Modern diatom combination characters and an influence factor analysis of the surface sediment of lakes in Tibet

Diatom samples of the surface sediment from 20 lakes in Tibet were collected and analyzed. The results showed that the diatom communities include 10 families, 27 genera, 212 species, and the alkaliphilous species are dominating in the Tibet lakes. The dominate genera are Navicula(17.5%), Nitzschia(10.8%), Cymbella(8.5%), Fragilaria(8.5%), Gomphonema(7.1%) and Pinnularia(6.1%); and the dominate species are Denticula elegans, Fragilaria pinnata and Nitzschia denticula. Navicula cincta var. leptocephala, Fragilaria leptostauron var. martyi and Amphora ovalis var. pediculus are found in these lakes also. Salinity proxies(T DS, SC,ρ(Mg2+), ρ(Mg2+)/ρ(Ca2+), ρ(CO2-3+HCO-3) and alkalinity are the main limit factors for the diatom distributions in the lakes in the northern part of the Qinghai-Tibet Plateau, and pH values control the diatom components in these lakes. Denticula elegans can grow well in lakes whose conductivity is 3.98 mS/cm, and the highest pH tolerance of Nitzschia denticula is 10.56. The optimal growth conditions for Fragilaria pinnata in Tibet are that pH is 8.68 and conductivity is 0.30 mS/cm. Fragilaria leptostauron var. martyi can grow under the conductivity lower than 3.98 mS/cm. Amphora ovalis var. pediculus grows well under the conductivity of0.48 mS/cm and pH 10.26. Amphora veneta is found with high abundance under a salinity(T DS) of 345 mg/L.The high abundance of Opephora martyi may indicate a rich nutritional environment of the lake.