水利工程对南四湖现代沉积速率的影响

利用放射性同位素(137Cs、210Pb)测年法计算山东省南四湖的沉积速率,采用高纯锗γ谱仪(美国EG&G ORTEC公司)对南四湖上级湖、下级湖的沉积岩柱(DS2和WS2)样品进行137Cs、210Pb放射性活度测试,分析水利工程建设对湖泊沉积影响的程度与后果. 结果表明:上级湖、下级湖137Cs总蓄积量之比为9.7,说明在二级坝水利工程影响下,流域内侵蚀泥沙及其所吸附的137Cs主要沉积于上级湖；137Cs在湖泊沉积物中的剖面分布与137Cs大气沉降时序的分布模式相背离,故137Cs蓄积峰不具备时标意义. 利用210Pb计年的CRS(恒定补给速率)模式分析2个沉积岩柱不同质量深度所对应的年代,结果显示,150多年来南四湖上级湖、下级湖的沉积速率不稳定,以1960年为界划分为两大时段:沉积岩柱底部所对应的年代至1960年,上级湖、下级湖沉积速率平均值分别为0.069、0.160 g/(cm2·a)；1960—2010年,二者沉积速率平均值分别为0.218、0.072 g/(cm2·a). 可见,二级坝水利工程对南四湖沉积速率产生了重要影响,210Pb计年的CRS模式分析结果可靠. 

Effects of Hydraulic Engineering Applications on Recent Sedimentation Rates in Nansi Lake

Fallout radionuclides 137Cs and 210Pb tracer techniques were used to measure recent sedimentation rates in Nansi Lake, Shandong Province. The effects of hydraulic engineering applications on the lake sedimentation patterns were analyzed to provide more information to guide sustainable development of Nansi Lake. The 137Cs and 210Pb dating of two sedimentation cores (DS2 and WS2), picked respectively from the Higher Lake and the Lower Lake of Nansi Lake, indicated that the ratio of accumulation of 137Cs between DS2 and WS2 was about 9.7. Affected by Grade Ⅱ dam application, 137Cs inventory and erosion losses of DS2 were much greater than that those of WS2. Vertical profiles of 137Cs in the lake sediment were different, with patterned distribution based on atmospheric deposition sequences. Besides 137Cs natural decay, post-depositional redistribution and water turbulence, the main possible reason was the catchment derived 137Cs input. The peak of 137Cs accumulation had no significance on time mark. The times based on sample mass-depth of the two cores calculated by 210Pb constant rate of supply (CRS) model indicated that the sedimentation rates of the Higher Lake and the Lower Lake were not stable over the past 150 years. Using the completion of the Grade Ⅱ dam (1960) as a time marker, it was estimated that the mean sedimentation rates for the Higher Lake and the Lower Lake were 0.069 and 0.160 g/(cm2·a) before 1960, and 0.218 and 0.072 g/(cm2·a) from 1960 to 2010, respectively. The results showed that the application of the Grade Ⅱ dam significantly affected the sedimentation rates in Nansi Lake. The dates derived from 210Pb CRS model were reliable. Further study should focus on the pollutant and nutrient transformation processes using 210Pb CRS technique.