鄱阳湖水流运动与污染物迁移路径的粒子示踪研究

湖泊水流运动和污染物的迁移路径对湖泊水质起着关键作用。采用水动力和粒子示踪耦合模型,并结合野外粒子示踪实验来调查鄱阳湖洪水季节空间水流运动和污染物迁移路径。模拟结果显示,流域五河点源入湖污染物和湖区空间面源分布污染物均会沿着不同方向迅速进入湖泊主河道,在快速水流推动下逐渐向北部湖区迁移,但部分污染物因东北部湖湾区存在顺时针方向环流而发生长时间滞留和富集。野外粒子示踪实验同样表明,东北部湖湾区污染物迁移路径随着该湖区水流运动表现得复杂多变,除了可以明显观察到顺时针方向的污染物运动,还可以发现污染物向湖岸边界和湖汊迁移,最终滞留在东北部湖湾区,而康山湖区污染物在快速水流推动下主要沿主河道向西北主湖区迁移,未发现污染物进入东北部湖湾区的迹象。鄱阳湖洪水季节水流运动和污染物迁移路径具有枯水期水流-污染物传输特性。模拟得出鄱阳湖洪水期的平均换水周期约89 d,表明其可能需要近3个月时间才能彻底完成一次换水。研究成果可为大型通江湖泊"江湖关系变化"研究提供参考,对保护"一湖清水"、保障长江中下游水环境安全具有重要现实意义。

RESEARCH OF WATER FLOW AND POLLUTANT TRANSPORT PATHWAYS IN POYANG LAKE USING PARTICLE-TRACKING TECHNIQUE

The water flow and associated pollutant transport pathways in many lakes strongly influence the fate of various pollutants, and may thus affect the spatiotemporal variations in the general water quality of the lake. Poyang Lake, the largest freshwater lake in China, are thought to have important implications for the steadily deteriorating water quality and the associated rapid environmental changes during the flood period. This study used a hydrodynamic model MIKE 21 in conjunction with a particle-tracking model to provide a comprehensive investigation of transport behaviors in a large floodplain Poyang Lake. For the pollutant inputs both directly to the lake and catchment rivers, model simulations indicate that the lake's prevailing water flow patterns cause a unique transport pathway that primarily develops from the catchment river mouths to the downstream area along the lake's main flow channels, similar to a river-transport behavior during the dry period of the lake. Particle-tracking experiment also shows that the pollutant transport pathways appear to exhibit random pathways along with the complex water flow patterns. That is, the released particles are trapped in the eastern bay of the lake, mainly due to influence of the clock-wise gyre. While the particles adjacent to the Kangshan station are more likely to be constrained in the lake's main flow channels and further move northward during this flood period. In addition, simulation results indicate that although the average residence time of the lake is 89 days, substantially longer residence time may occur at some bays, depending on the topographically controlled flow patterns related to the gyres for local lake areas. These results demonstrate that the water flow patterns play an important role in controlling the pollutant transport pathway across the lake. The current study represents a first attempt to use a coupled model approach to provide insights into the transport behaviors for a large river-lake system, given proposals to manage the pollutant within the lake and its catchment rivers.