Trace Elements in Suspended Particulate Matter and Sediments of the Cai River: Nha Trang Bay Estuarine System (South China Sea)

The distribution of particulate form of organic carbon (POC), Al, Fe, Ti, Li, Zn, Pb, U, Sc, Sn, Bi, Zr, Ba, As, Sr, W, V, Co, Cu, Ni, Mo, Cr, Mn, Ba, Sn, Sb, Hg, and Ag in the Cai river and Nha Trang Bay generally followed the distribution of total suspended matter (SPM) and was characterized by the most significant loss in the frontal zone of the estuary with highest horizontal gradients within the salinity interval of 8-20?. The most part of these elements are supplied to the estuary with the Cai river discharge. Sedimentary Al, Fe, Ti, Li, Sc, Co, Cs, Zr, Cr, Zn, Co, Ni, Cu, Pb, Sn, and V are most likely controlled by the accumulation of their most fine-grained host minerals in sea floor depression of the bay. Sedimentary Bi, W, As, U, and Mo are mainly deposited with the coarse river material near the river mouth. The distribution of Ca, Sr, Mn, and Ba is largely controlled by the total inorganic carbon (TIC) content in the sediments. Metal form study revealed the highest percent contents of the labile forms for Mn, Co, and Pb in the sediments. The high levels of weak acid-soluble Pb and Co (30% and 43% of the total content in sediment, on average, respectively) contributes to a contamination problem in the Nha Trang Bay which arises from the Cai River discharge.