太湖流域典型圩区磷素流失过程模拟- - 以尖圩为例

Polders are widely distributed in the plain area of Taihu Basin. Phosphorus loss from these polders is one of the main causes of water pollution in Taihu Basin. Modelling the process of phosphorus loss from these polders in Taihu Basin is a critical step to control non-point phosphorus pollution. However, existing models for phosphorus loss quantification neglect phosphorus transport in the polder system, and result in high uncertainties. This study is based on a procedure involving process monitoring, model development and mechanism analysis. Jian Polder, a typical polder in Taihu Basin, will be selected as the study area. The phosphorus loss will be monitored during heavy rainfall events. We will focus on the critical processes including phosphorus leaching from farmland and residential land, phosphorus transport in ditches, particulate phosphorus deposition in ponds, and phosphorus loss through drainage pump. Phosphorus loss will be analyzed based on above monitoring data. A phosphorus loss model for polder systems will be developed using environmental spatial dynamic modelling technique. This model aims to simulate the process of phosphorus loss and estimate the phosphorus load. Several simulations with different phosphorus transport assumptions during the heavy rainfall events will be carried out. They will be compared to quantify the response of phosphorus loss to three factors including phosphorus transport in ditches, particulate phosphorus deposition in ponds, and water pumping. Based on these simulation results, phosphorus loss mechanism of the polder system will be analyzed. This study provides theoretical and technical support for developing national phosphorus loss models for the polder systems in our country. It would benefit us to analyze non-point source phosphorus, identify phosphorus transport path, and control pollution.

太湖流域平原广泛分布圩区，磷素流失是造成水污染的重要原因之一。定量模拟圩区磷素流失过程是非点源磷污染控制的重要环节，现有模型缺乏考虑磷素在圩区系统内部的迁移过程，模拟结果不确定性较大。本项目以"过程监测-模型构建-机理分析"为研究主线，选择太湖流域的典型圩区- - 尖圩为研究对象，通过对强降雨事件圩区系统内部农田与住宅用地的磷素排放、排水沟磷素迁移、坑塘颗粒态磷滞留、泵站排水磷素输出等关键过程的监测，研究磷素流失特征；基于环境空间动态模拟技术，构建圩区磷素流失过程模型，开展强降雨条件下磷素流失过程模拟与通量估算；构建强降雨条件下的不同磷素迁移情景，定量模拟排水沟磷素迁移、坑塘颗粒态磷滞留、泵站排水对圩区磷素流失的影响，阐明圩区系统内部的磷素流失机制。本研究为发展适合我国平原圩区磷素流失过程模型提供理论与技术支撑，对平原圩区非点源磷污染来源解析、迁移路径识别、污染控制有重要意义。

圩区是广泛分布于长江中下游平原区的人工地理单元，其水文条件和营养盐输移过程受自然条件和人工控制措施的双重影响，具有圩内循环过程复杂、圩内外交换频繁等特征，目前仍缺乏精确的模拟方法。本项目选择了太湖流域典型圩区（常州溧阳尖圩），建设了典型圩区的农田径流试验区，布设了气象与水文的自动监测仪器，形成圩区水环境研究的定点观测与试验基地，开展了连续三年的气象、水文与营养盐输移的全过程定期监测，确定了圩区磷素流失的关键过程及其参数阈值，构建了圩区产流、汇流、人工控制出流、农田-沟渠-坑塘营养盐滞留等关键过程的概念模型与数学模型，研发了圩区水文与磷素输移过程模型，识别了圩区磷素流失的关键影响因子。项目主要研究结论如下：（1）本研究综合考虑了排水沟磷素迁移、坑塘颗粒态磷滞留、泵站排水对圩区磷流失的影响，研发了圩区水文与磷素输移过程模型，体现了圩区独特的水文规律与磷素流失特征，模型在解析平原区非点源磷污染来源、识别圩区磷素迁移路径、控制圩区非点源磷污染有广泛应用前景。（2）基于2014年的监测数据，估算了太湖流域典型圩区的磷素平衡，其中水田径流的磷素流失通量为0.52kg/ha/yr，人工排水的磷素流失通量为2.15kg/ha/yr，沟塘拦截的磷素为1.07kg/ha/yr，上述磷素平衡过程表明：圩区沟塘具有显著的磷素拦截效应。（3）施肥量是圩区磷素流失的关键影响因子，沟塘的面积与水生植物分布是圩区磷素拦截的重要影响因子；与非圩区集水单元相比，圩区水面率普遍较高，降雨期间，水面区域能够接纳农田与居民区径流的大量磷素，具有显著的磷素拦截效应。项目圆满完成了预期的研究内容与任务，发表SCI论文4篇（其中二区SCI论文3篇）、CSCD论文1篇，申请软件著作权1项，上述成果均与本项目密切相关（第一/二资助）。