摘要:

Three scales of temporal variability were present in methane (CH4) flux data collected during a 2.5 year (mid‐1990–1992) study at a small, poor fen in southeastern New Hampshire. (1) There was a strong seasonality to the fluxes (high in summer); monthly average fluxes range from 21.4 mg CH4m−2d−1(February 1992) to 639.0 mg CH4m−2d−1(July 1991). Annual fluxes were 68.8 g CH4m−2(1991) and 69.8 g CH4m−2(1992). (2) There was interannual variability; distribution of flux intensity was very different from 1991 to 1992, particularly the timing and rapidity of the onset of higher fluxes in the spring. (3) There was a high degree of variability in CH4flux during the warm season; four successive weekly flux rates in July 1991 were 957, 1044, 170, and 491 mg CH4m−2d−1. Fluxes were correlated with peat temperature (r2=0.44) but only weakly with depth to water table (r2= 0.14 for warm season data). Warm season fluxes appeared to be suppressed by rainstorms. Along with methane flux data we present an analysis of this temporal variability in flux, using a peatland soil climate model developed for this site. The model was driven by daily air temperature, precipitation, and net radiation; it calculated daily soil temperature and moisture profiles, water table location, and ice layer thickness. Temperature profiles were generally in good agreement with field data. Depth to water table simulations were good in 1992, fair in 1990, and poor in the summer of 1991. Using model‐simulated peat climate and correlations to methane flux developed from the field data, simulated methane fluxes exhibited the same three modes of temporal variability that were present in the field flux data, though the model underestimated peak fluxes in 1990 and 1991. We conclude that temporal variability in flux is significantly influenced by climate/weather variability at all three scales and that rainfall appears to suppress methane flux for at least seve

ISSN:0886-6236    

DOI:10.1029/94GB01839

年代:1994

数据来源: WILEY

摘要:

We investigated changes in soil‐atmosphere flux of CH4, N2O, and NO resulting from the succession of pasture to forest in the Atlantic lowlands of Costa Rica. We studied a dozen sites intensively for over one year in order to measure rates and to understand controlling mechanisms for gas exchange. CH4flux was controlled primarily by soil moisture content. Soil consumption of atmospheric CH4was greatest when soils were relatively dry. Forest soils consumed CH4while pasture soils which had poor drainage generally produced CH4. The seasonal pattern of N2O emissions from forest soils was related exponentially to soil water‐filled pore space. Annual average N2O emissions correlated with soil exchangeable NO3−concentrations. Soil‐atmosphere NO flux was greatest when soils were relatively dry. We found the largest NO emissions from abandoned pasture sites. Combining these data with those from another study in the Atlantic lowlands of Costa Rica that focused on deforestation, we present a 50‐year chronosequence of trace gas emissions that extends from natural conditions, through disturbance and natural recovery. The soil‐atmosphere fluxes of CH4and N2O and of NO may be restored to predisturbance rates during secondary succession. The changes in trace gas emissions following deforestation, through pasture use and secondary succession, may be explained conceptually through reference to two major controlling factors, nitrogen availability and soil‐atmosphere diffusive exchange of gases as it is influenced by soil moisture content and so

ISSN:0886-6236    

DOI:10.1029/94GB01660

年代:1994

数据来源: WILEY

摘要:

The global distribution of nitrogen input via application of chemical nitrogenous fertilizers to agricultural ecosystems is presented. The suite of 1° (latitude/longitude) resolution data bases includes primary data on fertilizer consumption, as well as supporting data sets defining the distribution and intensity of agriculture associated with fertilizer use. The data were developed from a variety of sources and reflect conditions for the mid‐1980s. East Asia, where fertilizer use is increasing at ∼10%/year, accounted for ∼37% of the total, while North America and western Europe, where fertilizer use is leveling off, accounted for 17% and 14% of global use, respectively. Former centrally planned economies of Europe consumed one fifth of the 1984 total, but rapid increases in the 1980s are slowing, and consumption trends are variable. The most widely used chemical nitrogenous fertilizer is urea which accounted for 40% of the world's total in the mid‐1980s. While almost every country consumes urea, ∼75% of the large East Asian fertilizer use is supplied by this one fertilizer. Ammonium nitrate, used primarily in the former centrally planned economies of Europe, in West Asia, and in Africa, accounted for about one quarter of global consumption. These data were used to estimate distributions of the annual emission of nitrous oxide (N2O) and of ammonia (NH3) associated with the use of fertilizers. Applying published ranges of emission coefficients for fertilizer types in the data base yields a median emission of 0.1 Tg N2O‐N, with lower and upper values of 0.03 and 2.0 Tg N2O‐N in 1984. This equals<1% to ∼3% of the total nitrogen applied via commercial fertilizers and represents<1% to 15% of the annual emission of N2O from terrestrial sources. Assuming that the ∼4% annual increase in consumption of nitrogenous fertilizers during the 1980s corresponds to a ∼4% rise in the release of N2O‐N, yearly increases in emissions from fertilizer use are<0.01 to 0.08 Tg N2O‐N equal to<1% to 3% of the current growth of atmospheric nitrous oxide. However, since no measurements of fertilizer‐derived nitrous oxide emissions are available for agricultural environments in the tropics/subtropics, where ∼40% of fertilizer N is consumed and where consumption is increasing rapidly, relative contributions of climatic regions to current and future emissions remain uncertain. Ammonia emission coefficients for simple groups of fertilizer types were applied to derive the global distribution of ammonia volatilization associated with nitrogenous fertilizer consumption. The 1984 total of ∼5–7 Tg NH3‐N, about 10–15% of the annual ammonia source, is concentrated overwhelmingly in subtropical Asia owing to the dominant use of urea with high rates of volatilization. However, the paucity of measurements in representative ecological and management environments suggests that the magnitude and distribution of current and future ammonia emission fr

ISSN:0886-6236    

DOI:10.1029/94GB01906

年代:1994

数据来源: WILEY

摘要:

The loss of carbon and organic nitrogen from the terrestrial ecosystem via streams and rivers is dependent on a number of factors such as basin vegetation, geography, geology, climate, and hydrology. We studied the export of dissolved carbon and nitrogen from 26 rivers varying in size from 45 to 92,500 km2located in Atlantic Canada. Twenty‐four of the basins studied were free of significant anthropogenic activity and were covered with coniferous and mixed hardwood forests. Our results showed that total organic carbon loss from the region, normalized for area, was approximately 29 kg ha−1yr−1, while inorganic C was considerably lower at 4.3 kg ha−1yr−1. We developed predictive statistical models using total precipitation, basin size, and basin slope to predict the export of organic carbon and nitrogen. Our results suggest that increases in regional precipitation will most likely increase the loss of organic carbon and nitrogen from terrestrial systems. We also found that inorganic carbon and nitrogen were not influenced by precipitation. Inorganic carbon seemed more influenced by geology, and inorganic nitrogen seemed more influenced by ba

ISSN:0886-6236    

DOI:10.1029/94GB02311

年代:1994

数据来源: WILEY

摘要:

Field and laboratory studies of anoxic sediments from Cape Lookout Bight, North Carolina, suggest that anaerobic methane oxidation is mediated by a consortium of methanogenic and sulfate‐reducing bacteria. A seasonal survey of methane oxidation and CO2reduction rates indicates that methane production was confined to sulfate‐depleted sediments at all times of year, while methane oxidation occurred in two modes. In the summer, methane oxidation was confined to sulfate‐depleted sediments and occurred at rates lower than those of CO2reduction. In the winter, net methane oxidation occurred in an interval at the base of the sulfate‐containing zone. Sediment incubation experiments suggest both methanogens and sulfate reducers were responsible for the observed methane oxidation. In one incubation experiment both modes of oxidation were partially inhibited by 2‐bromoethanesulfonic acid (a specific inhibitor of methanogens). This evidence, along with the apparent confinement of methane oxidation to sulfate‐depleted sediments in the summer, indicates that methanogenic bacteria are involved in methane oxidation. In a second incubation experiment, net methane oxidation was induced by adding sulfate to homogenized methanogenic sediments, suggesting that sulfate reducers also play a role in the process. We hypothesize that methanogens oxidize methane and produce hydrogen via a reversal of CO2reduction. The hydrogen is efficiently removed and maintained at low concentrations by sulfate reducers. Pore water H2concentrations in the sediment incubation experiments (while net methane oxidation was occurring) were low enough that methanogenic bacteria could derive sufficient energy for growth from the oxidation of methane. The methanogen‐sulfate reducer consortium is consistent not only with the results of this study, but may also be a feasible mechanism for previously documented anaerobic methane oxidation in both freshwater and marine

ISSN:0886-6236    

DOI:10.1029/94GB01800

年代:1994

数据来源: WILEY

摘要:

During three measurement campaigns on the Baltic and North Seas, atmospheric and dissolved methane was determined with an automated gas chromatographic system. Area‐weighted mean saturation values in the sea surface waters were 113 ± 5% and 395 ± 82% (Baltic Sea, February and July 1992) and 126 ± 8% (south central North Sea, September 1992). On the bases of our data and a compilation of literature data the global oceanic emissions of methane were reassessed by introducing a concept of regional gas transfer coefficients. Our estimates computed with two different air‐sea exchange models lie in the range of 11–18 Tg CH4yr−1. Despite the fact that shelf areas and estuaries only represent a small part of the world's ocean they contribute about 75% to the global oceanic emissions. We applied a simple, coupled, three‐layer model to evaluate the time dependent variation of the oceanic flux to the atmosphere. The model calculations indicate that even with increasing tropospheric methane concentration, the ocean will remain a source of atmosph

ISSN:0886-6236    

DOI:10.1029/94GB02181

年代:1994

数据来源: WILEY

摘要:

This paper compiles atmospheric budgets for the large‐scale cycling of sulfur and reactive nitrogen oxides in the atmosphere of the North Atlantic Ocean. Using model results and measurements reported in the literature, estimates are made of the following large‐scale fluxes: eastward from North America into the North Atlantic atmosphere, northward into the Arctic, eastward into and westward out of Europe, westward from Africa, and westward at the Caribbean. Marine emissions into the North Atlantic atmosphere and deposition to the ocean are estimated. Atmospheric transport from continental sources contributes 4.4–7.5 Tg S/yr and 1.7–3.4 Tg N/yr to the North Atlantic Ocean atmosphere, while 0.6–3.6 Tg S/yr comes from marine emissions. Atmospheric transport removes 1.4–1.9 Tg S/yr and 0.5–0.8 Tg N/yr, and deposition to the ocean accounts for 5.2–15.7 Tg S/yr and 1.6–5.7 Tg N/yr. The main input terms for sulfur are flow from North America, followed by marine dimethylsulfide emissions and flow from Africa; for nitrogen, North American and African inputs are comparable. Although outputs exceed inputs for both sulfur and nitrogen, the ranges of estimates overlap by approximately 75%. The spatial distribution of total sulfur deposition flux is generally consistent with known sources and flow regimes except for high values which occur near the European west coast and off the east coast of the Americas south of 30°N. The spatial distribution of total nitrogen deposition flux is more consistent with current knowledge, with the exception of high values across the 0–10° latitude band. The molar sulfur to nitrogen ratio of total deposition exceeds 2 north of 30°N but is close to or below 1 to the south. Both sulfur and nitrogen outputs exceed inputs in the northeastern and southwestern parts of the region, indicating that either inputs from adjacent continents are underestimated or that the depos

ISSN:0886-6236    

DOI:10.1029/94GB01395

年代:1994

数据来源: WILEY

摘要:

A database for the spatial and temporal distribution of the amount of biomass burned in tropical America, Africa, and Asia during the late 1970s is presented with a resolution of 5° latitude × 5° longitude. The sources of burning in each grid cell have been quantified. Savanna fires, shifting cultivation, deforestation, fuel wood use, and burning of agricultural residues contribute about 50, 24, 10, 11, and 5%, respectively, of total biomass burned in the tropics. Savanna fires dominate in tropical Africa, and forest fires dominate in tropical Asia. A similar amount of biomass is burned from forest and savanna fires in tropical America. The distribution of biomass burned monthly during the dry season has been derived for each grid cell using the seasonal cycles of surface ozone concentrations. Land use changes during the last decade could have a profound impact on the amount of biomass burned and the amount of trace gases and aerosol particles emitt

ISSN:0886-6236    

DOI:10.1029/94GB02086

年代:1994

数据来源: WILEY

摘要:

A process‐based ecosystem model, DEMETER, is used to simulate the sensitivity of the terrestrial biosphere to changes in climate. In this study, DEMETER is applied to the two following climatic regimes: (1) the modern observed climate and (2) a simulated mid‐Holocene climate (6000 years before present). The mid‐Holocene climate is simulated using the GENESIS global climate model, where shifts in the Earth's orbital parameters result in warmer northern continents and enhanced monsoons in Asia, North Africa, and North America. DEMETER simulates large differences between modern and mid‐Holocene vegetation cover: (1) mid‐Holocene boreal forests extend farther poleward than present in much of Europe, Asia, and North America, and (2) mid‐Holocene North African grasslands extend substantially farther north than present. The simulated patterns of mid‐Holocene vegetation are consistent with many features of the paleobotanical record. Simulated mid‐Holocene global net primary productivity is approximately 3% larger than present, largely due to the increase of boreal forest and tropical grasslands relative to tundra and desert. Global vegetation carbon is higher at 6 kyr B.P. compared to present by roughly the same amount (4%). Mid‐Holocene global litter carbon is larger than present by 10%, while global soil carbon is approximately 1% less. Despite the regional changes in productivity and carbon storage the simulated total carbon storage potential of the terrestrial biosphere (not including changes in peat) does not change significantly between th

ISSN:0886-6236    

DOI:10.1029/94GB01636

年代:1994

数据来源: WILEY