Seasonal variation in sulfate reduction and methanogenesis in peaty sediments of eutrophic Lake Loosdrecht,The Netherlands

During one year, concentration profiles of sulfate and methane were measured in sediment cores of eutrophic Lake Loosdrecht. Sulfate concentrations decreased exponentially with depth towards a constant threshold value of 7.6 ± 6.1 μM. Concentration profiles were used to calculate fluxes of sulfate and methane and to estimate the anaerobic mineralization rate. Anaerobic mineralization was highest in autumn which was probably due to an increased sedimentation of easily degradable organic carbon. At high rates (>600 μ mol organic carbon .m⁻².h⁻¹), sulfate reduction appeared to be limited by sulfate and methanogenesis accounted for over 80% of the anaerobic mineralization. At low anaerobic mineralization rates, measured in winter and spring, sulfate reduction was predominant. There was little methanogenesis below 5 cm depth in the sediment which indicated a rapid decrease of degradable organic matter with depth. There was a remarkable difference, especially in winter, between methane fluxes which were measured in batch experiments and those calculated from the concentration profiles in the sediment. These differences may be due to methane diffusing upward from deep layers.     

Carbon flow across the sediment-water interface in Lake Vechten,The Netherlands

The turnover and exchange rates, as well as the diffusion processes, concerning the input and output of carbon compounds at the mud-water interface, were studied. The carbon input rates were derived from the annual sedimentation rates of particulate organic matter (about 1 100 kg C · yr⁻¹). The nature of the sedimented POC, and its breakdown pathways and turnover rates towards important metabolic intermediates in methanogenesis, were examined. The breakdown kinetics ofChlorella cell walls, a dominant green alga in Lake Vechten, was studied using U-¹⁴C-labelled cell walls. The breakdown of the cell walls appears to the rate-limiting step in anaerobic mineralization. Using first order kinetic equations, and HPLC and GLC and radio-chemical methods, turnover rate constants (k-values) of between 0.18 and 0.32 day⁻¹ and pool sizes of algal cell walls of 37 to 80 μg · g⁻¹ wet mud were found, giving turnover rates of 7.7 to 25.6 μg · g⁻¹ · day⁻¹ of cell wall material. The turnover rates (k-values between 0.07 and 0.31 h⁻¹) of acetate, the most important breakdown product, and its concentration gradients (between 5 and 30 μmol) and diffusion coefficient (D_s = 2.2 × 10⁻⁶ cm² · s⁻¹) just in and above mud-water interface, was quantified. The diffusion of acetate, within the sediments, could not account for the turnover rates observed. Finally, from acetate flux data and from those on the rates of formation of carbon dioxide and methane, the output of carbon and its cycling in Lake Vechten are discussed.     

A comparative assessment of four methods for estimating ammonia emissions at microclimatic locations in a dairy building

Ammonia emissions were estimated at five microclimatic locations in a free stall dairy building using four different methods. Measurements were performed simultaneously with the different methods to enable comparison. In the first method, the rate of ammonia emission from manure was theoretically modeled utilizing Fick’s law and boundary layer theory. In the second method, recirculation flux-chamber technique was used to model ammonia emission from manure. In the third and fourth methods, respectively, carbon dioxide and methane balances were employed to calculate ammonia emission. The mean ammonia emissions measured from the five locations using the different methods ranged from 0.10 to 0.15 g m⁻² h⁻¹. The percentage of variation of ammonia emission from the different location ranged between 8 and 52% for the different methods. Recorded ammonia emission rates in the dairy building were from 0.04 to 0.25 g m⁻² h⁻¹. The percentage of variation in ammonia, carbon dioxide, methane, and manure properties in the building was 50%. Two-way statistical analysis of variance showed that there were no significant differences (p > 0.63) between the four different methods or between the measurements obtained at the five locations (p > 0.90).     

Toluene degradation in a polyurethane biofilter at high loading

In the present study, toluene elimination in the polyurethane (PU) biofilter during long-term (145 day) operation was characterized, and assessed the effects of changing the inlet loading and space velocity (SV). A very high elimination capacity of 3.7 kg·m⁻³·h⁻¹ was obtained at an inlet loading of 4.0 kg·m^–3·h⁻¹ (inlet toluene concentration of 900 ppmv at a SV of 1,040 h⁻¹). Backwashing with irrigation and compressed air allowed maintenance of a pressure drop of < 80 mm H₂O·m⁻¹-filter at an SV of 830 h⁻¹ and an elimination efficiency of > 90% during the 145 day of operation. In conclusion, the PU biofilter can overcome the problems of clogging caused by excess biomass growth and of low treatment capacities of conventional biofilters.     

Physiology and kinetics of trimethylamine conversion by two methylotrophic strains in continuous cultivation systems

The change of dilution rate (D) on both Methylophilus methylotrophus NCIMB11348 and Methylobacterium sp. RXM CCMI908 growing in trimethylamine (TMA) chemostat cultures was studied in order to assess their ability to remove odours in fish processing plants. M. methylotrophus NCIMB11348 was grown at dilution rates of 0.012–0.084 h⁻¹ and the biomass level slightly increased up to values of D around 0.07 h⁻¹. The maximum cell production rate was obtained at 0.07 h⁻¹ corresponding to a maximum conversion of carbon into cell mass (35%). The highest rate of TMA consumption was 3.04 mM h⁻¹ occurring at D=0.076 h⁻¹. Methylobacterium sp. RXM CCMI908 was grown under similar conditions. The biomass increased in a more steep manner up to values of D around 0.06 h⁻¹. The maximum cell production rate (0.058 g l⁻¹h⁻¹) was obtained in the region close to 0.06 h⁻¹ where a maximum conversion of the carbon into cell mass (40%) was observed. The maximum TMA consumption was 2.33 mM h⁻¹ at D=0.075 h⁻¹. The flux of carbon from TMA towards cell synthesis and carbon dioxide in both strains indicates that the cell is not excreting products but directing most of the carbon source to growth. Carbon recovery levels of approximately 100% show that the cultures are carbon-limited. Values for theoretical maximum yields and maintenance coefficients are presented along with a kinetic assessment based on the determination of the substrate saturation constant and maximum growth rate for each organism. Received: 25 February 1999 / Received revision: 14 May 1999 / Accepted: 17 May 1999     

Relations between carbon dioxide fluxes and environmental factors of Kobresia humilis meadows and Potentilla fruticosa meadows

Carbon dioxide fluxes of Kobresia humilis and Potentilla fruticosa shrub meadows, two typical ecosystems in the Qinghai-Tibet Plateau, were measured by eddy covariance technology and the data collected in August 2003 were employed to analyze the relations between carbon dioxide fluxes and environmental factors of the ecosystems. August is the time when the two ecosystems reach their peak leaf area indexes and stay stable, and also the period when the net carbon absorptions of Kobresia humilis and Potentilla fruticosa shrub meadows reach 56.2 g C·m⁻² and 32.6 g C·m⁻², with their highest daily carbon dioxide absorptions standing at 12.7 μmol·m⁻²·s⁻¹ and 9.3 μmol·m⁻²·s⁻¹, and their highest carbon discharges at 5.1 μmol·m⁻²·s⁻¹ and 5.7 μmol·m⁻²·s⁻¹, respectively. At the same photosynthetic photo flux densities (PPFD), the carbon dioxide-uptake rate of the Kobresia humilis meadow is higher than that of the Potentilla fruticosa shrub meadow; where the PPFD are higher than 1,200 μmol·m⁻²·s⁻¹. The carbon dioxide uptake rates of the two ecosystems declined as air temperature increased, but the carbon dioxide uptake rate of the Kobresia humilis meadow decreased more quickly (−0.086) than that of the Potentilla fruticosa shrub meadow (−0.016). Soil moistures exert influence on the soil respirations and this varies with the vegetation type. The daily carbon dioxide absorptions of the ecosystems increase with increased diurnal temperature differences and higher diurnal temperature differences result in higher carbon dioxide exchanges. There exists a negative correlation between the vegetation albedos and the carbon dioxide fluxes. Translated from Acta Bot Boreal—Occident Sin, 2006, 26(1): 133–142 [译自: 西北植物学报]     

Production of 1,3-Propanediol by Clostridium butyricum VPI 3266 in continuous cultures with high yield and productivity

The effects of dilution rate and substrate feed concentration on continuous glycerol fermentation by Clostridium butyricum VPI 3266, a natural 1,3-propanediol producer, were evaluated in this work. A high and constant 1,3-propanediol yield (around 0.65 mol/mol), close to the theoretical value, was obtained irrespective of substrate feed concentration or dilution rate. Improvement of 1,3-propanediol volumetric productivity was achieved by increasing the dilution rate, at a fixed feed substrate concentration of 30, 60 or 70 g l⁻¹. Higher 1,3-propanediol final concentrations and volumetric productivities were also obtained when glycerol feed concentration was increased from 30 to 60 g l⁻¹, at D=0.05–0.3 h⁻¹, and from 60–70 g l⁻¹, at D=0.05 and 0.1 h⁻¹·30 g l⁻¹ of 1,3-propanediol and the highest reported value of productivity, 10.3 g l⁻¹ h⁻¹, was achieved at D=0.30 h⁻¹ and 60 g l⁻¹ of feed glycerol. A switch to an acetate/butyrate ratio higher than one was observed for 60 g l⁻¹ of feed glycerol and a dilution rate higher than 0.10 h⁻¹; moreover, at D=0.30 h⁻¹ 3-hydroxypropionaldehyde accumulation was observed for the first time in the fermentation broth of C. butyricum.     

Major substrates for microbial sulfate reduction in the sediments of Ise Bay, Japan

To clarify the anaerobic microbial interactions in the process of carbon mineralization in marine eutrophic environments, the microbial sulfate reduction and methane production rates were examined in coastal marine sediments of Ise Bay, Japan, in autumn 1990. Sulfate reduction rates (51–210 nmol ml⁻¹ day⁻¹ at 24°C) were much higher than the methane production ones (<1.78 nmol ml⁻¹ day⁻¹) in the surface sediments (top 2 cm) at the six stations surveyed (water depth: 10.7–23.3 m). Substrates for sulfate-reducing bacteria (SRB) were estimated after the addition of a specific inhibitor for SRB (20 mmol l⁻¹ molybdate) into the sediment slurry, from the substrate accumulation rates. In the presence of the inhibitor, sulfate reduction was completely stopped and volatile fatty acids (mainly acetate) were accumulated, although hydrogen was not. Methane production occurred markedly accompanied by consumption of the accumulated acetate from the third day after the addition of molybdate. The maximum rate of methane production was 1.2–1.9 μmol ml⁻¹ day⁻¹, which was similar to those in highly polluted freshwater sediments such as the Tama River, Tokyo, Japan. These results show that acetate is a common major substrate for sulfate reduction and methane production, and SRB competitively inhibit potential acetoclastic methanogenesis in coastal sediments. Methanogens may potentially inhabit the sediments at low levels of population density and activity.     

Treatment of phenol in an anaerobic fluidized bed reactor (AFBR): continuous and batch regime

Results of this study describe the feasibility of anaerobic treatment of highly concentrated phenol synthetic wastewater using an anaerobic fluidized bed reactor (AFBR) in both continuous and batch modes. Wastewater with a maximum load of 2,100 mg C·l⁻¹ was prepared using phenol (maximum concentration of 1,600 mg C·l⁻¹) as substrate and a mixture of acetic, propionic and butyric acids (500 mg C·l⁻¹) as co-substrate. AFBR reached total organic carbon (TOC) and phenol removal efficiency over 95% treating the highest organic loading rate (OLR) containing phenol studied for this kind of reactor (5.03 g C·l⁻¹·d⁻¹). The phenol loading rate rise caused volumetric biogas rate increase up to 4.4 l·l⁻¹·d⁻¹ (average yield of 0.28 l CH₄·g⁻¹ COD_removed) as well as variation in the biogas composition; the CO₂ percentage increased while the CH₄ percentage decreased. Morphological examination of the bioparticles at 4.10 g C·l⁻¹·d⁻¹, revealed significant differences in the biofilm structure, microbial colonization and bacterial morphological type development. The five batch assays showed that phenol degradation may be favoured by the presence of volatile fatty acids (VFAs) (co-metabolism), whereas VFAs degradation may be inhibited by phenol. AFBR reached initial phenol degradation velocity of 0.25 mg C·l⁻¹·min⁻¹.     

Greenhouse gas emissions and carbon sequestration potential in restored wetlands of the Canadian prairie pothole region

North American prairie pothole wetlands are known to be important carbon stores. As a result there is interest in using wetland restoration and conservation programs to mitigate the effects of increasing greenhouse gas concentration in the atmosphere. However, the same conditions which cause these systems to accumulate organic carbon also produce the conditions under which methanogenesis can occur. As a result prairie pothole wetlands are potential hotspots for methane emissions. We examined change in soil organic carbon density as well as emissions of methane and nitrous oxide in newly restored, long-term restored, and reference wetlands across the Canadian prairies to determine the net GHG mitigation potential associated with wetland restoration. Our results indicate that methane emissions from seasonal, semi-permanent, and permanent prairie pothole wetlands are quite high while nitrous oxide emissions from these sites are fairly low. Increases in soil organic carbon between newly restored and long-term restored wetlands supports the conclusion that restored wetlands sequester organic carbon. Assuming a sequestration duration of 33 years and a return to historical SOC densities we estimate a mean annual sequestration rate for restored wetlands of 2.7 Mg C ha⁻¹year⁻¹ or 9.9 Mg CO₂ eq. ha⁻¹ year⁻¹. Even after accounting for increased CH₄ emissions associated with restoration our research indicates that wetland restoration would sequester approximately 3.25 Mg CO₂ eq. ha⁻¹year⁻¹. This research indicates that widescale restoration of seasonal, semi-permanent, and permanent wetlands in the Canadian prairies could help mitigate GHG emissions in the near term until a more viable long-term solution to increasing atmospheric concentrations of GHGs can be found.     

Diacetyl fermentation coupled with pervaporation using oleyl alcohol supported liquid membrane

Pervaporation using oleyl alcohol supported liquid membrane was successfully applied to diacetyl fermentation by immobilized lactic acid bacteria. Diacetyl productivity was about 10 g·m⁻³·h⁻¹, while productivity during batch fermentation was about 6 g·m⁻³·h⁻¹. Diacetyl yield from consumed glucose was about 0.04 g·g⁻¹ which was 4 times as large as that of batch fermentation. The pervaporation functioned favorably on actual fermentation broth. The flux of the permeate and the diacetyl separation factor for the pervaporation were about 9 g·m⁻²·h⁻¹ and 36, respectively, and these values were maintained at almost constant levels during fermentation. Diacetyl concentration in the permeate was about 2 kg·m⁻³, which is sufficiently high for commercial use.     

Continuous bio-catalytic conversion of sugar mixture to acetone–butanol–ethanol by immobilized <Emphasis Type="Italic">Clostridium acetobutylicum</Emphasis> DSM 792

Continuous production of acetone, n-butanol, and ethanol (ABE) was carried out using immobilized cells of Clostridium acetobutylicum DSM 792 using glucose and sugar mixture as a substrate. Among various lignocellulosic materials screened as a support matrix, coconut fibers and wood pulp fibers were found to be promising in batch experiments. With a motive of promoting wood-based bio-refinery concept, wood pulp was used as a cell holding material. Glucose and sugar mixture (glucose, mannose, galactose, arabinose, and xylose) comparable to lignocellulose hydrolysate was used as a substrate for continuous production of ABE. We report the best solvent productivity among wild-type strains using column reactor. The maximum total solvent concentration of 14.32 g L⁻¹ was obtained at a dilution rate of 0.22 h⁻¹ with glucose as a substrate compared to 12.64 g L⁻¹ at 0.5 h⁻¹ dilution rate with sugar mixture. The maximum solvent productivity (13.66 g L⁻¹ h⁻¹) was obtained at a dilution rate of 1.9 h⁻¹ with glucose as a substrate whereas solvent productivity (12.14 g L⁻¹ h⁻¹) was obtained at a dilution rate of 1.5 h⁻¹ with sugar mixture. The immobilized column reactor with wood pulp can become an efficient technology to be integrated with existing pulp mills to convert them into wood-based bio-refineries.     

Partitioning Effects during Terminal Carbon and Electron Flow in Sediments of a Low-Salinity Meltwater Pond near Bratina Island, McMurdo Ice Shelf, Antarctica

A study of anaerobic sediments below cyanobacterial mats of a low-salinity meltwater pond called Orange Pond on the McMurdo Ice Shelf at temperatures simulating those in the summer season (<5°C) revealed that both sulfate reduction and methane production were important terminal anaerobic processes. Addition of [2-¹⁴C]acetate to sediment samples resulted in the passage of label mainly to CO₂. Acetate addition (0 to 27 mM) had little effect on methanogenesis (a 1.1-fold increase), and while the rate of acetate dissimilation was greater than the rate of methane production (6.4 nmol cm⁻³ h⁻¹ compared to 2.5 to 6 nmol cm⁻³ h⁻¹), the portion of methane production attributed to acetate cleavage was <2%. Substantial increases in the methane production rate were observed with H₂ (2.4-fold), and H₂ uptake was totally accounted for by methane production under physiological conditions. Formate also stimulated methane production (twofold), presumably through H₂ release mediated through hydrogen lyase. Addition of sulfate up to 50-fold the natural levels in the sediment (interstitial concentration, ~0.3 mM) did not substantially inhibit methanogenesis, but the process was inhibited by 50-fold chloride (36 mM). No net rate of methane oxidation was observed when sediments were incubated anaerobically, and denitrification rates were substantially lower than rates for sulfate reduction and methanogenesis. The results indicate that carbon flow from acetate is coupled mainly to sulfate reduction and that methane is largely generated from H₂ and CO₂ where chloride, but not sulfate, has a modulating role. Rates of methanogenesis at in situ temperatures were four- to fivefold less than maximal rates found at 20°C.     

Kinetic analysis on the two-step processes of AOB and NOB in aerobic nitrifying granules

Complete granulation of nitrifying sludge was achieved in a sequencing batch reactor. For the granular sludge, batch experiments were conducted to characterize the kinetic features of ammonia oxidizers (AOB) and nitrite oxidizers (NOB) in the granules using the respirometric method. A two-step nitrification model was established to determine the kinetic parameters of both AOB and NOB. In addition to nitrification reactions, the new model also took into account biomass maintenance and mass transfer through the granules. The yield coefficient, maximum specific growth rate, and affinity constant for ammonium for AOB were 0.21 g chemical oxygen demand (COD) g⁻¹ N, 0.09 h⁻¹, and 9.1 mg N L⁻¹, respectively, whereas the corresponding values for NOB were 0.05 g COD g⁻¹ N, 0.11 h⁻¹, and 4.85 mg N L⁻¹, respectively. The model developed in this study performed well in simulating the oxygen uptake rate and nitrogen conversion kinetics and in predicting the oxygen consumption of the AOB and NOB in aerobic granules.     

Biodegradation kinetics of 1,4-benzoquinone in batch and continuous systems

Combining chemical and biological treatments is a potentially economic approach to remove high concentration of recalcitrant compounds from wastewaters. In the present study, the biodegradation of 1,4-benzoquinone, an intermediate compound formed during phenol oxidation by chlorine dioxide, was investigated using Pseudomonas putida (ATCC 17484) in batch and continuous bioreactors. Batch experiments were conducted to determine the effects of 1,4-benzoquinone concentration and temperature on the microbial activity and biodegradation kinetics. Using the generated data, the maximum specific growth rate and biodegradation rate were determined as 0.94 h⁻¹ and 6.71 mg of 1,4-benzoquinone l⁻¹ h⁻¹. Biodegradation in a continuous bioreactor indicated a linear relationship between substrate loading and biodegradation rates prior to wash out of the cells, with a maximum biodegradation rate of 246 mg l⁻¹ h⁻¹ observed at a loading rate of 275 mg l⁻¹ h⁻¹ (residence time: 1.82 h). Biokinetic parameters were also determined using the steady state substrate and biomass concentrations at various dilution rates and compared to those obtained in batch cultures.     

Microbial community of acetate utilizing denitrifiers in aerobic granules

Nitrite accumulates during biological denitrification processes when carbon sources are insufficient. Acetate, methanol, and ethanol were investigated as supplementary carbon sources in the nitrite denitrification process using biogranules. Without supplementary external electron donors (control), the biogranules degraded 200 mg l⁻¹ nitrite at a rate of 0.27 mg NO₂–N g⁻¹ VSS h⁻¹. Notably, 1,500 mg l⁻¹ acetate and 700 mg l⁻¹ methanol or ethanol enhanced denitrification rates for 200 mg l⁻¹ nitrite at 2.07, 1.20, and 1.60 mg NO₂–N g⁻¹ VSS h⁻¹, respectively; these rates were significantly higher than that of the control. The sodium dodecyl sulfate polyacrylamide gel electrophoresis of the nitrite reductase (NiR) enzyme identified three prominent bands with molecular weights of 37–41 kDa. A linear correlation existed between incremental denitrification rates and incremental activity of the NiR enzyme. The NiR enzyme activity was enhanced by the supplementary carbon sources, thereby increasing the nitrite denitrification rate. The capacity of supplementary carbon source on enhancing NiR enzyme activity follows: methanol > acetate > ethanol on molar basis or acetate > ethanol > methanol on an added weight basis.     

Production of nisin Z using <Emphasis Type="Italic">Lactococcus lactis</Emphasis> IO-1 from hydrolyzed sago starch

A membrane bioreactor for production of nisin Z was constructed using Lactococcus lactis IO-1 in continuous culture using hydrolyzed sago starch as carbon source. A strategy used to enhance the productivity of nisin Z was to maintain the cells in a continuous growth at high cell concentration. This resulted in a volumetric productivity of nisin Z, as 50,000 IU l⁻¹ h⁻¹ using a cell concentration of 15 g l⁻¹, 30^°C, pH 5.5 and a dilution rate of 1.24 h⁻¹. Adding 10 g l⁻¹ YE and 2 g l⁻¹ polypeptone, other inducers were unnecessary to maintain production of nisin. The operating conditions of the reactor removed nisin and lactate, thus minimizing their effects which allowed the maintenance of cells in continuous exponential growth phase mode with high metabolic activity.     

Influence of culture vessel characteristics and agitation rate on gaseous exchange,hydrodynamic stress,and growth of embryogenic cork oak (<Emphasis Type="BoldItalic">Quercus suber</Emphasis> L.) cultures

Somatic embryogenesis can be induced in the leaves of cork oak (Quercus suber L.) trees. The use of this propagation system in multivarietal forestry requires the mass production of cloned plants at low cost. Investigations were made into the influence of three types of Erlenmeyer flask and three orbiting speeds (60, 110, and 160 rpm) on oxygen transfer rate (K_L a), the shear force index (SFI), biomass production, and the proliferation of embryogenic clumps (EMCs) in cultures during the proliferation phase. K_L a varied between 0.11 and 1.47 h⁻¹ without biomass production being limited by oxygen availability. The EMCs grew even in hypoxic conditions, although the suppression of gaseous exchange strongly reduced biomass production. Cultures with different levels of hydrodynamic stress and SFI values (1.4·10⁻³–8.8·10⁻³ cm min⁻¹) were obtained. Proliferation rates of EMCs increased with agitation rate and the SFI. The largest number of EMCs was obtained in baffled flasks agitated at 160 rpm (K_L a of 1.47 h⁻¹, and SFI of 8.8·10⁻³ cm min⁻¹) with mild hydrodynamic stress enhancing growth. Biomass production increased with agitation and hydrodynamic stress, but only when the SFI value was below 5·10⁻³ cm min⁻¹. The greatest biomass production was obtained in smooth 100 ml flasks agitated at 160 rpm. The differentiation of embryos was favoured by the lowest K_L a (0.11 h⁻¹) and SFI (1.40·10³ cm min⁻¹) values, achieved using these flasks when agitated at 60 rpm.     

Biotreatment of phenol-contaminated wastewater in a spiral packed-bed bioreactor

A spiral packed-bed bioreactor inoculated with microorganisms obtained from activated sludge was used to conduct a feasibility study for phenol removal. The reactor was operated continuously at various phenol loadings ranging from 53 to 201.4 g m⁻³ h⁻¹, and at different hydraulic retention times (HRT) in the range of 20–180 min to estimate the performance of the device. The results indicated that phenol removal efficiency ranging from 82.9 to 100% can be reached when the reactor is operated at an HRT of 1 h and a phenol loading of less than 111.9 g m⁻³ h⁻¹. At an influent phenol concentration of 201.4 g m⁻³, the removal efficiency increased from 18.6 to 76.9% with an increase in the HRT (20–120 min). For treatment of phenol in the reactor, the maximum biodegradation rate (V _m) was 1.82 mg l⁻¹ min⁻¹; the half-saturation constant (K _s), 34.95 mg l⁻¹.     

Methane oxidation rates in forest soils and their controlling variables: a review and a case study in Korea

Methane is one of the strongest of the greenhouse gases, being 30-fold more radiatively active than carbon dioxide on a molar basis. In addition, its atmospheric concentrations have increased by 1% per year since the Industrial Revolution. As such, the dynamics of methane is of great importance for the prediction of global climatic changes caused by increasing concentrations of greenhouse gases in the atmosphere. One of the most important biological sinks for methane is forest soils, where methanotrophic bacteria oxidize methane to carbon dioxide. Based on data mined from a review of the literature, we determined that the mean methane oxidation rate was 1.90 mg CH₄ m⁻² day⁻¹ and that the main variables controlling this rate were soil water content and inorganic nitrogen in the soils. In contrast, the effects of temperature and pH are minimal. In addition to reviewing the literature, we monitored methane oxidation rates in a temperate forest soil in Korea on a monthly basis for a year, using a static chamber method. The mean oxidation rate was 1.96 mg CH₄ m⁻² day⁻¹ and was positively correlated with nitrate concentration in the soil.