Spatial And Temporal Distribution Characteristics Of Water Quality And Phytoplankton Community In Water Source Reservoir

In this study,the Heihe reservoir and Lijiahe reservoir were studied in situ for one year respectively.The water quality and the growth of phytoplankton in the two reservoirs were analyzed and compared,and the distribution of the anaerobic area in disparate water quality stages was analyzed.The control scheme of phytoplankton was put forward to provide the theory of water supply and aeration control in the water source.At the same time,high throughput DNA sequencing was used to diagnose the vertical heterogeneity of the population structure of the Heihe reservoir,providing a new insights on the relationship between water quality and fungal community composition during reservoir thermal stratified periods with algal bloom.The main research contents included:1)the stratified structure of Heihe reservoir and Lijiahe reservoir and the water quality response characteristics;2)the spatial and temporal pattern of phytoplankton quantity and population in Heihe reservoir and Lijiahe reservoir;3)the influence of the water aeration system on the phytoplankton population structure and the regulation of the nutrients of carbon,nitrogen,iron and manganese;4)the thermal stratification of Heihe reservoir induced the vertical succession characteristics of fungal community during algal bloom.The main results are following:（1）The stable stratification period of the water body of Heihe and Lijiahe reservoirs ranged from July to September.The dissolved oxygen in the bottom of the water body is exhausted,which leads to the reduction of the energy efficiency of the chemical oxidation of the water body.The thermocline has hindered the material exchange of the vertical water body.The thickness of the anaerobic layer is up to 21m in the Heihe reservoir stratification period,and the concentration of total nitrogen,iron and manganese in the water body of the constant temperature layer reaches 1.7,0.38 and0.12 mg/L.The thickness of the anaerobic layer is up to 25m in the Lijiahe reservoir stratification period.The total nitrogen,total phosphorus and iron concentration in the water body of the constant temperature layer exceed the standard of 3.2,0.2 and 0.4mg/L respectively.In October,under the condition of natural process and human intervention,the stability of water level structure decreased rapidly,and the hierarchical structure gradually disappeared.（2）The algal density of Heihe reservoir reached the highest value in stable stratification period（September 2016）,and the highest value was 4 million 510thousand cells/L,and chlorophyll a was as high as 5.5μg/L.The Dominant phytoplankton gate in the stratification stage is diatom gate,and the dominant algae species are Microalgae and straight chain algae,and the dominant algae gate in the stable stratification stage is Cyanobacteria.The dominant algae are Microcystis aeruginosa,mainly concentrated in the water body from 2m to 5m.Artificial mixed oxygenation can reduce the oxygen consumption rate in the bottom water,inhibit the release of nutrients,destroy the formation of water bodies and inhibit the growth of algae,and avoid the occurrence of"algal bloom".（3）The density of algal algae in the Lijiahe reservoir is 5 million cells/L and 300million cells/L in the stable stratification period（August）,and the chlorophyll a is up to11μg/L and 24μg/L.The dominant algae gate is Chlorella,and the dominant algae are Chlorella and oocyst,the dominant algae gate is Cyanobacteria,and the dominant algae is Microcystis aeruginosa,mainly concentrated in 2m to 5m.（4）The results of Illumina MiSeq sequencing showed that the species of fungi in different water depth of the Heihe reservoir were higher.Rhodotorula（27.23%）,Alternaria（24.28%）,Cladosporium（22.98%）,Alternaria（32.00%）,Didymella（17.47%）and Cladosporium（28.17%）were dominate species in 0.5m,10m,25m,40m,60m and70m water layers,respectively.Principle component analysis（PCA）indicated that water temperature,DO,TP,conductivity had a dramatic influence on vertical distribution of fungal community composition.TP,temperature and DO had significant influence on the population structure of 10,25 and 40m of water depth,and electrical conductivity and NO₃^--N had a significant influence on the population structure of 60m in water depth;Chl-a and pH were true of 0.5m in depth of water Chl-a and pH.The influence of bacterial community structure is more significant.TP,TN and NO₃^--N have significant effects on the fungal community structure with 70m depth water layer.