Seasonal Change Of Water Quality And Its Impact To Characteristics Of Bacteria And Algae Communities About Urban Lake In Cold-zone

Inner Mongolia Lake,as a typical representative of cold areas in China,which has obvious regional characteristics,plays an important role in maintaining the balance of ecological environment.Nanhai lake which located at the edge of the city is a part of Baotou section of the Yellow River wetland.Due to having the dual characteristics between cold region lake and urban lake,the change of water environment will inevitably change the sensitive microorganism and its community structure in the freeze-thaw process.The studies on the characteristics and the law of habitat change and succession in the surrounding lakes in the cold-zone was few,so it had great research value.Based on the seasonal changes of lakes in the cold-zone,taking eutrophic lake as the research object,the characteristics of water environment change were analyzed,the succession rules of microbes were recognized by means of high-throughput sequencing and niche analysis,and the mechanism of their relationship with lake environmental factors was ascertained.Characteristics of microbial ecological environment in the lakes were driven.The main results are as follows:(1)The water quality of Nanhai lake had a similar interannual change trend,the pollution degree was Tourism Area>Hydrophyte Area>Channel-flow Area>Central Island Area,the eutrophication degree was relatively serious in the mass.During the ice period,the pollutants in the ice precipitated and settled into the water,the pollutant content of the lake became higher in winter.Temperature as a key factor of water quality in the freeze-thaw process,Temperature showed a significant positive correlation with DO,and it had a significant positive correlation with EC,SAL and TDS,NH3-N had the most direct impact on TN content.(2)The isotopic trace showed that the source of organic matter pollution in different functional areas was different,which was related to the change of lake water quality.The data of the ?13C and ?15N of suspended organic matter in Channel-flow Area were significantly different from those in other areas,showed the characteristics different from the isotopic signals of the lake itself.It showed that the replenishment from the Yellow River brought more exogenous organic matter into the area and had a significant impact,which was consistent with the change of nutrients in the water affected by the replenishment of the Yellow River.The density of phytoplankton in Central Island Area was the highest,and the negative value of ?13C reflected the selective absorption effect of phytoplankton.There were many pollution sources in Tourism Area affected by human activities,which resulted in the peak value in suspended solids such as ?15N,TN and NH3-N.The highest contents of ?13C,?15N,TOC and TN in the surface sediment also had appeared in Tourism Area,which was related to the sewage discharge and mineralization and decomposition of aquatic plants in the middle island of the lake.The nature of intense primary productivity was belonged to the contiguous zone of the area which also had the Characteristic of a lower degree of complex degradation of organic matter sources.(3)Due to the process of freezing and thawing,the bacterial community structure of Nanhai lake changed greatly with seasons.The bacterial diversity in winter was lower than that in other seasons.The dominant species were Actinobacteria,Proteobacteria,Cyanobacteria and Bacteroidetes.Proteobacteria were always the dominant species and the lake had no obvious succession law at the level of phylum from freezing to thawing.Chlorophyta was the most dominant group of phytoplankton in Nanhai lake,followed by Cyanophyta and Diatom.The total characteristics of total phytoplankton species in time was summer>spring>autumn>winter.There were four dominant species:Aphanizomenon flosaquae,Merismopedia tenuissima,Scenedesmus quadricauda was dominant species in the four seasons,and their density distribution was relatively uniform throughout the all year.Aphanizomenon flosaquae had a broad niche all of the year,and it was found that algae with wider niche appeared more frequently as dominant species.In autumn,the species pairs with high niche overlap were the most,while in winter the species pairs with high niche overlap were the least.The niche breadth and niche overlap of each dominant species were different in different periods,and the adaptability of each species to environmental factors was also different.(4)Due to the pollution level of water environment and sediment was different in different seasons,the environmental factors that affected the growth of bacteria were different.DO,pH and CODCr were the main factors that affected the survival of bacteria in the water during the freezing period.Most of the microorganisms that became the dominant bacteria in the lake water showed a strongly positive correlation among them and a negative correlation with TN.It showed that in the special period of the freezing period,the demand for carbon source was greater than nitrogen,so the nitrogen was accumulated.In the freeze-thaw process TN and NH3-N were significantly affected the dominant bacteria in water.This phenomenon showed that the temperature increased,the number and abundance of bacteria and phytoplankton began to increase.TN and NH3-N became the growth limiting factors when the carbon source did not change.TN,NH3-N and TOC were the main environmental factors that affected the microbial community in the sediment.From winter to spring,the main environmental factors affecting phytoplankton density replaced T and CODCr by pH and DO,which indicated that the rate of algal cell division and the productivity of unit chlorophyll were greatly affected by water temperature.The composition and diversity of lake communities in the cold region were greatly affected by climatic conditions and human factors,and the input of nutrients,temperature,DO and TN were the main factors.The formation and ablation of lake ice cover made the change of microbe in genus(species)level inevitably lead to the corresponding change of lake water ecosystem.Focusing on the law of microbial change in the freeze-thaw process provided a new scientific basis for eutrophication control and ecological microenvironment improvement.