Stable Carbon and Nitrogen Isotope Ratios of Sediment in Ban Don Bay: Evidence for Understanding Sources of Organic Matters in the Coastal Environment

Abstract

Sedimental cores from Ban Don Bay and adjacent areas were collected by gravity core samplerfor examination of δ ¹³C, δ ¹⁵N, organic carbon and nitrogen contents. The δ¹³C of surface (0-1 cm) sediments from the whole sampling area ranged between –28‰ and -20‰. The δ¹⁵N values of sediments near the river mouth were somewhat higher than those in the outer part of the bay. Sediments with high organic carbon content occurred in the river and the most outer part of the bay. Organic nitrogen contents in the sediment showed almost same pattern as those of organic carbon contents. The atomic ratios of carbon to nitrogen were high in the river and river mouth. These ratios decreased with the increase in distance from the river mouth. Overall, our results clearly demonstrated most of the terrestrial organic matters discharged from the river into the Ban Don Bay had been deposited onto the bottom sediment inside the bay, they had not been expanded cover to the Angthong Islands.