Some physioco-chemical composition of bottom sediments in the gulf of Thailand

Study of physico-chemical compositions of bottom sediment in the Gulf of Thailand was carried out with the collaboration of the "M.V. SEAFDED" cruise No. 32-4/1996, during 23 April - 23 May 1996, by gathering data from 51 stations; 17 near shore stations (4 stations in the east coast and 13 stations in the west coast) and 34 stations in the deeper part of the gulf. Results of this study indicated that total organic matter in the near shore area were higher than those in the deeper part of the gulf. Average organic matter contents of bottom sediment in near shore area was 8.19 percent comparing to 7.32 percent in the deeper part of the gulf. Sulfide concentrations in the sediment in the deeper part of the gulf were very low (less than 0.001 mg/g sediment dry weight) and gradually increased when coming closer to the coast. It was also found that near shore sediments were low in calcium carbonate content with an average value of 13.19 percent while higher average content of 15.22 percent was found in the deeper part of the gulf. The average water contents in both areas were quite similar, 44.15 percent in near shore and 44.19 percent in the deeper part of the gulf. Correlation was found between organic matter content and quantity of silt and clay particles of the sediment as well as between water content and quantity of silt and clay particles. Relationship between water content and the oranic matter content of the sediment was well described by linear regression which had correlation coefficient (r) of 0.76. It is interesting that the western area of the Gulf of Thailand, especially near the Samui lsland, was the area that had the highest quantities of total organic matter (approximately 10-15 percent), acid volatile sulfide (0.256 mg/g dry weight) and water content of sediment (80 percent), but sediment in this area had the lowest quantity of calcium carbonate (5 percent). According to the results of this study the areas around the Samui Island should be intensively investigated. Measures and means should be developed for prevention and control of problems generated from high organic matter and high sulfide content in the sediment which may have some effects on benthic fauna.