A process-based model for methane emission from flooded rice paddy systems

A GIS-based method for modeling methane emissions from paddy fields by fusing multiple sources of data

Quantification of regional methane (CH₄) gas emission in the paddy fields is critical under climate warming. Mechanism models generally require numerous parameters while empirical models are too coarse. Based on the mechanism and structure of the widely used model CH4MOD, a GIS-based Regional CH₄ Emission Calculation (GRMC) method was put forward by introducing multiple sources of remote sensing images, including MOD09A1, MOD11A2, MOD15A2H as well as local water management standards. The stress of soil moisture condition (f(water)) on CH₄ emissions was quantified by calculating the redox potential (Eh) from days after flooding or falling dry. The f(water)-t curve was calculated under different exogenous organic matter addition. Combining the f(water)-t curve with local water management standards, the seasonal variation of f(water) was obtained. It was proven that f(water) was effective in reflecting the regulation role of soil moisture condition. The GRMC was tested at four Eddy Covariance (EC) sites: Nanchang (NC) in China, Twitchell (TWT) in the USA, Castellaro (CAS) in Italy and Cheorwon (CRK) in Korea and has been proven to well track the seasonal dynamics of CH₄ emissions with R² ranges of 0.738-0.848, RMSE ranges of 31.94-149.22 mg C/m²d and MBE ranges of -66.42- -14.79 mg C/m²d. The parameters obtained in Nanchang (NC) site in China were then applied to the Ganfu Plain Irrigation System (GFPIS), a typical rice planting area of China, to analyse the spatial-temporal variations of CH₄ emissions. The total CH₄ emissions of late rice in the GFPIS from 2001 to 2013 was in the range of 14.47-20.48 (10³ t CH₄-C). Ts caused spatial variation of CH₄ production capacity, resulting in the spatial variability of CH4 emissions. Overall, the GRMC is effective in obtaining CH₄ emissions from rice fields on a regional scale.

A novel permeable reactive biobarrier for ortho-nitrochlorobenzene pollution control in groundwater: Experimental evaluation and kinetic modelling

Three novel permeable reactive barrier (PRB) materials composed of Cu/Fe with 0.24% and 0.43% (w/w) Cu loadings or Fe⁰ supported on wheat straw were prepared (termed materials E, F and G). These materials exhibited excellent pollutant removal efficiency and physical stability as well as the ongoing release of organic carbon and iron. Column experiments showed that materials E, F and G removed almost 100% of ortho-nitrochlorobenzene (o-NCB) from water. The rates of iron release from the E and F columns exceeded those from column G but this had no significant effect on o-NCB removal. The bacteria that degraded o-NCB in E and F were also different from those in G. The levels of these bacteria in the columns were higher than those in the initial materials, with the highest level in column E. The simultaneous reduction and microbial degradation of o-NCB was observed, with the latter being dominant. A kinetic model was established to simulate the dynamic interactions and accurately predicted the experimental results. Organic carbon from the wheat straw supported the majority of the biomass in each column, which was essential for the bioremediation process. The findings of this study suggest an economically viable approach to mitigating o-NCB pollution.

Limited aerenchyma reduces oxygen diffusion and methane emission in paddy

Greenhouse gasses (GHG) emission from the agricultural lands is a serious threat to the environment. Plants such as rice (Oryza sativa L.) that are cultivated in submerged conditions (paddy field) contribute up to 19% of CH₄ emission from agricultural lands. Such plants have evolved lysigenous aerenchyma in their root system which facilitates the exchange of O₂ and GHG between aerial parts of plant and rhizosphere. Currently, the regulation of GHG and O₂ via aerenchyma formation is poorly understood in plants, especially in rice. Here, a reverse genetic approach was employed to reduce the aerenchyma formation by analyzing two mutants i.e., oslsd1.1-m12 and oslsd1.1-m51 generated by Tos17 and T-DNA insertion. The wild-type (WT) and the mutants were grown in paddy (flooded), non-paddy and hydroponic system to assess phenotypic traits including O₂ diffusion, GHG emission and aerenchyma formation. The mutants exhibited significant reductions in several morphophysiological traits including 20-60% aerenchyma formation at various distances from the root apex, 25% root development, 50% diffusion of O₂ and 27-36% emission of methane (CH₄) as compared to WT. The differential effects of the oslsd1.1 mutants in aerenchyma-mediated CH₄ mitigation were also evident in the diversity of (pmoA, mcrA) methanotrophs in the rhizosphere. Our results indicate the novel pathway in which reduced aerenchyma in rice is responsible for the mitigation of CH₄, diffusion of O₂ and the root growth in rice. Limited aerenchyma mediated approach to mitigate GHG specially CH₄ mitigation in agriculture is helpful technique for sustainable development.

Methane emissions from landfill: influence of vegetation and weather conditions

Vegetation plays an important role in CH₄ transport and oxidation in landfill cover soil. This study investigated CH₄ emission fluxes in two landfills with different surface coverage conditions and it found that the CH₄ emission fluxes presented spatial and temporal disparities. A significant discrepancy in CH₄ emission flux between day and night in areas covered with Kochia sieversiana indicated that enhanced diffusion induced by rising temperature was the main mechanism for CH₄ transport during daytime. A significant increase of CH₄ emission flux after the K. sieversiana and Suaeda glauca plants were cut indicated that these plants provide greater contributions to CH₄ oxidation than to CH₄ transport. Diel CH₄ emission flux was found closely correlated with the climatic conditions. Diffusion was determined as the main mechanism for CH₄ transport at daytime in bare area, mediated by solar radiation and air temperature. Diffusion and plant-mediated transport by convection was established as the main transport mechanism in areas covered with K. sieversiana. Our results further the understanding of both the CH₄ emission mechanism and the impact of vegetation on CH₄ oxidation, transport, and emission, which will benefit the development of a reliable model for landfill CH₄ emissions.

Simultaneous measurements of dissolved CH4 and H2 in wetland soils

Biogeochemical processes in wetland soils are complex and are driven by a microbiological community that competes for resources and affects the soil chemistry. Depending on the availability of various electron acceptors, the high carbon input to wetland soils can make them important sources of methane production and emissions. There are two significant pathways for methanogenesis: acetoclastic and hydrogenotrophic methanogenesis. The hydrogenotrophic pathway is dependent on the availability of dissolved hydrogen gas (H₂), and there is significant competition for available H₂. This study presents simultaneous measurements of dissolved methane and H₂ over a 2-year period at three tidal marshes in the New Jersey Meadowlands. Methane reservoirs show a significant correlation with dissolved organic carbon, temperature, and methane emissions, whereas the H₂ concentrations measured with dialysis samplers do not show significant relationships with these field variables. Data presented in this study show that increased dissolved H₂ reservoirs in wetland soils correlate with decreased methane reservoirs, which is consistent with studies that have shown that elevated levels of H₂ inhibit methane production by inhibiting propionate fermentation, resulting in less acetate production and hence decreasing the contribution of acetoclastic methanogenesis to the overall production of methane.

A simulation model for methane emissions from landfills with interaction of vegetation and cover soil

Global climate change and ecological problems brought about by greenhouse gas effect have become a severe threat to humanity in the 21st century. Vegetation plays an important role in methane (CH₄) transport, oxidation and emissions from municipal solid waste (MSW) landfills as it modifies the physical and chemical properties of the cover soil, and transports CH₄ to the atmosphere directly via their conduits, which are mainly aerenchymatous structures. In this study, a novel 2-D simulation CH₄ emission model was established, based on an interactive mechanism of cover soil and vegetation, to model CH₄ transport, oxidation and emissions in landfill cover soil. Results of the simulation model showed that the distribution of CH₄ concentration and emission fluxes displayed a significant difference between vegetated and non-vegetated areas. CH₄ emission flux was 1-2 orders of magnitude higher than bare areas in simulation conditions. Vegetation play a negative role in CH₄ emissions from landfill cover soil due to the strong CH₄ transport capacity even though vegetation also promotes CH₄ oxidation via changing properties of cover soil and emitting O₂ via root system. The model will be proposed to allow decision makers to reconsider the actual CH₄ emission from vegetated and non-vegetated covered landfills.

Site specific diel methane emission mechanisms in landfills: A field validated process based on vegetation and climate factors

Diel methane emission fluxes from a landfill that was covered by vegetation were investigated to reveal the methane emission mechanisms based on the interaction of vegetation characteristics and climate factors. The methane emissions showed large variation between daytime and nighttime, and the trend of methane emissions exhibited clear bimodal patterns from both Setaria viridis- and Neyraudia reynaudiana-covered areas. Plants play an important role in methane transportation as well as methane oxidation. The notable decrease in methane emissions after plants were cut suggests that methane transportation via plants is the primary way of methane emissions in the vegetated areas of landfill. Within plants, the methane emission fluxes were enhanced due to a convection mechanism. Given that the methane emission flux is highly correlated with the solar radiation during daytime, the convection mechanism could be attributed to the increase in solar radiation. Whereas the methane emission flux is affected by a combined impact of the wind speed and pedosphere characteristics during nighttime. An improved understanding of the methane emission mechanisms in vegetated landfills is expected to develop a reliable model for landfill methane emissions and to attenuate greenhouse gas emissions from landfills.

Tropical forest soil microbial communities couple iron and carbon biogeochemistry

We report that iron-reducing bacteria are primary mediators of anaerobic carbon oxidation in upland tropical soils spanning a rainfall gradient (3500-5000 mm/yr) in northeast Puerto Rico. The abundant rainfall and high net primary productivity of these tropical forests provide optimal soil habitat for iron-reducing and iron-oxidizing bacteria. Spatially and temporally dynamic redox conditions make iron-transforming microbial communities central to the belowground carbon cycle in these wet tropical forests. The exceedingly high abundance of iron-reducing bacteria (up to 1.2 x 10(9) cells per gram soil) indicated that they possess extensive metabolic capacity to catalyze the reduction of iron minerals. In soils from the higher rainfall sites, measured rates of ferric iron reduction could account for up to 44% of organic carbon oxidation. Iron reducers appeared to compete with methanogens when labile carbon availability was limited. We found large numbers of bacteria that oxidize reduced iron at sites with high rates of iron reduction and large numbers of iron reducers. The coexistence of large populations of iron-reducing and iron-oxidizing bacteria is evidence for rapid iron cycling between its reduced and oxidized states and suggests that mutualistic interactions among these bacteria ultimately fuel organic carbon oxidation and inhibit CH4 production in these upland tropical forests.

Water management--a tool for methane mitigation from irrigated paddy fields

Water drainage is considered to be one of the important practices that reduce the CH(4) efflux from paddy fields. In this study, four different drainage systems (continuous flooding, tillering stage drainage, mid-season drainage and multiple drainage) were compared to find out the best one, for attenuation of CH(4) emission from rice fields. Except for continuous flooding, from all the other three drainage systems, irrigation water from the paddy fields was drained out at the different stages of the crop cycle. Highest efflux of the methane was recorded from continuously flooded plots (346.6 mg/m(2)/day), followed by 9% less CH(4) efflux from tillering stage drainage (315.1mg/m(2)/day), 36.7% less efflux from mid-season drainage (219.3mg/m(2)/day) and the least 41% CH(4) efflux from multiple drainage plots (204.7 mg/m(2)/day). Among all the four different drainage systems applied, mid-season drainage and multiple drainage were found to be highly effective in mitigating methane efflux. Redox potential of the soil of the drainage system was found to be inversely proportional to the methane efflux from all the treatments.