Calculation Of The Carbon Footprint Of The Aquaculture System Lifecycle For The Chinese Mitten Crab (Eriocheir Sinensis)

With the increasing demand for high-quality protein,the rise of aquaculture has been one of the most significant global market changes in the past 100 years.China,as the largest producer of aquaculture products in the world,accounts for over 50% of global seafood exports.With the growth of aquaculture,freshwater aquaculture is undergoing transformation,with pond farming gradually replacing other farming types such as lakes,rivers,and reservoirs,becoming the predominant model in China.In 2018,the total area of pond farming reached 2,667 hectares,accounting for 51.82% of the total area of freshwater aquaculture.However,due to the high stocking density and increased intensity of pond farming,its impact on the environmental ecosystem should not be overlooked.Currently,research on greenhouse gas emissions in aquatic ecosystems mainly focuses on reservoirs,lakes,and estuaries,while studies on pond farming are severely lacking.As one of the famous and excellent significant aquaculture species in China,Eriocheir sinensis occupied the highest output in the world and were experiencing a rapid growth.However,the continuous improvement of intensive culture of E.sinensis had led to serious environmental stress.One of the prerequisites for solving this environmental issue is to develop a quantitatively assessments for the effects of E.sinensis culture on environment.In the present study,Yangcheng Lake modern Fishery Industrial Park in Kunshan City was selected as the research site.We explored the effects of E.sinensis cultures on environment throughout their whole lifecycle.Firstly,the methane（CH₄）and carbon dioxide（CO₂）exchange fluxes in the juvenile crab and adult crab ponds during different seasons（spring,summer,and autumn）were measured using the floating static chamber method.Environmental factors such as water temperature,various nutrients,and sediment characteristics were also assessed to investigate the influencing factors on CH₄ and CO₂ exchange fluxes.Then,indoor experiments were designed with a control group and two experimental groups: one for rearing juvenile crabs and another for rearing mature crabs.The groups were maintained at temperatures of 15°C,20°C,25°C,30°C,and35°C for one week,with daily measurements of CO₂ concentrations.By comparing the CO₂concentrations between the control group and the experimental groups,the impact of E.sinensis on CO₂ emissions was examined.Additionally,by comparing the CO₂ concentrations between the juvenile crab group and the mature crab group at different temperatures,the influence of temperature on CO₂ emissions in E.sinensis was explored.The carbon emissions of E.sinensis were investigated under different temperatures during the stages of juvenile crab and mature crab farming.Finally,based on the life cycle assessment theory,the carbon footprint of the entire lifecycle of E.sinensis was calculated.This assessment included energy production and consumption during various stages,such as seedling cultivation,larval rearing,juvenile crab farming,and the harvest,processing,and transportation of mature E.sinensis.A carbon footprint inventory analysis was conducted,collecting data from various sources within the lifecycle and incorporating emission factors from authoritative institutions such as the IPCC database to calculate indirect greenhouse gas emissions.The carbon footprint of the entire lifecycle of E.sinensis farming was then determined.The main conclusions of this study are as follows:（1）The measured values of exchange fluxes of CH₄ and CO₂ were positive in both juvenile and adult crab ponds,indicating that the two ponds were the sources of CH₄ and CO₂.Variation in exchange fluxes of CH₄ and CO₂ were observed among different seasons,with higher fluxes in summer and lower fluxes in spring and autumn.The CH₄ flux ranged from 3.294 to 6.655 mg/m²·h,and the CO₂ flux ranged from 350.403 to 792.488 mg/m²·h in the summer.In contrast,lower fluxes were observed in the spring and autumn,with CH₄ exchange fluxes ranging from 0.089 to 0.692mg/m²·h and CO₂ fluxes ranging from 27.535 to 142.975 mg/m²·h.The exchange fluxes of CH₄and CO₂ were influenced by various environmental factors,with water temperature and nutrient levels（nitrate,total nitrogen,etc.）being important factors affecting CH₄ and CO₂ emissions.These factors showed a significant positive correlation with the exchange fluxes of CH₄ and CO₂.Based on the obtained CO₂ and CH₄ gas exchange fluxes in the ponds for juvenile and mature crabs,the greenhouse gas emissions from the E.sinensis farming ponds in Yangcheng Lake Modern Fishery Industrial Park,Kunshan City,were estimated.The total CH₄ emissions from the ponds for juvenile and mature crabs were 404.4 kg and 209.7 kg,respectively,while the total CO₂emissions were 8141.2 kg and 11,759.6 kg,respectively.The total CH₄ emissions from the entire E.sinensis farming ponds were 614.1 kg,and the total CO₂ emissions were 19,900.8 kg.（2）The emission of CO₂ was remarkably increased during the cultural process of E.sinensis and water temperature was determined as a significant driver for CO₂ emission.The emission flux of the juvenile crabs group ranged from 223.29 to 958.53 mg/m²·h,while the emission flux of the mature crab group ranged from 272.88 to 904.21 mg/m²·h.The water temperature of the aquaculture system significantly affects the CO₂ emission flux of both juvenile and mature crabs.During the non-feeding period in the daytime,the total emission flux of CO₂ for the crab group was 10,988.63 mg/m²·h,while for the mature crab group,it was 11,910.69 mg/m²·h.The CO₂emission flux of E.sinensis shows a trend of increasing and then decreasing with increasing temperature.The temperatures of 30°C and 25°C were the highest for CO₂ emission flux in the juvenile crab and mature crab groups,reaching 831.76 mg/m²·h and 640.93 mg/m²·h,respectively.During the feeding period at night,the total emission flux of CO₂ for the juvenile crab group was14,689.09 mg/m²·h,while for the mature crab group,it was 17,045.5 mg/m²·h,significantly higher than the CO₂ emission flux during the daytime for both groups.The CO₂ emission flux of both crab and mature crab groups exhibits a wave-like pattern of variation with increasing temperature.（3）During the culture-cycle of E.sinensis,the carbon footprint of producing 1 kg of megalopa,juvenile crab and adult crab were 9.885,5.914 and 11.746 kg CO₂-eq,respectively.Among the influential factors,electricity consumption was the absolute dominant factor influencing the carbon footprint of E.sinensis,accounting for 10.11 kg CO₂-eq,which represented 39.69% of the total carbon emissions.The next significant carbon emission source was the commodity feed,with a carbon emission of 8.58 kg CO₂-eq,accounting for 14.91% of the total emissions.（4）Combined with the carbon footprint results calculated above,and the actual production conditions,we provide some strategies in terms of scientific emission reduction: Strengthening the environmental management of the upstream industry of E.sinensis cultures;Optimizing the bait composition ratio of E.sinensis;Establishing the carbon footprint label of E.sinensis,to guide green consumption in the market.