西南岩溶灌区农业湿地系统氮磷迁移转化和归趋研究

The field tests will be conducted to determine the nitrogen and phosphorus contents, pH and DO in agricultural wetlands sysrtem in karst irrigation area in Southwest China. The agricultural wetlands sysrtem consists of paddy field, drainage channel, pond, reservoir and river. The spatial and temporal variation characteristics of nitrogen and phosphorus in agricultural wetlands system are analyzed based on the detection of concentration and forms of nitrogen and phosphorus in different environmental media. The field tests aim to analyze the forming mechanism of non-point source pollution nitrogen and phosphorus in karst irrigation area, and describe the environmental fate of nitrogen and phosphorus in agricultural wetlands sysrtem. It is hoped that the test results can reveal the characteristic of transfer and transformation of nitrogen and phosphorus in agricultural wetlands sysrtem, and clarify the mechanism of nitrogen and phosphorus pollution load at different scale in karst irrigation area. Considering the influence of karst development, water movement, and distribution of channel and pond wetlands on transport of nitrogen and phosphorus in karst irrigation area, the main controlling factors of transfer and transformation of nitrogen and phosphorus are respected to be identified. According to the characteristics of hydrology and nutrient cycle in karst irrigation area in Southwest China, SWAT (Soil and Water Assessment Tool) model is modified to develop the karst irrigation area non-point source pollution model. The movement of water in channel and pond wetlands is revised, and transfer and transformation of nitrogen and phosphorus in channel and pond wetlands are improved. Also, the epi-karst zone water cycle and transport of nitrogen and phosphorus module are added to SWAT. Impact of agricultural management and underlying surface conditions on the transport and fate of nitrogen and phosphorus in agricultural wetlands sysrtem are evaluated by scenario analysis using the improved model.The resultes can provide the scientific evidence for the pollution control and treatment of nitrogen and phosphorus in agricultural wetlands system in karst irrigation area in Southwest China, and it is extraordinary significant to the agricultural water environment protection and the ecological security.

开展西南岩溶灌区氮磷野外原位监测试验，分析稻田→农沟→塘堰→斗沟、支沟→水库→干沟→河流等农业湿地系统各环节的环境介质中氮磷，以及pH、溶解氧等指标，从岩溶分布、水文过程、径流排水、土壤性质等方面综合分析，辨析岩溶灌区氮磷污染发生机理，描述农业湿地系统内氮磷环境归趋特点，揭示氮磷迁移转化机理，深入分析岩溶灌区不同尺度氮磷污染负荷排放差异的原因。考虑岩溶发育、水分运动、沟渠塘堰等湿地分布对氮磷运移的影响，识别农业湿地系统各环节氮磷迁移转化的主控因素。在申请者对SWAT 模型改进而建立的灌区分布式水文模型基础上，增加SWAT的表层岩溶带水分和氮磷运移模块、改进沟渠塘堰水运动和氮磷运移模块，构建岩溶灌区面源污染模型。分析环境因子对氮磷污染负荷的贡献，模拟下垫面条件和农业管理措施具体因子对氮磷运移的影响。研究成果可为岩溶灌区氮磷污染控制与治理提供依据，对于农业水环境保护、生态安全等具有重要意义。

西南岩溶灌区的沟渠、塘堰、河流等农业湿地具有灌溉和排水的双重功能，田间氮磷随径流排水经排水沟网汇流后，进入农业湿地聚集或渗入地下水；灌区内的岩溶发育地区，裂隙发育，土层薄，对氮磷污染物的过滤和净化作用弱。岩溶灌区生态环境脆弱，湿地系统氮磷运移研究对于面源污染控制十分重要。本项目在漓江流域青狮潭灌区建立了会仙岩溶试区和金龟河非岩溶试区，采用灌区调查、试区监测、室内实验、数据分析和SWAT模型模拟等方法，进行岩溶灌区农业湿地系统氮磷污染排放特征、湿地系统氮磷迁移转化的过程和机理、变化环境下氮磷运移的响应等方面的研究。结果表明，不同沟渠/河流湿地的氮磷排放在时空分布上差异较大；岩溶试区和非岩溶试区的土壤/底泥氮磷含量有差异但不显著，土壤氮磷含量处于较高水平；地下水氮磷污染较为严重；在多个空间尺度上，呈现雨季/灌溉季的氮磷排放负荷大于干季/非灌溉季的总体特征；不同尺度之间土地利用、岩溶分布、湿地分布、外源污染汇入、水系交汇等存在差异，氮磷排放浓度和负荷呈现非线性的波动变化，存在空间尺度效应；小尺度氮磷浓度与大、中尺度存在显著性差异，大、中尺度之间的氮磷浓度差异性不显著；氮磷排放负荷在大、中、小尺度之间存在差异但不显著；单位面积氮磷排放负荷与覆盖型岩溶区面积比例呈显著线性正相关关系；化肥施用量减少对总氮、总磷排放的削减效果优于灌溉水量减少的消减效果；同时改变湿地面积和蓄水容量对总氮、总磷排放的影响，超过单独改变其中一个湿地属性影响的叠加值。获取了青狮潭灌区和两个试区多年、多测点的沟渠河流、土壤、地下水氮磷等水质数据，青狮潭灌区长序列水文数据，以及青狮潭灌区土地利用、岩溶分布、土壤分布等基本图件。研究结果揭示氮磷流失的排放规律和运移过程，剖析岩溶灌区湿地系统氮磷运移与环境因子的内在关系，为灌区氮磷污染治理提供依据，研究成果对于西南岩溶地区农业面源污染控制、灌区生态安全等具有重要意义。