150年来青藏高原南红山湖的介形类与环境变化

Ostracoda and environmental changes of South Hongshan Lake on Tibetan Plateau during the past 150 years

青藏高原西北部南红山湖 2孔湖芯沉积物中的介形类动物群计有 4属 4种 ,据其分布特征划分出 5个组合 ,各组合间的差异表现在介形类动物群丰度和每个种的丰度变化以及特征种的出现。通过分析介形类属种生态特征和组合变化对 150年来的南红山湖环境变化进行了探讨。分析结果表明 :1884年前为有缓慢水流注入的滨岸浅水期 ;1885～ 1970年间为湖水相对温暖期 ,在这期间湖泊环境仍有次一级的变化 ,其中 ,1885～ 190 5年湖面迅速抬升 ,水深增大 ,水温也较高 ,192 3～ 194 4年为湖水温度另一个稍高期 ,196 1～ 196 9年湖面再次出现明显上升 ;1970年以来湖泊退缩、咸化。

A 107cmlong lake core was drilled in the South Hongshan Lake (35°10′N, 80°04′E, 5060m asl) and cut in the laboratory with an interval of 1 cm. From the core, four species of Ostracoda which belong to 4 genera have been identified. These species are Limnocythere inopinata (Baird), Leucocythere mirabilis Kaufmann, Ilyocypris biplicata (Baird) and Eucypris inflata (Sars). According to Ostracoda distribution in the core, five Ostracoda assemblages can be distinguished as follows: (1) Ilyocypris biplicata-Limnocythere inopinata assemblage; (2) Limnocythere inopinata-Leucocythere mirabilis assemblage, in which the dominant species is Leucocythere mirabilis; (3) Leucocythere mirabilis-Limnocythere inopmata assemblage, in which the dominant species is Limnocythere inopinata; (4) Eucypris inflata-Limnocythere inopinata assemblage; and (5) single species Limnocythere inopinata assemblage. Based upon the ecological characters of Ostracoda species, variations of Ostracoda assemblages, sediment ages and sedimentary features, the environmental evolution of the South Hongshan Lake in the past 150 years may be preliminarily inferred. From 1853 to 1884 A.D., Assemblage I was dominant in the core. Most of the species were Ilyocypris biplicata , which lived in shallow and running water environment. It implied that the South Hongshan Lake was a shallow water lake, into which slow running water flowed. Assemblages II and III appeared during1885-1970 AD. Limnocythere inopinata and Leucocythere mirabilis were dominant with big abundance. The occurrence of plenty of Ostracoda might reflect a relative warm period to lake water temperature. According to the difference of dominant species and the quantity changes, 5 stages might be further divided, from which three of them were characterized with relative deep water and high water temperature. During the period of 1885-1905 A.D., water level of the lake rose rapidly while the depth and the temperature of the lake water all substantially increased. From 1923 to 1944 A.D., the temperature of lake water might be relatively high. From 1961 to 1969 A.D., the lake became comparatively deep. Assemblages IV and V appeared in the section since 1970 with less quantities of Ostracoda. The halophile species, Eucypris inflata appeared in Assemblage IV. These suggested that the lake has been shrinking while the quality of lake water became gradually saline since 1970 A.D.