Studies On CH₄ And CO₂ Fluxes At Water-air Interface And Carbon Budgets Of Different Culture Systems With Portunus Trituberculatus, Marsupenaeus Japonicas And Ruditapes Philippinarum

As the possible sink or source of CO2 and CH4, aquatic ecosystems have been playing a significant role in greenhouse gases concentrations of the atmosphere even in the regional climate change. Aquaculture ponds are a kind of special aquatic systems which are under strong artificial interference, and scientists, as so far, still know little about its role in the global carbon cycle. Therefore, to investigate the CO2 and CH4 emission characteristics of aquaculture ponds during culture period actively seems urgently necessary especially in such a big aquaculture country. This thesis focused on the typical culture systems with Portunus trituberculatus, Marsupenaeus japonicas and Ruditapes philippinarum in Ganyu, Jiangsu province and determined the CO2 and CH4 fluxes at the water-air interface as well as its main influencing factors of different culture systems aiming to provide basic data for the CO2 and CH4 fluxes list of aquatic ecosystems and to lay the foundation for the further research of the mechanism and control measures of the CO2 and CH4 flux in the seawater aquaculture ponds and the fluxes differences were also compared briefly. Meanwhile, the carbon budgets of culture systems during culture period were studied aiming to understand the role of aquaculture systems in the global carbon cycle. The exact results of this thesis are as follows.I Study on the CO2 fluxes at water-air interface of different culture systems with Portunus trituberculatus, Marsupenaeus japonicas and Ruditapes philippinarum and its main influencing factorsCO2 fluxes at water-air interface of typical culture systems with Portunus trituberculatus, Marsupenaeus japonicas and Ruditapes philippinarum in Ganyu, Jiangsu province were measured using a static chamber-gas chromatography method from July to October in 2013 and the meteorological as well as the physical, chemical and biological factors of water body were simultaneously in situ measured. The results indicated that the monoculture of crab and polyculture of crab and shrimp both performed as the stable sink of CO2 to the atmosphere during observation period. The CO2 fluxes of the two systems ranged from-68.22 to-30.50 mg/m2/h and-74.11 to-41.12 mg/m2/h, with the average values of-47.06 mg/m2/h and-49.99 mg/m2/h respectively, and no significant difference was found between them(P>0.05). The CO2 flux of polyculture of crab, shrimp and clam ranged from-27.06 to 104.88 mg/m2/h performing as the CO2 source to the atmosphere during the early and middle stages of culturing while as the CO2 sink during the later stage. Generally speaking, the polyculture of crab, shrimp and clam performed as the CO2 source to the atmosphere with an average value of 39.49 mg/m2/h during observation period. The variations of environmental factors which is closely related to the culture management, biological processes of cultured species and weather changes etc. were the main reasons influencing the CO2 flux at water-air interface. We found that the differences of the flux between the monoculture of crab, the polyculture of crab and shrimp and the polyculture of crab, shrimp and calm were mainly involved with water pH, dissolved oxygen (DO) and so on after comparing the environmental factors. The results of stepwise regression analysis showed that water pH, wind speed, concentrations of chlorophyll a and TN of water body were the main factors influencing CO2 flux at water-air interface of the monoculture of crab which explained 89.6% variations of CO2 flux. Water pH, wind speed, concentrations of dissolved organic carbon (DOC) and NH4+-N were the key factors influencing CO2 flux of the polyculture of crab and shrimp which explained 84.1% variations of CO2 flux. And the concentrations of dissolved inorganic carbon (DIC), total alkalinity (TA) and DO of water body were the main factors influencing CO2 flux of the polyculture of crab, shrimp and clam which explained 92.3% variations of CO2 flux.2 Study on the CH4 fluxes at water-air interface of different culture systems with Portunus trituberculatus. Marsupenaeus japonicas and Ruditapes philippinarum and its main influencing factorsCH4 fluxes at water-air interface of typical culture systems with Portunus trituberculatus. Marsupenaeus japonicas and Ruditapes philippinarum in Ganyu, Jiangsu province were measured using a static chamber-gas chromatography method from July to October in 2014 and the meteorological as well as the physical, chemical and biological factors of water body and the sediment were simultaneously in situ measured. The results indicated that the polyculture of crab and shrimp and polyculture of crab, shrimp and clam both performed as the stable source of CH4 to the atmosphere during observation period. The CH4 fluxes at the water-air interface rose with time at first, and then decreased, and the peak appeared in the middle of August. The CH4 flux of polyculture of crab and shrimp ranged from 21.89 to 143.75 μg/m2/h with an average value of 66.03 μg/m2/h. The polyculture of crab, shrimp and clam ranged from 11.22 to 138.98μg/m2/h, and the average CH4 flux during the observation period was 68.73 μg/m2/h and no significance difference was found between the two culture systems(P>0.05). The results of stepwise regression analysis showed that water temperature, NO2-N and NH4+-N concentrations of water body and pH value of sediment were the key factors influencing CH4 flux of the polyculture of crab and shrimp which explained 89.5% variations of CH4 flux. And the air temperature, water pH and concentrations of NO3-N, PO43-P and chlorophyll a of water body were the main factors influencing CH4 flux of the polyculture of crab, shrimp and clam which explained 78.6% variations of CH4 flux.3 Study on carbon budgets of different culture systems with Portunus trituberculatus, Marsupenaeus japonicas and Ruditapes philippinarumCarbon budgets of different culture systems with Portunus trituberculatus, Marsupenaeus japonicas and Ruditapes philippinarum were studied using the checklist method.The results showed that water inflow was the major carbon source of the polyculture of crab and shrimp and the polyculture of crab, shrimp and clam, accounting for 37.84% and 42.01%, respectively. The feed ranked at the second place and accounted for 30.63% and 36.03% of the two culture systems, respectively. The stocking organism contributed little to the carbon input considering its tiny size. In terms of output items, water outflow was the main carbon output accounting for 31.72% and 48.99% in the polyculture of crab and shrimp and the polyculture of crab, shrimp and clam, respectively. The proportion of carbon accumulating in the water was also relatively high, accounting for 23.13% and 40.18%, respectively. The carbon migration direction at the water-air interface differed in the two culture systems and the polyculture of crab and shrimp absorbed 215.54kg C during culture period in total while the polyculture of crab, shrimp and clam emitted 530.04kg C totally, which means the role of culture system changed from the carbon sink to carbon source after culturing clam. In addition, the harvest organism of the polyculture of crab, shrimp and clam accounted for 17.68% of total carbon output which was significantly higher than the polyculture of crab and shrimp (5.71%) (P<0.05), and in terms of carbon utilization efficiency of the culture systems, the polyculture of crab, shrimp and clam(19.56%) was also higher than the polyculture of crab and shrimp(5.26%) significantly(P<0.05).