Volume 3, Issue 7 (July 2006)
Seawater Quality, Suspended Solids, and Settling Particles in the Wood Pool Area of Shimizu Port, Japan
The transport and contamination of suspended solids in a wood pool were quantitatively studied as a case study for the environmental assessment of an enclosed sea area. To assess the present contamination of Shimizu Port (Japan), seawater, suspended solids, and settling particles were collected from three rivers, the wood pool, and Shimizu Port. Physical and chemical properties of the samples were analyzed. In addition, tidal currents were observed to investigate the transport process of chemical substances by suspended solids. The results showed that the amount of lithogenic particles discharged into Shimizu Port was approximately 12 000 kg/day. Suspended solids discharged from rivers and the biological particles produced in the port caused a reduction in seawater transparency and an increase in chemical oxygen demand. Trace metals, such as Mn, Co, and Pb, were highly concentrated in suspended solids. Tributyltin adsorbed onto settling particles was approximately 300 µg/kg. Concentration factors for Mn, Fe, Cd, and Pb from water and settling particles are comparable to those of plankton. Hydroxides were found in suspended solids from the wood pool, which locates in the inner part of Shimizu Port. The results showed that these suspended particles could accumulate metals from seawater as effectively as biogenic particles. After particle deposition, trace metals are regenerated into seawater under anaerobic conditions. This process plays an important role in the accumulation of chemicals in seawater and sediments, especially in enclosed sea areas.