Abstract: The ecological effects of restoration of flood lands and buffers from Mencheng lake to Lianshi lake along Yongding river in Beijing were discussed. From July to October in 2013, water samples were periodically collected at the 8 selected sites along the west bank, and the concentrations of dissolved oxygen(DO), nitrate nitrogen(NO₃^-—N ), ammonia nitrogen (NH₄⁺—N), and total phosphorus(TP) were measured and analyzed. The results showed that there were obvious seasonal variations in the concentrations of these nutrients and DO in Yongding river. For most of the sites, water quality could not meet the requirements for the surface water standard class IV. The NH₄⁺—N concentration was low where the amount of hydrophytes was relatively large. During the growing season, higher coverage of hydrophytes led to higher DO and NO₃^-—N concentrations and lower TP concentration, while at the end of the growing period, much small contributions to the higher TP and lower DO concentrations. The convex river bank could enhance the DO and NO₃^-—N concentrations and reduce the NH₄⁺—N concentration. In short, changes in the structure characteristics of riparian zone such as bank material, abundance of hydrophytes, and curvilinearity of banks had great effects on water quality in Yongding river.

Key words: riparian zone structure, DO concentration, NH₄⁺—N concentration, NO₃^-—N concentration, TP concentration