摘要
本文是137Cs质量平衡法测算青海湖现代沉积速率的尝试.青海湖和其他低沉积速率湖泊沉积物剖面中,深度数cm处的137Cs蓄积峰,也可能是沉降到底泥表面的137Cs尘埃,以扩散和迁移的方式向下入渗形成.因此,将沉积剖面中的137Cs蓄积峰解释为1963年的沉积,并据此计算沉积速率,未必合理.青海湖湖滨草地测得的2005年137Cs本底值为117.7mBq/cm2.湖泊中部海心山到东南部渔场一线的6个孔的137Cs面积活度介于92.9-325.0mBq/cm2,其中青海湖东南部两个孔的137Cs面积活度较高,分别为本底值的155%和270%;湖泊中部4个孔的137Cs面积活度略高于或低于本底值.显然,湖泊东南部有明显沉积发生,特别是位于江西沟冲积扇前缘水下部分的QHH02孔,沉积强烈,水深也最小;湖泊中部沉积轻微.根据表层底泥样品的137Cs浓度,入湖河流泥沙的137Cs浓度和流域内草地表层土壤137Cs浓度的分析,初步确定C=30mBq/g,为1963年以来青海湖沉积泥沙的平均137Cs浓度.利用137Cs质量平衡模型求得的湖泊中部的平均沉积速率为0.020cm/a,和根据布哈河输沙模数求算出的青海湖平均沉积速率0.018cm/a吻合,远低于已报导的断代法测定的青海湖沉积速率.湖泊东南部的沉积速率大于湖泊中部,QHH02孔的沉积速率高达0.229cm/a,是已报导的青海湖沉积速率的两倍.
This paper was an attempt to use the 137Cs mass balance model for assessment of recent deposition rates in Lake Qinghai. 137Cs concentration peak at the depth of a few centimeters in the deposit profiles of Lake Qinghai and other lakes with lower deposition rates may be caused by the nuclide downward diffusion and migration progresses after the 137Cs deposited on the surface of lake bottom mud. Therefore, the interpretation of the sediment layer at the 137Cs peak depth depositing in 1963 and the calculation method of sediment deposition rates under that assumption may not be reasonable. Local 137Cs reference inventory was 117.7mBq/cm2 in 2005 obtained from grass land of the flat lakeside. 137Cs inventories of the six lake sediment cores collected from the Island Hill of the center of Lake Qinghai to the Fish Port in the south-eastern lake ranged from 92.9mBq/cm2 to 325.0mBq/cm2. It was clear that sediment deposition apparently occurred in the south-western part of the lake, particularly, the deposition is quite fast at the QHH02 Core position, which is located in the front of the underwater alluvial fan. However, sediment deposition was very slow at the centre part of the lake. The average 137Cs concentration of the deposited sediments in Lake Qinghai since 1963 was estimated to be 30rnBq/g by analyses of the 137Cs concentrations from the lake mud in surface layers, the sediment discharged from inlet rivers,and the soil in surface layers on the grass land in the catchment. The average deposition rate in the centre of the lake was 0.020cm/a calculated by the 137Cs mass balance model, which agreed to 0.018cm/a of the specific sediment yield of the Buha River, but much lower than the reported deposition rates estimated by conventional dating techniques. The deposition rate of the QHH02 Core was 0.229cm/a, suggesting that the deposition rates in the south-western part of the lake were much higher than the rates in the centre part of the lake and which was twice of the reported deposition rate of Lake Qinghai.
出处
《湖泊科学》
EI
CAS
CSCD
北大核心
2009年第6期827-833,共7页
Journal of Lake Sciences
基金
国家自然科学基金项目(40599420
40971169)资助
