Aquatic Ecosystem Health Assessment Of The Ganjing River Water Ranch In The Three Gorges Reservoir

Construction of water ranch by stocking plankton-consumer silver carp and bighead carp in it has achieved commercial and social benefits in the Three Gorges Reservoir.However,the ecological effects of this fishery model still remain to bestudied.To elucidate the influence of this ecological fishery model on aquatic ecosystem,in this study,sampling points siteswere set in Ganjing River water ranch.Sampling sites located in the upstream,interior and downstream area of haul net of water ranch.The multiple data such as water quality physical and chemical indexes,plankton,benthic invertebrate and fish were investigated and monitored.at each sampling sites from December,2017 to September,2018.The monitoringof physical and chemical indexes of water quality,and the species identification and quantitative analysis of aquatic organisms were implemented in order to understand their spatio-temporal pattern.Thenusing index system method and analytic hierarchy process assessed the aquatic ecosystem health condition in Ganjing River water ranch.The main results are as follows:?The evaluation of physical and chemical indexes of water quality inside and outside of water ranch.Water quality physical and chemical indexes s including water temperature?T?,dissolved oxygen?DO?,pH,electrical conductivity?EC?,transparency?SD?,chemical oxygen demand?COD?,total nitrogen?TN?,total phosphorus?TP?,ammonia nitrogen?NH₃-N?,nitrate nitrogen?NO₃-N?,nitrite nitrogen?NO₂-N?and phosphate?PO₄-P?inside and outside haul net were measured.The results showed that the evaluation results of the inside haul net wasbetter than that of the upstream area,and worse than that of the downstream area,which basically accorded with the environmental quality standard of type?surface water,and basically belonged to light pollution or clean,the overall water quality was good.?The evaluation of aquatic organisms inside and outside of water ranch.?1?Species of benthic invertebrate were 18,15 and 16 species in the upstream,interior and downstream area of the haul net respectively,and the number of species were low,therefore,the diversity of benthos were generally poor.Then,the water quality of benthos was evaluated and the result shows that the water quality in the upstream and downstream of the haul net was better than insideof the haul net,but the generalsituation was poor,and most of them belong to light pollution.?2?Species of fishes wererespectively 22 and 34 in the inside and outside area of the haul net,compared with the outside,the fish richness and diversity inside of the haul net were poor.Otherwise,the water quality evaluation based on fishes was better state outside of the haul net,which was basically clean state.The evaluation of water quality inside of the haul net was basically in a“light polluted state”.?3?115 taxa of zooplankton were identified,which belonged to 3 phyta inside and outside of the haul net.The result showed that the average density of zooplankton was higher and the biodiversity was higher,but the biomass was slightly lower than that in the upstream area.The water quality evaluation based on zooplankton in water ranch was high and basically in a“clean state”i inside and outside the haul net.?4?161 taxa of phytoplankton were identified,which belonged to 7 phyta inside and outside of haul net.The results showed that the diversity of phytoplankton inside the haul net was high,and the average density and biomass of phytoplankton were lower than those in the upstream but higher than those in the downstream.The results of water quality evaluation based on phytoplankton were high and basically belong to“clean state”.?The aquatic ecosystem health assessment inside and outside of water ranch.Based on the actual situation of the Ganjign River waterranch,14 indicators among the three main index levels,includingwater quality index,nutrient index and aquatic biological index werefinally determined.The index evaluation method and analytic hierarchy process were used to evaluate the health status of aquatic ecosystem inside and outside the Ganjing River water ranch.The evaluation results show that in the index evaluation method,the scores of upstream and internal ranchin Ganjing River were 0.58and 0.56 respectively,which were in an“averagestate”.The score of downstream was0.75,and the evaluation result was good.In the analytic hierarchy process,the scores of upstream,interior and downstream of water ranch in Ganjing River were 5.72,5.98 and7.51 respectively,which werein an“average state”.In summary,the evaluation of water quality,zooplankton and phytoplankton in Ganjing River water ranch were good,but the fishes and benthic invertebrate evaluation of water ranch were poor.In the index evaluation method,the health level of the aquatic ecosystem in the water ranch was the same as that in the upstream area,but lowers than that in the downstream area.In the analytic hierarchy process,the ecosystem health level of water ranch was higher than that of the upstream area,but lower than that of the downstream area.The overall evaluation of the aquatic ecosystem health level of water ranch was lower than that in the downstream area,but higher than that in the upstream area.These results indicated that,until now,the farming mode of stocking of silver carp and bighead carp in the water ranch of Ganjing River has not brought about adverse effect on ecosystem health,and has achieved a win-win result in economic and environmental benefits.Ganjing River water ranch is a successful case of environment-friendly ecological fisheries.