Effects Of Filter-feeding Bivalve On Nutrient Dynamics Of Mariculture System In Shallow Sea

In the bivalves culture system of shallow sea, forms and dynamics of nutrients affect the growth of filter-feeding bivalves, on the other hand, bivalve culture affects the nutrient dynamic. Many foreign researchers had done lots of work on that, but few in China. This paper mainly includes two parts: From Spring to July of 1998, 9 culture systems and 1 control system were established with 10 indoor breeding tanks in a mariculture laboratory of Yantai. Monoculture of scallops Gb] amys farreri, polyculture of scallops and sea kelps Laminaria japonica, polyculture of scallops, sea kelps and sea cucumbers Apostichopus japonicus were conducted under different densities. Concentrations of POC, PN, ammonia, phosphate and silicate were determined regularly, about half a month. The results are as follows. 1. The particulate matters in water column could be filtered by the scallops and reduced. when the particulate matters were reduced to a certain concentration, POC about 0.O9mgIL, PN about 0.01 5mg/L, the growth of scallops would be limited. In the polyculture systems, the kelp could provide a part of particulate matters. 2. The scallop excreted inorganic nutrients into the sea water. Ammonia was the main part of dissolve inorganic nitrogen excreted by scallops and it will be benefit to the supply of nutrients for phytoplankton. 3. Silicate concentration was very low during the experiment, so it probably limited the growth of diatom and reduced the food supply of scallops. Nitrogen concentration was lOw in the last stage of the experiment and probably limited the growth of phytoplankton 4. Organic matter, organic carbon, organic nitrogen and phosphate in the sediment g reduced with the increment of the densities of the scallops in the shellfish monoculture systems and polyculture systems of shellfish, seaweed and seacucumber.. 5. The growth rate of scallops in the monoculture systems was slower than in the polyculture systems of shellfish and seaweed. The growth rate of kelp in the polyculture systems of shellfish and seaweed is slower than in the polyculture systems of shellfish, seaweed and seacucumber. From Spring to Autumn of 1998, three times sediment investigations were carried out in Sishiliwan Bay in Yantai. The core samples of sediment were acquired at aquaculture area of scallop and non-aquaculture area. The contents of organic carbon in sediment and the nutrients concentration of interstitial water were determined. The diffusive fluxes of nutrients across sediment-seawater were calculated. The results are as follows. 6. The organic matter at aquaculture area was higher than that at non-aquaculture area. 7. The concentration of ammonia, phosphate and the diffusive fluxes of nutrients across sediment-seawater at aquaculture area were higher than that at non- aquaculture area, but the concentrations of nitrite and nitrate of interstitial water were similar at these two areas. The concentrations of nutrients of interstitial water was low in Winter, but high in Spring and Summer. Ammonia was the main part of dissolve nitrogen of interstitial water. 8. The average fluxes of ammonia, phosphate, nitrite and nitrate across sediment- seawater were 249...