Diatom Seasonality and Sedimentation in a Subtropical Alpine Lake (Lugu Hu, Yunnan-Sichuan, Southwest China)

摘要

The diatom succession and sedimentation during 2011 in a subtropical, deep alpine lake (Lugu Hu, Southwest China) were studied. The seasonal patterns in diatom assemblages were related to light, nutrient availability, and thermal regime. Peaks in the concentration of the planktonic diatoms (Asterionella formosa and Cyclotella ocellata ) occurred in the metalimnion during autumn when light penetration was greater and silica concentrations were higher. The spring peak of Cyclostephanos dubius appeared to be a result of the combination of a well-mixed water column, higher nutrient concentration, and low light availability. Its sedimentation in late spring suggests that the sinking rates of C. dubius increased rapidly with the onset of stratification. However, the minimal catches of A. formosa and C. ocellata in sediment traps during autumn suggest they were still actively growing with very low sedimentation losses. The catch of benthic Fragilaria species in sediment traps during early spring and autumn reflected their resuspension from shallow water and transfer into pelagic zone as thermal stratification breaks down. The results provide important information for the interpretation of paleolimnological records from the lakes in Southwest China.