Influence Of Cascade Damming On Temporal And Spatial Succession Of Phytoplankton Functional Groups

The Wujiang catchment,as the largest water system in Guizhou Province,is a canyon river,with high altitude and abundant water resources.Therefore,more and more dams have been built on this river for electricity generation,irrigation,flood control,and so on.But the cascade dams were bound to change the aquatic ecology environment,and phytoplankton as the main primary producer of aquatic ecology system,which is the most sensitive to the artificial changes and will also be affected.In order to explore the influence of cascade damming on spatial and temporal succession of phytoplankton functional groups,the phytoplankton and water has been collected respectively for the determination of nutrient concentrations and the identification of phytoplankton in different season.The date analysis results show that:There were 47 genus and 4 phyla phytoplankton has been identified in Wujiang River,the river and reservoir were 43 genus and 33 genus respectively.Diatoms had the largest numbers of species in the reservoir,follow by green algae,the river was mainly diatoms.Phytoplankton abundance showed significant seasonal change and fallowed the order: Summer>Autumn>Spring>Winter,autumn and summer were dominated by diatoms and green algae,and the diatoms was mainly in winter and spring.The Jaccard similarity coefficient indicated there are a high level of similarity between river and river,between reservoir and reservoir,but the similarity coefficient between river and reservoir was very low.Phytoplankton functional groups diversity index showed different temporal and spatial changes,means followed the order: Spring>Summer>Autumn>Winter;Reservoir>River.Total 17 phytoplankton functional groups were classified in Wujiang River with six dominated groups B,C,D,J,MP,P.16 functional groups lived in river ecosystem with 7 dominated groups,14 functional groups lived in reservoir ecosystem with 6 dominated groups.The dominated phytoplankton groups have obvious succession with the seasons.In river ecosystem has the succession characteristic:B/D?Autumn??B?Winter??B/C/MP/P?Spring??B/P?Summer?,and in reservoir ecosystem has the succession characteristic:B?Autumn??B/P?Winter??Lo/P?Spring??B/P?Summer?.Phytoplankton functional groups biomass showed different temporal and spatial changes,means followed the order: Summer>Autumn>Spring>Winter,Reservoir>River.There were obvious temporal and spatial changes in the main nutrients of C,N and P in Wujiang River.On the season scale,total content of dissolved inorganic carbon?DIC?was followed the order: Autumn > Summer > Winter > Spring,the dissolved inorganic nitrogen?DIN?was followed the order: Summer>Spring>Winter>Autumn and dissolved inorganic phosphorus?DIP?was followed the order: Winter>Spring>Summer>Autumn.On the river scale,The contents of DIC in river ecosystem than in reservoir ecosystem,The contents of DIP in river ecosystem than in reservoir ecosystem,DIN have no significant between the two ecosystem.On the vertical scale,the content of DIC and DIP gradually increased with the depth,DIN increased with the depth up the 30 m,30m below gradually decreased.The maximum values of DIC,DIP and DIN were located in Maotiaohe river,Wujiangdu reservoir and Luojiaohe river.The principal component analysis?PCA?based on phytoplankton functional groups biomass showed the biomass contributed the most to reservoir ecosystem.The redundancy analysis indicated the Temp,DO,DTP,DIN,Na+,Mg²⁺ were the main factors affecting the distribution of dominate phytoplankton functional groups in reservoir ecosystem and the Temp,pH,DIN,TN,Phosphorus were the main factors affecting the distribution of dominate phytoplankton functional groups in river ecosystem.