| The ecological effects of restoration of flood lands and banks in the Zhuanhe River of Beijing are discussed. From July to September in 2009, water samples were periodically collected in the 13 chosen sample sites, and the concentrations of nutrients and dissolved oxygen (DO) were measured and analyzed. The results showed that there were obvious seasonal variations in the concentrations of ammonia nitrogen (NH+4-N), nitrate nitrogen (NO-3-N), total phosphorus (TP), and DO in the Zhuanhe River. The increase of domestic sewage with rising water consumption in mid and late July and early August resulted in the great increase of NH+4-N and TP concentrations. The NO-3-N concentration was controlled by the seasonal variations of precipitation and surface runoff. In the higher precipitation seasons, it depended on the interval time between two rainfalls just before the sample; in the lower precipitation seasons, it depended on the time from last rainfall or the interval time between two rainfalls just before the sample. DO concentration was due to the relationship between oxygen release in photosynthesis and oxygen consumption in decomposition of organic matter in the river, which was controlled by phenological periods of hydrophytes. It also served to slight changes of NO-3-N and NH+4-N concentration. As a whole, the Zhuanhe River was not eutrophicated, but reducing the concentration of NH+4-N in early August and that of NO-3-N in the wet seasons was still the key to improve water quality. The NO-3-N and NH+4-N concentrations were lower where the amount of hydrophytes was relatively large. In the growing seasons, the stronger growth and larger coverage of hydrophytes led to the lower TP and higher DO concentration in the river; while in the late growing period, much more litters contributed to the higher TP and lower DO concentration. In both periods, Calamus affected more than Scirpus tabernaemontani. Concentrations of NO-3-N, NH+4-N and TP near vertical cement banks were generally higher than those near stone banks blended with clay. The curved river bank could enhance the DO concentration, and reduce the NO-3-N and NH+4-N concentrations within a certain range. Moreover, land use types surrounding the river also greatly affected the water quality. In brief, besides human activities, such factors as existence, type, abundance and biomass of hydrophytes, bank material, and shape of river banks (curved or straight) had great effects on water quality in the Zhuanhe River. |
