基于农业面源污染控制的湿地恢复优先性评估研究

In recent years, wetlands in parts of China have been shrinking dramatically due to water resources shortage. Currently, ecological water supply represents the main restoration measure. This is primarily achieved by conveying floodwater and return water from farmland irrigation to critical wetland areas. However, water supply alone will induce agricultural non-point source pollution (NPS), especially nitrogen, and will not be able to meet the requirements for hydrological restoration. Therefore, guaranteeing sufficient water supply and improving purification efficiency of wetlands have become key sustainable development challenges. There are currently only a few studies dealing with restored wetlands as potential Best Management Practices for water pollution control. However, they are at the exploratory stage with few in-depth analyses of priority restoration plan design and dynamic assessment of NPS control. In order to provide a robust scientific basis, there is a need for a comprehensive study on nitrogen removal rate of restored wetlands and key driving variables using continuous monitoring of water quality, 3S (GIS, RS, and GPS) technologies, and statistical analysis. Determining the leading factors of wetland purification efficiency and considering the risk of occurrence and migration of NPS pollution will provide the basic knowledge to develop a priority index of wetland restoration. The ensuing results will be used to define the framework to elaborate wetland priority restoration plans. Moreover, a mechanistic model simulating wetland hydrological processes will be used to explore different wetland restoration scenarios at the watershed scale. The outcome of this project will provide strong scientific and technological support for wetland restoration and NPS prevention and control in parts of China under water resources shortage.

我国部分地区因水资源短缺导致湿地面积剧减，目前多采用生态补水工程即利用汛期洪水与农业退水恢复湿地水文条件。但简单输水，既造成农业面源污染又难以满足湿地恢复需求。因此，如何利用有限水资源恢复关键区域湿地，同时提升其水质净化功能，是亟待解决的问题。目前将恢复湿地作为潜在水质BMPs措施的研究还较少，以面源污染控制为目标的湿地优先恢复方案设计与动态评估也尚未大规模开展。本项目选取吉林西部泡沼湿地群为研究对象，通过连续监测、3S技术与数理统计方法，识别恢复湿地氮素去除率与关键驱动变量，为湿地优先恢复评估指数设计提供依据；在辨析影响湿地净化能力主导驱动变量基础上，综合考虑面源污染产生与运移同时发生概率，建立有针对性的湿地恢复优先性评价指数，进而生成恢复方案；最终利用能够模拟湿地水文过程的机理模型进行湿地恢复方案综合评估。研究成果将会对水资源短缺地区湿地恢复与农业面源污染防治提供有力的科技支撑。

受气候与人为活动影响，吉林西部地区湿地面积逐年递减。当地政府针对天然径流补给不足而引起的湿地面积萎缩与退化问题，主要采用生态补水工程，即利用汛期洪水与农业退水进行湿地生态系统恢复与改善。但区域农业生产强度非常大，导致输入湿地水体中携带大量营养盐。因此，如何充分利用有限的季节性洪水与农田退水重点保障关键区域的湿地恢复，发挥其水质净化功，是改善这区域生态环境的关键。本项目选取吉林省西部干涸、半干涸泡沼湿地群为研究对象，通过实地监测、资料调查、3S技术与数理统计方法，识别影响湿地恢复的关键驱动因素，为湿地恢复工程设计与优先恢复评估指数建立提供基础数据；定量估算面源污染发生与运移的风险，建立更有针对性的湿地恢复优先性评价方法；以恢复湿地核心功能为目标，通过对水文、植被、景观格局等关键指标的精准评估，识别出最优恢复方案与实施比例，为评估指数体系改进与降低项目成本提供技术支撑。研究结果表明泡沼湿地群水质呈显著季节变化，丰水期水质恶化明显，大部分处于重度富营养状态。运用洪水恢复水文条件后，影响湿地土壤生态系统的主导因子发生变化，相对于微生物组成，土壤微生物生物量的改善比较明显。改善水文连通性并适当种植本地湿地植被可有效提高湿地净化功能；基于面源污染运移特征，构建的五因子综合测算法，主要包括降雨驱动因子、地形驱动因子、地表径流因子、地下蓄渗/地下水径流因子、截留因子，该方法能够准确的定量估算吉林西部地区面源污染实际入河量；基于湿地核心功能（水文、土壤、植被、景观配置），选取湿地面积、缓冲带与人为土地利用强度、水文、栖息地变化与发育、特殊湿地群落、植被，散布，微地貌六大类做为评价指标，实现了对大型退化湿地恢复效果的快速定量评价。研究成果对我国水资源短缺地区湿地生态系统保护与流域农业面源污染防治，具有十分重要的科学意义和广泛的应用价值。