| Dissolved oxygen（DO） is an important indicator for water pollution. In order to study the effects of Potamogeton crispus population on water quality, the DO content around the P. crispus population was monitored in Xuanwu Lake in Nanjing. The result showed that the photosynthesis of P. crispus significantly improved DO content in the water.（1）DO content within the P. crispus population was generally higher during daytime than that during the night. DO content increased after sunrise and declined after sunset; it dropped at 19：30 at 20~80 cm depth, then recovered slightly from 21：30 and finally dropped until sunrise. DO content at the open waters increased continuously from sunrise to sunset, and dropped from sunset to sunrise. DO content did not show significant difference at each water depth. DO content in the junction water area showed similar phenomenon with that within population and the open waters.（2）DO content within water containing P. crispus population decreased from the surface to the bottom during daytime; DO content was higher at 60~80 cm than that at both 20~40 cm and 100 cm during the night. DO content, which was far away from P. crispus population in the open waters decreased from the surface to the bottom, while DO content in the open waters close to the population showed no significant differences at each depth because the water area was relatively shallow. DO content in the junction area decreased from the surface to the bottom during both the daytime and night.（3）DO content for the water surrounding the population was the highest at all periods and all depths; DO content which is outside the water containing population and close to the open water was the lowest at 20~40 cm. During the daytime, DO content in the water containing population and close to the open water was lowest at 60 cm, while it was the lowest in the junction water at night. DO content in the water containing population was the highest in 80 cm depth; it was the lowest in the junction water. DO content decreased from the water containing population to the open waters at 100 cm at night. P. crispus population played an important role in improving DO content in water. |
