems. Dissolved organic carbon (DOC) is a key regulator of aquatic metabolism, yet knowledge of the mechanistic controls on DOC biodegradability is currently poor due to a scarcity of long-term data sets, limited spatial coverage of available data, and methodological diversity. Here, we performed parallel biodegradable DOC (BDOC) experiments at six Arctic sites (16 experiments) using a standardized incubation protocol to examine the effect of methodological differences commonly used in the literature. We also synthesized results from 14 aquatic and soil leachate BDOC studies from across the circum-arctic permafrost region to examine pan-arctic trends in BDOC. An increasing extent of permafrost across the landscape resulted in higher DOC losses in both soil and aquatic systems. We hypothesize that the unique composition of (yedoma) permafrost-derived DOC combined with limited prior microbial processing due to low soil temperature and relatively short flow path lengths and transport times, contributed to a higher overall terrestrial and freshwater DOC loss. Additionally, we found that the fraction of BDOC decreased moving down the fluvial network in continuous permafrost regions, i.e. from streams to large rivers, suggesting that highly biodegradable DOC is lost in headwater streams. We also observed a seasonal (January–December) decrease in BDOC in large streams and rivers, but saw no apparent change in smaller streams or soil leachates. We attribute this seasonal change to a combination of factors including shifts in carbon source, changing DOC residence time related to increasing thaw-depth, increasing water temperatures later in the summer, as well as decreasing hydrologic connectivity between soils and surface water as the thaw season progresses. Our results suggest that future climate warming-induced shifts of continuous permafrost into discontinuous permafrost regions could affect the degradation potential of thaw-released DOC, the amount of BDOC, as well as its variability throughout the Arctic summer. We lastly recommend a standardized BDOC protocol to facilitate the comparison of future work and improve our knowledge of processing and transport of DOC in a changing Arctic.

Biogeosciences↗

USGS2001

Methanogenic biodegradation of charcoal production wastes in groundwater at Kingsford, Michigan, USA

A house exploded in the City of Kingsford, Michigan USA. The explosion was caused by CH4 that leaked into the basement from the surrounding soil. Evidence suggests that biodegradation of products from the distillation and spillage at or near a former wood carbonization plant site was the major source of CH4 and CO2 in the groundwater system. The plant area is directly upgradient from deep groundwater, samples of which are green-yellow in colour, have a very strong odour of burnt wood, contain high concentrations of mononuclear aromatic and phenolic compounds, and extremely high concentrations of volatile fatty acids. The majority of the dissolved compounds in these groundwater samples have been shown, using laboratory microcosms, to be anaerobically biodegradable to CH4 and CO2. The biodegradable compounds, and the amounts of CH4 and CO2 produced in the microcosms, are consistent with observations from field samples.

Michigan↗

USGS2018

Validation of stable isotope ratio analysis to document the biodegradation and natural attenuation of RDX, ESTCP Project ER-201208

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a common soil contaminant at current and former military facilities, including many training and testing ranges. Because RDX is readily transported through soils to the subsurface, this nitramine explosive now also impacts groundwater and drinking water at numerous locations across the country. A significant issue with RDX contamination on ranges and at other military installations is that it often occurs over expansive areas, where in situ or ex situ treatment technologies are difficult to implement. One potential alternative for military ranges and other facilities is monitored natural attenuation (MNA), in which contaminant degradation by natural processes, including biodegradation, are evaluated. However, one limitation of this approach for RDX is the inability to accurately evaluate whether the nitramine is biodegrading under field conditions, as rates may be relatively slow. One potential technique to overcome this limitation is the use of compound-specific stable isotope analysis (CSIA), where biological contaminant destruction can be documented as changes in the ratio of stable isotopes of specific elements in a molecule; for RDX, ratios of 15 N/ 14 N and 13 C/ 12 C are relevant. The objective of this project is to validate a CSIA method to confirm and constrain rates of aerobic and anaerobic biodegradation of RDX at field sites. This technique can be utilized by DoD to provide critical data to support MNA as a remedy for treating this energetic in groundwater, and confirm the effectiveness of in situ enhanced bioremediation remedies. The stable isotopic composition of NO 3 - and NO 2 - was also measured when these anions co-occurred with RDX to evaluate whether these potential degradation products from RDX could be used to further demonstrate MNA in the field.

Report↗