The Structure Characteristics Of Protozoa Community In The Middle And Upper Reaches Of The Lhasa River And Its Relationship With The Water Environment

To study community diversity of protozoan and its relationship with water environment in middle and upper reaches of Lhasa River,96 water samples were collected from 8 sampling sites by using 25# standard plankton net from May 2015 to December 2016 divided into three seasons(spring,summer and autumn).The methods of microscopic observation in vivo and fixed-staining was applied for protozoan species identification,and the number of the protozoan species was counted by direct counting method.The protozoan and its relationship with water environment in middle and upper reaches of Lhasa River were analyzed by using biometric parameter,similarity analysis and correlation analysis,the results were as follows.(1)A total of 148 species of protozoan was identified in this study,among them there were 74 species in spring,73 in summer and 83 in autumn.In spring,the species belonged to 2 phylas,5 classes,18 orders,31 families and 40 generas;in summer,the species belonged to 2 phylas,6 classes,15 orders,24 families and 34 generas;and in autumn,the species belonged to 2 phylas,4 classes,17 orders,27 families and 35 generas.Ciliophora was preponderant no matter in the dominant species or in all species among three seasons.(2)The mean Margalef richness index were really low(2.73),summer(2.98)>autumn(2.70)> spring(2.49);Shannon-Wiener diversity index were lower(2.34),autumn(2.55)>summer(2.26)> spring(2.23);Pielou eveness index were relatively high(0.83),autumn(0.91)> spring(0.81)> summer(0.78);Simpson dominance index were really low,summer(0.23)> spring(0.17)> autumn(0.10);saprobic index were really high(2.91),summer(3.13)> spring(2.84)> autumn(2.77).It indicated that the species diversity was really low,but the dominant index was not apparent,which were indicating that species of protozoan in the river were well distributed and the structure of the community was stable in the study area.(3)The functional-trophic group of protozoan in middle and upper reaches of Lhasa River accorded with variation trend of the exogenous nutrients and functional groups in all the seasons,which a growing number of the BS groups were shown from the upper reaches to middle,while the PA group were dropped off.(4)The Jaccard similarity index were really low among all sites in middle andupper reaches of Lhasa River,which showed all the sites were very dissimilar to each other in the three seasons,which indicatied that the points have significant temporal and spatial differences.(5)The results of Pearson correlation analysis between the community structure of protozoan and major environmental factors suggested that dissolved oxygen and turbidity were the major factor for controlling the variations of protozoan community structure in spring,pH and dissolved oxygen were the major factor in summer,and turbidity and ammonia nitrogen were the major factor in autumn.(6)The water environment of the middle and upper reaches of Lhasa River was evaluated by combining the biological parameters and the physical and chemical factors,which suggested the water quality were in light pollution or clean(Os)in the three seasons.In spring,except for S5(light pollution),all the points showed water quality were clean;in summer,except for S3(light pollution),all the points showed water quality were clean;and in autumn,all the points showed water quality were clean.