Evaluation of the oceanographical conditions and environmental capacity for mariculture development in coastal waters of Khanh Hoa province

Abstract

This paper focused on introducing the research results of some principal characteristics for planning of mariculture development such as the space for construction of mariculture projects, characteristics of climate, meteorology, hydrology, dynamics, environmental quality and carrying capacity of the coastal waters. The optimum area for intensive mariculture development is 9,460 ha, located between the depths of 6-20-25 m with the bottom which is a thick sandy mud - muddy sand ground. At present, the exploited area for mariculture is only about 780 ha, covering 8.2% of the optimum area, less than 0.5% of total area suitable for mariculture. The wind velocity in the coastal zone often ranges between 0.6 – 9.0 m/s. The wave height often ranges between 0.3-0.9m, within the present safety limit for construction of mariculture projects. The maximum current velocity reaches to 29-52cm/s, usually the current velocity is below 10cm/s, satisfying the limit of dynamics for mariculture development. The water exchange time in the coastal bays ranges between 6-12 days. The environment quality in the coastal waters of Khanh Hoa province has shown signs of local pollution, especially, pollution of sedimental environment in the developed mariculture, condensed residential and developed industrial areas. The average toxic index of the water environment ranges between 0 - 49.2%, the maximum value reaches to 54.5% and in the sedimental environment, the average value ranges between 21.9 – 67.5%, and the maximum value reaches to 97.0%. The total carrying capacity of the coastal waters ranges between 3.13-12.71 tons nitrogen/day. The organic assimilative capacity is 0.01– 0.42 tons BOD/day. Nowadays, the carrying pressure of the coastal areas of Khanh Hoa province has reached to 35-55% of the carrying limit of the waters, although mariculture is not developed yet. Therefore the farming methods and the policies for management of development must be changed.