EFFECTS OF INNER-CIRCULATION POND AQUACULTURE ON DISTRIBUTION AND RELEASE FLUX OF PHOSPHORUS IN THE OVERLAYING-SEDIMENT-INTERSTITIAL WATER

To reveal the spatial and temporal distribution characteristics of different phosphorus forms in the overlying-sediment-interstitial water, the release flux of phosphorus at sediment-water interface as well as relevant main influence factors from the Inner-circulation Pond Aquaculture (IPA), 4 IPA tanks were sampled to measure the composition of phosphorus forms in sediment by the Standards Measurements and Testing Program of the European commission (SMT method). Each IPA tank has 6 sampling points at the front and rear ends, and the Usual Pond Aquaculture (UPA) has 5 sampling points. The results showed that: (1) different forms of phosphorus content from overlying and interstitial water of IPA were lower than those of UPA, and the spatial distribution of phosphorus in IPA water body was quite different. The P at the front of water tank diffused from the sediment to overlaying water, while the P at the rear end of water tank collected from overlaying water into sediment. (2) In the middle and later stage of aquaculture, different phosphorus forms in the sediment at the back of IPA tank gradually decreased with the increase of distance, which were lower than those in the UPA. TP, IP, OP and Fe/AL-P increased significantly with the proceeding of agriculture under both modes, while Ca-P showed a trend of first decreasing and then increasing. (3) In the UPA mode, phosphorus was basically absorbed by the sediment, while in the IPA mode, phosphorus release flux varied greatly with time and space. In the early stage of aquaculture, phosphorus was absorbed at the front end of water tank, and a small amount of phosphorus was released within 10 m from the back end of water tank. In the middle or late stages of aquaculture, a large amount of phosphorus were released from sediment within 10 m from the back end of water tank. At 20 m and 30 m from the rear end, the initial phosphorus flux was small, and phosphorus was absorbed in the middle stage of agriculture, and phosphorus was released at the end of aquaculture. (4) The relationship between phosphorus flux and environmental factors was generally consistent in both models. There was a significant positive correlation between TP/IP release flux and pH, while there was a significant negative correlation between release flux for forms of phosphorus and sediment Eh. The increase of T significantly promoted the release of various inorganic forms of phosphorus. IPA sediment was significantly different in time and space. Sediments were mainly distributed within 10 m from the rear end of water tank, and a large amount of P was released upward into the overlying water in the middle or late stage of aquaculture. This study provides a theoretical support for improving solid particle interception method, promoting efficiency for collection of residual bait and feces, and regulating aquaculture water environment under IPA mode.