Abstract: In August 15-28, 2009, a preliminary study was conducted on the spatial distribution characteristics of heterotrophic bacteria (HB), inorganic phosphate bacteria (IPB), organic phosphate bacteria (OPB), denitrifying bacteria (DB), and ammonifying bacteria (AB) in the hypoxic zone of Yangtze River Estuary. In the water surface, water bottom, and sediment surface of the zone, the average quantity of AB was the largest, being 307.52×10⁴ cells·L^-1, 184.50×10⁴ cells·L^-1, 199.97×10² cells·g^-1, followed by that of HB (87.35×10⁴  cfu·L^-1, 86.85×10⁴ cfu·L^-1, and 19.56×10² cfu·g^-1), and of OPB (19.26×10⁴  cfu·L^-1, 18.82×10⁴ cfu·L^-1, and 19.56×10² cfu·g^-1, respectively). IPB was only observed within the Yangtze Estuary, south passage of the Estuary, and Zhoushan inshore, and its average quantity in the water surface, water bottom, and sediment surface was 18.50×10⁴  cfu·L^-1, 31.00×10⁴  cfu·L^-1, and 7.17×10² cfu·g^-1 respectively. DB had a wide distribution, but its average quantity was low, being 3.94×10⁴ cells·L^-1, 23.08×10⁴  cells·L^-1, and 6.22×10² cells·g^-1 in the water surface, water bottom, and sediment surface, respectively. Salinity, NO₃^--N, PO₄^3--P, SiO₃²-Si, and pH were the main factors affecting the distribution of HB, IPB, OPB, and DB in water body and sediment surface. The HB, IPB, and OPB in water bottom and sediment surface had significant positive correlation with water temperature; the HB and OPB in water bottom and the IPB in sediment surface were significantly positively correlated with dissolved oxygen (DO); while the AB in sediment surface was significantly negatively correlated with DO. Cluster analysis showed that hypoxia affected the bacterial community structure in sediment surface.

Key words: Yangtze River Estuary, hypoxia zone, heterotrophic bacteria, nitrogen bacteria, phosphate bacteria