Chinese Academy Of Geological Sciences Doctoral Dissertation

103 surface sediment samples in 71 water bodies,such as lakes with different salinity,swamps,shallow puddles and rivers on the Qinghai-Tibetan Plateau(QTP),were collected to study the ecological distribution of living ostracods and their environmental implications.Total of 12 genus and 45 species living ostracods are identified.According to the frequencies and abundance of ostracods occurrence,Limnocythere dubiosa,Limnocytherellina kunlunensis,Ilyocypris bradyi,Candona candida,Eucypris rischtanica and Leucocythere dilatata are the common species on the QTP,with occurrence frequency of more than 8 and abundance of more than 570 in the 71 water bodies.Among them,Limnocythere dubiosa,occurring in 28 water bodies with 2177 shells,is the most widely distributed ostracod in this research.As for salinity implication,Ilyocypris tuberculata,Ilyocypris gibba,Ilyocypris echinata,Leucocythere parasculta,Candona candida and Leucocythere exilitropis mainly live in fresh water,although Candona candida and Leucocythere exilitropis are also found in oligohaline water in very small number.Cypricercus moguntiensis,Heterocypris salinus,Leucocythere subsculpta,Leucocythere pseudosculpta,Leucocythere mirabilis and Candona xizangensis also indicate low salinity water as they only appear in fresh water or oligohaline water with larger percentage in oligohaline water than Candona candida and Leucocythere exilitropis do.Candoniella lacteal,Candona rawsoni,Candona lijiangensis and Cyprideis littoralis only live in oligohaline water.Limnocytherellina trispinosa,Limnocytherellina bispinosa and Candona houae mainly live in oligohaline water and little in polyhaline water and hyperhaline water.Eucypris inflata only live in polyhaline water and Candoniella albicans,Prionocypris gansenensis and Ilyocypris xizangensis only live in euhaline water and hyperhaline water.Leucocythere dorsotuberosa,Leucocythere tropis,Leucocythere dilatata,Leucocythere postericosta,Eucypris rischtanica,Limnocytherellina kunlunensis,Ilyocypris bradyi and Limnocythere dubiosa can be found in all kinds of water bodies,among which,Leucocythere postericosta and Limnocytherellina kunlunensis prefer to euhaline water and hyperhaline water,while Ilyocypris bradyi prefers to fresh water.Canonical Correspondence Analysis(CCA)indicates high correlation between ostracods species and environmental variables,suggesting that the occurrence of species is strongly related to the changes in ecological conditions of habitats.Among eight environmental factors,salinity and pH value are the most affective variables that influence the species occurrence.Limnocytherellina kunlunensis is positively correlated with salinity while Eucypris rischtanica is negatively correlated with salinity.Candona candida has a positive correlation with salinity,as does Ilyocypris bradyi although there is not such a strong correlation.Limnocythere dubiosa displays a positive correlation with pH value.Consequently,we discuss the environmental implications of the common living ostracods on the QTP based on the CCA as well as the distribution of ostracod species in different salinity and pH values water.Limnocythere dubiosa,Limnocytherellina kunlunensis and Eucypris rischtanica are euryhaline species,among which,Limnocythere dubiosa is the most adaptable species on the QTP with large occurrence in sundry salinity water and widely adaptive range for pH values.Limnocytherellina kunlunensis prefers to saline water while Eucypris rischtanica prefers to fresh water.Both Limnocytherellina kunlunensis and Eucypris rischtanica can live in water from faintly acid to alkaline,in contrast,Limnocythere dubiosa only appears in neutral and alkaline water bodies.Ilyocypris bradyi only occurs in fresh water and oligohaline water with a large pH tolerance range from weakly acidic water to alkaline water.Candona candida lives in freshwater,with pH value above eight.The six common species reach maximum abundance in alkaline water(pH 8-10)except for Ilyocypris bradyi.Accoreding to the trace elements analysis for Ilyocypris bradyi shells in the QC-1 drilling,we find that the environmental implications of trace elements are the same as the environmental implications indicated by the ecological distribution of Ilyocypris bradyi.