DISTRIBUTION AND ACCUMULATION OF ARSENIC, CADMIUM AND MERCURY IN COASTAL WETLAND SEDIMENT OF NORTHERN BEIBU GULF

The spatial distribution, accumulation mechanism and controlling factors of Arsenic, Cadmium and Mercury in the last hundred years were studied based on the chemical and ²¹⁰Pb, ¹³⁷Cs dating data from the surface and coring sediments retrieved from the coastal wetland of north Beibu Gulf within a water depth of 0~6 m. The surface sediment is dominated by sand. The grain size of the sediment in the eastern part is coarser than that in the western part to the Dafeng river estuary. The contents of As, Cd, Hg and organic matter in the surface sediment are 8.11±5.80 μg/g、0.08±0.11 μg/g、0.034±0.028 μg/g and (0.73±0.74)%, respectively. High anomalies are found in the top part of the Tieshangang bay, the east estuary of the Nanliu river, the Qinzhou bay and the middle part of the Dafeng river estuary. Grain size is the principle factor controlling the elements distribution pattern in the surface sediment. The average sedimentation rates are 0.93 cm/a, 1.75 cm/a and 1.35 cm/a for the three cores collected from the Qin river estuary, Nanzhou (Nanliu) river estuary and Shankou mangrove conservation area during the period from 1920s to 2008, determined by ²¹⁰Pb and ¹³⁷Cs dating. The contents of As, Cd and Hg show an increasing trend in the period from 1985s to 2008, particularly for the cores retrieved from the estuaries of Qin river and Nanliu river due to the impacts of human activities.