Spatial Heterogeneity Of Bacteiral Community Compositions And The Environmental Factors In Lake Bosten

To investigate Spatial heterogeneity of bacterial community compositions and theenvironmental factors in Lake Bosten, a large brackish inland lake, in the arid region ofXinjiang Province, in northwestern China, water qualities of six stations were monitoredfrom June2010to June2011, firstly. The results showed that water qualities weredistinctly different among these stations, but monthly variations of water quality amongstations were not uniform. In the large lake area of Lake Bosten: water quality was worst innorthwest; water quality in the river mouth of River Kaidu was best, while it changedgreatly from month to month; and the water quality in middle and east reachedintermediate level. In the small lake area of Lake Bosten: water quality was best in LakeLama with the categories fromⅠto Ⅲ; water quality in lake wetlands was worst with thecategories of Ⅴ or even worse. The main pollutants in Lake Bosten were salinity, totalnitrogen, sulfate and chloride. In general, the trophic level of Lake Bosten is mesotrophic,and in sometimes it reaches light eutrophic. Agricultural non-point source pollutions,hydrology, lake currents and aquatic plants were the main factors attributed to thespatio-temporal heterogeneity of water quality in Lake Bosten. The variation of waterquality in the past50years shows that Lake Bosten has converted from the largest inlandfreshwater lake to a brackish lake since1970s. Accompanied by the lake salinization,concentrations of other pollutants increased rapidly as well.Secondly, for the further research of bacterial community compositions and theenvironmental factors in Lake Bosten, water samples of23stations in Lake Bosten werecollected in June,2010. On the one hand, the DAPI-combined epifluorescence directcounting method （DAPI-FDC） was used to identify the spatial distribution pattern ofbacterial abundance and the relationship with the environmental parameters. The resultsshowed that the concentration of total nitrogen （TN） in the water of Lake Bosten wasranged0.26～1.45mg/L （mean=0.91mg/L）, which indicated that Lake Bosten hasreached to mesotrophic and eutrophic level. The concentration of total dissolved solids（TDS） varied from219mg/L to1696mg/L （mean=1125mg/L）, which indicated thatLake Bosten is a brackish lake now. The abundance of bacteria was ranged1.41～4.57×10⁶cells/ml （mean=2.89×10⁶cells/ml）, with the higher values appeared in station5andother heavenly polluted northwest lake regions, and the lowest value appeared in station14located in the estuary. Cluster analysis showed that the23sampling stations can be dividedinto two groups: freshwater region （FR） and brackish lake region （BLR）. Compared with freshwater region, the concentrations of TDS, electrical conductivity, salinity, COD_Mn,chloride and sulfate in brackish lake region were significantly higher （P<0.01）. Thebacterial abundance was significantly positive correlated with COD_Mnand Cl-（P<0.01）.On the other hand, we analyzed the diversity and bacterial community composition（BCC） in Lake Bosten, in June2010as well. We studied23sites, and used PCR-DGGE,and cloning and sequencing of the16S rRNA genes of six selected samples. A total of374bacterial16S rRNA gene sequences from six stations were successfully obtained, and theywere numerically dominated by members of the Betaproteobacteria （35.8%）, Bacteroidetes（25.4%） and Epsilonproteobacteria （21.4%） groups. The statistical analysis of BCC, asdetermined by∫-Libshuff comparisons of the six clone libraries, demonstrated significantspatial heterogeneity in Lake Bosten. Salinity was the most important contributor, solelyaccounting for20.4%of the variation in BCC.Our investigation showed: the variation of water quality in Lake Bosten is controlledby natural factors and human factors. In recent decades human activities have exacerbatedthe salinization and eutrophication of Lake Bosten. the spatial distribution pattern ofbacterial abundance was a response to different levels of nutrients and salinity in the waterof Lake Bosten. a lower taxonomic richness in Lake Bosten than is found in referencelakes in eutrophic floodplain and marine systems, a high percentage of unidentifiedbacteria and a low percentage of dominant species in the BCC. Salinity was found to be thedominating contributor controlling bacterial community composition （BCC） and theabundance of Betaproteobacteria in the oligosaline Lake Bosten.