长江口崇明东滩不同植被带沉积速率研究

The determination of sedimentation rates in various vegetational zones of Chongming tidal flat of the Changjiang Estuary

利用2007年丰水期、枯水期在崇明东滩芦苇带、藨草带和光滩采集的6根沉积物柱状样,研究了沉积物的粒度特征和过剩的210Pb和228 Th及7Be活度的垂向分布特征,探讨了由陆地向海洋不同植被间的沉积物粒度变化规律。依据恒定比活度沉积速率模型,估算了不同时间尺度的崇明东滩芦苇带、藨草带和光滩的表观沉积速率。结果表明:3种核素示踪的崇明东滩的表观沉积速率都随潮滩植被的不同从陆到海方向逐渐降低,同时依过剩的210Pb和228 Th,7Be的次序而增大。由过剩的210Pb和228 Th计算的夏季沉积速率比冬季的稍高,而由7 Be计算的夏季表观沉积速率则明显高于冬季的。结合沉积物粒度的时空分布和这些核素的大气通量,对利用这些核素测定潮滩沉积速率的影响因素进行了探讨。

Six sediment cores,collected from Chongming tidal flat of the Changjiang Estuary in flood and dry seasons of 2007,were used to measure the sedimentation rates by the depth profiles of radionuclide excess 210Pb,and 228Th,and 7Be.Based on the constant activity model（CA）,various sedimentation rates on different time scales were evaluated by excess 210Pb and 228Th,,and 7Be.The results show that the sedimentation rates by excess 210Pb and 228Th,and 7Be were decreased from phragmites australis to bare flat zone.More,all the sedimentation rates were decrease from short-time to long-time scale,reflecting the tidal flat being rebuilt by hydrological dynamics.Combined with the distribution patterns of particle size of sediment on temporal and spatial scales and atmospheric deposition flux of these nuclides,the impact factors on sedimentation rate were discussed in details.