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1.
Sources of methane (CH4) become highly variable for countries undergoing a heightened period of development due to both human activity and climate change. An urgent need therefore exists to budget key sources of CH4, such as wetlands (rice paddies and natural wetlands) and lakes (including reservoirs and ponds), which are sensitive to these changes. For this study, references in relation to CH4 emissions from rice paddies, natural wetlands, and lakes in China were first reviewed and then reestimated based on the review itself. Total emissions from the three CH4 sources were 11.25 Tg CH4 yr?1 (ranging from 7.98 to 15.16 Tg CH4 yr?1). Among the emissions, 8.11 Tg CH4 yr?1 (ranging from 5.20 to 11.36 Tg CH4 yr?1) derived from rice paddies, 2.69 Tg CH4 yr?1 (ranging from 2.46 to 3.20 Tg CH4 yr?1) from natural wetlands, and 0.46 Tg CH4 yr?1 (ranging from 0.33 to 0.59 Tg CH4 yr?1) from lakes (including reservoirs and ponds). Plentiful water and warm conditions, as well as its large rice paddy area make rice paddies in southeastern China the greatest overall source of CH4, accounting for approximately 55% of total paddy emissions. Natural wetland estimates were slightly higher than the other estimates owing to the higher CH4 emissions recorded within Qinghai‐Tibetan Plateau peatlands. Total CH4 emissions from lakes were estimated for the first time by this study, with three quarters from the littoral zone and one quarter from lake surfaces. Rice paddies, natural wetlands, and lakes are not constant sources of CH4, but decreasing ones influenced by anthropogenic activity and climate change. A new progress‐based model used in conjunction with more observations through model‐data fusion approach could help obtain better estimates and insights with regard to CH4 emissions deriving from wetlands and lakes in China.  相似文献   

2.
At the southern margin of permafrost in North America, climate change causes widespread permafrost thaw. In boreal lowlands, thawing forested permafrost peat plateaus (‘forest’) lead to expansion of permafrost‐free wetlands (‘wetland’). Expanding wetland area with saturated and warmer organic soils is expected to increase landscape methane (CH4) emissions. Here, we quantify the thaw‐induced increase in CH4 emissions for a boreal forest‐wetland landscape in the southern Taiga Plains, Canada, and evaluate its impact on net radiative forcing relative to potential long‐term net carbon dioxide (CO2) exchange. Using nested wetland and landscape eddy covariance net CH4 flux measurements in combination with flux footprint modeling, we find that landscape CH4 emissions increase with increasing wetland‐to‐forest ratio. Landscape CH4 emissions are most sensitive to this ratio during peak emission periods, when wetland soils are up to 10 °C warmer than forest soils. The cumulative growing season (May–October) wetland CH4 emission of ~13 g CH4 m?2 is the dominating contribution to the landscape CH4 emission of ~7 g CH4 m?2. In contrast, forest contributions to landscape CH4 emissions appear to be negligible. The rapid wetland expansion of 0.26 ± 0.05% yr?1 in this region causes an estimated growing season increase of 0.034 ± 0.007 g CH4 m?2 yr?1 in landscape CH4 emissions. A long‐term net CO2 uptake of >200 g CO2 m?2 yr?1 is required to offset the positive radiative forcing of increasing CH4 emissions until the end of the 21st century as indicated by an atmospheric CH4 and CO2 concentration model. However, long‐term apparent carbon accumulation rates in similar boreal forest‐wetland landscapes and eddy covariance landscape net CO2 flux measurements suggest a long‐term net CO2 uptake between 49 and 157 g CO2 m?2 yr?1. Thus, thaw‐induced CH4 emission increases likely exert a positive net radiative greenhouse gas forcing through the 21st century.  相似文献   

3.
Livestock manure management accounts for almost 10% of greenhouse gas emissions from agriculture globally, and contributes an equal proportion to the US methane emission inventory. Current emissions inventories use emissions factors determined from small‐scale laboratory experiments that have not been compared to field‐scale measurements. We compiled published data on field‐scale measurements of greenhouse gas emissions from working and research dairies and compared these to rates predicted by the IPCC Tier 2 modeling approach. Anaerobic lagoons were the largest source of methane (368 ± 193 kg CH4 hd?1 yr?1), more than three times that from enteric fermentation (~120 kg CH4 hd?1 yr?1). Corrals and solid manure piles were large sources of nitrous oxide (1.5 ± 0.8 and 1.1 ± 0.7 kg N2O hd?1 yr?1, respectively). Nitrous oxide emissions from anaerobic lagoons (0.9 ± 0.5 kg N2O hd?1 yr?1) and barns (10 ± 6 kg N2O hd?1 yr?1) were unexpectedly large. Modeled methane emissions underestimated field measurement means for most manure management practices. Modeled nitrous oxide emissions underestimated field measurement means for anaerobic lagoons and manure piles, but overestimated emissions from slurry storage. Revised emissions factors nearly doubled slurry CH4 emissions for Europe and increased N2O emissions from solid piles and lagoons in the United States by an order of magnitude. Our results suggest that current greenhouse gas emission factors generally underestimate emissions from dairy manure and highlight liquid manure systems as promising target areas for greenhouse gas mitigation.  相似文献   

4.
It has been well recognized that converting wetlands to cropland results in loss of soil organic carbon (SOC), while less attention was paid to concomitant changes in methane (CH4) and nitrous oxide (N2O) emissions. Using datasets from the literature and field measurements, we investigated loss of SOC and emissions of CH4 and N2O due to marshland conversion in northeast China. Analysis of the documented crop cultivation area indicated that 2.91 Mha of marshland were converted to cropland over the period 1950–2000. Marshland conversion resulted in SOC loss of ~240 Tg and introduced ~1.4 Tg CH4 and ~138 Gg N2O emissions in the cropland, while CH4 emissions reduced greatly in the marshland, cumulatively ~28 Tg over the 50 years. Taking into account the loss of SOC and emissions of CH4 and N2O, the global warming potential (GWP) at a 20‐year time horizon was estimated to be ~180 Tg CO2_eq. yr?1 in the 1950s and ~120 Tg CO2_eq. yr?1 in the 1990s, with a ~33% reduction. When calculated at 100‐year time horizon, the GWP was ~73 Tg CO2 _eq. yr?1 in the 1950s and ~58 Tg CO2_eq. yr?1 in the 1990s, with a ~21% reduction. It was concluded that marshland conversion to cropland in northeast China reduced the greenhouse effect as far as GWP is concerned. This reduction was attributed to a substantial decrease in CH4 emissions from the marshland. An extended inference is that the declining growth rate of atmospheric CH4 since the 1980s might be related to global loss of wetlands, but this connection needs to be confirmed.  相似文献   

5.
Methane (CH4) is an important greenhouse gas, contributing 0.4–0.5 W m?2 to global warming. Methane emissions originate from several sources, including wetlands, rice paddies, termites and ruminating animals. Previous measurements of methane flux from farm animals have been carried out on animals in unnatural conditions, in laboratory chambers or fitted with cumbersome masks. This study introduces eddy covariance measurements of CH4, using the newly developed LI‐COR LI‐7700 open‐path methane analyser, to measure field‐scale fluxes from sheep grazing freely on pasture. Under summer conditions, fluxes of methane in the morning averaged 30 nmol m?2 s?1, whereas those in the afternoon were above 100 nmol m?2 s?1, and were roughly two orders of magnitude larger than the small methane emissions from the soil. Methane emissions showed no clear relationship with air temperature or photosynthetically active radiation, but some diurnal pattern was apparent, probably linked to sheep grazing behaviour and metabolism. Over the measurement period (days 60–277, year 2010), cumulative methane fluxes were 0.34 mol CH4 m?2, equating to 134.3 g CO2 equivalents m?2. By comparison, a carbon dioxide (CO2) sink of 819 g CO2 equivalents m?2 was measured over the same period, but it is likely that much of this would be released back to the atmosphere during the winter or as off‐site losses (through microbial and animal respiration). By dividing methane fluxes by the number of sheep in the field each day, we calculated CH4 emissions per head of livestock as 7.4 kg CH4 sheep?1 yr?1, close to the published IPCC emission factor of 8 kg CH4 sheep?1 yr?1.  相似文献   

6.
Wetlands can influence global climate via greenhouse gas (GHG) exchange of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Few studies have quantified the full GHG budget of wetlands due to the high spatial and temporal variability of fluxes. We report annual open‐water diffusion and ebullition fluxes of CO2, CH4, and N2O from a restored emergent marsh ecosystem. We combined these data with concurrent eddy‐covariance measurements of whole‐ecosystem CO2 and CH4 exchange to estimate GHG fluxes and associated radiative forcing effects for the whole wetland, and separately for open‐water and vegetated cover types. Annual open‐water CO2, CH4, and N2O emissions were 915 ± 95 g C‐CO2 m?2 yr?1, 2.9 ± 0.5 g C‐CH4 m?2 yr?1, and 62 ± 17 mg N‐N2O m?2 yr?1, respectively. Diffusion dominated open‐water GHG transport, accounting for >99% of CO2 and N2O emissions, and ~71% of CH4 emissions. Seasonality was minor for CO2 emissions, whereas CH4 and N2O fluxes displayed strong and asynchronous seasonal dynamics. Notably, the overall radiative forcing of open‐water fluxes (3.5 ± 0.3 kg CO2‐eq m?2 yr?1) exceeded that of vegetated zones (1.4 ± 0.4 kg CO2‐eq m?2 yr?1) due to high ecosystem respiration. After scaling results to the entire wetland using object‐based cover classification of remote sensing imagery, net uptake of CO2 (?1.4 ± 0.6 kt CO2‐eq yr?1) did not offset CH4 emission (3.7 ± 0.03 kt CO2‐eq yr?1), producing an overall positive radiative forcing effect of 2.4 ± 0.3 kt CO2‐eq yr?1. These results demonstrate clear effects of seasonality, spatial structure, and transport pathway on the magnitude and composition of wetland GHG emissions, and the efficacy of multiscale flux measurement to overcome challenges of wetland heterogeneity.  相似文献   

7.
Drainage has turned peatlands from a carbon sink into one of the world's largest greenhouse gas (GHG) sources from cultivated soils. We analyzed a unique data set (12 peatlands, 48 sites and 122 annual budgets) of mainly unpublished GHG emissions from grasslands on bog and fen peat as well as other soils rich in soil organic carbon (SOC) in Germany. Emissions and environmental variables were measured with identical methods. Site‐averaged GHG budgets were surprisingly variable (29.2 ± 17.4 t CO2‐eq. ha?1 yr?1) and partially higher than all published data and the IPCC default emission factors for GHG inventories. Generally, CO2 (27.7 ± 17.3 t CO2 ha?1 yr?1) dominated the GHG budget. Nitrous oxide (2.3 ± 2.4 kg N2O‐N ha?1 yr?1) and methane emissions (30.8 ± 69.8 kg CH4‐C ha?1 yr?1) were lower than expected except for CH4 emissions from nutrient‐poor acidic sites. At single peatlands, CO2 emissions clearly increased with deeper mean water table depth (WTD), but there was no general dependency of CO2 on WTD for the complete data set. Thus, regionalization of CO2 emissions by WTD only will remain uncertain. WTD dynamics explained some of the differences between peatlands as sites which became very dry during summer showed lower emissions. We introduced the aerated nitrogen stock (Nair) as a variable combining soil nitrogen stocks with WTD. CO2 increased with Nair across peatlands. Soils with comparatively low SOC concentrations showed as high CO2 emissions as true peat soils because Nair was similar. N2O emissions were controlled by the WTD dynamics and the nitrogen content of the topsoil. CH4 emissions can be well described by WTD and ponding duration during summer. Our results can help both to improve GHG emission reporting and to prioritize and plan emission reduction measures for peat and similar soils at different scales.  相似文献   

8.
Agricultural drainage of organic soils has resulted in vast soil subsidence and contributed to increased atmospheric carbon dioxide (CO2) concentrations. The Sacramento‐San Joaquin Delta in California was drained over a century ago for agriculture and human settlement and has since experienced subsidence rates that are among the highest in the world. It is recognized that drained agriculture in the Delta is unsustainable in the long‐term, and to help reverse subsidence and capture carbon (C) there is an interest in restoring drained agricultural land‐use types to flooded conditions. However, flooding may increase methane (CH4) emissions. We conducted a full year of simultaneous eddy covariance measurements at two conventional drained agricultural peatlands (a pasture and a corn field) and three flooded land‐use types (a rice paddy and two restored wetlands) to assess the impact of drained to flooded land‐use change on CO2 and CH4 fluxes in the Delta. We found that the drained sites were net C and greenhouse gas (GHG) sources, releasing up to 341 g C m?2 yr?1 as CO2 and 11.4 g C m?2 yr?1 as CH4. Conversely, the restored wetlands were net sinks of atmospheric CO2, sequestering up to 397 g C m?2 yr?1. However, they were large sources of CH4, with emissions ranging from 39 to 53 g C m?2 yr?1. In terms of the full GHG budget, the restored wetlands could be either GHG sources or sinks. Although the rice paddy was a small atmospheric CO2 sink, when considering harvest and CH4 emissions, it acted as both a C and GHG source. Annual photosynthesis was similar between sites, but flooding at the restored sites inhibited ecosystem respiration, making them net CO2 sinks. This study suggests that converting drained agricultural peat soils to flooded land‐use types can help reduce or reverse soil subsidence and reduce GHG emissions.  相似文献   

9.
Willow coppice, energy maize and Miscanthus were evaluated regarding their soil‐derived trace gas emission potential involving a nonfertilized and a crop‐adapted slow‐release nitrogen (N) fertilizer scheme. The N application rate was 80 kg N ha?1 yr?1 for the perennial crops and 240 kg N ha?1 yr?1 for the annual maize. A replicated field experiment was conducted with 1‐year measurements of soil fluxes of CH4, CO2 and N2O in weekly intervals using static chambers. The measurements revealed a clear seasonal trend in soil CO2 emissions, with highest emissions being found for the N‐fertilized Miscanthus plots (annual mean: 50 mg C m?² h?1). Significant differences between the cropping systems were found in soil N2O emissions due to their dependency on amount and timing of N fertilization. N‐fertilized maize plots had highest N2O emissions by far, which accumulated to 3.6 kg N2O ha?1 yr?1. The contribution of CH4 fluxes to the total soil greenhouse gas subsumption was very small compared with N2O and CO2. CH4 fluxes were mostly negative indicating that the investigated soils mainly acted as weak sinks for atmospheric CH4. To identify the system providing the best ratio of yield to soil N2O emissions, a subsumption relative to biomass yields was calculated. N‐fertilized maize caused the highest soil N2O emissions relative to dry matter yields. Moreover, unfertilized maize had higher relative soil N2O emissions than unfertilized Miscanthus and willow. These results favour perennial crops for bioenergy production, as they are able to provide high yields with low N2O emissions in the field.  相似文献   

10.
As a controversial strategy to mitigate global warming, biochar application into soil highlights the need for life cycle assessment before large‐scale practice. This study focused on the effect of biochar on carbon footprint of rice production. A field experiment was performed with three treatments: no residue amendment (Control), 6 t ha?1 yr?1 corn straw (CS) amendment, and 2.4 t ha?1 yr?1 corn straw‐derived biochar amendment (CBC). Carbon footprint was calculated by considering carbon source processes (pyrolysis energy cost, fertilizer and pesticide input, farmwork, and soil greenhouse gas emissions) and carbon sink processes (soil carbon increment and energy offset from pyrolytic gas). On average over three consecutive rice‐growing cycles from year 2011 to 2013, the CS treatment had a much higher carbon intensity of rice (0.68 kg CO2‐C equivalent (CO2‐Ce) kg?1 grain) than that of Control (0.24 kg CO2‐Ckg?1 grain), resulting from large soil CH4 emissions. Biochar amendment significantly increased soil carbon pool and showed no significant effect on soil total N2O and CH4 emissions relative to Control; however, due to a variation in net electric energy input of biochar production based on different pyrolysis settings, carbon intensity of rice under CBC treatment ranged from 0.04 to 0.44 kg CO2‐Ckg?1 grain. The results indicated that biochar strategy had the potential to significantly reduce the carbon footprint of crop production, but the energy‐efficient pyrolysis technique does matter.  相似文献   

11.
Inland waters were recently recognized to be important sources of methane (CH4) and carbon dioxide (CO2) to the atmosphere, and including inland water emissions in large scale greenhouse gas (GHG) budgets may potentially offset the estimated carbon sink in many areas. However, the lack of GHG flux measurements and well‐defined inland water areas for extrapolation, make the magnitude of the potential offset unclear. This study presents coordinated flux measurements of CH4 and CO2 in multiple lakes, ponds, rivers, open wells, reservoirs, springs, and canals in India. All these inland water types, representative of common aquatic ecosystems in India, emitted substantial amounts of CH4 and a major fraction also emitted CO2. The total CH4 flux (including ebullition and diffusion) from all the 45 systems ranged from 0.01 to 52.1 mmol m?2 d?1, with a mean of 7.8 ± 12.7 (mean ± 1 SD) mmol m?2 d?1. The mean surface water CH4 concentration was 3.8 ± 14.5 μm (range 0.03–92.1 μm ). The CO2 fluxes ranged from ?28.2 to 262.4 mmol m?2 d?1 and the mean flux was 51.9 ± 71.1 mmol m?2 d?1. The mean partial pressure of CO2 was 2927 ± 3269 μatm (range: 400–11 467 μatm). Conservative extrapolation to whole India, considering the specific area of the different water types studied, yielded average emissions of 2.1 Tg CH4 yr?1 and 22.0 Tg CO2 yr?1 from India's inland waters. When expressed as CO2 equivalents, this amounts to 75 Tg CO2 equivalents yr?1 (53–98 Tg CO2 equivalents yr?1; ± 1 SD), with CH4 contributing 71%. Hence, average inland water GHG emissions, which were not previously considered, correspond to 42% (30–55%) of the estimated land carbon sink of India. Thereby this study illustrates the importance of considering inland water GHG exchange in large scale assessments.  相似文献   

12.
Methane (CH4) fluxes from world rivers are still poorly constrained, with measurements restricted mainly to temperate climates. Additional river flux measurements, including spatio‐temporal studies, are important to refine extrapolations. Here we assess the spatio‐temporal variability of CH4 fluxes from the Amazon and its main tributaries, the Negro, Solimões, Madeira, Tapajós, Xingu, and Pará Rivers, based on direct measurements using floating chambers. Sixteen of 34 sites were measured during low and high water seasons. Significant differences were observed within sites in the same river and among different rivers, types of rivers, and seasons. Ebullition contributed to more than 50% of total emissions for some rivers. Considering only river channels, our data indicate that large rivers in the Amazon Basin release between 0.40 and 0.58 Tg CH4 yr?1. Thus, our estimates of CH4 flux from all tropical rivers and rivers globally were, respectively, 19–51% to 31–84% higher than previous estimates, with large rivers of the Amazon accounting for 22–28% of global river CH4 emissions.  相似文献   

13.
Rice production is a substantial source of atmospheric CH4, which is second only to CO2 as a contributor to global warming. Since CH4 is produced in anaerobic soil environments, water management is expected to be a practical measure to mitigate CH4 emissions. In this study, we used a process‐based biogeochemistry model (DNDC‐Rice) to assess the CH4 mitigation potentials of alternative water regimes (AWR) for rice fields at a regional scale. Before regional application, we tested DNDC‐Rice using site‐scale data from three rice fields in Japan with different water regimes. The observed CH4 emissions were reduced by drainage of the fields, but were enhanced by organic amendments. DNDC‐Rice gave acceptable predictions of variation in daily CH4 fluxes and seasonal CH4 emissions due to changes in the water regime. For regional application, we constructed a GIS database at a 1 × 1 km mesh scale that contained data on rice field area, soil properties, daily weather, and farming management of each cell in the mesh, covering 3.2% of the rice fields in Japan's Hokkaido region. We ran DNDC‐Rice to simulate CH4 emissions under five simulated water regimes: the conventional water regime and four AWR scenarios with gradually increasing drainage. We found that AWR can reduce CH4 emission by up to 41% compared with the emission under conventional water regime. Including the changes in CO2 and nitrous oxide emissions, potential mitigation of greenhouse gas (GHG) was 2.6 Mg CO2 Eq. ha?1 yr?1. If this estimate is expanded to Japan's total rice fields, expected GHG mitigation is 4.3 Tg CO2 Eq. yr?1, which accounts for 0.32% of total GHG emissions from Japan. For a reliable national‐scale assessment, however, databases on soil, weather, and farming management must be constructed at a national scale, as these factors are widely variable between regions in Japan.  相似文献   

14.
An agronomic assessment of greenhouse gas emissions from major cereal crops   总被引:8,自引:0,他引:8  
Agricultural greenhouse gas (GHG) emissions contribute approximately 12% to total global anthropogenic GHG emissions. Cereals (rice, wheat, and maize) are the largest source of human calories, and it is estimated that world cereal production must increase by 1.3% annually to 2025 to meet growing demand. Sustainable intensification of cereal production systems will require maintaining high yields while reducing environmental costs. We conducted a meta‐analysis (57 published studies consisting of 62 study sites and 328 observations) to test the hypothesis that the global warming potential (GWP) of CH4 and N2O emissions from rice, wheat, and maize, when expressed per ton of grain (yield‐scaled GWP), is similar, and that the lowest value for each cereal is achieved at near optimal yields. Results show that the GWP of CH4 and N2O emissions from rice (3757 kg CO2 eq ha?1 season?1) was higher than wheat (662 kg CO2 eq ha?1 season?1) and maize (1399 kg CO2 eq ha?1 season?1). The yield‐scaled GWP of rice was about four times higher (657 kg CO2 eq Mg?1) than wheat (166 kg CO2 eq Mg?1) and maize (185 kg CO2 eq Mg?1). Across cereals, the lowest yield‐scaled GWP values were achieved at 92% of maximal yield and were about twice as high for rice (279 kg CO2 eq Mg?1) than wheat (102 kg CO2 eq Mg?1) or maize (140 kg CO2 eq Mg?1), suggesting greater mitigation opportunities for rice systems. In rice, wheat and maize, 0.68%, 1.21%, and 1.06% of N applied was emitted as N2O, respectively. In rice systems, there was no correlation between CH4 emissions and N rate. In addition, when evaluating issues related to food security and environmental sustainability, other factors including cultural significance, the provisioning of ecosystem services, and human health and well‐being must also be considered.  相似文献   

15.
Inland waters transport and emit into the atmosphere large amounts of carbon (C), which originates from terrestrial ecosystems. The effect of land cover and land‐use practises on C export from terrestrial ecosystems to inland waters is not fully understood, especially in heterogeneous landscapes under human influence. We sampled for dissolved C species in five tributaries with well‐determined subcatchments (total size 174.5 km2), as well as in various points of two of the subcatchments draining to a boreal lake in southern Finland over a full year. Our aim was to find out how land cover and land‐use affect C export from the catchments, as well as CH4 and CO2 concentrations of the streams, and if the origin of C in stream water can be determined from proxies for quality of dissolved organic matter (DOM). We further estimated the gas evasion from stream surfaces and the role of aquatic fluxes in regional C cycling. The export rate of C from the terrestrial system through an aquatic conduit was 19.3 g C m?2(catchment) yr?1, which corresponds to 19% of the estimated terrestrial net ecosystem exchange of the catchment. Most of the C load to the recipient lake consisted of dissolved organic carbon (DOC, 6.1 ± 1.0 g C m?2 yr?1); the share of dissolved inorganic carbon (DIC) was much smaller (1.0 ± 0.2 g C m?2 yr?1). CO2 and CH4 emissions from stream and ditch surfaces were 7.0 ± 2.4 g C m?2 yr?1 and 0.1 ± 0.04 g C m?2 yr?1, respectively, C emissions being thus equal with C load to the lake. The proportion of peatland in the catchment and the drainage density of peatland increased DOC in streams, whereas the proportion of agricultural land in the catchment decreased it. The opposite was true for DIC. Drained peatlands were an important CH4 source for streams.  相似文献   

16.
We estimate the mitigation potential of local use of bioenergy from harvest residues for the 2.3 × 10km2 (232 Mha) of Canada's managed forests from 2017 to 2050 using three models: Carbon Budget Model of the Canadian Forest Sector (CBM‐CFS3), a harvested wood products (HWP) model that estimates bioenergy emissions, and a model of emission substitution benefits from the use of bioenergy. We compare the use of harvest residues for local heat and electricity production relative to a base case scenario and estimate the climate change mitigation potential at the forest management unit level. Results demonstrate large differences between and within provinces and territories across Canada. We identify regions with increasing benefits to the atmosphere for many decades into the future and regions where no net benefit would occur over the 33‐year study horizon. The cumulative mitigation potential for regions with positive mitigation was predicted to be 429 Tg CO2e in 2050, with 7.1 TgC yr ?1 of harvest residues producing bioenergy that met 3.1% of the heat demand and 2.9% of the electricity demand for 32.1 million people living within these regions. Our results show that regions with positive mitigation produced bioenergy, mainly from combined heat and power facilities, with emissions intensities that ranged from roughly 90 to 500 kg CO2e MWh?1. Roughly 40% of the total captured harvest residue was associated with regions that were predicted to have a negative cumulative mitigation potential in 2050 of ?152 Tg CO2e. We conclude that the capture of harvest residues to produce local bioenergy can reduce GHG emissions in populated regions where bioenergy, mainly from combined heat and power facilities, offsets fossil fuel sources (fuel oil, coal and petcoke, and natural gas).  相似文献   

17.
The long‐term effects of conservation management practices on greenhouse gas fluxes from tropical/subtropical croplands remain to be uncertain. Using both manual and automatic sampling chambers, we measured N2O and CH4 fluxes at a long‐term experimental site (1968–present) in Queensland, Australia from 2006 to 2009. Annual net greenhouse gas fluxes (NGGF) were calculated from the 3‐year mean N2O and CH4 fluxes and the long‐term soil organic carbon changes. N2O emissions exhibited clear daily, seasonal and interannual variations, highlighting the importance of whole‐year measurement over multiple years for obtaining temporally representative annual emissions. Averaged over 3 years, annual N2O emissions from the unfertilized and fertilized soils (90 kg N ha?1 yr?1 as urea) amounted to 138 and 902 g N ha?1, respectively. The average annual N2O emissions from the fertilized soil were 388 g N ha?1 lower under no‐till (NT) than under conventional tillage (CT) and 259 g N ha?1 higher under stubble retention (SR) than under stubble burning (SB). Annual N2O emissions from the unfertilized soil were similar between the contrasting tillage and stubble management practices. The average emission factors of fertilizer N were 0.91%, 1.20%, 0.52% and 0.77% for the CT‐SB, CT‐SR, NT‐SB and NT‐SR treatments, respectively. Annual CH4 fluxes from the soil were very small (?200–300 g CH4 ha?1 yr?1) with no significant difference between treatments. The NGGF were 277–350 kg CO2‐e ha?1 yr?1 for the unfertilized treatments and 401–710 kg CO2‐e ha?1 yr?1 for the fertilized treatments. Among the fertilized treatments, N2O emissions accounted for 52–97% of NGGF and NT‐SR resulted in the lowest NGGF (401 kg CO2‐e ha?1 yr?1 or 140 kg CO2‐e t?1 grain). Therefore, NT‐SR with improved N fertilizer management practices was considered the most promising management regime for simultaneously achieving maximal yield and minimal NGGF.  相似文献   

18.
Livestock manure is applied to rangelands as an organic fertilizer to stimulate forage production, but the long‐term impacts of this practice on soil carbon (C) and greenhouse gas (GHG) dynamics are poorly known. We collected soil samples from manured and nonmanured fields on commercial dairies and found that manure amendments increased soil C stocks by 19.0 ± 7.3 Mg C ha?1 and N stocks by 1.94 ± 0.63 Mg N ha?1 compared to nonmanured fields (0–20 cm depth). Long‐term historical (1700–present) and future (present–2100) impacts of management on soil C and N dynamics, net primary productivity (NPP), and GHG emissions were modeled with DayCent. Modeled total soil C and N stocks increased with the onset of dairying. Nitrous oxide (N2O) emissions also increased by ~2 kg N2O‐N ha?1 yr?1. These emissions were proportional to total N additions and offset 75–100% of soil C sequestration. All fields were small net methane (CH4) sinks, averaging ?4.7 ± 1.2 kg CH4‐C ha?1 yr?1. Overall, manured fields were net GHG sinks between 1954 and 2011 (?0.74 ± 0.73 Mg CO2 e ha?1 yr?1, CO2e are carbon dioxide equivalents), whereas nonmanured fields varied around zero. Future soil C pools stabilized 40–60 years faster in manured fields than nonmanured fields, at which point manured fields were significantly larger sources than nonmanured fields (1.45 ± 0.52 Mg CO2e ha?1 yr?1 and 0.51 ± 0.60 Mg CO2e ha?1 yr?1, respectively). Modeling also revealed a large background loss of soil C from the passive soil pool associated with the shift from perennial to annual grasses, equivalent to 29.4 ± 1.47 Tg CO2e in California between 1820 and 2011. Manure applications increased NPP and soil C storage, but plant community changes and GHG emissions decreased, and eventually eliminated, the net climate benefit of this practice.  相似文献   

19.
The high uncertainty in land‐based CO2 fluxes estimates is thought to be mainly due to uncertainty in not only quantifying historical changes among forests, croplands, and grassland, but also due to different processes included in calculation methods. Inclusion of a nitrogen (N) cycle in models is fairly recent and strongly affects carbon (C) fluxes. In this study, for the first time, we use a model with C and N dynamics with three distinct historical reconstructions of land‐use and land‐use change (LULUC) to quantify LULUC emissions and uncertainty that includes the integrated effects of not only climate and CO2 but also N. The modeled global average emissions including N dynamics for the 1980s, 1990s, and 2000–2005 were 1.8 ± 0.2, 1.7 ± 0.2, and 1.4 ± 0.2 GtC yr?1, respectively, (mean and range across LULUC data sets). The emissions from tropics were 0.8 ± 0.2, 0.8 ± 0.2, and 0.7 ± 0.3 GtC yr?1, and the non tropics were 1.1 ± 0.5, 0.9 ± 0.2, and 0.7 ± 0.1 GtC yr?1. Compared to previous studies that did not include N dynamics, modeled net LULUC emissions were higher, particularly in the non tropics. In the model, N limitation reduces regrowth rates of vegetation in temperate areas resulting in higher net emissions. Our results indicate that exclusion of N dynamics leads to an underestimation of LULUC emissions by around 70% in the non tropics, 10% in the tropics, and 40% globally in the 1990s. The differences due to inclusion/exclusion of the N cycle of 0.1 GtC yr?1 in the tropics, 0.6 GtC yr?1 in the non tropics, and 0.7 GtC yr?1 globally (mean across land‐cover data sets) in the 1990s were greater than differences due to the land‐cover data in the non tropics and globally (0.2 GtC yr?1). While land‐cover information is improving with satellite and inventory data, this study indicates the importance of accounting for different processes, in particular the N cycle.  相似文献   

20.
Understanding the dynamics of methane (CH4) emissions is of paramount importance because CH4 has 25 times the global warming potential of carbon dioxide (CO2) and is currently the second most important anthropogenic greenhouse gas. Wetlands are the single largest natural CH4 source with median emissions from published studies of 164 Tg yr?1, which is about a third of total global emissions. We provide a perspective on important new frontiers in obtaining a better understanding of CH4 dynamics in natural systems, with a focus on wetlands. One of the most exciting recent developments in this field is the attempt to integrate the different methodologies and spatial scales of biogeochemistry, molecular microbiology, and modeling, and thus this is a major focus of this review. Our specific objectives are to provide an up‐to‐date synthesis of estimates of global CH4 emissions from wetlands and other freshwater aquatic ecosystems, briefly summarize major biogeophysical controls over CH4 emissions from wetlands, suggest new frontiers in CH4 biogeochemistry, examine relationships between methanogen community structure and CH4 dynamics in situ, and to review the current generation of CH4 models. We highlight throughout some of the most pressing issues concerning global change and feedbacks on CH4 emissions from natural ecosystems. Major uncertainties in estimating current and future CH4 emissions from natural ecosystems include the following: (i) A number of important controls over CH4 production, consumption, and transport have not been, or are inadequately, incorporated into existing CH4 biogeochemistry models. (ii) Significant errors in regional and global emission estimates are derived from large spatial‐scale extrapolations from highly heterogeneous and often poorly mapped wetland complexes. (iii) The limited number of observations of CH4 fluxes and their associated environmental variables loosely constrains the parameterization of process‐based biogeochemistry models.  相似文献   

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