CH4 Accumulation Research Articles

Mineralization rates of peat from eroding peat islands in reservoirs

Reservoirs are sources of greenhouses gases to the atmosphere, primarily due to organic carbon mineralization in flooded plants and soils to carbon dioxide (CO2) and methane (CH4). Floating peat islands are common in reservoirs that inundated peatlands. These islands can decompose on mass, or small pieces of peat can erode from islands to decompose in the water column or on the bottom of reservoirs. Here we used large 450 liter sealed enclosures to measure mineralization rates of small peat pieces and larger peat blocks collected from floating peat islands. Mineralization rates were calculated by quantifying dissolved inorganic carbon (DIC), CO2 and CH4 accumulation within the water and headspace of the enclosures over time. We found that peat did decompose under water, but rates of mineralization of peat pieces were not different than rates of mineralization of larger peat blocks. Mineralization rates ranged between 59 and l40 μg C g−1 d−1. Peat pieces acidified the water, shifting the bicarbonate equilibrium to almost exclusively dissolved CO2, which was then readily able to flux to the atmosphere. We estimated that 2.4–5.6% of peat carbon was mineralized annually, suggesting that fluxes of CO2 and CH4 from reservoirs that flood peatlands could last at minimum 18–42 years from this carbon source alone.

Contribution of winter to the annual CH4 emission from a eutrophied boreal lake

The springtime methane (CH4) emission from a small, eutrophied boreal lake was assessed during the winter ice-cover by measurement of gas ebullition and CH4 accumulation in the water column in association with the development of oxygen depletion after ice formation. The winter CH4 production was estimated to result in a loss of 3.6-7.9 g CH4 m(-2) from the lake to the atmosphere during the short period of ice melt. This could account for 22-48% of the annual CH4 emission from the pelagic zone of the lake. The contribution of winter to the annual CH4 release can be similar or even higher in seasonally ice-covered northern aquatic ecosystems than in northern terrestrial wetlands, thus winter must be considered in any studies into the aquatic CH4 emissions. The trophic state and wintertime oxygen conditions, linked to the changes in land-use in the catchments and climate, are important factors controlling the springtime lake CH4 emissions.

Kinetics of microbial Fe(III) oxide reduction in freshwater wetland sediments

The kinetics of microbial amorphous Fe(III) oxide reduction was investigated in sediments from a freshwater wetland in north central Alabama, USA. Fe(III) oxide concentrations decreased exponentially with time during anaerobic incubation of sediment slurries and homogenized surface sediments. Rates of organic carbon mineralization (ΣCO2 + CH4 accumulation) did not change markedly during the course of Fe(III) oxide reduction, which indicated that the exponential decline in Fe(III) oxide concentration over time resulted primarily from Fe(III) limitation rather than a decrease in organic matter decay rate. Initial rates of Fe(III) oxide reduction were linearly correlated with initial Fe(III) oxide concentrations in experiments with mixtures of Fe(III)‐rich and Fe(III)‐depleted sediment slurries. Similar results were obtained in experiments with sediment from various depth intervals in the upper 3 cm of freshly collected cores. These findings provide explicit evidence that microbial Fe(III) oxide reduction rates are first order with respect to amorphous Fe(III) oxide concentration in the wetland sediment. The observed first‐order relationship between Fe(III) oxide concentration and reduction rate is consistent with established models of surface area‐controlled mineral transformation. An experiment in which Fe(III) oxide‐rich sediment slurries were amended with different amounts of labile organic matter demonstrated a direct correlation between first‐order Fe(III) reduction rate constants and initial rates of organic carbon mineralization. These results provide empirical support for existing approaches to modeling organic matter decay‐dependent Fe(III) oxide reduction kinetics in sediments.

Greenhouse gases in non-oxygenated and artificially oxygenated eutrophied lakes during winter stratification.

Concentrations of dissolved methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) were measured in the water columns of non-oxygenated and artificially oxygenated, ice-covered eutrophied lakes in the mid-boreal zone in Finland during late winter 1997 and 1999. Sampling was conducted during winter stratification, the critical period for oxygen (O2) deficiency in seasonally ice-covered, thermally stratified lakes. Oxygen concentrations were maintained at least at a moderate level throughout the oxygenated water columns, whereas the non-oxygenated columns suffered anoxic hypolimnia. The mean concentrations of dissolved CH4 exceeding the atmospheric equilibrium were greater in the non-oxygenated water columns (20.6-154 microM) than in the oxygenated ones (0.01-1.41 microM). In contrast, the mean excess CO2 concentrations varied less between the non-oxygenated and oxygenated sites (0.28-0.47 and 0.25-0.31 mM, respectively). Oxygenated water columns had greater mean excess concentrations of N2O (0.018-0.032 microM) than the non-oxygenated ones (0.005-0.024 microM). If the accumulated greenhouse gas stores in the water columns during winter are assumed to be released to the atmosphere during the spring overturn, the global warming potentials (GWP, time horizon 100 yr) of these potential emissions at the non-oxygenated, eutrophic study sites ranged from 177 to 654 g CO2 equivalent (CO2-e) m-2 compared with 144 to 173 g CO2-e m-2 at the oxygenated sites. The increase in the accumulation of CH4 was the main reason for the higher GWP of the non-oxygenated sites. Anthropogenic eutrophication of lake ecosystems can generate increased CH4 emissions due to associated O2 depletion of their sediment and water column.

In Vitro Mixed Ruminal Microorganism Fermentation of Whole Cottonseed Coated with Gelatinized Corn Starch and Urea

We conducted an in vitro mixed ruminal microorganism fermentation study to determine the effect of coating whole cottonseed with gelatinized corn starch and feed grade urea. Treatments were arranged as a 3 × 4 factorial to provide three concentrations of starch (0.0, 2.5, and 5.0%) and four concentrations of urea (0.0, 0.25, 0.5, and 1.0%). All treatments were prepared from one lot of whole cottonseed. Batch culture fermentations were conducted using anaerobic medium that contained 20% (vol/vol) ruminal fluid in 160-ml serum bottles. Whole cottonseed was ground to pass through a 6-mm screen and weighed amounts (0, 0.4, 0.8, and 1.2g) were added to the serum bottles. As starch increased, H2,CH4, total volatile fatty acids, and molar proportions of propionate increased linearly, whereas pH, molar proportions of acetate, and the acetate to propionate ratio decreased linearly. l-Lactate concentrations were highest with 2.5% starch compared with 0 or 5.0%. As the amount of urea in the coating increased, pH and CH4 increased linearly, whereas H2 concentrations decreased linearly. Ammonia concentrations exhibited a quadratic response due to moderate increases with the addition of 0.25 and 0.5% urea, and a greater increase was observed with 1.0% urea. Interactions between starch and urea were observed for H2,CH4,NH3, and l-lactate. Concentrations of H2 decreased and CH4 was relatively constant as urea increased in the presence of 0 and 2.5% starch, but increased with 5% starch. l-Lactate concentrations were unchanged (0% starch), higher (2.5% starch), or lower (5.0% starch) as urea increased. Ammonia concentrations increased after urea exceeded 10% of the starch concentration. The addition of urea did not prevent the decline in pH, but did reduce H2 and CH4 accumulation with 2.5% starch.

Methane emissions from rice microcosms: The balance of production, accumulation and oxidation

In rice microcosms (Oryza sativa, var. Roma, type japonica),CH4 emission, CH4 production, CH4oxidation and CH4 accumulation were measured over an entirevegetation period. Diffusive CH4 emission was measured inclosed chambers, CH4 production was measured in soil samples,CH4 oxidation was determined from the difference between oxicand anoxic emissions, and CH4 accumulation was measured byanalysis of porewater and gas bubbles. The sum of diffusiveCH4 emission, CH4 oxidation, andCH4 accumulation was only 60% of the cumulativeCH4 production. The two values diverged during the first 50days (vegetative phase) and then again during the last 50 days (latereproductive phase and senescence) of the 150 day vegetation period. Duringthe period of day 50–100 (early reproductive phase/flowering), theprocesses were balanced. Most likely, gas bubbles and diffusion limitationare responsible for the divergence in the early and late phases. The effectof rice on CH4 production rates and CH4concentrations was studied by measuring these processes also in unplantedmicrocosms. Presence of rice plants lowered the CH4concentrations, but had no net effect on the CH4 productionrates.

Atmospheric composition calculations for evaluation of climate scenarios

The future radiative forcing by non-CO2 greenhouse gases depends strongly on the behavior of the OH radical, which represents the primary sink for CH4, CO and H(C)FCs in the atmosphere. We present a simple model to describe the changes in the concentration of the main greenhouse gases. The focus is on the description of the atmospheric chemistry of OH and the important tropospheric oxidant and greenhouse gas O3. Changes in the equilibrium concentrations of these oxidants will change the trends in the concentrations of greenhouse gases, especially CH4. The model is applied to the 1992 IPCC emissions scenarios, as well as to an IMAGE 2.0 scenario, based on “Conventional Wisdom” assumptions. We find the following major results: for the central estimate of emissions assuming no additional policies (IS92a), the concentration of CH4 keeps rising at rates similar to those observed over the last decades; results for the other IS92 scenarios range from stabilization early in the next century (IS92d) to an ever increasing rate of accumulation of CH4 in the atmosphere (IS92f), even though these scenarios assume no policy interventions. The IMAGE 2.0 Conventional Wisdom scenario is similar to IS92a before the year 2025; afterwards the expansion of agricultural area significantly decreases the emissions of hydrocarbons and NOX from savanna burning, not represented in the IS92 scenarios. This leads to stable levels of atmospheric CH4 after 2025.

Fate of methane in the Hudson River and Estuary

Methane (CH4) concentrations and oxidation rates were measured throughout the Hudson River Estuary in March and August of 1991. Methane concentrations ranged from 50 to 940 nM and were supersaturated with respect to the atmosphere along the entire length of the river, with generally higher CH4 values in the lower, saline portion of the estuary. A seasonally averaged diffusive flux to the atmosphere from the Hudson River was estimated to be 5.6 mg CH4 m−2 d−1, corresponding to an annual flux of 0.76 × 109 g CH4. The Hudson River Estuary also releases approximately 0.2 × 109 g CH4 annually to nearshore marine waters. Diffusive flux across the air/river interface was the dominant removal mechanism for Hudson River CH4 in March. In August, CH4 oxidation was the dominant CH4 sink in freshwater and brackish (<6‰) sections of the river, removing up to 70% of ambient CH4 per day compared to maximum daily removal rates of 13% in March. Thus methane oxidation can play a major role in limiting releases of CH4 to the atmosphere from rivers and other freshwater environments. Methane oxidation activity decreased rapidly as salinity increased, with less than 2% of ambient CH4 being oxidized per day at salinities greater than 25‰. Addition of NaCl or seawater to freshwater samples resulted in comparable inhibition of methanotrophic activity. Budget calculations showed that flux to the atmosphere and CH4 oxidation in March removed less water column CH4 than was supplied to the Hudson River over its entire length. In August, however, CH4 removal approximately equaled CH4 supply with the result that there was no net accumulation of CH4 over the length of the river.

Rate of accumulation and emission of N2, N2O and CH4 from a flooded rice soil

In a field experiment using microplots, a flooded Crowley silt loam (Typic Albaqualfs) rice soil was fertilized with 15N labelled (60–74 atom %) urea and KNO3. Emission of N2, N2O and CH4 and accumulation in soil were measured for 21 d after fertilizer application.

The warming of the industrialized middle latitudes 1985?2050: Causes and consequences

The dominant influence on global climate for the indefinite future is expected to be a warming in the middle and high latitudes of both hemispheres. The speed of the warming is uncertain. The warming in winter may exceed 1.0 degree per decade. The warming in summer is expected to be less. The cause is the accumulation of infra-red absorptive gases, especially CO2 and CH4, in the atmosphere. The sources are the combustion of fossil fuels, the destruction of forests and their soils, and, possibly, the warming itself, which can be expected to stimulate decay of organic matter in soils.

The influence of acidic gas absorption on certain metabolic processes occurring in anaerobically incubated soils

CH4 accumulation was markedly reduced and acetate accumulation was enhanced by the presence of a vial of alkali in flasks containing soils incubated anaerobically at a moisture content of 80% of saturation. The presence of the vial of alkali had little effect on acetate accumulation until after the commencement of CH4 formation. No hydrogen was found to accumulate in the soils studied regardless of whether acidic gases were absorbed during incubation. The effect of acidic gas absorption on other metabolic processes in two of the soils was studied. The absorption of acidic gases reduced the amounts of extractable Fe and S2− (or volatile mercaptans), the soil pH, and in the more acid soil (Tetonka) net ammonification during anaerobic incubation. In a further experiment the effect of the presence of a vial of alkali on gas, acetate, NH 4 + and S2− accumulation as well as pH changes during anaerobic incubation of the Tetonka soil treated with CaCO3 was studied. CH4, acetate and S2− accumulation were suppressed, net ammonification was little affected, and the soil pH values were higher as a result of the absorption of acidic gases. The rates of CO2, CH4, acetate and S2− accumulation were increased as a result of the addition of CaCO3 to the Tetonka soil.

The effect of nitrate and nitrous oxide on hydrogen and methane accumulation in anaerobically-incubated soils

The effect of KNO3 and N2O on the accumulation of CH4, H2 and denitrification products in two North Dakota soils during anaerobic incubation at 30°C was studied by means of gas chromatography. KNO3 and N2O (500 ppm N) reduced the rate of accumulation of CH4 by a Tetonka soil regardless of whether the soil was in an air-dried condition or had been pre-incubated and actively producing CH4 prior to the treatment application. Both KNO3 and N2O completely suppressed H2 accumulation by the remoistened air-dried soil; no H2 either in the presence or absence of added KNO3 or N2O was accumulated by the pre-incubated Tetonka soil subsequent to the treatment application. KNO3 (250 ppm N) reduced the rate of accumulation of CH4 by a Cavour loam during anaerobic incubation. No H2 was accumulated by this soil during anaerobic incubation. At equivalent K+ concentrations, KNO3 suppressed CH4 accumulation by the Tetonka and Cavour soils to a greater extent than did KCl.