| The construction of water conservancy projects often leads to the slowdown of water flow rate and the obstruction of nutrient transport,which aggravates the potential of eutrophication.Eutrophication and cyanobacterial blooms are major environmental problems in the world and are obstacles restricting China's environmental protection.They restrict the availability of water resources and the development of social economy in China.The formation of algal blooms depends not only on the conditions of suitable nutrients,temperature,light,but also are closely related to hydrodynamic conditions and suspended particulate matter?SPM?content in water body.Therefore,understanding the response of phytoplankton's physiological and ecological characteristics to the changes of hydrodynamic conditions and environmental factors,and analysing the survival strategies of phytoplankton in the above-mentioned environments have certain reference value for understanding the ecological environmental effects of water conservancy projects and assessing the ecological risks.In this paper,Yulin River,a secondary river in the Three Gorges Reservoir area,is taken as the research object.From the perspective of hydrodynamics?turbulent flow?and its driven environmental factors?focusing on SPM?on the growth and effects of phytoplankton in the reservoir area.An approximately homogeneous turbulence simulation system?AHTS?is established to study the effects of turbulent environment on phytoplankton growth and community structure.Through the construction of turbulent flow and SPM co-interference system,the effects of turbulent flow and SPM on the ecological processes of phytoplankton community,and the suitable strategies of phytoplankton community under this condition are studied.Based on the analysis of the spatial and temporal distribution of Microcystins?MCs?in the secondary river of the Three Gorges Reservoir,Yulin River,and its relationship with environmental factors,the response model of hydrodynamic-sediment-MCs is elaborated from the point of view of in-situ monitoring results.Through the above research,the following main conclusions are obtained:?1?In turbulent systems,higher turbulence intensity(1.80×10-2 m2/s3)increases the density of phytoplankton in the system.Compared with the treatment with a turbulence intensity of 2.25×10-3 m2/s3,the higher turbulence intensity treatment promoted the growth of the population phytoplankton?Scenedesmus sp.?,Microcystis sp.is more likely to survive under higher turbulence.?2?Under the turbulent and SPM co-interference system,the higher turbulence intensity,the greater density of phytoplankton and the higher the proportion of colony algae.On the other hand,during SPM-algae co-incubation period,extracellular polymeric substances?EPS?released by algae cells attaches to SPM surface,which makes the SPM form larger particles and a smoother surface.By adjusting the surface characteristics of SPM,this can reduce the damage of algae cells caused by the shear force formed by the collision of SPM.These results confirm that phytoplankton can adapt to the above-mentioned dual stresses by releasing EPS,changing the surface properties of SPM and changing its aggregation state in the sediment resuspension environment driven by turbulence with high intensity,so as to reconstruct the ecosystem.?3?The temporal and spatial distribution characteristics of MCs and the physical and chemical indicators of water quality were monitored in Yulin River.It was found that the phytoplankton density varied with the fluctuation of water level and seasons in the six monitoring sections of Yulin River.MC-RR is the main isomer of MCs in Yulin River.Its maximum concentration is 3.55 ug/L,the maximum concentration of MC-LR exceeds the threshold of 1.0 ug/L recommended by WHO.In addition,in the temporal distribution,the concentration of MCs in the discharge period is higher,and the spatial distribution of MCs from the upstream reaches to the estuary is on the rise.MCs are negatively correlated with phosphorus and water flow rate in storage period,but positively correlated with water temperature,SPM and phytoplankton density.In discharge period,MCs are negatively correlated with total phosphorus and SPM,but positively correlated with water flow rate.Furthermore,the ecological risk assessment results show that MC-LR have a high negative impact on benthic invertebrates.?4?The results of in-situ assessment of Yulin River shows that SPM is an important factor to reduce the dissolved MCs in Yulin River.By comparing the concentration of MCs in sediments and SPM of Estuary and Paihua sections,it is found that the MCs content in sediments of above sections is 1.70-20 times higher than that of SPM.Based on the analysis of SPM and sediment surface characteristics by FTIR and XRD,it is found that SPM has high homology with sediment at each sampling point,indicating that suspension-sedimentation of sediment under hydrodynamic action is a key process affecting MCs concentration in water body.In summary,the effects of turbulent and SPM on the physiological processes of phytoplankton and the in-situ monitoring of MCs in Yulin River were studied.The effects of hydrodynamically driven sediment suspension on the ecological characteristics of phytoplankton were discussed.The active survival strategy of phytoplankton under the above conditions was analyzed,and the coupling relationship between turbulence and sediment suspension-phytoplankton response-MCs ecological risk was analyzed.The results provide a basis for further understanding of the response characteristics and effects of algae under hydrodynamic forces. |
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