Greenhouse gas emissions of Megalobrama amblycephala culture pond ecosystems during sun drying of pond

Abstract: Global warming and ozone depletion caused by greenhouse gases are currently two major global environmental issues. While China's freshwater aquaculture production has long been ranked first in the world, greenhouse gas emissions from freshwater ponds becomes an important source of China's greenhouse gas emissions. But the research on greenhouse gas emission in freshwater aquaculture ecosystem is limited. In order to investigate greenhouse gas emissions and comprehensive global warming potential of Megalobrama amblycephala culture pond ecosystems during pond basked, we used the static opaque chamber-GC techniques to conduct an in situ determination of greenhouse gas emissions (CO2, CH4, N2O) of Megalobrama amblycephala culture pond ecosystems. The results showed that the CO2 fluxes measured in every 15 days were (2652.46±325.36), (2313.82±245.14), (1456.42±124.67) and (1373.27±167.39) mg/(m2·d) respectively for the air temperature of 8.9, 7.2, 5.8 and 6℃, at the ponds during sampling. The potential of hydrogen at the ponds during the sampling at each temperature was (7.73±0.26), (8.26±0.35), (7.75±0.37) and (7.68±0.48), respectively. The total organic carbon at the ponds for each sampling was (3.61±0.43), (3.32±0.17), (3.16±0.31) and (3.23±0.27), respectively. The redox potential for each sampling was (206.7±34.9), (216.8±27.6), (56.8±9.3) and (124.8±16.5) mV, respectively. The moisture content of sediment for samples taken at 11.2, 10.3, 9.6 and 9.8℃ was (55.25%±2.54%), (54.53%±5.61%), (46.62%±4.38%), and (48.35%±3.14%), respectively. Among December 28, January 13, January 28, February 13, 2014, when the pond temperature was the highest on December 28, the CO2 emission flux peaked (2652.46±325.36) mg/(m2·d)). In comparison, on February 13 2015, the smallest CO2 emission flux (1373.27±167.39) mg/(m2·d)) corresponded with the lowest pond temperature, CH4 is transformed from methane bacteria via an organic carbon source. As culturing activity increased with rising temperatures, phytoplankton dies and the organic artificial diets left over by fish increases, providing a rich carbon source for methane bacteria. In this study, CH4 emission flux paralleled that of CO2, and in general, CH4 emission flux was positively correlated with temperature. On December 28, 2014, there was a peak of CH4 emission flux (82.42 ± 6.32) mg/(m2·d)) in the freshwater ponds. From December 28, 2014 to February 13 2015, the measured CH4 emission fluxes were (82.42±6.32), (81.08±7.43), (7.63±1.84) and (7.06±2.93) mg/(m2·d), respectively. On February 13 2015, the lowest water temperature was accompanied by the smallest CH4 emission flux (7.06±2.93) mg/(m2·d). From December 28, 2014 to February 13 2015, the N2O emission fluxes were (172.34±10.56), (204.57±16.84), (160.36±12.87), and (90.39±10.67) μg/(m2·d), respectively. Megalobrama amblycephala culture ponds during pond basked were the source of CO2, CH4 and N2O, of which CO2 emission during pond basked amounted to (86.72.10±12.46) g/m2, CH4 emission of (2.01±0.34) g/m2, and N2O emission of (7.44±0.98) mg/m2. For 20-years Megalobrama amblycephala culture pond ecosystems during pond basked, greenhouse gas warming potential had an increase trend. Comprehensive global warming potential was (157.28±24.31) g/m2. Therefore, there was a great potential in greenhouse gas emission reduction in Megalobrama amblycephala culture pond ecosystems.