多因素影响下河道悬浮物物源的定量判别及对营养物的控制作用研究

Modern rivers are influenced by various factors from nature and anthropogenic activities. Suspended sediments of river take an important role in material transporting in the watershed. Suspended matter in river is controlled by source materials and also influences the interaction between water and polutants. But little studies have attempted to expound source discrepancies by comparing characteristics of typical materials in the multi-source rivers, and effective approach is absent for quantifying source contributions to suspended sediments. Moreover, the control mechanisms of suspended sediment compositions and structures on the mobility and transformation of nutrients are limited understood, which is adverse for bioavailability identification of nitrogen and phosphorus compounds in the watershed. This project will research the geochemical discrepancies of typical source materials and their origin in the Tiaoxi drain of the northern Zhejiang province, and apportion suspended sediment sources using a modified procedure combining statistical analysis and numerical modelling. We will research the control processes of suspended sediment compositions and structures on nitrogen and phosphorus fractions. Investigations will be performed for the relationships between suspended sediment properties and geological setting, soil types and land uses in order to recognize the characteristic signs of original materials in the watershed. We will select the geochemical variables of source materials and suspended sediments, set up a composite fingerprinting model by the mathematical optimization approach. The mean contributions from individual source types can be achieved. The numerical mixing model can also be used to establish the load-weighted relative contribution of the two tributaries to a main channel. Based on spatial and temporal differences of chemical compositions in suspended sediments, we will investigate the control mechanisms of suspended sediment on the nitrogen and phosphorus mobility and transformation in the rivers. These research contents can be spread to similar hilly-plain rivers, and the research approaches will promote the research aspects of geology, geochemistry and environmental sciences.

现代河流受到自然和人类活动的多种因素影响，河道悬浮物是流域物质输移的重要介质，它的性质既受来源物质的控制，也影响污染物与水体的相互作用。然而目前对多来源河道悬浮物的物源性差异研究不够，缺少评估物源定量贡献的有效手段，悬浮物的物质组分和结构对氮磷营养物的控制作用尚不清楚。本项目选择浙江北部的苕溪流域研究河流悬浮物的物源类型差异，分析不同物源对悬浮物的定量贡献，探讨悬浮物的物质组分和结构对氮磷的控制作用。分别就地质背景、土壤类型、土地利用类型研究探讨物源特征的差异，阐述典型物源特征的意义；测定悬浮物和源区物质的主要地球化学指标，通过数理统计方法建立相关混合指纹模型，分析主要物源对特定悬浮物的定量贡献，同时研究支流悬浮物对干流的贡献；探讨悬浮物物源组成的时空差异，研究它们对流域氮磷迁移与转化的控制作用。本项目的研究能够扩展到相似的丘陵-平原流域，同时将丰富地质学、地球化学和环境科学的研究内容。

本项目围绕苕溪流域悬浮物物源的定量分析，开展物源土壤和悬浮物的多种地球化学指标测定，利用数理统计工具SPSS筛选有效指标；建立悬浮物物源贡献的定量模型，通过METLAB软件构建运算程序，采用多次迭代方法，获得悬浮物物源的贡献值。通过模型的计算，获得东、西苕溪不同河段悬浮物物源的时空变化特征，并分析其成因；根据苕溪流域悬浮物和沉积物的氮磷形态组成和空间变化，分析流域土地利用类型对氮磷形态组成的影响。在此基础上，对比研究了不同地质背景流域沉积物的氮磷分布特征及环境意义，研究苕溪流域干湿季节氮磷流失的风险。通过本项目的工作，取得了以下的重要成果：1）通过悬浮物和物源土壤的多种地球化学指标测定和数理统计方法应用，建立了河流悬浮物物源的地球化学定量模型，获得了太湖西部苕溪流域悬浮物物源的贡献值；2）研究了苕溪流域悬浮物和沉积物中氮磷的形态变化，对比分析了悬浮物和沉积物氮磷组成的时空差异，阐述了其理化性质对氮磷形态的不同影响；3）根据苕溪流域地形地貌和土地利用图，拟定氮磷源因子指标和氮磷迁移因子指标，建立流域氮磷指数输出模型，计算流域不同类型氮源和磷源的流失风险值，并绘制小流域氮磷流失的综合风险分布图；4）利用TM/ETM 遥感影像数据获得苕溪流域的土地利用数据，计算各支流流域不同土地利用类型的面积和相应的百分比，将主要支流水质指标数值与对应流域的土地利用类型面积比例作Spearman 相关分析，研究土地利用类型对支流水质的影响；5）根据苕溪悬浮物和沉积物中氮磷形态组成在上、中、下游的变化，分析流域氮磷的迁移转化规律，阐明其主要的迁移转化机制以及与周边物源的关系。在应用成果方面，本项目建立的悬浮物物源定量模型和流域氮磷输出模型的研究方法推广应用到洪泽湖流域和闽江上游流域，为重点农业区和林业区的水环境评估和管理提供服务。