Environmental quality of coastal waters in Southern Central and East South Vietnam - occurrence of red tide phenomena

The coastal waters in Southern Central and East South Vietnam are in eutrophicated status. Nitrate and COD were the main factors that determine the eutrophication. Organic substance budget is high. Among the heavy metals zinc usually has the concentrations higher than critical value described in Vietnamese Fishery Water Standard (1995). HAB were sometimes recorded. It usually prevails in hot dry season when the high water temperature and weak dynamic regime can accelerate the mineralization of organic matter and stimulate excystment of dinoflagellate cysts. High concentration of zinc may also contribute to the occurrence of HAB. However, up to now the knowledge on the relation between water quality and red tide phenomenon is not enough and there is no effective approach for the prediction of this phenomenon established. Therefore, comprehensive studies are necessary for the waters that are potentially threaten by HAB in order to prevent this phenomenon and/or to minimize its consequences.