城市河流沉积物钙的富集对水环境中磷归趋的影响

Sediment of aquatic systems has dual function as both sources and sinks of water pollutants. As one of the main components in the sediment the content and mineral forms of calcium can determine, to a large extent, the source-sink function of sediments. Enrichment of calcium in the sediment caused by anthropogenic factors is common in highly urbanized areas. However, its effects on the fate of phosphorus and other water pollutants have drawn little attention. This project was designed to collect sediment and overlying water samples from Qinhuai River and Nanfei River, two highly urbanized river systems, and from Pai River in which watershed rural land use is dominant. The variation of chemical composition of river sediments and overlying waters along the river continuum, along with composition of atmospheric dry and wet deposition in the urban area will be studied to reveal the characteristics of anthropogenic calcium-enriched sediments. Phosphorus fractionation method which was specially designed for the calcium enriched sediments will be conducted to explore the interaction between anthropogenic calcium and phosphorus in the sediment. Isothermal adsorption and equilibrium P sorption capacity at zero net sorption and desorption （EPC0） will also be analyzed along the river continuums. Phosphorus burial efficiency (PBE) of surface sediment from the estuaries of Nanfei River and Pai River will be compared. Finally, the impacts of the enrichment of calcium in river sediments on the source-sink function will be studied with a incubation experiment.

水体沉积物对于水污染物具有源和汇双重功能。钙是沉积物的主要成分之一，其含量和矿物形态在很大程度上决定了沉积物源-汇功能的发挥。在高度城市化地区,人为因素造成的沉积物钙富集十分普遍，而这一现象对磷等水污染物归趋的影响没有受到应有的关注。本项目拟在秦淮河、南淝河及派河开展调查研究，通过采样分析和模拟实验，揭示城市河流沉积物和水化学特征的沿程变化，结合城区地表降尘调查，分析沉积物中人为来源钙的组成特征；选择针对富钙沉积物的磷形态分级方法，研究沉积物磷形态特征及其与钙富集之间的关系，揭示人为来源的磷和钙在沉积物中的相互作用及其机理。通过分析城市河流沉积物磷等温吸附曲线、测定磷零吸持平衡浓度等表征沉积物固磷能力指标的沿程变化，对比流域内城市化程度有显著差异的南淝河和派河河口地区沉积物的磷埋藏效率，辅之以不同加钙量的沉积物磷释放模拟实验，初步阐明人为导致的钙富集对沉积物源/汇功能的影响程度。

钙是沉积物的主要成分之一，其含量和矿物形态在很大程度上决定了沉积物源-汇功能的发挥。在高度城市化地区，人为因素造成的沉积物钙富集十分普遍，而这一现象对磷和重金属等污染物归趋的影响没有受到应有的关注。本研究以城市化程度较高的秦淮河流域和南淝河为研究对象，在两条河流的城市化梯度带上分别沿程采集33和20个表层沉积物(0-5 cm)样品，测定了上覆水的部分水质指标和沉积物基本理化性质。采用SEDEX磷分级方法，分析了沉积物易交换态磷 (LP)、易还原态磷 (FeP)、自生钙结合态磷 (CaP)、碎屑钙磷 (DeP)和有机磷 (OP)组分，通过沉积物磷等温吸附实验，获取了沉积物磷吸附过程的关键参数。同时利用卫星影像，解译了秦淮河流域及河流沿岸缓冲区的土地利用类型，收集了流域内前期土壤调查数据，揭示了城市化背景下的表层土壤、河流沉积物钙的空间分布规律及影响因素，分析了城乡梯度带上河流沉积物磷的赋存形态变化及对钙富集的响应，以及沉积物磷源汇功能变化及与钙富集的关系。.研究结果表明，城市建设用地表层土壤CaO含量最高，沿岸居民区用地对沉积物CaO的富集有重要贡献，总体上城市化对秦淮河下游表层沉积物钙的贡献量达到27.6% - 69.9%。秦淮河下游沉积物Ca:P与LP、FeP和CaP呈显著负相关，表明沉积物钙富集对磷赋存形态有重要影响。沉积物CaO含量升高可显著增加LP、CaP以及CaP+DeP的含量，表明秦淮河下游沉积物钙富集促进了磷向钙结合态磷的转化。秦淮河沉积物钙富集与磷的可能作用机制为上游河段二者主要以P与CaCO3的共沉淀方式固磷。而下游，自郊区至城区，秦淮河河水pH逐渐降低、SRP浓度逐渐增加，Ca与P的作用方式逐渐转变为形成各种磷酸钙矿物为主。南淝河与秦淮河下游沉积物磷的源汇功能表现为上游沉积物向水体释放磷，而下游则与水体磷基本保持平衡或向水体吸附磷。大体上，当水体SRP浓度低于0.503 mg L-1时，沉积物开始向水体释放磷。沉积物的铁、铝组分可显著降低磷的释放风险，而高富营养化环境可显著提高沉积物本底磷吸附量，增加沉积物磷的释放风险。