GRAIN SIZE VARIATION AND HEAVY METALS DISTRIBUTION DURING LAST HUNDRED YEARS UNDER THE IMPACT OF HUMAN ACTIVITIES IN THE INNER LINGDINGYANG BAY OF THE PEARL RIVER ESTUARY

3 sediment cores were collected in August 2012 at the Lingdingyang Bay of the Pearl River Estuary, the South China. On the basis of heavy metal analysis and ²¹⁰Pb dating, sedimentation rates over the past century are acquired. The distribution pattern and accumulation factors of heavy metals are discussed on the roles of natural and human activities. The results show that the mean grain size changes from 4φ~7.5φ in the 3 sediment cores. Obvious bimodal distribution is observed in the sensitive components in the Shenzhen and Hengmen sea areas, where the coarse component was divided from the fine at 5.25φ, whereas the sensitive components around the Qi'ao Island is not obvious, suggesting a stable sedimentary environment. Modern sedimentation rates are calculated with ²¹⁰Pb dating data by CIC model. It was 1.6 cm/a in the Hengmen sea area, but 4.08 cm/a near the Qi'ao Island. Within 0~70 cm of the depth of the core, the sedimentation rate was 2.58 cm/a in the Shenzhen sea area, and below the depth of 70 cm it was as high as 4.47 cm/a. Heavy metal contents analysis shows that the contents of the Cr, Ni, Cu, Zn and Pb from 1923 to 1986 remained on a high level with little change. A rapid increase occurred in the sea area of Shenzhen from 1967 to 1983 and in the sea area of the Qi'ao Island from 1983 to 2004. From 2003 to 2005 and from 2008 to 2012, the heavy metal content decreased year by year, except for the period from 2005 to 2008 while heavy metals increase. The changes in heavy metal content are closely related with socio-economic development there and the heavy metal flux into the sea area.