长江中下游湖泊沉积速率的测定及环境意义——以洪湖、巢湖、太湖为例

SEDIMENTATION RATES IN HONGHU, CHAOHU AND TAIHU LAKES IN THE MIDDLE AND LOWER REACHES OF THE YANGTZE RIVER

对长江中下游洪湖、巢湖和太湖沉积物采用^210Pb和^137Cs相结合的方法测定沉积速率。洪湖钻孔中^210Pb、随深度的增加没有呈现指数衰减分布，因此获得的平均沉积速率并不可靠；而根据^137Cs蓄积峰计算得出洪湖钻孔在1963-1986年沉积速率最大，这可能是因为当时大规模开垦导致湖区周围水土流失，大量的侵蚀物质被带入湖中，从而导致沉积速率上升。对巢湖钻孔用^210Pb法和^137Cs得到的沉积速率具有可比性，研究发现20世纪70年代以来随着深度的减少，巢湖钻孔中沉积通量在增加，说明巢湖流域内水土流失逐步加重，可能与土地开发、植被破坏等人为活动有关。对太湖钻孔利用^137Cs 1963年对应的蓄积峰进行校正，采用^210Pb计年的CRS模式获得不同时段的沉积速率发现在80年代末尾沉积物堆积通量最高，达到0．6g·cm^-2·a^-1。两种计年方法的结合有助于认识沉积速率的变化情况。

Three lakes, i.e. Honghu, Chaohu and Taihu Lakes in the middle and lower reaches of Yangtze River were selected for understanding the change of sedimentation rates. Environmental ^210Pb （natural） and ^137Cs （anthropogenic） dating techniques were used. The relationship between exponential ^210Pb and depth is non-linear in Honghu Lake core. Based on ^137Cs dating markers, the sediment rate from 1963 to 1986 was the greatest, and it decreased from 1986 to 2002, which was attributed to human activities such as the reclaiming. The chronologies calculated by ^210Pb CIC method were consistent with ^137Cs dating markers in Chaohu Lake core. It is concluded that since 1970＇s the flux of deposit increased with the decrease of depth for Chaohu Lake due to the increase of soil erosion. In Taihu Lake core, the average sedimentation rate was 0.34 cm/a calculated by ^137Cs markers, while the value 0.41 cm/a was obtained based on ^210Pb CIC method. The ^210Pb chronologies were corrected using the 1963 ^137Cs marker in Tauihu Lake core. The results show that sedimentation flux rates are very high, reaching to 0.6 g·cm^-2· a^-1 near 1990s in Taihu Lake. The combination of these radionuclide dating methods is useful to understand the sedimentation process of the lakes where sedimentation rates have changed.