| Studies have found that there is a close relationship between the occurrence of sea cucumber diseases and the acutely changes in environmental conditions, such as temperature, salinity and pH. So it is particularly important to study the changing rules of water quality, the internal structure, the accumulation and emissions of various nutrients in farming systems, which can maintain a good breeding environment for the aquaculture industry to reduce environmental impact of the offshore aquaculture. Nitrogen (N) and phosphorus (P) are important elements in aquatic ecology, whose conversion efficiency and deposit status in system are often used to evaluate aquaculture techniques, pattern and state of pollution within system.Coastal sediments are important accumulation storage vault of biogenic elements such as nitrogen and phosphorus. It can purify but release nutrients to the overlying water as a nutritional source at the same time, which can play an important role in eutrophication. Nutrients pollution of water bodies can be divided into exogenous and endogenous pollution. It is confirmed that there is a direct relevance between the distribution and forms of nitrogen and phosphorus and the endogenous pollution. The water may remain in the eutrophic water body status because the endogenous nitrogen and phosphorus in the sediments can still be exchanged between the pore and overlying water on the physical, chemical and biological methods after the exogenous nutrients source are under control. Therefore, it is very necessary to study budgets, distribution, dynamic and conversion efficiencies of N and P in aquaculture system.These studies were designed and conducted to investigate hydrochemistry, vertical distribution of N, P in sediments and budgets of N and P in systems of sea cucumber culture ponds with land-based experimental enclosures. The chief results were as followings:1. Preliminary studies of water quality in the feeding and unfed sea cucumber culture ponds The experiment which lasted about 6-month studied the impact of the feeding and water changing to the water quality in the feed and unfed sea cucumber ponds.The result showed that between the two category ponds, the pH value increased slowly and the salinity declined slowly with time elapsed during the whole experiment and both changed significantly in the rainy season; The temperature and the concentrations of NH4+-N,NO3--N,NO2--N,NH3-N and SRP in both ponds had a seasonal fluctuations, which were lower in spring and autumn and the higher in summer; The rank of concentrations of TN and TP were spring >summer >autumn; The water of two ponds are both medium nutrient with limited phosphorous. The effect of feeding to the water quality in both ponds was that the concentrations of the NO2--N in the feeding pond was much higher than the unfed pond (P<0.05). but the other parameters were not significantly different(P>0.05). After changing the water, the fluctuations of pH and salinity in the two ponds tended to be smooth.; the concentrations of TN did not changed significantly (P>0.05)but the concentrations of TP declined significantly(P<0.05) and the concentrations of NH4+-N,COD,NH3-N increased significantly(P<0.05); After changing the water, it appeared different about NO3--N and NO2--N between the two ponds and the concentrations of the unfed pond declined significantly(P<0.05) but the feeding pond increased significantly.(P<0.05). The effect of water changing may be concerned about the sediments of the ponds and the feeds.2. An Experimental Study on Effect of Feeding and Density to Nitrogen and Phosphorus Budgets in Sea Cucumber PondsThe experiment was carried out with land-based experimental enclosures set in one pond, in which sea cucumber were stocked at five different densities, 5 ind/m2(A), 10 ind/m2 (B), 15 ind/m2(C), 25 ind/m2(D), 35 ind/m2 (E). There are two patterns: feeding and unfed.The results showed that water exchanged accounted for 89.62%～90.21% N and 66.42%～84.54%N of the total inputs while 54.7%～64.8%P and 81.6%～88.7% P in feeding and unfed groups systems; and 87.72%～107.10% N and 63.19%～83.14%N of the total outputs while 46.88%～57.33%P and 22.96%～43.28% P in feeding and unfed groups systems; that feeding accounted for 6.24%～25.66% N and 25.93%～64.09%P of the total inputs in feeding groups systems. The output of N and P in the sediments, which accounted for -24.80%～5.84% N and 7.20%～23.28% N and 8.78%～20.49%P and 28.72%～56.39%P in systems. N and P deposited in the sediments of feeding systems were higher than those in unfed systems.3. An Experimental Study on Effect of different reefs to Nitrogen and Phosphorus Budgets in Sea Cucumber PondsThe experiment was carried out with land-based experimental enclosures set in one pond at the same density :5 ind/m2, in which sea cucumber were stocked at five different reefs, ST(A), EA (B), PL(C), BR (D), CP (E).The results showed that water exchanged accounted for 90.7% N and 91.1%P of the total inputs while 64.3%～76.9%N and 50.2% P of the total outputs in systems; The proportion of N deposited in the sediments to outputs of total N from high to low was C(22.1%)>B(17.3%)>D(11.8%)>E(10.3%)>A(6.1%) while the proportion of P was A(22.3%)>B(19.9%)>D(17.6%)>E(17.1%)>C(14.5%).the N and P outputs of Cladophora oligoclona was 2.2%-3.3% and 16.3%-19.0%.4. An Experimental Study in polyculture of sea cucumber with shrimp to Nitrogen and Phosphorus BudgetsThe experiment was carried out with land-based experimental enclosures set in one pond at the different density :A(5 ind/m2),B(10 ind/m2)in which shrimp were stocked at four different density : 0 ind/m2, 2 ind/m2, 4 ind/m2, 8 ind/m2。The results showed that the sea cucumber harvest groups accounted for 0.26%-0.34% N and 0.43%-0.58%P of the total outputs in the A groups while 0.30%～0.35%N and 0.35%-0.85% P of the total outputs in the B groups. The shrimp harvest accounted for 0.87%-0.93% N and 1.34%-1.52%P of the total outputs in the A groups while 0.88%～0.96%N and 1.57%-1.60% P of the total outputs in the B groupsThe proportion of N deposited in the sediments was 1.85%-2.05% while the proportion of P was 12.49%-12.66% in the A groups. The proportion of N deposited in the sediments was 4.52%-5.08% while the proportion of P was 10.05%-15.08% in the A groups5. An Experimental Study on impact of different reefs to the vertical distribution of N and P forms in the sediments of sea cucumber ponds.The experiment was carried out with land-based experimental enclosures set in one pond at the same density :5 ind/m2, in which sea cucumber were stocked at five different reefs, ST(A), EA (B), PL(C), BR (D), CP (E).The result showed that the concentration of TN in the sediments was low. The changing range of TN in the sediments was 430-1260 mg kg-1, and the average concentration was 711 mg kg-1, which the rank of concentration was the surface> the middle> the bottom. The average concentration of TN in the different reefs were D>C>E>B>A; The proportion of NH4-N and NO3-N were 3.97% and 1.08%. The concentration of TN forms changed regularly as seasons; the concentration of TN in the sediments was low. The changing range of TP in the sediments was 366.6-1228.1 mg kg-1, and the average concentration was 825.3 mg kg-1, which the rank of concentration was the surface< the middleB>C>D>E. The proportion of L-P,Fe-P Ca-P,D-P and O-P were 2.81%,37.56%,4.04%,10.12% and 61.60%. The concentration of TN forms changed complex as seasons, which show different rules.6. An Experimental Study on the vertical distribution of N and P forms in the sediments of Tri-polyculture of sea cucumber and shrimp.The experiment was carried out with land-based experimental enclosures set in one pond at the different density: A(5 ind/m2),B(10 ind/m2)in which shrimp were stocked at four different density: 0 ind/m2, 2 ind/m2, 4 ind/m2, 8 ind/m2The result showed that the concentration of TN in the sediments was low. The changing range of TN in the sediments was 140-480 mg kg-1, and the average concentration was 282.4 mg kg-1. The changing range of TP in the sediments was 858.1-3369.5 mg kg-1, and the average concentration was 1551.7 mg kg-1, The proportion of L-P,Fe-P Ca-P,D-P and O-P were 3.0%,22.8%,3.9%,3.0% and 71.1%. The concentration of TN forms changed complex as seasons, which show different rules.
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