北京转河河岸带生态修复对河流水质的影响

Influence of Ecological Restoration of Riparian Zone on Water Quality of Zhuanhe River in Beijing

以北京转河为例,探讨一系列河岸带生态修复措施(尤其是河漫地和护岸的改造)对河流水质的影响.于2009年7～9月进行实地调查,沿河岸选取13个采样点,并定期采集水样,测定其中营养物质和溶解氧(DO)等的浓度.结果表明,转河氨氮(NH 4+-N)、硝氮(NO 3--N)、总磷(TP)和DO的浓度均有非常明显的季节变化.在居民用水量较大的7月中下旬和8月上旬,河流中NH 4+-N和TP浓度有较大增加.NO 3--N浓度主要受降雨和地表径流量季节变化的控制.在降雨量较高的季节,NO 3--N浓度主要决定于采样前2次降雨的间隔时间;在降雨量较低的季节,其浓度决定于距上次降雨时间或采样前2次降雨的间隔时间.DO浓度决定于光合放氧和分解耗氧之间的关系,主要受水生植物的生长节律控制,其浓度季节变化对NO 3--N和NH 4+-N的消长关系进行着微调.总体上,转河没有形成富营养化的状况,但降低8月上旬的NH 4+-N浓度和丰水期的NO 3--N浓度仍是防控重点.在水生植物相对较多的河岸带处,河流中NO 3--N和NH 4+-N的浓度较低.在生长旺季,水生植物生长越密集,覆盖度越大,河流中TP浓度越低,DO浓度越高;而在生长末期,枯落物越多,河流中TP浓度越高,DO浓度越低.其中,菖蒲比水葱的影响更大.直立水泥护岸的NH 4+-N、NO3--N和TP的浓度普遍比石块+泥土护岸高.弯曲的河岸可在一定范围内提高河流DO的浓度,而降低NH 4+-N和NO 3--N的浓度.另外,河流周边的土地利用方式对河流水质也有较大影响.总之,除人类活动之外,水生植物的有无、类型、多度和生物量,护岸材料,河岸的曲直均对转河水质有重要影响.

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 （NH4^＋-N）, nitrate nitrogen （NO3 -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 NH4 -N and TP concentrations. The NO3--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 NH4^＋ -N concentration. As a whole, the Zhuanhe River was not eutrophicated, but reducing the concentration of NH4 -N in early August and that of NO3^- -N in the wet seasons was still the key to improve water quality. The NO3- -N and NH4＋-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 NO3- -N, NH4^＋ -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 NO3- -N and NH4＋-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.