寒区沙地水库氮磷内外源协同作用污染机理研究

The water resources from reservoirs (the main focus being lakes in this research) in the cold and sandy areas play a key role in maintaining the stable relationship between residents and land, and also in ensuring the security of living and ecological water. Recently, the pollution caused by large-scale external input from the atmosphere and the problem of water eutrophication lying in the release of sediment over freeze-thaw process have been a great challenge to the protection and control of water over the sandy and cold regions. This project takes Dahekou reservoir from Inner Mongolia as the research object. It makes full use of the long-term monitoring data of the reservoir, including water environment, regional hydrology, meteorology and atmospheric dry and wet deposition, as well as the analysis of the chemical form of nitrogen and phosphorus nutrients from different pollution sources, distribution characteristics and seasonal variation rule. Through field monitoring and indoor simulation experiments, the environmental pollution effects of atmospheric nitrogen and phosphorus atmospheric deposition in the reservoirs of sand reservoirs were investigated. The exchange characteristics of nitrogen and phosphorus in the sediment-overlying water and its response to the water environment were studied so as to analyze the effects of sand and dust. Endogenous pollution caused by suspended sediment and, changes in the water environment caused by water temperature stratification are discussed as well. This research will firstly analyses the characteristics of chemical pollution from external and endogenous sources, and thereafter reveal the mechanism of nitrogen and phosphorus pollution in reservoirs under the synergistic action of dust, water, sediment, and the interaction between internal and external sources, so as to lay the foundation for the staged and multi-target pollution treatment over reservoirs (lakes) from the cold and sandy regions and offer the theory and technical support.

寒区沙地水库（湖泊）蓄存的水资源，对维护沙区人地关系稳定、保证生活与生态用水安全极为重要。近来污染物通过大气介质的大尺度外源输入和冻融过程底泥内源释放引发的水体富营养化问题，使寒区沙地水域的水环境保护和防治工作受到了巨大挑战。本项目以内蒙古大河口水库为研究对象，充分利用库区水环境、区域水文、气象、大气干湿沉降长期监测资料，分析水库不同污染源氮磷营养盐的化学形态、分布特征及季节性变化规律。通过野外监测和室内模拟实验，探明沙区水库大气氮磷干湿沉降水环境污染效应，研究底泥-上覆水氮磷交换特征及其与水环境的响应关系，剖析因风沙降尘而引起的外源污染，因底泥悬浮而导致的内源污染及由于水温分层而造成的水环境变化过程。力求从外源、内源的化学污染特征入手，揭示降尘-水-底泥两界面三介质内外源协同作用下的水库氮磷污染机理，为寒区沙地水库（湖泊）分期、多目标污染治理奠定基础理论和提供技术支撑。

我国北方沙源区水体受大气风沙携带污染物沉降、沉积物营养盐季节性释放及上游河流输入等多重影响，使得寒区沙地水域的水环境污染复杂多变且具有显著地域特征。针对沙源区水库内外源协同污染问题本项目重点开展了大气沉降污染特征分析，污染物溯源，降尘-水-沉积物内外源协同作用下水库氮磷污染机理研究。成果如下：.分析沙源区水库大气降尘粒度特征及化学特征。大气降尘颗粒物分选性整体偏好，颗粒大小较为均匀。各形态氮含量大小排序依次为NH4+-N >NO3--N>DON> NO2--N，通量比例为100：85：63：1。磷沉降较少，总磷质量浓度年均值为0.08 mg/L。湿沉降有机氮浓度在总氮中占比与降水量呈正相关，硝氮浓度在总氮中占比与降水量呈负相关，亚硝氮和氨氮与降水量相关性不明显。.探析水体悬浮颗粒总有机质碳、氮污染物主要来源。水库表层沉积物以远源搬运的风成沉积物为主。通过端元混合模型对有机质来源进行定性和半定量分析表明，陆生C3植物、土壤有机质和淡水水生植物是水库沉积物有机质主要的3种来源，其中陆生C3植物贡献最大，其次是土壤有机质，个别断面有淡水水生植物来源。水库整体初级生产力不高，有机质来源组成差异较小，有机质来源大都为外源。.解析研究区大气氮沉降污染成因及主要来源。不同季节大气氮干沉降来源差异性较大。春季主要来源为可识别的沙地；夏季主要来源于水库正北及西北方向处的耕地。秋季大气氮干沉降样品中45%来源于西南方向距离水库约4.9 km处的沙地。冬季大气沉降中35%来源于可分辨沙地，不可识别的混合源为52.5%。.揭示大气沉降-河流输入-沉积物释放协同作用下水库氮磷污染机理。全年河流径流、大气沉降、沉积物释放对水库总氮污染贡献的比例关系为5:1:2，总磷污染贡献的比例关系为6:3:1。河流径流氮磷输入是影响水库水环境的主要污染源项，春季大气沉降氮输入成为了藻类等初级生产者的氮营养盐主要来源之一。夏季河流径流氮磷输移对水库水质富营养化起到了关键作用。冬季沉积物释氮成为了冬季冰封期水库氮营养盐的最主要来源。