Seasonal dynamics of main phytoplankton in Qiantang River (Hangzhou section) and its relationship with environmental factors
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Abstract:
The Qiantang River (Hangzhou Part) is located in the lower reaches of the Yangtze River Economic Belt.It is not only an important source of drinking water,but also related to ecological safety of Hangzhou City and Zhejiang Province.In recent years,due to the rapid social and economic development in the Qiantang River basin,impact of human activities on the water environment has further deepened,and pressure on environmental governance and ecological protection of Qiantang River has significantly increased.Residents in the river basin have further increased their expectations for better water environment,which put forward higher requirements for the water environment management of the Qiantang River (Hangzhou part). To explore the seasonal dynamics of planktonic algae in the Qiantang River (Hangzhou section) and their relationships with environmental factors,and to provide technical support for water environment protection,phytoplankton and environmental factors were monthly monitored in Qiantang River (Hangzhou part) in 2018,including four main sites.Environmental factors mainly include water temperature (T),water pH,turbidity,conductivity,dissolved oxygen (DO),permanganate index (CODMn),ammonia nitrogen mass concentration (NH3-N),total nitrogen mass concentration (TN),and total phosphorus mass concentration (TP). The monthly mass concentration of total chlorophyll of phytoplankton was ranged from 1.74 to 22.86 μg/L,and the monthly chlorophyll mass concentration of cyanobacteria was ranged from 0.02 to 10.82 μg/L.The composition of planktonic algae throughout the year was dominated by cyanobacteria and diatom.The site with highest total chlorophyll mass concentration was Yanlingwu in the four seasons of spring,summer,autumn and winter.The site with the highest mass concentration of cyanobacteria in spring was Jiangjunyan,while the highest mass concentration site in summer,autumn and winter was all Yanlingwu.For all monitoring sites,the highest mass concentration of planktonic algae chlorophyll always occurred in summer.The total chlorophyll mass concentration and the cyanophyll chlorophyll mass concentration showed almost the same seasonal variation trend at Jiangjunyan,indicating that the cyanobacteria had an absolute advantage in composition.It was worth noting that from spring to summer,the chlorophyll mass concentration of cyanobacteria both had increased from the lowest value to the highest value throughout the year at Yanlingwu and Yinzhu.Environmental factors had obvious impacts on the mass concentration of chlorophyll of phytoplankton.There was a significant positive correlation between the annual mass concentration of total chlorophyll of phytoplankton and water temperature.There was a significant positive correlation between the annual mass concentration of cyanobacteria chlorophyll and water temperature.There was a significant negative correlation between the seasonal mass concentration of diatom chlorophyll and total phosphorus. Therefore,the chlorophyll mass concentration of planktonic algae was greatly affected by the physical and chemical factors in Qiantang River (Hangzhou part).Water temperature and total phosphorus were the main environmental factors that affected the seasonal dynamics of planktonic algae.Monitoring and management of different sites all need to focus on different emphasis.It was necessary to implement classified management,linkage monitoring and comparative monitoring of major environmental factors and important points.Preventing and controlling environmental risks as much as possible can help realize the early warning function of monitoring and analysis of plankton algae environment.
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