洪水事件对长江中下游地区湖泊沉积的影响——以网湖为例

Impact of Flood Events on Lake Sediments in the Middle and Lower Reaches of the Yangtze River: A Case Study on Wanghu Lake

通过对长江中游网湖沉积物中粒度组成、磁性参数、营养盐含量以及花粉组合的分析,结合湖区的历史文献资料,研究了网湖洪水高频时期(20世纪30年代、40年代末至50年代中以及90年代)湖泊沉积物中各类指标的变化特征.结果发现:洪水时期湖泊沉积物粒度相对较粗,且分选性较差;磁化率与频率磁化率有所增加;营养盐中TOC和TN含量增加,TP含量减少;花粉组合中孢粉浓度增加、种类增多.结果表明:洪水通过改变湖泊沉积物的物源,使更多的陆源物质进入湖泊,从而影响湖泊的沉积.

The indices of the core sediments of Wanghu lake, such as grain-size, magnetic parameters, total organic carbon（TOC）, total nitrogen（TN）, total phosphorus（TP） and pollens are sampled and tested. The features of sediment vertical distribution are compared with that shown in the frequently-occurred flooding periods（1930s, from end 1940 s to middle 1950 s, and 1990s） at the lake surrounding areas, which are collected from the local historical documents. The results show that the average grain-size of the sediments has been growing larger and the coefficient of sorting is adversely varying; both the magnetic susceptibility and frequency magnetic susceptibility are showing relatively high values; TOC and TN concentrations have increased substantially, and lower value of TP concentrations is observed; the pollen concentration and pollen types have been on the rise. Based on these results, it can be found that the environment indices of Wanghu lake are very sensitive to the catchment-related floods, and more land materials washing into the lakes exert influence on the lake sediment and environmental evolution.