Study on limiting nutrients and phytoplankton at long-line-cultureareas in Laizhou Bay and Sanggou Bay, northeastern China

摘要

Concentrations of major nutrients (NH sub(4) super(+)-N, NO sub(3) super(-)-N, NO sub(2) super(-)-N, HPO sub(4) super(-)-P, Si(OH) sub(4)-Si) were measured, nutrient enrichment experiments (oxygen-production bioassay) were conducted and phytoplankton were analysed at typical long-line-culture areas in Laizhou Bay and Sanggou Bay, northeastern China, from March 2001 to March 2002. Generally, much variation of nutrient indices was detected among the sampling stations, between the two bays and in different seasons: the concentration of dissolved inorganic nitrogen (DIN) fluctuated more violently and ranged much more widely in Sanggou Bay. N-limitation was usually found in both bays, and the ranking of limiting potentials of major nutrients was N>Fe>P=Si in Laizhou Bay and N>P>Fe>Si in Sanggou Bay. Diatoms dominated the phytoplankton community in Sanggou Bay, but only dominated in eight months (with flagellates dominant in four months) in Laizhou Bay. Linear and nonparametric correlation analyses suggested that a large number of the nutrient and phytoplankton variables measured have intrinsic relationships within themselves. Much more complicated correlations between phytoplankton and nutrient indices were found in Laizhou Bay than in Sanggou Bay. This, together with the violent fluctuations of DIN concentrations, indicated a more fragile ecosystem stability in Sanggou Bay. The relatively exposed locations and less crowded settings of the rafts in the long- line-culture areas in Laizhou Bay allowed for a better water exchange, and the effect of aquaculture activity on the environment was not significant. Because of the intensity of aquaculture activities in Sanggou Bay, the biological, chemical and physical characteristics in the bay are greatly affected; a reduced cultivation density based on more comprehensive studies of carrying capacity of the bay is suggested.