中文摘要：

采用活塞取样器采集了月湖湖中央2处钻孔沉积物，分析了其中硅藻种类与密度的垂直变化，同时采用^210Pb/^137Cs推测沉积物的沉积速率，关进行了总有机质．生物硅含量分析，以了解月湖各个不同年代的水质变化。结果表明，2个柱状沉积物中硅藻的优势属为：小环藻属、直链藻属、舟形藻属、Cyclostephanos属。Z－1钻孔优势种为：梅尼小环藻、颗粒直链藻、Navicuta porifera、Cyclostephanos tholifomis. Z-2钻孔中优势种为：梅尼小环藻、颗粒直链藻、舟形藻、Cyclostephanos invisitatus。就硅藻密度而言，总趋势是上层最多，平均7．14×10^5～58．65×10^5ind·g^-1，中层其次，平均0．08×10^5-13．98×10^5ind·g^-1，下层最少，平均0．24×10^5-0．64×10^5ind·g^-1.硅藻种类数变化虽然没有明显规律，但种类最少的样品出现在中层，^210Pb/^137Cs测年数据表明中层为19世纪90年代－20世纪70年代。相天分析表明：Z－1孔生物硅与沉积硅藻密度显著正相关（r=0．933，P=0．021〈0．05），总有机质含量与种类数显著负相关（r=－0．972，P=0．005〈0．05）；Z－2孔生物硅与沉积硅藻密度显著正相关（r=0．985，P=0．002〈0．05），沉积硅藻密度与种类数显著负相关（r＝－0．933，P=-0．021〈0．05）。研究结果表明，月湖沉积物中硅藻种类与密度的垂直变化可以反映月湖的富营养演化历程：19世纪60年代－19世纪80年代，月湖水质较好；19世纪90年代－20世纪10年代，月湖开始由贫营养状态向中营养状态转变，为水体富营养化开始发生时间；20世纪20年代－20世纪40年代，月湖水体营养等级持续增加，已富营养化；20世纪50年代－20世纪70年代，周边人口数量急刷上升与污水的直接排放导致月湖水质持续恶化；20世纪80年代至月湖截污前这段时期使月湖最终沦为劣五类水体的湖泊。

英文摘要：

This article described and analyzed the vertical distribution of diatom species and their density in two bored sediment cores collected from the center part of the Moon Lake. ^210Pb/^137Cs analysis was adopted to estimate the sedimentary rate of these two cores; The content analysis of TOM and BSi was conducted to find out the water quality change during different periods in the Moon Lake. The result indicated that the dominant genera in two columnar sediment cores were Cyclotella, A ulacoseira, Navicula and Cyclostephanos. The dominant species of Z-1 bored sediment cores were Cyclotella meneghiniana, Auloacoseira granulata, Navicula porifera and Cyelostephanos tholifomis, the dominant species of Z-2 bored sediment cores were Cyclotella meneghiniana, A ulacoseira granulata, Navicula sp. and Cyclostephanos invisitatus. The diatom density in the two cores shares similar trends：the highest density existed in the upper layer, with an average range of 7.14×10^5- 58.65×10^5 individuals·g^-1, which follwed by the intermediate layer presenting an average range of 0.08 ×10^5-13.98×10^5 individuals·g^-1, and the lowest density was in the bottom layer, with an average range of 0.24×10^5-0.64×10^5 individuals·g^-1. No obvious regular pattern was found for the change of diatom species number in either core; However, the lowest species number was in the middle layer of the two sediment cores, which corresponded to the periods between the 1890＇s and the 1970＇s according to ^210Pb/^137Cs analysis. The result of correlational analysis showed that in Z-1 bored sediment eore, the Bsi density was positively correlated with sediment diatom density（r=0.933, P=0.021〈0.05 ）, and the TOM content was negatively con＇elated with diatom species number（r=-0.972, P=0.005〈0.05）; In Z-2 bored sediment core, the BSi density was positively con＇elated with sediment diatom density（r=0.985, P=0.002〈0.05 ）, and the TOM content was negatively correlated with diatom species number（ r=-0.933, P=0.021 〈0.05 ）. Th