IMPACTS OF MARINE RANCHING CONSTRUCTION ON SEDIMENT PORE WATER CHARACTERISTIC AND NUTRIENT FLUX ACROSS THE SEDIMENT–WATER INTERFACE IN A SUBTROPICAL MARINE RANCHING (ZHELIN BAY, CHINA)

Marine ranching is an effective way to restore depleted stocks and increase fisheries production. The effects of marine ranching construction on sediment pore water characteristics and nutrient flux across the sediment–water interface were determined by incubation experiments. Nine stations were selected along an inshore to offshore gradient of different sediment types representing different zones used for marine ranching in Zhelin Bay, China. The results showed that nutrient concentrations of overlying water and pore water varied by zone and were influenced by biological and physical characteristics. In the macroalgae zone (MA), macroalgae was cultured from September to May Decayed macroalgae in this zone during winter lead to pH variation (ranged from 8.05 to 8.16) and highest nitrite (range from 0.1719 to 0.9210 umol m -2 D -1 ), ammonia (range from 1.778 to 4.448 umol m -2 D -1 ) and total nitrogen (range from 23.43 to 140.6 umol m -2 D -1 ). In the benthic molluscs’ area, shellfish activities led to higher ammonia (range from 0.3312 to 7.725 umol L -1 ) and total nitrogen (range from 59.67 to 447.7 umol L -1 ) concentration in the overlying water during the summer season. In the artificial reef zone (depth 15-20 m), the deployment of artificial reef materials altered the sea floor which resulted in upwelling and a consequent increase in the flux of total phosphate. The results of this study will be useful to improve marine ranching efforts in China and worldwide.