官厅水库沉积物中大量元素的历史分布特征

以官厅水库沉积物为研究对象,建立年代序列,解析有机质及TOC、TN、TS的含量和沉积通量的年变化,探明官厅水库大量元素的历史沉积特征.结果表明:采用210Pb和137Cs测定官厅水库线性沉积速率分别为0.33 cm·a-1和0.32 cm·a-1,累积质量沉积速率从1954年水库建成后缓慢递增到1980年左右的0.156 g·cm-2·a-1,之后递减至当前的0.090 g·cm-2·a-1.沉积物中有机质含量为36.8~100.7 g·kg-1,在水库南部库区略高;有机质沉积通量在时间尺度上随年代呈先增加后减少,与沉积物沉积速率年变化趋势相似.沉积物中TOC含量为1.18%~7.83%,TN含量为0.04%~0.73%,TS含量为0.07%~0.50%.TOC和TN的沉积通量在20世纪90年代左右出现峰值,而TS沉积通量呈逐渐下降趋势.总体而言,官厅水库沉积物中C、N、S等大量元素呈连续分布,其沉积通量主要受沉积速率影响,颗粒物沉积过程可能在污染物迁移转化中扮演重要角色.

Historical distribution characteristics of major elements in Guanting Reservoir sediment

The sediment cores of Guanting Reservoir in Beijing were collected and the sediment time series were established. Furthermore, the annual changes of content and sedimentation flux of organic matter (OM) and TOC, TN, TS were analyzed to clarify the historical sedimentary characteristics in Guanting Reservoir. The results showed: the linear sedimentation rates of sediment calculated separately by radionuclide ²¹⁰Pb and ¹³⁷Cs dating methods were 0.33 cm·a^-1 and 0.32 cm·a^-1. The mass accumulation rates (MAR) of sediment increased slowly around 0.156 g·cm^-2·a^-1 from 1954 to 1980, and then reduced to 0.090 g·cm^-2·a^-1 at present. The contents of organic matter in sediment ranged in 36.8~100.7 g·kg^-1. The contents of the south reservoir were slightly higher than those of the north in space, and the vertical distribution of OM in sediment of Guanting Reservoir decreased with depth. However, the sedimentation fluxes of OM showed increased at first and then decreased, similar to the annual variation trend of the MAR. The contents of TOC, TN and TS in sediments were 1.18%~7.83%, 0.04%~0.73% and 0.07%~0.50%, respectively. Both sedimentation fluxes of TOC and TN underwent a process of increasing and then decreasing, but the changing range of TOC was slightly larger than TN, while the TS sedimentation flux gradually reduced with time. The results revealed that the distribution of C, N, and S in sediment of Guangting Reservoir was consecutive, and MAR was one of the most important factors dominating the flux, which indicated that the sedimentation process of particles in Guangting Reservoir probably played a key role in the geochemical cycles of these major elements.