A special kind of rice field exists in China that is flooded year-round. These rice fields have substantially large CH4 emissions during the rice-growing season and emit CH4 continuously in the non-rice growing season...A special kind of rice field exists in China that is flooded year-round. These rice fields have substantially large CH4 emissions during the rice-growing season and emit CH4 continuously in the non-rice growing season. CH4 emission factors were used to estimate the CH4 emissions from year-round flooded rice fields during the rice-growing season in China. The CH4 emissions for the year-round flooded rice fields in China for the rice growing season over a total area of 2.66 Mha were estimated to be 2.44 Tg CH…展开更多
Aquatic ecosystems have been identified as a globally significant source of nitrous oxide(N_2O) due to continuous active nitrogen involvement, but the processes and influencing factors that control N_2O production are...Aquatic ecosystems have been identified as a globally significant source of nitrous oxide(N_2O) due to continuous active nitrogen involvement, but the processes and influencing factors that control N_2O production are still poorly understood, especially in reservoirs. For that, monthly N_2O variations were monitored in Dongfeng reservoir(DFR)with a mesotrophic condition. The dissolved N_2O concentration in DFR displayed a distinct spatial–temporal pattern but lower than that in the eutrophic reservoirs. During the whole sampling year, N_2O saturation ranging from 144% to 640%, indicating that reservoir acted as source of atmospheric N_2O. N_2O production is induced by the introduction of nitrogen(NO_3^-, NH_4^+) in mesotrophic reservoirs, and is also affected by oxygen level and water temperature. Nitrification was the predominate process for N_2O production in DFR due to well-oxygenated longitudinal water layers.Mean values of estimated N_2O flux from the air–water interface averaged 0.19 μmol m^(-2)h^(-1) with a range of 0.01–0.61 μmol m^(-2)h^(-1). DFR exhibited less N_2O emission flux than that reported in a nearby eutrophic reservoir, but still acted as a moderate N_2O source compared with other reservoirs and lakes worldwide. Annual emissions from the water–air interface of DFR were estimated to be 0.32×10~5 mol N–N_2O, while N_2O degassing from releasing water behind the dam during power generation was nearly five times greater. Hence, N_2O degassing behind the dam should be taken into account for estimation of N_2O emissions from artificial reservoirs, an omission that historically has probably resulted in underestimates. IPCC methodology should consider more specifically N_2O emission estimation in aquatic ecosystems, especially in reservoirs, the default EF5 model will lead to an overestimation.展开更多
文摘A special kind of rice field exists in China that is flooded year-round. These rice fields have substantially large CH4 emissions during the rice-growing season and emit CH4 continuously in the non-rice growing season. CH4 emission factors were used to estimate the CH4 emissions from year-round flooded rice fields during the rice-growing season in China. The CH4 emissions for the year-round flooded rice fields in China for the rice growing season over a total area of 2.66 Mha were estimated to be 2.44 Tg CH…
基金financially supported by the National Key Research and Development Program of China through grant 2016YFA0601000the National Major Scientific Research Program Grant No.2013CB956401+1 种基金the National Natural Science Foundation of China through Grants Nos.41325010,41403082,and 41302285the Tianjin Research Program of Application Foundation and Advanced Technology Grant No.14JCQNJC08800
文摘Aquatic ecosystems have been identified as a globally significant source of nitrous oxide(N_2O) due to continuous active nitrogen involvement, but the processes and influencing factors that control N_2O production are still poorly understood, especially in reservoirs. For that, monthly N_2O variations were monitored in Dongfeng reservoir(DFR)with a mesotrophic condition. The dissolved N_2O concentration in DFR displayed a distinct spatial–temporal pattern but lower than that in the eutrophic reservoirs. During the whole sampling year, N_2O saturation ranging from 144% to 640%, indicating that reservoir acted as source of atmospheric N_2O. N_2O production is induced by the introduction of nitrogen(NO_3^-, NH_4^+) in mesotrophic reservoirs, and is also affected by oxygen level and water temperature. Nitrification was the predominate process for N_2O production in DFR due to well-oxygenated longitudinal water layers.Mean values of estimated N_2O flux from the air–water interface averaged 0.19 μmol m^(-2)h^(-1) with a range of 0.01–0.61 μmol m^(-2)h^(-1). DFR exhibited less N_2O emission flux than that reported in a nearby eutrophic reservoir, but still acted as a moderate N_2O source compared with other reservoirs and lakes worldwide. Annual emissions from the water–air interface of DFR were estimated to be 0.32×10~5 mol N–N_2O, while N_2O degassing from releasing water behind the dam during power generation was nearly five times greater. Hence, N_2O degassing behind the dam should be taken into account for estimation of N_2O emissions from artificial reservoirs, an omission that historically has probably resulted in underestimates. IPCC methodology should consider more specifically N_2O emission estimation in aquatic ecosystems, especially in reservoirs, the default EF5 model will lead to an overestimation.
