Evaluating The Life-cycle Environmental Impacts Of Chinese Mitten Crab Aquaculture System

As a typical native species in China,Chinese mitten crab(Eriocheir Sinensis)has been very popular.Currently,China's production of Chinese mitten crab ranks first in the world and is at a stage of rapid growth.However,resource and environmental problems caused by the excessive feeding,the direct discharge of drainage and the accumulation of sediment outdoors are getting more and more attention.Therefore,it is urgent to quantitatively assess the environmental impacts of Chinese mitten crab aquaculture system.From the perspective of life cycle,it is helpful to identify key contributors among on-site aquaculture processes and the upstream processes so as to achieve improvement in environmental performance.Considering the structure of Chinese mitten crab aquaculture,a systematic model including pond aquaculture and lake aquaculture was constructed.It covers three main stages,namely megalopa cultivation stage,juvenile crab cultivation stage,and adult crab cultivation stage.Using field survey and sampling data from farms in representative regions in Jiangsu Province,supplemented by literature review and life cycle inventory database,the life cycle inventory of Chinese mitten crab aquaculture system was established.Based on this,life cycle environmental impacts were analyzed by assessment methods of CML2001 baseline and Cumulative Energy Demand.Environmental impacts of pond aquaculture and lake aquaculture were also compared.Evaluated impact categories include Global Warming Potential(GWP),Acidification Potential(AP),Eutrophication Potential(EP),Freshwater Aquatic Ecotoxicity Potential(FAETP)and Cumulative Energy Demand(CED).1.The results show that 1 ton live-weight of Chinese mitten crab production in China generates 7.65 t of CO2 eq,0.03 t of SO2 eq,0.23 t of PO4 eq,1.82 t of 1,4-DB eq,and required 115.78 GJ of energy.Based on analysis results,key stages and contributors were identified.Specifically,key contribution process of GWP is the electricity production,the transportation of quicklime raw materials and the cultivation of soybean which is the raw material of adult crab commercial feed of adult crab cultivation stage.Key contribution process of AP is the electricity production of adult crab cultivation stage and the cultivation of soybean in adult crab commercial feed.Key contributor of EP is the N and P emission in on-site aquaculture.Metal emission from coal ash and slime treatment and pesticide use in soybean planting are key contributors of FAETP.All kinds of raw materials of crab commercial feed production and hard coal for electricity generation are key contributors for energy demand.2.The results also show that except for EP,the effects of GWP,AP,FAETP and CED of lake aquaculture are lower than those of pond aquaculture,which is related to the no use of grid power in adult crab cultivation stage of lake aquaculture.If measures are taken to reduce the N and P emissions from lake aquaculture,the environmental impacts of lake aquaculture will be lower than those of pond aquaculture in an all-round way.It is not advisable to prohibit lake aquaculture in one-size-fits-all solution.The possible measures to reduce the N and P emissions of lake aquaculture include determining the appropriate feeding amount and appropriate stockings based on the estimated N and P emissions,and reducing the high feeding rate of lake aquaculture farmers.For pond aquaculture,it should optimize power supply mode and reduce the dependence on grid power.3.The results show that the proportion of all kinds of environmental impacts in megalopa cultivation stage is the smallest,which is less than 1%.It means that it has less room for environmental improvement.The contribution of adult crab cultivation stage is the largest.Due to the growth of biomass,the feed conversion rate(FCR)of adult crab cultivation stage is the highest.It is important to improve the utilization rate of feed and reduce FCR to reduce the environmental impacts of adult crab cultivation.In addition,the environmental impacts of adult crab cultivation stage also comes from the intensive electricity consumption,a large number of direct drainage and sediment in the field management.Therefore,for adult crab cultivation,it should save electricity and reduce power consumption.Build wastewater treatment facilities,recycle N and P nutrients to reduce direct emissions.4.Finally,the environmental impacts differences were further compared between aquatic products like fish,shrimp,crab and livestock products like pig,cattle and other.In all,life cycle environmental impacts of aquatic products are less than those of livestock products.Among different kinds of aquatic products,crustaceans such as shrimp and crab have higher impacts than those of fish.Therefore,from the perspective of future agricultural development,the proportion of aquaculture can be appropriately expanded.When considering the optimization of aquaculture structure,the proportion of planned aquaculture of fish can be appropriately increased..From the perspective of consumers,crustaceans,especially Chinese mitten crab,are not necessarily daily food so that consumption can be reduced considerately.