Study On Aquatic Biodiversity Of Dongfanghong Reservoir In Xinjiang And Its Relationship With Environment

Located in the middle section of the Yarkand River in the Kashgar region of southern Xinjiang,the Dongfanghong Reservoir is a locally important ecologically functional reservoir,and was designated as the Yarkand River National Wetland Reserve in 2019,which is extremely important in terms of ecological functional zoning.To investigate the aquatic biodiversity of Dongfanghong Reservoir and its relationship with key environmental factors,this study was conducted in three seasons,spring（March-May）,summer（June-August）and autumn（September-November）,from March 2019 to November 2020,to monitor the aquatic environment and investigate the aquatic biodiversity resources of Dongfanghong Reservoir,and to investigate the relationship between aquatic organisms and physicochemical indicators,with the following results.Among the 12 physical and chemical indicators of Dongfanghong Reservoir,dissolved oxygen is in Class I standard,permanganate index is in Class I-II standard,total nitrogen exceeds the national Class III standard,and the rest are between Class I-II standard.The overall evaluation of the reservoir water quality is in theⅢstandard,and the reservoir is in the middle nutrient level.The phytoplankton consisted of 78 genera in 23 orders and 39 families in 8 phyla,of which the Bacillariophyt were the most abundant species.The top three dominant species were Achnanthes exigua,Nitzschia palea and Cyclotella stelligera.The average abundance of phytoplankton was 0.09×10⁵cells/L,and the average biomass was 0.15 mg/L.The diversity index evaluation criteria indicated that the water quality of Donhganghong Reservoir was in an oligotrophic state.Redundancy analysis（RDA）showed that the environmental factors that mainly affected the phytoplankton community structure in Dongfanghong Reservoir were Water Temperature（WT）,Total Phosphorus（TP）and Total Nitrogen（TN）.There were 28 species of zooplankton in 22 genera and 11 families in 2 phyla,with the most species of Cladocera.The top three dominant zooplankton species were Bosmina longirostris,Keratellacochlearis,Asplanchna priodonta and Mesocyclops leuckarti.The abundance of zooplankton in Dongfanghong Reservoir didn’t change significantly in the 2 seasons,and the Shannon-winner diversity index and Pielou evenness index were significantly different in summer and autumn（P<0.05）.RDA analysis showed that the main environmental factors affecting the zooplankton community structure in the reservoir were Total Nitrogen（TN）,Ammonia Nitrogen（NH₄⁺-N）and permanganate index（CODMn）.There were 16 species in 16 genera and 7 families in 3 orders of fish,with the largest proportion of cypriniformes.The dominant species were exotic species such as Pseudorasbora parva,Aristichthys nobilis,Eucyclogo biusnewberryi and Ctenopharyngodon idellus.The three diversity indices in the reservoir varied widely,and the fish community structure was generally unstable.RDA analysis showed that Electrical Conductivity（EC）and Total Dissolved Solid（TDS）were the main environmental factors affecting the distribution of fish community structure in the reservoir.By investigating the physical and chemical indicators of water quality,changes of aquatic organisms and their relationship with environmental factors in the Dongfanghong Reservoir,this study aims to provide a scientific basis for enriching the biodiversity of the Yarkand River basin,constructing the ecological function zoning of reservoir in the basin and maintaining the sustainable development of the Tarim River basin.