| Freshwater aquaculture wetlands have attracted worldwide attention as an important source of global atmospheric methane(CH4).China is the world's largest producer of freshwater aquaculture and is growing rapidly,with crab/fish being the most important type of farming.Using different methods to observe CH4 emission from freshwater crab/fish farming wetlands can offered references in methodology as well as,understand the seasonal variation and emission intensity of CH4 emissions from freshwater crab/fish farming wetlands in southern China.It also can help us to reveal the main impact factors for CH4 emissions.The research content consists of two parts of studies:(1)The first study measured the CH4 fluxes from a crab/fish farming wetland over the period of 2017 to 2018 in southeast China.The floating chamber technique and diffusion model method were applied at the same time for comparison.(2)Based on appropriate observation methods,the seasonal CH4 emission intensities,patterns and driving mechanisms were analyzed.The main results and conclusions are summarized as follows:1.In crab-fish farming wetland,the seasonal variation of CH4 fluxes measured by the floating chamber technique and diffusion model method showed a similar pattern with highest CH4 emissions in summer and fall and lowest in winter and spring.The peak of CH4 flux measured by the floating chamber technique and diffusion model method were appeared in July and August,respectively.Liner regression analysis showed that CH4 flux measured by chamber were higher than the model estimate.The result suggested that the floating chamber technique is more suitable than the diffusion model method for measurements on CH4 fluxes in crab-fish farming wetland.2.The CH4 emissions showed a distinctively seasonal varaiation during the whole observation period from the crab farming wetland.High CH4 emissions were mainly concentrated in the flooding period.In the flooding period,the highest intensity of CH4 emission were found in summer,and there were almost no CH4 emissions during the drainage period.A short-term emission peaks were apperared at the beginning of the drainage period.Aquatic vegetations have a certain impact on CH4 emissions.The increase of aquatic vegetations in crab ponds leaded to a higher CH4 release in each sampling sits in 2018 than the same period of the previous year.The average flux of CH4 from the three sampling sites was 0.50 mg m-2 h-1,0.45 mg m-2 h-1,0.55 mg m-2 h-1 respectively.The CH4 emissions showed no significant difference among three sampling sites.Water temperature DO,COD and DOC were important factors affecting the CH4 emissions in crab farming wetland,while the physical and chemical indicators such as pH and conductivity showed weakly response to CH4 emissions.3.The CH4 emissions showed a distinctively seasonal varaiation during the whole observation period from the fish farming wetland with the peak appearing during the summer.The average CH4 emissions among the three sampling sites was 0.59 mg m-2 h-1 for bridge one,1.57 mg m-2 h-1 for bridge two,and 0.35 mg m-2 h-1 for bridge three.Due to the special location with high organic matters accumulations in bridge two.Bridge three was near the automatic feeder and fish activities were frequent,so the oxygen was easily transported to the bottom of the pond,so the CH4 emission was lower than the normal level in bridge three.Water temperature DO,COD and DOC were important factors affecting the CH4 emissions in fish farming wetland,Overall,the seasonal variation of CH4 fluxes measured by the floating chamber technique and diffusion model method showed a similar pattern with the peak appeared in summer from crab/fish farming wetland.Generally,model-estimated CH4 fluxes were lower than the chamber-measured fluxes.The result suggested that the floating chamber technique is more suitable than the diffusion model method for measurements on CH4 fluxes in crab/fish farming wetland.The freshwater crab/fish farming wetlands showed similar seasonal variation during the whole observation period with highest CH4 emissions in spring and summer and lowest in fall and winter which were greatly affected by water temperature.The seasonal variation of CH4 emissions from freshwater crab/fish farming wetlands is mainly affected by water temperature,DO,COD and DOC.Freshwater aquaculture wetlands is one of the important sources of CH4 emissions in China.Due to the specific management patterns,the magnitude of CH4 emissions in freshwater crab/fish farming wetlands is different from other freshwater ecosystems... |
PDF Full Text Request