Greenhouse Gases Concentration, Emission And Influence Factors In Farming Waters

With increasing greenhouse gas emission in atmosphere, more and more nitrous oxide(N2O), methane(CH4) and carbon dioxide(CO2) dissolve in water bodies. At the same time, the emission of greenhouse gas from water bodies have also increased. Thus, water bodies become one of the important source or sink of greenhouse gas. Even though farming waters only occupies a small part of hydrosphere, they are still play an important role in the global cycles of carbon and nitrogen. However, the concentration, saturation and emission of greenhouse gases in farming waters are not well known. Therefore, from January to November in 2014, farming waters in the No.2 Teaching Base of Fisheries College, Huazhong Agricultural University, are chosen as sampling position. The concentration, saturation and fluxes of N2 O, CH4 and CO2 are measured using an static opaque chamber and gas chromatography method. At the same time, the water temperatures, p H, dissolved carbon or nitrogen and other environmental factors are also measured. The effect of environmental factors on the emissions of greenhouse gases are investigated. The study provides scientific evidence for the greenhouse gases mitigation.The results are following:(1) In farming waters, greenhouse gases distribute with various pattern in different water depths: N2 O distributes uniformly in the surface, middle and underlying layers. The range of N2 O is 0.33~15.79 μg L-1; CH4 are highest in the underlying layer, especially in Autumn. The range of CH4 is 1.11~84.09 μg L-1; CO2 are lowest in the underlying layer, and it’s range is 840~10910 μg L-1.(2) N2 O, CH4 and CO2 in farming waters are all saturated or supersaturated. The saturation of N2 O and CO2 do not have significant differences in various water depths. The saturation of N2 O is higher in summer than other seasons. Management can influent on the saturation of CO2. In summer and autumn, The saturation of CH4 is significantly higher in underlying layer than that in surface and middle layers. The range of CH4 saturation is similar to that in lakes.(3) In general, farming water body is the source of N2 O, CH4 and CO2. The fluxes of N2 O, CH4 and CO2 between air-water interface are in the range of-0.033~0.462 μg m-2 h-1, 0.014~6.231 μg m-2 h-1and-15.372~2395.543 μg m-2 h-1, respectively. The peak of N2 O emissions appeared in summer and autumn. Compared to rivers in plain、natural wetlands、headwaters and shallow ponds, the emissions of N2 O and CH4 in farming waters are lesser. The fluxes of CH4 are far less than shallow ponds, but greater than some eutrophication lakes.(4) In farming waters, N2 O is released from the coupled processes of nitrification and denitrification. Nitrification is the major contributor for the fluxes of N2 O. NO3-and dissolved total nitrogen are the most important environmental factors which can control the production and consumption of N2O; SO42- would inhibit the production of CH4 if its concentration was high. In the case of oxygen deficit, dissolved inorganic carbon can promote the emissions of CH4; p H can control the production of CO2. When dissolved oxygen is enough in the waters, CH4 can be oxidized to CO2 during it diffusing from sediments.