长江流域总磷问题思考

Consideration on total phosphorus problem in Yangtze River Basin

“十三五”以来,长江干流水体中总磷浓度达标,但中上游支流和中下游湖泊水体中的总磷超标明显,总磷已经成为长江流域水体主要污染指标。尤其是长江上游梯级水库的建成运行,改变了水沙条件,颗粒态磷大幅减少,溶解态磷有所增加,磷输移形态的改变加剧了中下游的总磷问题,并产生了系列生态环境效应。上游支流水体中磷的输入加速了梯级水库水体中磷的累积,水质污染和富营养化潜在风险增加;中下游颗粒态磷减少改变了磷形态的分布,增加了环境脆弱性;下游浅水湖泊水体中磷超标驱动了内源循环,加速了湖泊富营养化过程;长江入海磷通量剧减,将对近岸水域生态环境产生深远影响。针对长江总磷问题开展了分析研究,结果表明:(1)应对磷输入源头采取控制措施,诸如加强“三磷”问题治理,遏制中上游重点支流的磷超标趋势,同时要加快城镇污水收集/处理基础设施建设,完善农业面源管控和湖泊生态修复体系,控制中下游磷排放源;(2)应当实施上游梯级水库群泥沙联合调度,减少库内淤积,增加输沙能力以及增加中下游颗粒态磷水平和磷入海通量;(3)建议完善总磷监测的标准方法,强化全沙总磷的监测,磷浓度和通量监测并重,以便为长江总磷管控提供科学系统的数据支撑。

During the 13th Five-Year Plan period,the total phosphorus concentration in the main stream of the Yangtze River met the water quality standard,but the total phosphorus in the middle and upper reaches of tributaries and lakes in the middle and lower reaches of the Yangtze River has exceeded the standard obviously.The establishment and operation of the cascade reservoirs in the upper reaches of the Yangtze River changed the water and sediment conditions,resulting in a significant reduction of particulate phosphorus but an increase of dissolved phosphorus.The change of phosphorus transport patterns aggravated the total phosphorus problem in the middle and lower reaches,and produced a series of ecological and environmental effects.The input of phosphorus from upstream tributaries accelerated the accumulation of phosphorus in cascade reservoirs and increased the potential risk of water pollution and eutrophication.The reduction of particulate phosphorus in the middle and downstream changed the distribution of phosphorus form and increased environmental vulnerability.The excessive phosphorus levels in shallow lakes drove the internal circulation mechanism and accelerated the eutrophication process.The steep decrease of phosphorus flux from the Yangtze River to the sea would have a profound impact on the ecological environment of the coastal waters.In view of the total phosphorus problem in the Yangtze River,it is suggested that the input source control should be carried out first,such as strengthening the control of the"three phosphorus"problem,curbing the trend of exceeding the standard of phosphorus in key tributaries in the middle and upper reaches of the Yangtze River.Meanwhile,the construction of urban sewage collection and treatment infrastructure should be accelerated,agricultural non-point source control and lake ecological restoration system should be improved,and phosphorus emission sources in the middle and lower reaches should be controlled.Secondly,it is suggested to implement joint sediment regulation of upstream cascade reservoirs to reduce siltation in the reservoir,increase sediment transport capacity,and increase particulate phosphorus level and phosphorus flux in the middle and lower reaches of the reservoir.Finally,it is suggested to improve the standard method of total phosphorus monitoring,strengthen the monitoring of total phosphorus in the whole sediment,and pay equal attention to the monitoring of phosphorus concentration and flux,so as to provide scientific and systematic data support for the control of total phosphorus in the Yangtze River.