Wetlands act as a net source of methane and a net sink of carbon dioxide
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Scientific literature confirms that wetlands function as a source of atmospheric methane due to microbial decomposition processes while simultaneously acting as sinks for carbon dioxide through photosynthetic sequestration and organic matter storage in soils.
Wetlands are one of the most important sources of atmospheric methane (CH 4 ), but the strength of this source is still highly uncertain. To improve estimates of CH 4 emission at the regional and global scales and predict future variation requires a process‐based model integrating the controls of climatic and edaphic factors and complex biological processes over CH 4 flux rates. This study used a methane emission model based on the hypothesis that plant primary production and soil organic matter decomposition act to control the supply of substrate needed by methanogens; the rate of substrate supply and environmental factors, in turn, control the rate of CH 4 production, and the balance between CH 4 production and methanotrophic oxidation determines the rate of CH 4 emission into the atmosphere. Coupled to data sets for climate, vegetation, soil, and wetland distribution, the model was used to calculate spatial and seasonal distributions of CH 4 emissions at a resolution of 1° latitude × 1° longitude. The calculated net primary production (NPP) of wetlands ranged from 45 g C m −2 yr −1 for northern bogs to 820 g C m −2 yr −1 for tropical swamps. CH 4 emission rates from individual gridcells ranged from 0.0 to 661 mg CH 4 m −2 d −1 , with a mean of 40 mg CH 4 m −2 d −1 for northern wetland, 150 mg CH 4 m −2 d −1 for temperate wetland, and 199 mg CH 4 m −2 d −1 for tropical wetland. Total CH 4 emission was 92 Tg yr −1 . Sensitivity analysis showed that the response of CH 4 emiss
Microorganisms act as both the source and sink of methane, a potent greenhouse gas, thus making a significant contribution to the environment as an important driver of climate change. The rhizosphere and phyllosphere of plants growing in natural (mangroves) and artificial wetlands (flooded agricultural ecosystems) harbor methane-utilizing bacteria that oxidize methane at the source and reduce its net flux. For several decades, microorganisms have been used as biofertilizers to promote plant growth. However, now their role in reducing net methane flux, especially from flooded agricultural ecosystems is gaining momentum globally. Research in this context has mainly focused on taxonomic aspects related to methanotrophy among diverse bacterial genera, and environmental factors that govern methane utilization in natural and artificial wetland ecosystems. In the last few decades, concerted efforts have been made to develop multifunctional microbial inoculants that can oxidize methane and alleviate greenhouse gas emissions, as well as promote plant growth. In this context, combinations of taxonomic groups commonly found in rice paddies and those used as biofertilizers are being explored. This review deals with methanotrophy among diverse bacterial domains, factors influencing methane-utilizing ability, and explores the potential of novel methane-utilizing microbial consortia with plant growth-promoting traits in flooded ecosystems.
Abstract In many countries wetlands are constructed or restored for removing nutrients from surface water. At the same time vegetated wetlands can act as carbon sinks when CO 2 is sequestered in biomass. However, it is well known that wetlands also produce substantial amounts of greenhouse gasses CH 4 and N 2 O. Especially N 2 O, resulting from nitrification and denitrification, is a very potent GHG. To assess the environmental sustainability of constructed wetlands the benefit of carbon sink and the downside of GHG emissions have to be evaluated. Since nutrient and carbon cycles in wetlands are complex and variable among wetlands and in time such a balance always contains uncertainties. Several studies have addressed this issue and indicated that CW can be either a sink or a source of CO 2 equivalents depending on the time scale of research and the environmental and management conditions involved. Here we balance carbon sequestration with CH 4 and N 2 O emissions in a multi-functional constructed wetland, dominated by emergent Phragmites vegetation. Detailed measurements were combined with a nitrogen budget, and all fluxes were expressed as a range indicating the uncertainties in measurements and extrapolation techniques. Measured methane emissions were variable and showed clear relationship with temperature and density of the emergent vegetation. Average CH 4 emissions in the vegetation were 7.8 at 15 °C and 24.5 mg m −2 h −1 at 24 °C. Estimated N 2 O emissions ranged from
Wetlands are prominent ecosystems lying at the interphase between terrestrial and aquatic ecosystems storing nearly 20–30% of the global carbon pool and are considered as the first ecosystem to experience the impact of climate change. Carbon storage in wetlands depends on the balance between carbon input and output influenced by several environmental and micro-meteorological factors such as temperature, moisture, pH, redox conditions, topography, geological position, the hydrological regime and type of vegetation. Globally rice paddies share a significant portion of the wetlands functioning as a major sink or source of carbon micromanaging the emissions of major greenhouse gases. Studies conducted by the authors in selected paddy wetlands of Kerala, India, have established that they are net source of methane during the flooded paddy growth period (92.638 mg m−2 h−1), whereas they act as sink during the summer fallow period (−2.0176 mg m−2 h−1). The carbon dioxide fluxes in the paddy act as a source (−0.45 to 2.3 g m−2 h−1) during the entire study period. Seasonal carbon dioxide was higher in the summer fallow period than in the flooded cultivation period. Fallow period facilitates the aeration of soil, thereby resulting in net loss of soil organic carbon by oxidizing it to carbon dioxide. Highest nitrous oxide emission (0.76 mg m−2 h−1) was observed during the end of first crop season whereas lowest (−0.017 mg m−2 h−1) was during summer fallow months of April. During the stud
Methane (CH4), an important greenhouse gas (GHG), contributes ~33.0% to the total global GHGs emissions and accounts for 15–20% to the global warming. As the second most important human-generated GHG after CO2, CH4 is strongly linked with various climate phenomena. Most of the wetlands from tropics to temperate have been reported to have significantly enhanced emissions of CH4 during recent years. In wetland, microbial communities are a major determining factor in controlling the carbon cycle. The terrestrial wetlands are also among the key CH4 emitters and play a major role to climate change. The role of wetland expansion in CH4 emissions and its consequences on climate change and global warming might be a major concern for the future world. The methanogens and methanotrophs, two physiologically different microbial communities, seem to be crucial for future research investigations while comparing the CH4 production and consumption in wetland ecosystems. Anthropogenic disturbances related to wetlands are likely to influence the altering of microbial community composition of methanogens and methanotrophs and consequently net CH4 flux. The terrestrial wetlands have been reported to act as a source and sink for atmospheric CH4. Therefore, recent concerns about CH4 emission from terrestrial wetlands could be addressed properly because it is one of the major causes in contributing the status of CH4 in the environment.
Phragmites australis wetlands act as a sink for greenhouse gases by photosynthetic assimilation of carbon dioxide (CO2) from the atmosphere and sequestration of the organic matter produced in the wetland soil. The wetlands also act as a source for greenhouse gases by emission of sediment-produced methane (CH4) to the atmosphere. In P. australis wetlands, the dominant mechanism of CH4 release to the atmosphere is internal gas transport in the plants, primarily by pressurized convective gas flow. The time periods of carbon fixation and CH 4 release therefore vary seasonally and diurnally. The balance between net CO2-assimilation and CH4 emission determines if a wetland can be regarded as a net sink or a net source of greenhouse gases, and hence, the function of the wetland in relation to global climate change. On an annual basis up to 15% of the net carbon fixed by the wetlands may be released to the atmosphere as CH 4. Because of the different infrared absorption characteristics and atmospheric longevity of CH4 and CO2, the warming effect of CH4 in the atmosphere is about 21 times higher on a mass basis than CO2 over a 100-year timescale. Thus, the immediate carbon balance, coupled with the different physical characteristics of the two gases, would suggest that although some wetlands function as a net sink for CO2, the wetlands still increase the greenhouse effect because of their release of CH4. However, the short adjustment time for CH4 in the atmosphere means that, over a l
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