Carrying Capacity Of Cage Culture In Xiaowan Reservoir,the Lancang River

In recent years,with the rapid development of the cage culture,the water environment impact of the cage culture gradually has aroused people's widespread interest.After large-scale hydropower development of the Lancang River,the impoundment of the reservoir newly forms large water surface,providing the breeding places for fishery development.For exploiting and utilizing the fishery resources of Xiaowan reservoir that is the first high dam in the middle and lower reaches of the Lancang River,government departments of fisheries are taking efforts to develop the cage culture.So,they can meet the goals of helping local farmers increase their income,and promoting local economic developments.However,if the cage culture expanded blindly,it would deteriorate the water environment quality of the reservoir.It is important of determining carrying capacity threshold as standard of fisheries cage culture with reasonably planning,to develop cage culture,by the way of meeting the standard of the water quality of Xiaowan reservoir,providing the security of water supply in downstream and keeping the relative stability of the ecosystem.Therefore,this paper selected Xiaowan reservoir as the study area,investigated the situation about cage culture in the reservoir,obtained information of the cage culture by interview,adopted pollution load forecasting method to calculate the carrying capacity of cage culture in the reservoir.On the base of that,we also estimated the maximum annual output,the cages numbers,the total phosphorus concentration,the economic benefits,and the bait quota restrictions,when the quantity of cage culture reaches the relief valve.So,this studying provided the theoretical basis for establishing the sustainable development measure of cage culture in the Xiaowan reservoir.Main conclusions are as follows:(1)If every ton of Cyprinus(Cyprinus)carpio,Ctenopharyngodon idellus and Tilapia mossambica is bred by cage culture in Xiaowan reservoir,the amount of the phosphorus waste discharged into water respectively is 13.67kg,21.38 kg and 14.78 kg.(2)In Xiaowan reservoir,the cage culture areas of breeding Cyprinus(Cyprinus)carpio,Ctenopharyngodon idellus and Tilapia mossambica should not be larger than 1.08‰,1.04‰ and 1.82‰ of the reservoir total water areas.(3)The total areas of cage culture in Xiaowan reservoir are 49335m2 at present,which is far less than 202657m2,the maximum areas of cage culture with Sustainable development.(4)The maximum annual production of cage culture in Xiaowan reservoir is 49780t and the allowable quantity of cages in Xiaowan reservoir is 1126.(5)When the annual input value of cage culture reach the maximum allowable threshold in Xiaowan reservoir,the annual value of production will reaches 600 million yuan.Meanwhile,the annual income will reaches 50 million yuan.If cage culture in Xiaowan reservoir is focused within an area of 5km2 of breeding sites of Xinmangjiedu Bridge,we can predict that,the total phosphorus and the total nitrogen of the cage culture waters will increase 11%and 3.4%respectively by using the lake complete mixing model,when the quantity of cage culture reaches the maximum allowable threshold.(6)The maximum of baits used for cage culture in Xiaowan reservoir is 110287t per year,which equals 2.76 million bags,when every bag of bait weighs 40kg.