Effect of Biological Floating Island on Water Quality and Algae in a Tributary Bay Typical of the Three-Gorge Reservoir

A biological floating island was built in the estuary bay of the Gaolan River, which is a tributary of the Xiangxi River in the Three-Gorge Reservoir region. Samples were collected from several sites around the island for monitoring of changes in physico-chemical parameters and phytoplankton. Results show that the water is moderately to lightly eutrophied, with algae blooming in August. The water around the island is lower than the water in CK in content of Chl-a, DO and COD_Mn, but higher in NH₄⁺-N. The plants on the floating island follow an order of Canna indica > Cyperus alternifolius > Pontederia cordata > Acorus calamus Linn, in TN removal rate, and an order of Canna indica > Cyperus alternifolius > Acorus calamus Linn > Pontederia cordata in TP removal rate. In the island area and CK, a total of 31 genera of algae, belonging to 7 phyla were identified. Chlorophyta and Bacillariophyta dominated in April while Cyanophyta did in August. No significant difference was found between the island area and CK in algal community structure. The density of algae in the floating island area is significantly different（P＜0.05）from that in the control area in April and August, with the former significantly lower than the latter.