北运河流域河流沉积物中氮磷污染物释放规律

北京市北运河流域属于典型缺水型城市纳污河流,沉积物释放的氮磷污染物已成为阻碍水环境质量持续改善的主要因素。利用自制环形水槽,对不同流速下沉积物中氮磷的动态释放规律进行研究,结果表明,静态条件下,沉积物中氨氮平均释放速率1 136 mg/(m~2·d),磷酸盐平均释放速率为145 mg/(m~2·d),在流速0.05 m/s的缓流水体中,氨氮平均释放速率为1 408 mg/(m~2·d),而磷酸盐平均释放速率为125 mg/(m~2·d)。流速增加会显著促进氮素的硝化作用,使水体中氨氮浓度降低,硝酸盐氮浓度上升。同时,流速增加导致水体中颗粒物含量增加,促进磷吸附行为,水体中磷酸盐浓度下降。

Release Law of Nitrogen and Phosphorus Pollutants in Sediments of Beiyun River Basin

The nutrients are very rich in sediments of Beiyun river basin in Beijing, and its release rate is significantly affected by hydraulic condition. Sediment release plays important role to restrict local water quality improvement. The dynamic release law of nitrogen and phosphorus pollutants in sediments at various flow rates was studied using self-made annular flume. The results showed that the average release rate of nitrogen-phosphorus and phosphate was 1 136 mg/(m²·d) and 145 mg/(m²·d) in static conditions, 1 408 mg/(m²·d) and 125 mg/(m²·d) in flow of 0.05 m/s, respectively. An increase of flow rate brought about faster release rate, as well as significantly increased the dissolved oxygen content in the water, which can greatly promote the nitrification and then reduced the concentration of ammonia. Besides, a fast water flow would disturb the sediment and then increase the content of particulates in water body. Adsorption of phosphorus would be improved and the concentration of phosphate would decrease then.