1985-2016年南漪湖湖泊面积变化对沉积速率及泥沙输移通量的影响

Impact of lake areas on sediment accumulation rates and transport fluxes in Nanyi Lake during the period of 1985-2016

通过测试南漪湖2008年、2014年和2015年沉积物柱芯中的环境放射性核素^(210)Pb_(ex)和^(137)Cs,辅以相互印证的^(210)Pb CRS计年模式和^(137)Cs定年时标方法,定量估算了南漪湖过去百余年间的沉积速率变化;基于遥感目视解译方法获得了南漪湖1985—2016年湖泊面积时空变化,结合构建的湖泊泥沙输移模型,定量估算了南漪湖出湖河流的年均泥沙输移量;基于此,进一步分析了湖泊沉积速率和泥沙输移通量与湖泊面积变化之间的相关关系。结果表明:南漪湖同一湖区不同年份沉积物柱芯剖面中^(210)Pb_(ex)和^(137)Cs比活度分布特征相近,^(210)Pb_(ex)比活度遵循随深度增加而减小的趋势,^(137)Cs则在24和16 cm左右分别记录了1954年首次沉降和1963年最大沉降蓄积峰值;南漪湖沉积速率整体呈现波动变化趋势,在20世纪50年代前后沉积速率出现极大值,随后至采样年份该沉积速率呈缓慢上升趋势,这种变化可能与不同历史时期的自然因素和人类活动密切相关;过去31年间,南漪湖湖泊面积整体上呈缩小趋势,减少了57.37 km^(2),主要集中于西北、东北和东南部等区域,湖泊周边过度围垦是影响湖泊面积变化的主导性因素;南漪湖出湖河流的年均泥沙输移量约为1904.60 t/a,湖泊沉积速率和泥沙输移通量受湖泊面积变化影响较大,随着湖泊面积的增加,湖泊沉积速率和泥沙输移通量分别呈指数降低和线性增加的趋势。

By testing the environmental radionuclides^(210)Pb_(ex)and^(137)Cs in the sediment cores of Nanyi Lake in 2008,2014 and 2015 supplemented by the mutually confirmed^(210)Pb CRS dating model and^(137)Cs dating time scale method,the sediment accumulation rates(SARs)over the past 100 years were quantitatively estimated.According to remote sensing visual interpretation method,the spatial and temporal variation of lake areas in Nanyi Lake during the period of 1985-2016 were obtained.Combined with the constructed lake sediment transport model,the annual amount of sediment transport fluxes(STFs)via the outflow river of Nanyi Lake was quantitatively estimated.Based on this,the correlation between lake SARs,STFs and lake area change was further analyzed.The results indicated that the distribution characteristics of^(210)Pb_(ex)and^(137)Cs in the sediment core section of the same lake area in different years were similar,and the distribution of^(210)Pb_(ex)showed the trend of decreasing with increasing depth,while^(137)Cs recorded the first sedimentation in 1954 and the maximum peak of sedimentation accumulation in 1963 at the depths of 24 and 16 cm,respectively.SARs of Nanyi Lake showed a fluctuating trend as a whole.High SARs appeared around the 1950s and a slow rising trend was observed since then,which maybe closely related to the dual impacts of natural and anthropogenic influences in different historical periods.Overall,a shrinking trend was found and the area decreased by 57.37 km^(2)over the past 31 years.Spatially,the declined areas were focused on the northwest,northeast and southeast regions of the lake.The excessive reclamation around the lake was the dominant factor influencing the declined lake areas over the past decades.The annual amount of STFs of Nanyi Lake was about 1904.60 t/a.Both of SARs and STFs were greatly affected by the lake areas,and SARs showed an exponential increase trend but a linear decrease for STFs along with the expanding of lake areas.