摘要:

Over the past 6 years (1988–1993), we have examined the effects of soil temperature, soil moisture, site fertility, and nitrogen fertilization on the consumption of atmospheric CH4by temperate forest soils located at the Harvard Forest in Petersham, Massachusetts. We found that soil temperature is an important controller of CH4consumption at temperatures between −5° and 10°C but had no effect on CH4consumption at temperatures between 10° and 20°C. Soil moisture exerts strong control on CH4consumption over a range of 60 to 100% water‐filled pore space (% WFPS). As moisture increased from 60 to 100% WFPS, CH4consumption decreased from 0.1 to 0 mg CH4‐C m−2h−1because of gas transport limitations. At 20 to 60% WFPS, site fertility was a strong controller of CH4consumption. High‐fertility sites had 2 to 3 times greater CH4consumption rates than low‐fertility sites. Nitrogen‐fertilized soils (50 and 150 kg NH4NO3‐N ha−1yr−1) had annually averaged CH4consumption rates that were 15 to 64% lower than annually averaged CH4consumption by control soils. The decrease in CH4consumption was related to both the years of application and quantity of nitrogen fert

ISSN:0886-6236    

DOI:10.1029/94GB02651

年代:1995

数据来源: WILEY

摘要:

Methane (CH4) emission from Philippine rice paddies was monitored with a closed chamber technique during the 1992 dry and wet season. CH4emissions were significantly higher in the dry season. Application of green manure stimulated CH4emissions. In plots that received more than 11 t ha−1of fresh green manure, CH4emission was highest during the first half of the growing season. Significant amounts of CH4 may evolve during or immediately after transplanting, if the organic amendments are incorporated 1 to 3 weeks before transplanting. Laboratory incubations of soil cores show that CH4production is highest near the soil surface. CH4production in green manure treated fields is higher than in urea‐fertilized fields, but toward the end of the season this difference is less pronounced. Around panicle initiation, the fraction of CH4produced, which was emitted to the atmosphere, is lower than at tillering or ripening. The impact of organic amendments on CH4emissions at different locations of the world can be described by a dose response curve, if CH4emission from organically amended plots is expressed relative to CH4emission from mineral fertilized plots of the same location and season. Various organic amendments (e.g., straw, fermented residues) have a similar effect on CH4emissions after correction for differences in easily decomposable carbon cont

ISSN:0886-6236    

DOI:10.1029/94GB03197

年代:1995

数据来源: WILEY

摘要:

We use semi‐mechanistic, empirically based statistical models to predict the spatial and temporal patterns of global carbon dioxide emissions from terrestrial soils. Emissions include the respiration of both soil organisms and plant roots. At the global scale, rates of soil CO2efflux correlate significantly with temperature and precipitation; they do not correlate well with soil carbon pools, soil nitrogen pools, or soil C:N. Wetlands cover about 3% of the land area but diminish predicted CO2emissions by only about 1%. The estimated annual flux of CO2from soils to the atmosphere is estimated to be 76.5 Pg C yr−1, 1–9 Pg greater than previous global estimates, and 30–60% greater than terrestrial net primary productivity. Historic land cover changes are estimated to have reduced current annual soil CO2emissions by 0.2–2.0 Pg C yr−1in comparison with an undisturbed vegetation cover. Soil CO2fluxes have a pronounced seasonal pattern in most locations, with maximum emissions coinciding with periods of active plant growth. Our models suggest that soils produce CO2throughout the year and thereby contribute to the observed wintertime increases in atmospheric CO2concentrations. Our derivation of statistically based estimates of soil CO2emissions at a 0.5° latitude by longitude spatial and monthly temporal resolution represents the best‐resolved estimate to date of global CO2fluxes from soils and should facilitate investigations of net carbon exchanges between the atmosphere and terrest

ISSN:0886-6236    

DOI:10.1029/94GB02723

年代:1995

数据来源: WILEY

摘要:

To date, the areal extent, carbon pools, rate of carbon accumulation, and role of peatlands of the former Soviet Union (FSU) in the terrestrial carbon cycle has not been fully recognized. This is a consequence of the fact that many peatlands in the FSU, especially noncommercial peatlands, were never studied and properly mapped. An estimate of the areal extent, carbon pools, and rate of carbon accumulation in peatlands of the FSU obtained by interrelating a number of regional databases and maps, including formerly classified maps, is presented herein. Commercial peatlands were categorized by regional type which facilitated an evaluation of their age and quality. Noncommercial peatlands were evaluated from classified regional topographic maps. Air photographs were used to identify peatlands of northern landscapes. The total peatland area of the FSU was estimated at 165 Mha (106hectares) which was two times greater than the most recent estimates based on thematic maps. The peat carbon pool was estimated at 215 Pg C. Half of this amount was in raised bogs. The rate of peat accumulation varied from 12 g C m−2yr−1(polygonal mires) to 72–80 g C m−2yr−1(fens and marshes). The total rate of carbon accumulation in FSU peatlands was 52 Tg C yr−1. Carbon emissions from peat utilization in the FSU were estimated at 122 Tg C yr−1. Thus, at present, peat accumulation/utilization in the FSU is a net source of approximately 70 Tg C yr−1to

ISSN:0886-6236    

DOI:10.1029/94GB03156

年代:1995

数据来源: WILEY

摘要:

Reactive chlorine in the lower atmosphere (as distinguished from chlorofluorocarbon‐derived chlorine in the stratosphere) is important to considerations of precipitation acidity, corrosion, foliar damage, and chemistry of the marine boundary layer. Many of the chlorine‐containing gases are difficult to measure, and natural sources appear to dominate anthropogenic sources for some chemical species. As a consequence, no satisfactory budget for reactive chlorine in the lower atmosphere is available. We have reviewed information on sources; source strengths; measurements in gas, aqueous, and aerosol phases; and chemical processes and from those data derive global budgets for nine reactive chlorine species and for reactive chlorine as a whole. The typical background abundance of reactive chlorine in the lower tropospheric is about 1.5 ppbv. The nine species, CH3Cl, CH3CCl3, HCl, CHClF2, Cl2* (thought to be HOCl and/or Cl2), CCl2= CCl2, CH2Cl2, COCl2, and CHCl3, each contribute at least a few percent to that total. The tropospheric reactive chlorine burden of approximately 8.3 Tg Cl is dominated by CH3Cl (≈45 %) and CH3CCl3(≈25 %) and appears to be increasing by several percent per year. By far the most vigorous chlorine cycling appears to occur among seasalt aerosol, HCl, and Cl2*. The principal sources of reactive chlorine are volatilization from seasalt (enhanced by anthropogenically generated reactants), marine algae, volcanoes, and coal combustion (natural sources being thus quite important to the budget). It is anticipated that the concentrations of tropospheric reactive chlorine will continue to increase in the next several decades, particularly near urban areas in the rapidly developing co

ISSN:0886-6236    

DOI:10.1029/94GB03103

年代:1995

数据来源: WILEY

摘要:

A database of dissolved C2‐C4hydrocarbons in the surface water of the oceans is compiled based on more than 1000 measurements. Hydrocarbon emission rates are calculated using a diffusive microlayer approach and climatologic wind data. This database is used to calculate averages and ranges of variation, and an attempt is made to identify the environmental factors which have an impact on the hydrocarbons dissolved in seawater. The paper focuses on data obtained in situ since other techniques generally contain larger uncertainties. Mean concentrations are 134 pmol/L for ethene, 59 pmol/L for propene, and 37 pmol/L for 1‐butene. Alkane concentrations are lower with an average value of 22 pmol/L for ethane and less than 14 pmol/L for the other alkanes and acetylene. Ninety percent of the concentrations of an individual compound generally ranges within an order of magnitude. Ethene concentrations are significantly anticorrelated with the transfer velocities of the sea‐air exchange (r=−0.49; r0.01=0.29). Ethene concentrations are not correlated with the solar radiation, chlorophylla, and the water temperature. Averaged emissions of C2‐C4hydrocarbons extrapolated to the global ocean of 2.1 × 1012g/yr are calculated, with ethene alone contributing about 40% to the total. Thus the oceanic source is on the low side of previous estimates and plays a minor role in global budgets compared to continent

ISSN:0886-6236    

DOI:10.1029/94GB02416

年代:1995

数据来源: WILEY

摘要:

An adjoint model was developed for the conservation of a tracer and used to assimilate phosphate observations from the North Pacific. The adjoint model estimated optimal values for new production, remineralization length scale of particulate organic matter (POM), phosphate field, and circulation field. Allowing no modifications to the circulation field computed by the Hamburg large‐scale geostrophic (LSG) model, we could not produce optimal estimates of new production and phosphate concentrations that were consistent with the observations. However, by allowing modifications to the LSG model's circulation field the adjoint model demonstrated that a model with only POM transport of organic matter produced results which were consistent with observations of new production and phosphate concentrations. In this model only small modifications to the circulation field were required to produce consistent estimates of new production and phosphate concentrations. This showed that the modeled phosphate field and new production were sensitive to small changes in the circulation. Furthermore, the data assimilation model implied that dissolved organic phosphorus did not necessarily play an important role in the cycling of phosphate in the North Pacifi

ISSN:0886-6236    

DOI:10.1029/94GB03104

年代:1995

数据来源: WILEY

摘要:

We estimate anthropogenic carbon emissions required to stabilize future atmospheric CO2at various levels ranging from 350 ppm to 750 ppm. Over the next three centuries, uptake by the ocean and terrestrial biosphere would permit emissions to be 3 to 6 times greater than the total atmospheric increase, with each of them contributing approximately equal amounts. Owing to the nonlinear dependence of oceanic and terrestrial biospheric uptake on CO2concentration, the uptake by these two sinks decreases substantially at higher atmospheric CO2levels. The uptake also decreases with increased atmospheric CO2growth rate. All the stabilization scenarios require a substantial future reduction in emissions.

ISSN:0886-6236    

DOI:10.1029/94GB01779

年代:1995

数据来源: WILEY

摘要:

The perceived budget imbalance in the global carbon cycle has been suggested to result from, among other processes, CO2fertilization of the terrestrial biosphere and/or enhanced regrowth of previously felled temperate forest. These two processes are incorporated into a box diffusion model of the ocean‐atmosphere system coupled to a five‐box terrestrial biosphere. The extent to which historical fossil fuel and land use change emission data can be reconciled with the observed atmospheric CO2concentration record is examined. Furthermore, the sensitivity of future CO2projections to the nature of the budget imbalance is investigated. It is found that the CO2record can accommodate a carbon budget balanced by CO2fertilization but that the balance with forest regrowth is more difficult. Future CO2projections are found to be sensitive to how the carbon budget is balanced, even relative to uncertainties in future emissi

ISSN:0886-6236    

DOI:10.1029/94GB02819

年代:1995

数据来源: WILEY

摘要:

Accurate global carbon cycle models are needed to estimate the future change of atmospheric CO2for specified scenarios of CO2emissions. Model accuracy cannot be tested directly because of the difficulty in estimating the carbon flux to the oceans and the terrestrial biosphere. However, one test of model consistency is the requirement that the model reproduce past changes and spatial distributions of14C. A model for carbon exchange within and among the atmosphere, oceans, and terrestrial biosphere is found to satisfy this test. The ocean is modeled as an upwelling‐diffusion column capped by a mixed layer with recirculation of the polar bottom water to complete the thermohaline circulation. This ocean advection scheme contains only two key dynamic parameters, the vertical eddy diffusivity κ and the upwelling velocityw, which are calibrated to match the vertical distribution of preanthropogenic14C. The thermocline depth scale κ/w= 1343 m found by calibration is considerably deeper than that required to match the steady vertical temperature profile (500 m). This is consistent with the hypothesis that isopycnal mixing, which is much more rapid than diapycnal mixing, has a stronger effect on14C than on temperature since isopycnals are nearly isothermal. This model is found to match measured values, within measurement error, of the prebomb decrease in14C in the atmosphere and the mixed layer due to the Suess effect, the bomb14C in the mixed layer, the bomb14C penetration depth, the bomb14C ocean inventory, and the vertical distribution of total carbon. Results are compared to those of other schematic carbon cycle models as well as those of ocean general circulation mod

ISSN:0886-6236    

DOI:10.1029/94GB02394

年代:1995

数据来源: WILEY