Global Warming Potential Of CH4 Research Articles

SPATIAL VARIABILITY OF METHANE EMISSIONS FROM SOILS OF WET FORESTS: A BRIEF REVIEW

SPATIAL VARIABILITY OF METHANE EMISSIONS FROM SOILS OF WET FORESTS: A BRIEF REVIEW

Higher rice grain yield and lower methane emission achieved by alternate wetting and drying in central Vietnam

Rice is the main staple food for more than half of the world’s population, but rice cultivation is a significant source of atmospheric methane (CH4). Alternate wetting and drying (AWD) reduces CH4 emission from paddy field, but the effect on rice yield remains unclear. Organic soil amendment increases grain yield but simultaneously increases CH4 emission. Therefore, the combination of AWD and organic amendment may compensate for each other’s shortcomings. The objective of this study was to assess whether AWD and organic amendment can increase rice yield while mitigating CH4 emission. The experiments were conducted in a farmer’s paddy field in Thua Thien Hue province, Vietnam, during five consecutive rice growing seasons in 2019–2021. Two water management practices, continuous flooding (CF) and AWD, with (+O) or without (−O) the application of a commercially available organic fertilizer were examined under normal cultivation conditions. Compared with CF, AWD significantly reduced CH4 emission by 34 %, increased nitrous oxide (N2O) by 46 %, and increased grain yield by 4.4 %. The +O treatment significantly increased the yield by 3.7 % relative to −O. Relative to CF−O by season, AWD+O significantly increased the yield. The integrated global warming potential of CH4 and N2O emissions was decreased by 33 % and irrigation water use was reduced by 33 % in AWD plots relative to that in CF plots. These results indicate that AWD by itself has the potential to increase rice yield as well as reduce CH4 emission, and the combination of AWD with organic amendment would ensure yield increase.

Land use drives large CH4 fluxes from a highly urbanized Indian estuary

There is growing awareness of the need to better constrain the contribution of atmospheric methane (CH4) fluxes from urbanized estuaries due to the high global warming potential of CH4 and the accelerating growth of urban expansion. This study undertook seasonal sampling campaigns to understand the impact of urbanization on atmospheric CH4 fluxes and their drivers in a large, tropical estuary in India. Overall, the study found that the Cochin estuary emitted large amounts of CH4 (398.8 ± 141.6 μmolm−2d−1) to the atmosphere with CH4 hotspots reaching up to 939.7 μmolm−2d−1 were identified. The strongest drivers of CH4 dynamics in different anthropogenically impacted zones were traced. The source of organic matter for CH4 production was revealed to be terrestrial C3 plants, autochthonous production, marine phytoplankton, and sewage inputs. The study suggests that monsoonal urbanized tropical estuaries may be an important but under-recognized element of the global CH4 budget.

Альтернативная оценка вклада метана в парниковый эффект

Methane is one of the greenhouse gases (GHG), the increase in the concentration of which in the atmosphere is of particular concern to environmentalists and climatologists. The main sources of CH4 emissions are the extraction and processing of hydrocarbon raw materials, cattle and sheep breeding, and rice cultivation. To reduce CH 4 emissions, various countries are making commitments aimed at reducing production volumes in their respective sectors of the economy. However, our estimates show that the contribution of methane to global warming accepted by the IPCC is greatly exaggerated. The simplest model of the greenhouse effect, presented in the works of S.M. Semenov, was used as the main tool for theoretical analysis. The values of the GHG absorption spectra are taken from the HITRAN database. The results obtained showed that the greenhouse effect and the formation of the average global temperature of the Earth’s surface are caused almost exclusively by two substances – water and carbon dioxide, while the total contribution of CH 4 and N2O does not exceed 1.4%. The results of the calculations provide grounds for a critical assessment of the widespread opinion about the high risk of current CH4 emissions from the point of view of global warming and the observed climate changes. Anthropogenic emissions of CH4 are estimated to be 9390 million tons per year in CO2 equivalent, or, taking into account the global warming potential of CH4 accepted by IPCC – 375.6 million tons per year. Of these, 30% (112.7 million tons) fall on the cattle breeding. With the complete cessation of milk and beef production, the decrease in the average global temperature due to the reduction of CH4 emissions will be less than 0.04 оC, which does not exceed 2.5% of the target limiting the growth of global warming at a level of no more than 1.5 оC.

The low greenhouse gas emission intensity in water-saving and drought-resistance rice in a rainfed paddy field in Southwest China

Water shortage has become one of the major threats to global food security. To meet the challenge of increasing food demand and water scarcity, water-saving and drought-resistant rice (WDR) is increasingly cultivated in China. However, there are few comprehensive studies on the effect of WDR on grain yields as well as CH4 and N2O emissions in the literature. A three-year field experiment was conducted with one common rice (CR) and three WDR varieties in a rainfed paddy field in Southwest China. The results showed that in the WDR treatments, both CH4 emissions and the global warming potential of CH4 and N2O emissions decreased by 6.2–15% on average. Seasonal CH4 emission was positively correlated with the mean tiller number but negatively correlated with the harvest index. Moreover, WDR increased the mean grain yield by 18–23% compared to CR, and especially in 2017, an increase within the range of 31–61% was observed when precipitation was low. The increasing grain yield was mainly due to the rise in the percentage of filled grains, and as a result, the greenhouse gas emission intensity was higher by 12–83% in CR than in WDR, while the lowest value was observed in one of the WDR varieties (Hanyou 73). Here, we report for the first time that planting water-saving and drought-resistance rice, especially the Hanyou 73 variety, under rainfed conditions would increase plant grain yield and decrease greenhouse gas emission intensity in regions with water shortage in Southwest China.

Determining effect of seagrass-mediated CO2 flux on the atmospheric cooling potential of a subtropical intertidal seagrass meadow

Atmospheric greenhouse gas (GHG) emissions from seagrass meadows that determine the ecosystem atmospheric cooling effect have rarely been quantified. This study measured the simultaneous fluxes direct to the atmosphere of three GHGs (CO2, CH4 and N2O) within a Halophila beccarii seagrass meadow and an adjacent unvegetated bare intertidal flat, and their relationships to seagrass abundance and relevant soil parameters. The results showed that seasonal variation in seagrass abundance was strongly linked with the CO2 exchange rate. The CH4 and N2O fluxes were similarly low at both sites and comparable between winter and summer. The global warming potential of CH4 and N2O reduced the ecosystem CO2 uptake by only 5 % at the seagrass site. The results indicated that the H. beccarii meadow had a stronger atmospheric cooling effect than the bare flat and that the seagrass-mediated CO2 flux in this oligotrophic seagrass meadow primarily determined the atmospheric cooling effect.

Land use intensification significantly reduced CH4 emissions while increasing N2O emissions: Taihu Lake region, China

Land use intensification is becoming increasingly common in China’s Taihu Lake region because of economic interests. Frequent intensification is the conversion from natural wetlands (NW) to conventional rice-wheat rotation fields (RW), and from conventional RW to greenhouse vegetable fields (GH). However, the impact of land use intensification on greenhouse gas emissions in this area is still unknown. In our study, we chose typical NW, RW, and GH to compare and measure methane (CH4) and nitrous oxide (N2O) emissions from the three land use types through two-year in-situ field experiments. The results showed that land use intensification significantly reduced CH4 emissions, and NW, RW, and GH emissions were 970.66 ± 100.09, 896.71 ± 300.44, and −71.23 ± 63.62 kg C ha-1. Land use intensification significantly increased N2O emissions, and NW, RW, and GH emissions were 3.35 ± 0.44, 14.38 ± 4.09, and 81.62 ± 4.89 kg N ha-1. The global warming potential of CH4 and N2O under different land use types was in the order of RW (28,137.98 ± 9077.12 kg eq-CO2 ha-1) > NW (27,123.76 ± 2703.34 kg eq-CO2 ha-1) > GH (20,360.44 ± 2651.51 kg eq-CO2 ha-1). Overall, we observed that the comprehensive greenhouse effect of CH4 and N2O was enhanced by conversion from NW to RW and weakened by conversion from RW to GH. Our study provides a predictive understanding of how land use intensification changes greenhouse gas emissions in the Taihu Lake region and in regions with similar land use types.

Climate impacts of fossil fuels in todays electricity systems

Oil, coal, and gas account for approximately 80% of global primary energy, but only a portion of total airborne CO2eq (approx. 35% at GWP20 to 65% at GWP100), even though they account for 95% of total measured CO2 emissions. The benefits of these energy sources, as well as their related costs, are not all incorporated in current energy policy discussions. Global greenhouse gas policies must include documented changes in measured airborne CO2eq to avoid spending large amounts of public funds on ineffective or sub-optimal policies. The authors examined airborne CO2, which is less than half of emitted CO2, as well as reported CH4 emissions and the global warming potential of CH4 as published by the IPCC for coal and natural gas. The surprising conclusion is that surfaced-mined coal appears 'better for the climate' than the average natural gas, and all coal appears beneficial over LNG. Therefore, current CO2-only reduction policies and CO2 taxes are leading to unintended consequences and the switch from coal to natural gas, especially LNG, will not have the desired impact of reducing predicted future global warming; in fact, quite the contrary. A large portion of anthropogenic global warming is attributed by the IPCC and IEA to CH4, but it must be noted that CH4 emissions from natural sources and from agriculture account for approximately 40% and 25% of annual global CH4 emissions respectively. Energy accounts for about 20% of documented CH4 emissions. CO2 contributes only approximately 35% of annual airborne anthropogenic GHG emissions after accounting for CH4, over a 20-year horizon. At a 100-year horizon, the contribution of CO2 increases to approximately 60%. Energy policies that do not consider all GHG emissions along the entire value chain will lead to undesired economic and environmental distortions. All carbon taxation and CO2 pricing schemes are incorrect and need to be revised. At IPCC's GWP20 an approximately 2%1 higher loss of CH4 across the value chain prior to combustion of natural gas versus coal will lead to 'climate parity' of coal with natural gas. According to public data, natural gas value chains have high CH4 and undocumented CO2 losses. On a global average, using only IEA-documented CH4 data, natural gas emits approximately 15% more CO2eq than surface-mined coal, over a 20-year horizon. This difference will increase as the use of shale gas and LNG expands. Investors should support all energy systems in a manner that avoids an energy crisis, including intermittent renewable energy systems where they make sense. If CO2 emissions need to be reduced, one of the most effective ways would be to install ultra-supercritical power plants with CCUS technology. However, the undisputed benefits of increased CO2 concentrations in the atmosphere because of its promotion of photosynthesis and plant growth effects (fertilization) need to be considered in energy policy decisions as well. The authors suggest that future research and development should concentrate on reducing net emissions from fossil fuel power plants and providing cost-effective and reliable new conventional power generation capacity, utilizing clean coal and clean natural gas technology.

Coupling plant litter quantity to a novel metric for litter quality explains C storage changes in a thawing permafrost peatland.

Permafrost thaw is a major potential feedback source to climate change as it can drive the increased release of greenhouse gases carbon dioxide (CO2) and methane (CH4). This carbon release from the decomposition of thawing soil organic material can be mitigated by increased net primary productivity (NPP) caused by warming, increasing atmospheric CO2, and plant community transition. However, the net effect on C storage also depends on how these plant community changes alter plant litter quantity, quality, and decomposition rates. Predicting decomposition rates based on litter quality remains challenging, but a promising new way forward is to incorporate measures of the energetic favorability to soil microbes of plant biomass decomposition. We asked how the variation in one such measure, the nominal oxidation state of carbon (NOSC), interacts with changing quantities of plant material inputs to influence the net C balance of a thawing permafrost peatland. We found: (1) Plant productivity (NPP) increased post‐thaw, but instead of contributing to increased standing biomass, it increased plant biomass turnover via increased litter inputs to soil; (2) Plant litter thermodynamic favorability (NOSC) and decomposition rate both increased post‐thaw, despite limited changes in bulk C:N ratios; (3) these increases caused the higher NPP to cycle more rapidly through both plants and soil, contributing to higher CO2 and CH4 fluxes from decomposition. Thus, the increased C‐storage expected from higher productivity was limited and the high global warming potential of CH4 contributed a net positive warming effect. Although post‐thaw peatlands are currently C sinks due to high NPP offsetting high CO2 release, this status is very sensitive to the plant community's litter input rate and quality. Integration of novel bioavailability metrics based on litter chemistry, including NOSC, into studies of ecosystem dynamics, is needed to improve the understanding of controls on arctic C stocks under continued ecosystem transition.

Methane Emissions Offset Net Carbon Dioxide Uptake From an Alpine Peatland on the Eastern Qinghai‐Tibetan Plateau

AbstractPeatlands store large amounts of carbon (C) and actively exchange greenhouse gases (GHGs) with the atmosphere, thus significantly affecting global C cycle and climate. Large uncertainty exists in C and GHG estimates of the alpine peatlands on Qinghai‐Tibetan Plateau (QTP), as direct measurements of CO2 and CH4 fluxes are scarce in this region. In this study, we provided 32‐month CO2 and CH4 fluxes measured using the eddy covariance (EC) technique in a typical alpine peatland on the eastern QTP to estimate the net C and CO2 equivalent (CO2‐eq) fluxes and investigate their environmental controls. Our results showed that the mean annual CO2 and CH4 fluxes were −68 ± 8 g CO2‐C m−2 yr−1 and 35 ± 0.3 g CH4‐C m−2 yr−1, respectively. While considering the traditional and sustained global warming potentials of CH4 over the 100‐year timescale, the peatland acted as a net CO2‐eq source (1,059 ± 30 and 1,853 ± 31 g CO2‐eq m−2 yr−1, respectively). The net CO2‐eq emissions during the non‐growing seasons contributed to over 40% of the annual CO2‐eq budgets. We further found that net CO2‐eq flux was primarily influenced by global radiation and soil temperature variations. This study was the first assessment to quantify the net CO2‐eq flux of the alpine peatland in the QTP region using EC measurements. Our study highlights that CH4 emissions from the alpine peatlands can largely offset the net cooling effect of CO2 uptake and future climate changes such as global warming might further enhance their potential warming effect.

A novel green substrate made by sludge digestate and its biochar: Plant growth and greenhouse emission

Anaerobic digestion of sludge produces a large amount of sewage sludge anaerobic digestate (SSAD) that can be reused. A novel green substrate was prepared by mixing SSAD and its biochar (SSBC) filled with perlite and quartz sand for plant growth, as a replacement of soil. We carried out pot experiment, measured ryegrass biomass, seedling survival rate, and evaluated the emission of greenhouse gas (GHG), NH3 volatilization. The results showed that the seedling survival rate and individual biomass of ryegrass in green substrate were 100% and 100.02 mg, which were 14.4% and 231.4% higher than those in only SSAD, but were 1.3% and 19.6% higher than those in soil. SSBC significantly reduced N2O and CO2 emission, inhibited the NH3 volatilization, but increased CH4 emission. However, the cumulative emission of N2O and CH4 was approximation to that in soil. Global warming potential of CH4 and N2O (GWP(CH4+N2O)) green substrate was 11,842.01 kg CO2·hm−2, which was 1.35-fold higher than that of soil. Microbial community structure analysis showed that fermentative bacteria and methanogenic archaeal had a higher abundance in green substrate than in soil, which caused the different gas emission. This study will provide an effective and economical way to dispose excessive SSAD.

The Study of Chicken Manure and Steel Slag Amelioration to Mitigate Greenhouse Gas Emission in Rice Cultivation

Organic matter, fertilizers, and soil amendments are essential for sustainable agricultural practices to guarantee soil productivity. However, these materials can increase the emission of greenhouse gases (GHGs) such as CH4 and N2O. Thus, technologies for reducing GHG emissions in concert with the increase in rice production from rice fields are needed. The objectives of this study were to determine the best chicken manure (CM) and steel slag (SS) combination to mitigate CH4, N2O, and CO2 emissions in an incubation experiment, to identify the best CM:SS ameliorant mixture to mitigate CH4 and N2O, and to evaluate dry biomass and grain yield in a pot experiment. A randomized block design was established with four treatments, namely conventional (chemical fertilizer only) and three combinations of different ratios of CM and SS (1:1, 1:1.5, and 1:2.5), with five replications in a pot experiment. CM:SS (1:2.5) was identified as the best treatment for mitigating CH4, N2O, and CO2 in the incubation experiment. However, CM:SS (1:1.5) was the best CM and SS ameliorant for mitigating CH4 and N2O in the pot experiment. The global warming potential of CH4 and N2O revealed that CM:SS (1:1.5) had the lowest value. None of the combinations of CM and SS significantly increased dry biomass and grain yield.

„Climate Impacts“ of Fossil Fuels in Today’s Energy Systems

The main fossil fuels oil, coal, and gas provide ~80% of global energy. In the next few years, “renewables” may meet only half the additional growth in global electricity demand or only about 20% of primary energy demand growth. The remaining increased energy demand will need to be matched by increased conventional energy generation. Coal and gas together account for 50% of primary energy and 60% of electricity. Therefore, the authors examine the global warming potential for both fuels. The surprising conclusion is that surfaced-mined coal appears “better for the climate” than the average natural gas and all coal appears beneficial over LNG. Therefore, current CO2-only reduction policies and CO2 taxes are leading to misguided consequences and the switch from coal to gas, especially LNG, will not have the desired impact of reducing predicted future global warming, quite the contrary. With IPCC’s global warming potential of CH4 over 20 years, a ~2% higher loss of methane across the value chain prior to combustion of gas vs. coal will lead to “climate parity” of coal with gas. Analyzing IEA information, natural gas value chains have high methane and undocumented CO2 losses. On global average, natural gas emits ~20% more CO2eq than surface-mined coal. This difference increases as the use of shale gas and LNG expands. Global GHG policies need to include documented changes in measured airborne CO2eq to avoid spending large amounts of public funds on ineffective or sub-optimal policies. I.e., most global funds, international banks, conglomerates, and insurances have publicly announced that, mostly for climate protection reasons, they will abandon coal but will continue to support LNG and pipeline natural gas projects which are all required to power human life. This is likely to have unexpected consequences. The potential effects of a warming climate system should not be discounted or played down. However, the undisputed benefits of increased CO2 concentrations in the atmosphere because of its photosynthetic and growth effects (fertilization) on plants need to be considered in energy policy decisions as well. The authors suggest sponsoring ultra-super-critical power plants, whether fossil fuel fired, nuclear, or renewable, at no cost to developing nations to reduce their emissions while also providing essential and reliable energy to encourage industrial growth. Such “technological” gifts could replace less efficient existing plants or even provide new power plants that have far higher emission reduction factors thereby supporting economic and environmental activities in both developing and developed nations. NOTE: This is a draft paper, currently for review

Effects of Different Rotation Patterns of Oil-Rice on Methane and Nitrous Oxide Emissions in Rice Fields

A field experiment was carried out to investigate the effects of different rice-rape rotation systems on methane and nitrous oxide emissions, which were measured using the static chamber/gas chromatography method, prediction of their global warming potentials (GWP), and greenhouse gas intensity (GHGI) in paddy fields. The results showed that the average cumulative emissions of CH4from a double cropping paddy field, single season rice field (including middle or late), rape field, and leisure land were 135.25, 55.64, 5.05, and 1.89 kg ·hm-2, respectively. The CH4 emission during the rice season accounted for 91.8%-98.5% of the annual CH4 emission in different rotation years, and the contents of dissolved organic carbon in paddy soil exhibited a significantly positive correlation with CH4 emission. The CH4 emission in conventional late rice paddy was 18.7% higher than that of hybrid late rice paddy (P<0.05). The average cumulative emissions of N2O from double cropping paddy field, single season rice field (including middle or late), rape field, and leisure land were 0.94, 0.64, 1.38, and 0.24 kg ·hm-2, respectively. Out of the total annual N2O emission, 57.2% to 70.2% was from the rape field; 17.8% and 30.6% was due to the winter fallow treatments with previous crop type of double corpping rice and single season rice, respectively. There was no significant difference in N2O emission between hybrid rice and conventional rice paddy fields. The GWP of double cropping rice-winter fallow and double cropping rice-rape was higher than that of rice-rape and rice-winter fallow, and the GWP of CH4 in rice season accounted for 71.2% to 90.9% of the annual GWP of rotation. The highest treatment of GHGI was rice-rice-rape, and the treatment of rice-oil and rice-winter slack was lower. According to the comprehensive environmental and economic benefits, the late hybrid rice-rape patterns should be selected to reduce greenhouse gases in multiple cropping rice fields of South China.

Invited Review: Methane sources, quantification, and mitigation in grazing beef systems

ABSTRACT Purpose The purpose of the review was to examine enteric methane emissions, quantification methods, and mitigation strategies in grazing beef systems. Sources Peer-reviewed literature and conference abstracts were the main sources of information for this review. Synthesis Methane emissions (CH4) can be reduced by improving forage quality by including more cool-season forages and legumes and rotationally grazing animals. Including forages with beneficial secondary compounds such as condensed tannins and saponins also has CH4-mitigation potential. Providing nutritional supplements that improve the nutritional status of the animal and the efficiency of feed energy use has the potential to reduce CH4 emissions from grazing cattle. Genetic selection has shown some viability in reducing herd emissions, but heritability estimates are low for CH4 yield. More research is needed to understand the potential. Soil methanotrophy may partially offset CH4 emissions when animals are stocked moderately but soil CH4 uptake rates are relatively low in most grazing ecosystems. A new metric to quantify the global warming potential of CH4, GWP*, may allow future models to more appropriately consider the behavior and effects of CH4 in the atmosphere. Conclusions and Applications Methane mitigation strategies in grazing environments are limited, but producer decisions that improve the nutritional status of animals, the quality of the forage base, and supplementation of known CH4-mitigation compounds can reduce CH4 production. Now that less expensive, easier to use quantification tools exist, researchers need to conduct more long-term monitoring experiments and focus on reducing CH4 production of grazing animals where potential for reduction is largest.

Responses of soil CO2 and CH4 emissions to changing water table level in a coastal wetland

Global climate change and in particular sea level rise have resulted in water table level rise in the coastal wetland, which may alter the magnitude and direction of carbon flux. However, the degree to which different water table level affects soil CO2 and CH4 emissions remains uncertain in coastal wetland. Here, a soil microcosm experiment with five water table levels (−40, −30, −20, −10, 0 cm) was conducted in the Yellow River Delta, China. The water table level was controlled by manual. The soil CO2 and CH4 emissions of each water table levels were measured during 150-days incubation in 2018. Our results showed that water table level rise decreased soil CO2 emissions, while increased soil CH4 emissions. However, there was no significant difference in soil CO2 and CH4 emissions from −20 to −40 water table levels, respectively. In addition, water table level rise significant alter soil physical and chemical properties in the uppermost soil layer (0–10 cm) in coastal wetland, in particular soil moisture and salinity, which probably jointly affected soil CO2 and CH4 emissions. Furthermore, cumulative soil CH4 emission was positively significantly correlated to soil organic carbon and total carbon, suggesting that carbon component can supply energy and nutrients and benefit for soil CH4 production. Additionally, there was a significant relationship between cumulative soil CO2 emission and dissolved organic carbon, which indicated that CO2 was mainly contributed from dissolved organic carbon. Cumulative soil CO2 emission was significantly correlated with soil microbial biomass carbon, suggesting that microbial activity played an important role in CO2 emissions in coastal wetlands. Our results also indicate that water table level rise caused by sea level rise may contribute to the storage of soil organic carbon and produces a lower global warming potentials of CH4 and CO2 in the further climate change. Therefore, it is necessary to estimate the effect of hydrological, especially water table level on carbon cycles in coastal wetland when evaluating the climate–carbon feedback scenarios.

Comprehensive assessments of carbon dynamics in an intermittently-irrigated rice paddy

Rice is a major crop that feeds more than half of the global population. Rice paddies play a complex role in the carbon cycle by emitting CH4 to the atmosphere while either sequestering or releasing CO2 to the atmosphere. Here, we present 3.5 years of eddy covariance measurements of CO2 and CH4 fluxes over an intermittently irrigated, single crop rice paddy in South Korea in tandem with carbon stock measurements for leaves, stems, grains, and roots. The rice paddy acted as a slight sink or neutral in CO2 (−47 ± 51 g C m−2y−1; mean ± 95% confidence interval) with 941 ± 130 g C m−2y−1 and 894 ± 108 g C m−2y−1 as the gross primary production (GPP) and ecosystem respiration (Reco), respectively. The mean annual net primary productivity (NPP) was 666 ± 31 g C m−2y−1, which was partitioned to leaves (9%), stems (30%), grains (51%), and roots (10%), for a harvest index of 57%. The paddy emitted 20.6 ± 1.5 g C m−2y−1 in the form of CH4, of which between 82 and 96% was emitted during the cultivation period (~132 days) . The CH4 flux showed a mid-season decline caused by mid-season drainage, which produced aerobic soil conditions that inhibited CH4 emissions. The proportion of estimated ebullitive flux to total CH4 flux ranged from 10 to 17% during the cultivation period. GPP, Reco, and CH4 fluxes varied by 12%, 11%, and 7%, respectively, over the 3-year period. When considering the harvest and the global warming potential of CH4, the paddy shifted from a greenhouse gas sink to a strong source (2,741 ± 468 g CO2 eq m−2y−1). These findings will improve our understanding of carbon budgets and cycles, and help develop greenhouse gas and water management strategies for rice paddies.

The Net Landscape Carbon Balance-Integrating terrestrial and aquatic carbon fluxes in a managed boreal forest landscape in Sweden.

The boreal biome exchanges large amounts of carbon (C) and greenhouse gases (GHGs) with the atmosphere and thus significantly affects the global climate. A managed boreal landscape consists of various sinks and sources of carbon dioxide (CO2 ), methane (CH4 ), and dissolved organic and inorganic carbon (DOC and DIC) across forests, mires, lakes, and streams. Due to the spatial heterogeneity, large uncertainties exist regarding the net landscape carbon balance (NLCB). In this study, we compiled terrestrial and aquatic fluxes of CO2 , CH4 , DOC, DIC, and harvested C obtained from tall-tower eddy covariance measurements, stream monitoring, and remote sensing of biomass stocks for an entire boreal catchment (~68km2 ) in Sweden to estimate the NLCB across the land-water-atmosphere continuum. Our results showed that this managed boreal forest landscape was a net C sink (NLCB=39gCm-2 year-1 ) with the landscape-atmosphere CO2 exchange being the dominant component, followed by the C export via harvest and streams. Accounting for the global warming potential of CH4 , the landscape was a GHG sink of 237gCO2 -eqm-2 year-1 , thus providing a climate-cooling effect. The CH4 flux contribution to the annual GHG budget increased from 0.6% during spring to 3.2% during winter. The aquatic C loss was most significant during spring contributing 8% to the annual NLCB. We further found that abiotic controls (e.g., air temperature and incoming radiation) regulated the temporal variability of the NLCB whereas land cover types (e.g., mire vs. forest) and management practices (e.g., clear-cutting) determined their spatial variability. Our study advocates the need for integrating terrestrial and aquatic fluxes at the landscape scale based on tall-tower eddy covariance measurements combined with biomass stock and stream monitoring to develop a holistic understanding of the NLCB of managed boreal forest landscapes and to better evaluate their potential for mitigating climate change.

Lime application lowers the global warming potential of a double rice cropping system

Liming is a common practice to alleviate soil acidification in agricultural systems worldwide. Because liming affects soil microbial activity and soil carbon (C) input rates, it can affect soil greenhouse gas (GHG) emissions as well. However, little is known about the effect of liming on GHG emissions from rice agriculture, one of the main sources of anthropogenic methane (CH4). Here, we report on the first experiment to measure the effect of liming on GHG emissions from rice paddy fields. We studied a double rice cropping system in an acid paddy for two years and measured the impacts of liming on GHG emissions and rice growth with or without straw incorporation. We found that liming reduced CH4 emissions in the early rice season, but it did not affect nitrous oxide (N2O) emissions. Over the two-year study, lime application reduced total CH4 emissions by 12.5% and 15.4% in plots without and with straw incorporation, respectively. Lime application significantly enhanced rice aboveground biomass, while reducing the area- and yield-scaled global warming potential of CH4 and N2O emissions. Lime application stimulated soil respiration during the fallow season and reduced the abundance of methanogens during the early rice growing season. Together, these results suggest that liming reduces CH4 emissions by promoting the decomposition of organic matter during the fallow season, thereby reducing C availability for methanogens. We conclude that in the short term, liming is an effective practice to reduce greenhouse gas emissions from acidic paddy soils.

Effect of spent mushroom substrate as a bulking agent on gaseous emissions and compost quality during pig manure composting.

The aim of this study was to investigate the gaseous emissions (CH4, N2O, and NH3) and compost quality during the pig manure composting by adding spent mushroom substrate (SMS) as a bulking agent. The control treatment was also studied using corn stalk (CS) as a bulking agent. The experiment was conducted in a pilot scale composting reactor under aerobic condition with the initial C/N ratio of 20. Results showed that bulking agents significantly affected gaseous emissions and compost quality. Using SMS as a bulking agent improved composting efficiency by shortening the time for maturity. SMS increased germination index and humic acid of the final compost (by 13.44 and 41.94%, respectively) compared with CS. Furthermore, composting with SMS as a bulking agent could reduce nitrogen loss, NH3, and N2O emissions (by 13.57, 35.56, and 46.48%, respectively) compared with the control. SMS slightly increased CH4 emission about 1.1 times of the CS. However, a 33.95% decrease in the global warming potential of CH4 and N2O was obtained by adding SMS treatment. These results indicate that SMS is a favorable bulking agent for reducing gaseous emissions and increasing compost quality.