Response of phytoplankton community structure to the vertical mixing process in Lake Fuxian
During winter,the decline of thermal stratification and the mixing of water in deep lakes can alter the distribution pat-tern of nutrients,and potentially affect the succession of phytoplankton communities in lake ecosystems.In this study,high-fre-quency observations of physicochemical environmental factors and phytoplankton communities were conducted along vertical profiles during stratification decline,mixing,and stratification formation periods in Lake Fuxian,a deep plateau lake,from November 2022 to April 2023.The spatiotemporal characteristics of phytoplankton communities in response to the thermodynamic mixing process were investigated.The results showed that the mixing process caused significant spatiotemporal changes in physicochemical environmental parameters.Compared with the stratification-declining period and stratification-formation period,the concentrations of total phosphorus(TP),dissolved organic phosphorus(DOP),phosphate(PO43--P),and chlorophyll-a(Chl.a)in the water were significantly increased during the mixing period,while the concentrations of total nitrogen(TN),dissolved nitrogen(DN),particulate nitrogen(PN),ammonium nitrogen(NH3-N),and nitrate nitrogen(NO3-N)were significantly decreased by mixing.Among the phytoplankton community,the green algae Mougeotia and Chlorella had higher densities than other species throughout the observation period,while the cyanobacteria Dolichospermum and Cylindrospermopsis had the highest densities during the stratifi-cation-declining period,and the diatom Melosira and the cryptomonad Cryptomonas had the highest densities during the mixing pe-riod,and the green algae Scenedesmus had the highest densities during the stratification formation period.Redundancy analysis showed that the dynamic changes in NH3-N,PO43--P,and alkaline phosphatase activities significantly influenced the composition of the phytoplankton community.Moreover,the sensitivity of phytoplankton to nitrogen and phosphorus nutrients varied among dif-ferent species.Dolichospermum and Mougeotia showed a positive correlation with N nutrients and a negative correlation with nutri-ents,while the densities of other phytoplankton species exhibited an opposite pattern,showing a negative correlation with nitrogen and a positive correlation with phosphorus.Structural equation modeling was used to analyze the driving mechanisms of phytoplank-ton community dynamics during the water mixing period.On one hand,water temperature directly impacted the structure of the phytoplankton community.On the other hand,water temperature indirectly drove changes in the structure of the phytoplankton com-munity by regulating the concentrations of different forms of nitrogen(NO3--N,NH3-N)and phosphorus(PO43--P and dissolved organic phosphorus).Ultimately,these direct and indirect effects collectively contribute to the changed in the concentration of Chl.a.This study contributed to our understanding of the effects of thermal stratification changes on the structure and function of lake eco-systems in deep lakes.In the context of global changes,strengthening research on mechanisms and ecological environmental effects of thermal stratification in lakes and reservoirs can support the protection and management of lake ecosystems.
Lake Fuxianvertical mixingphytoplanktonnutrientdriving factors
万方数据
维普
