摘要
Based on studies of the geochemical elements of core sediments collected from the subaqueous Yangtze River delta front, combined with 210Pb and 137Cs nuclide dating, element recording profiles were set up and anthropogenic impacts on the sedimentary records were considered. The results suggest that (1) The core formed since 1945, of homogeneous clay and silt sediments. (2) The content of most elements underwent little change, but the content of S and Nb increased gradually. In particular concentrations of these elements and heavy metals increased rapidly and were maintained at high levels in the surface and sub-surface layers (i.e. since the 1990s). The elements S, As and Nb and principal factor 4 (F4), which were sensitive to anthropogenic impacts, could be used as indicators of human activities. (3) The value of each indicator has increased gradually since 1945, with a sharp increase over the last 20 years. When divided according to changing values of the indicators at 185 cm (1955), 97 cm (1978), 47 cm (1992), and 7 cm (2003), five periods of the geochemical elements records were obtained. These corresponded to the ages of from the Chinese Civil War to the early stages of planned economy, the implementation of planned economy, the reform and opening-up period, the market economy establishment phase and the environment control and protection stage after 2003, respectively.
Based on studies of the geochemical elements of core sediments collected from the subaqueous Yangtze River delta front, com- bined with 210pb and 137Cs nuclide dating, element recording profiles were set up and anthropogenic impacts on the sedimentary records were considered. The results suggest that （1） The core formed since 1945, of homogeneous clay and silt sediments. （2） The content of most elements underwent little change, but the content of S and Nb increased gradually. In particular concentra- tions of these elements and heavy metals increased rapidly and were maintained at high levels in the surface and sub-surface lay- ers （i.e. since the 1990s）. The elements S, As and Nb and principal factor 4 （F4）, which were sensitive to anthropogenic impacts, could be used as indicators of human activities. （3） The value of each indicator has increased gradually since 1945, with a sharp increase over the last 20 years. When divided according to changing values of the indicators at 185 cm （1955）, 97 cm （1978）, 47 cm （1992）, and 7 cm （2003）, five periods of the geochemical elements records were obtained. These corresponded to the ages of from the Chinese Civil War to the early stages of planned economy, the implementation of planned economy, the reform and opening-up period, the market economy establishment phase and the environment control and protection stage after 2003, respec- tively.
基金
supported by the National Natural Science Foundation of China (40976020)
the National Basic Research Program of China (2005CB422304)
