中文摘要：

大小苏干湖是位于柴达木盆地北缘的一个内陆封闭的生态系统，本文对湖泊的浮游植物多样性及其季节变化特征进行了初步研究。通过春季（5月）、夏季（8月）和秋季（10月）的采样分析，发现大苏干湖中共有浮游植物61种，小苏干湖中共有68种；在3次所采水样中，浮游植物的密度春季最低，夏季最高；大苏干湖中硅藻门一直占据着绝对的优势，即使在相对较少的8月份，也占到了总体的41．5％左右；其次是蓝藻门，在8月份占总量的56．1％；而小苏干湖中硅藻门也是一直占据着绝对的优势，占到了总量的70％左右；其次是蓝藻门，在8月份占总量的20．1％。大苏干湖的绿藻指数为4．00，小苏干湖的绿藻指数为3．67，大苏干湖样品的藻类综合指数为5．00，小苏于湖样品的藻类综合指数为8．67，说明水体属于中度以上富营养型；大苏干湖相同月份各区的Shannon指数差别不明显，Pielou均匀度指数的差别也不大，全湖的变化不显著。Shannon指数H’在各月的变动范围平均在1．823—2．192之间，小苏干湖的Shannon指数H’在各月的变动范围平均在2．068～3．036之间。两湖相比，无论从Shannon指数还是Pielou指数来看，小苏干湖生物多样性指数高于大苏干湖。

英文摘要：

Lake Suganhu is a closed inland ecosystem situated in the northern of Chadm Basin, the largest plateau inland lake in Gansu Province, China. It is an important habitat for transient birds and other animals. There are two lakes called Lake Suganhu, ie big and small one, which are over 110km2 totally. Most of water is originated from Haerteng River thawed from the glacier of Qilian Mountains. It will cause the decrease in the amount of water into Lake Suganhu to build a catchwater on the upriver of Haerteng River. Therefore, it is necessary to understand the community composition of phytoplankton in the lake. Phytoplankton species composition, diversity and Spatio-temporal distribution were investigated in spring （May） , summer （August） and autumn （October） of 2006 in this paper. A total of 61 and 68 species （ including subspecies, variety and form） were identified in the big and small Lake Suganhu, respectively. In big Lake Suganhu, there were 18 genera and 37 species in the phylum Baeillariophyta, 11 genera and 15 species in the phylum Cyanophyta, 7 genera and 8 species in the phylum Chlorophyta. In small lake, 16 genera and 42 species belonged to the phylum Bacillariophyta, 9 genera and 13 species ascribed to the phylum blue-green algae, 6 genera and 11 species affiliated to the phylum Chlorophyta, and the only two species appeared in the phyla Euglenophyta and Pyrrophyta. In the two lakes, lower cell densities were found in spring and autumn, and more number was found in the season of summer during the three samplings, indicating the summer is the best season for algae growth and reproduction. The Bacillariophyta was the dominant phylum absolutely in big lake, which accounts for Ca 41.5% of the collectivity even in August when the amounts comparatively were small. The Cyanophyta was in the next place, accounted for 56.1% in the summer （August）. Accordingly, there was similar trend in species composition in small Lake Suganhu, the Bacillariophyta accounted for 70% of the collec-tivity, and th