Abstract: In July (summer) and October (autumn) 2007 and in January (winter) and April (spring) 2008, an investigation was made on the spatiotemporal distribution of nitrifying and denitrifying bacteria in the surface seawater, overlying water, and sediment in Xiangshan Bay. A cylindrical high-fidelity gravity sampler instead of conventional grab sampler was used for collecting samples, and principal component analysis and multivariate linear stepwise regression analysis were adopted to analyze the relationships between bacterial abundance and environmental parameters. The abundance of nitrifying and denitrifying bacteria in the water and sediment in July and October 2007 and in January and April 2008 ranged from 30×10⁴-2.4×10⁴ cells·ml^-1 and 30×10⁴-2.4×10⁴ cells·g^-1, with the mean values in surface water, overlying water, and sediment being 2.24×10³ cells·ml^-1, 3.61×10³ cells·ml^-1, and 6.45×10³ cells·g^-1, respectively for nitrifying bacteria, and 4.84×10³ cells·ml^-1, 5.31×10³ cells·ml^-1, and 3.12×10³ cells·g^-1, respectively for denitrifying bacteria. The abundance of nitrifying bacteria in surface seawater and overlying water was significantly higher in winter, compared to other three seasons, and that in sediment was higher in autumn and winter, compared to the other two seasons. For denitrifying bacteria, its abundance was higher in autumn and summer than in spring and winter. In investigation period, there was an apparent spatial distribution of nitrifying and denitrifying bacterial abundance in the Bay. Vertically, the abundance of denitrifying bacteria was higher in surface water than in overlying water and sediment, but that of nitrifying bacteria was in adverse; horizontally, the abundance of both nitrifying and denitrifying bacteria was significantly higher in the middle part of the Bay and in the junction of branch and main ports. Such a spatial distribution pattern of nitrifying and denitrifying bacteria in the Bay demonstrated that the coastal land pollution from human industrial and agricultural activities and mariculture played key roles. Multivariate statistical analysis demonstrated that nutrients N and P, dissolved oxygen, water temperature, salinity, organic pollution, and primary productivity were the main factors affecting the spatiotemporal distribution of nitrifying and denitrifying bacteria in Xiangshan Bay.

Key words: Organic contaminants, Plant uptake, Ecotoxicology, Phytoremediation