Sea Water Quality Changes in a Water Multi-utilization Pattern System

Water multi-utilization pattern system is of great significance for seawater utilization and the reduction of waste seawater discharge of aquaculture. However, the change analysis of seawater quality in the water multi-utilization pattern system is little reported. The water multi-utilization pattern system of Cynoglossus semilaevis-Penaeus vannamei-Artemia-ocean chemical industry was employed to determine the changes of seawater quality. Results showed that with seawater utilized continuously, pH, inorganic N and P, organic N, total N and COD concentrations were all increased significantly(p0.05),which indicated that aqua-cultivation can lowering seawater quality significantly. Compared with continuous increase of organic N, total N and COD concentrations, inorganic N and P concentrations of seawater changed in the wave-shaped patterns,showing significantly higher than those of un-utilized seawater(p0.01). Wave-shaped patterns probably resulted from the organic N and P utilization by living beings in seawater. With seawater salinity increasing, the increase of organic N, total N and COD concentrations boosted greatly, which suggested that self-cleaning capacity of seawater was inhibited obviously.Compared with un-utilized seawater, organic N, total N and COD concentrations of seawater in Artemia cultivating pond increased by 6.27, 6.15 and 3.90 times respectively. Based on change rules of seawater, the seawater quality demands of components in water multi-utilization pattern systems should decrease in turn. At the same time, high efficient cultivating and cleaning technologies are also needed to improve seawater quality.