Spatial and Temporal Distribution of Trace Metals (Cd, Cu, Ni, Pb, and Zn) in Coastal Waters off the West Coast of Taiwan

Surface water samples were collected along the west coast of Taiwan during two expedition cruises which represent periods of different regional climatic patterns. Information on hydrochemical parameters such as salinity, nutrients, suspended particulate matter (SPM), and Chlorophyll a concentrations were obtained, and dissolved and particulate trace metal (Cd, Cu, Ni, Pb, and Zn) concentrations were determined. Spatial variations were observed and the differences were attributed to (1) influence of varying extents of terrestrial inputs from the mountainous rivers of Taiwan to the coast, and (2) urbanization and industrialization in different parts of the island. Geochemical processes such as desorption (Cd) and adsorption to sinking particles (Pb) also contributed to the variability of trace metal distributions in coastal waters. Results showed temporal variations in chemical characteristics in coastal waters as a consequence of prevailing monsoons. During the wet season when river discharges were higher, the transport of particulate metals was elevated due to increased sediment loads. During the dry season, lower river discharges resulted in a lesser extent of estuarine dilution effect for chemicals of anthropogenic sources, indicated by higher dissolved concentrations present in coastal waters associated with slightly higher salinity.