The Research Of The Characteristics Of Phytoplankton Communities And Their Influencing Factors In The Main Basins Of Eastern Qilian Mountains

Qilian Mountains is the origin and runoff formation area of the inland river of Shiyang River,Black River,Shule River and the Yellow River upper reaches of the Huangshui-DaTong River,and is also the main water supply area of the Yellow River and many inland rivers,and is also the priority area for biodiversity conservation of China.In recent years,under the influence of both human activities and climate change,the ecological problems of Qilian Mountains have been widely concerned,especially the problem of river ecology.Phytoplankton plays the role of primary producer in the river ecosystems and is the basis for the survival of high-nutrition aquatic organisms.However,few studies so far have focused on the phytoplankton in the main basin of Qilian Mountains.Therefore,in this study,the phytoplankton characteristics and water quality of 29 sites in the Shiyang River and Huangshui-Datong River(short for the Huangshui)basin in the eastern part of Qilian Mountains were systematically studied through sampling,field survey,and laboratory measurement,and the spatial distribution pattern and their interaction relationship were explored.The main results are as follows:(1)A total of 150 species of phytoplankton(including variants)were identified in the eastern part of Qilian Mountains,belonging to 8 phylum 10 class 22 order 35 family 65 genus,115 species of which belong to Shiyang River system and 71 species of which belong to Huangshui River system.Bacillariophyta was the dominant group,accounting for 47.33% of the total number of species,followed by Chlorophyta and Cyanophyta.The dominant species of main water system in the eastern part of Qilian Mountains was Fragilaria.brevistriata,the dominance and occurrence frequencies were 0.051 and 44.83%.The dominant species of the Shiyang River system was F.brevistriata(dominance 0.064),with occurrence frequency of 44.44%.The dominant species of Huangshui River system were Navicula simplex(dominance 0.075),F.brevistriata(dominance 0.034)and Navicula graciloides(dominance 0.023),and the occurrence frequencies are 54.55%,45.45% and 36.36 %,respectively.In addition,the complexity and stability of phytoplankton communities in Huangshui River system were higher than that of Shiyang River system.(2)Nitrogen nutrient is the main excessive indicator in the main river system of the eastern part of Qilian Mountains.The correlation analysis of the water quality physical and chemical characteristics and the spatial distribution pattern showed that there existed significant correlations between most of the 21 indicators measured by this study.The water quality physical and chemical characteristicsof the main river system were influenced less by the spatial pattern.While,the water quality physical and chemical characteristics of the Huangshui River system were more affected by the spatial pattern than the Shiyang River system.(3)The water quality factors mainly affecting the density of phytoplankton were the total nitrogen content,nitrous nitrogen content,water temperature and lead content at all kinds of sites in the eastern river system of Qilian Mountains.The phytoplankton density was significantly and positively correlated with the total nitrogen content in the Shiyang and Huangshui River system,while,the phytoplankton density was significantly and positively correlated with water temperature in the Huangshui water system.The water quality factors affecting species number of the main river system in the eastern were mainly total nitrogen content and water temperature.The phytoplankton species number of Huangshui River system was significantly and positively correlated with total nitrogen,water temperature and potassium.In addition,phytoplankton density and species number of the main river system were significantly and positively correlated with longitude,while were significantly and negatively correlated with latitude and altitude.These results not only clarified the phytoplankton communities characteristics of the main river in the eastern part of Qilian Mountains,but also evaluated the current situation of the water environment in the main water system in the eastern part of Qilian Mountains.Moreover,we analyzed the correlation and spatial patterns of the phytoplankton communities,which providing scientific supporting and application reference for the real-time monitoring of aquatic organisms in the basin and integrated management of watersheds.