Abstract: Taking Xiangxi River, a tributary of the Three Gorges Reservoir as the study object, and according to the monitoring data obtained in summer of 2011, the temporal and spatial distribution characteristics of nutrients and chlorophyll a in the tributary bay before and after an algal bloom, and their relevance were analyzed. The results showed that the algal bloom lasted during June 21-29, 2011, and the maximal value of chlorophyll a achieved 125.8 mg·m^-3. The algal bloom had a significant influence on the spatial distribution of DIN and DIP, and the nutrients were at high concentrations in middle reaches, and low concentrations in the estuary, but diminished from the estuary to the upper reaches, and sharply declined in the algal bloom area. The high background concentrations of nutrients in Yangtze River increased the risk of algal blooms in the tributary bay. The outflow position of the Yangtze River water with high background concentrations of nutrients in the Xiangxi River bay was just the region with the most severe algal bloom. The nutrient supply of mainstream water to the tributary bay surface water was the key factor affecting the algal bloom fluctuation.

Key words: carbon density, Pinus massoniana, aerially seeded plantation, distribution characteristics.