澜沧江中下游浮游植物时空变化及其水生态评价OA

The structure of phytoplankton communities is an important indicator of water quality and ecological conditions.In this study,the Yunnan section of the Lancang River basin was selected for re-search,and we investigated phytoplankton community structure at the basin scale using functional group classification.Based on the results,response relationships between phytoplankton community and water environmental factors were elucidated and the aquatic ecological environment was evaluated.The aim of the study was to assess the aquatic ecological health of the Lancang River basin after construction of cas-caded reservoirs,and provide scientific data to support the protection of aquatic ecology and management of dammed rivers.The study was based on sampling surveys conducted during March and April at 57 sites in 2017 and at 86 sites in 2019,including natural river reaches and cascaded reservoirs.A total of 102 phytoplankton species from 70 genera and 7 phyla were detected in the two surveys,with diatoms and green algae as the dominant taxa.The biomass ranges of phytoplankton were 0.021-4.402 mg/L in 2017 and 0.046-98.503 mg/L in 2019,with average values of 0.929 mg/L and 26.033 mg/L.A total of 25 functional taxa were identified and 19 were dominant.From 2017 to 2019,the dominant functional groups shifted from A,D,and MP to P and MP,and the proportion of mesotrophic functional groups in-creased significantly,resulting in a decrease in the average cycle threhold(Qr)value from 4.07 to 3.74.Overall,the aquatic ecosystem of Lancang River basin was in excellent condition based on multiple indi-cators,with only a few sampling sites showing severe eutrophication or heavy pollution.Correlation and redundancy analysis showed that temperature(T)was the key factor influencing spatiotemporal variations in phytoplankton community composition.Impounding water behind dams also affected dissolved oxygen(DO)and nutrient levels that,together with water temperature,control phytoplankton community compo-sition and drive changes in the aquatic ecology of the cascaded reservoirs in the middle and lower reaches of Lancang River.The average temperature of the surface water in the cascaded reservoirs in the Lancang River basin increased by 7.3 ℃ from 2017 to 2019 and the average phytoplankton density at the same sam-pling sites increased by a factor of 8.6.Temperature was the primary factor causing changes in phyto-plankton community structure and the combined effects of global warming and damming pose a big chal-lenge for protecting aquatic ecology in the Lancang River and other river systems.