In order to investigate the natural ecosystem of Lake Dianchi and to assess its anthropogenic impacts, a stratigraphic study
of bulk and molecular compositions of organic matter was conducted using a 63-cm long sediment core. The results show that
two apparent environmental changes occurred during the evolution of Lake Dianchi: (1) the first change occurred in the 43–63 cm
sediment depth, and was revealed by the amount and the composition of organic matter in the stage. Natural changes were possibly
major factors responsible for triggering the environmental change, but the influence of human activities could not be excluded.
Subsequently, the lake entered into a relatively stable and oligotrophic stage, which maintained until 20-cm sediment depth.
(2) Eutrophication started in the upper 20 cm depth. Human activities became a major factor influencing environmental changes
in this stage. Vertical profiles of various organic geochemical variables in the upper 20-cm sediments show evidence that
primary productivity of the lake increased progressively and that the lake started eutrophic. Especially in the uppermost
10 cm, notable excursions to less negative δ13Corg and δ15Ntotal and high TOC concentrations have recorded an abrupt change in the lacustrine environment, suggesting that the lake entered
a hypereutrophic stage. In addition, enhancement of αβ-hopanes reflects the contribution of fossil fuels to the lake sediments. 相似文献
海洋一号C/D(HY-1C/D)卫星中国海洋水色水温扫描仪(Chinese Ocean Color and Temperature Scanner,COCTS)主要用于探测海洋水色、水温等要素,这些要素需要经过卫星资料处理才能获取,而几何定位是预处理的核心,直接影响这些要素的质量。COCTS具有114°视场角和四元逐点摆扫的特征,据此研究出一套完整的几何定位方法。从0级数据中提取卫星星历,利用插值法从中获取采样时间对应的卫星位置和速度,进而得到轨道(ORB)坐标系到地心旋转(ECR)坐标系的转换矩阵。基于四元逐点摆扫的特征,中心视矢量分别绕X轴、Y轴旋转相应角度,获得扫描行各采样点ORB视矢量,建立视矢量与地球交叉点关系模型,从而对根据波段数据绘制的遥感图像进行地理定位。本文使用插值法替代了传统需要6个轨道根数来计算卫星位置的复杂方法,同时直接计算ORB到ECR的转换矩阵,而不采用传统的两步转换方法。经过多组数据计算及定性定量验证,HY-1C/D COCTS几何定位结果一致;采样像元尺度效应导致从星下点到两侧边缘、从赤道到两极,误差逐渐增大,约在两个像元内。该方法满足一定的定位精度要求,可以用于COCTS的几何定位。 相似文献