ASSESSMENT OF POTENTIAL NUTRIENT RELEASE FROM DREDGING ACTIVITIES

摘要

Concerns about management of dredged material and its environmental effect on water quality are constantly increasing in Thailand. One of the major concerns is the release of nutrients from dredged spoils and the consequent effects of eutrophication. There are two major modes of potential nutrient release from dredging activities. The first results from release of pore water nutrients when dredge spoil is deposited in the bay as a disposal option and the other is the direct flux of nutrients from deep sediments that are exposed when dredge material is removed. The nutrient release was determined by collecting sediment cores from the mouth of the Tachin River (Thailand) and analyzing for nutrient concentrations in pore water to estimate the maximum nutrient release during disposal. A flux experiment was also conducted with deep sediment core sections (simulating exposed sediment) to examine changes in nutrient release over a 24-hour period. The results show an extremely high initial flux of ammonium, which decreased rapidly to ambient surface sediment flux rates. Despite high phosphate concentrations in the pore water, the high rate of sediment oxidation of iron sul-fide minerals resulted in a minimal release of phosphate.