湿地演替带氧化还原电位变化特征与氮素迁移转化机理

Wetlands are widely distributed in the world. The redox potential (Eh) is an important indicator of redox environment, which changes in the process of wetland succession. Nitrogen, as a relatively active chemical element, is sensitive to the changes of Eh, and its occurrence, migration and transformation are closely relevant to Eh. Promoted by the fact that lakes are commonly polluted by nitrogen, and lake eutrophication is very serious nowadays, we select South Dongling Lake as the test field in this subject research. The changing patterns of Eh versus soil depth, hydrological elements, temperature and pH are monitored in the field. Water samples are collected in Eh monitoring point; the occurrence and features of nitrogen are also determined and analyzed. Eh profile is constructed in wetland succession to study Eh variation with nitrogen occurrence and transformation mechanism. Simultaneously, laboratory experiments are conducted to determine the soil permeability of wetland succession. Computerized tomography (CT) is incorporated to explore the nitrogen migration law in different types of soil. By studying Eh of wetland succession and nitrogen migration and transformation mechanisms, the relationship of Eh versus soil, hydrological features, and nitrogen migration and transformation are discussed. Based on the experimental findings, mathematic model of nitrogen migration and transformation are developed to predict the temporal & spatial variation of wetland environment. The results will be of great significance for pollution control and water environmental protection.

湿地在世界上广泛分布，湿地演替过程中氧化还原环境随之发生改变，而氧化还原电位（Eh）是反映氧化还原环境变化的重要指标。氮作为一种化学性质比较活跃的多价态元素，对Eh变化反映非常敏感，其存在状态、迁移和转化规律都与Eh密切相关。针对目前湖泊普遍存在的氮污染和富营养化问题，本课题拟以南洞庭湖湿地演替带为试验现场，监测Eh随土壤深度、水文要素、温度和pH的变化规律，并在Eh监测点采集水样，测定和分析氮的存在形态及特征，构建湿地演替带Eh剖面，研究Eh变化对氮赋存状态及转化的机理。同时进行室内模拟试验，测定湿地演替带土壤的渗透性，采用CT扫描研究不同土质类型中氮的迁移规律。通过对湿地演替带Eh和氮迁移转化机理的研究，探讨Eh与土壤、水文要素、氮迁移转化的关系，揭示湿地土壤和地下水中氮污染物迁移转化规律。在此基础上建立氮迁移转化数学模型，预测湿地环境时空变化趋势，对污染防治和水环境保护具有重要意义。

湿地演替带是湖泊湿地地表水和地下水相互作用的区域，具有降解污染物和净化水质的功能。湖泊地表水体富营养化会破坏演替带的生态环境并引发区域性的地下水环境问题。氮循环作为湿地生态系统中重要的子系统，对湖泊富营养化有重要作用。氧化还原电位（Eh）是反映氧化环境的重要指标，氮的赋存状态、迁移和转化规律都与Eh紧密相关。针对上述问题，本课题以西洞庭湖湿地演替带为试验现场，在澧水和沅水演替带各布设两个监测断面，进行一个完整水文年的地表水和地下水样采集，对地下水Eh、pH和温度进行现场测定，对水样的NO3-、NO2-、NH4+以及PO43-浓度进行实验室检测。. 通过对实验数据的分析和研究得出：1)湿地演替带Eh时空变化规律，湿地演替带和地下水均属于还原环境，随演替带剖面深度增大Eh在一定范围内逐渐减小。地下水Eh变化特征与地表水位变化相关,丰水期演替带未被地表水淹没时地下水Eh值较高，被淹没时地下水Eh值较低；枯水期Eh值一般较低；平水期Eh值处于以上两者之间。2)地下水Eh和pH决定了地下水中三氮比例,澧水和沅水演替带地下水Eh范围为-381mV~193mV之间,pH处于6~8之间，NH4+在演替带地下水是主要的存在形式。3)湿地演替带氮素来源及分布，澧水演替带的氮素主要来源于农业施肥；沅水演替带主要来源于生活污水，前者地下水中三氮浓度高于后者。4)湿地演替带氮素的迁移转化过程主要受环境因素驱动，Eh是最主要的驱动因子,与pH、温度、降雨量、土地利用方式等因子,协同驱动氮素在演替带内发生迁移转化。5)建立HYDRUS模型对湿地演替带地下水中氮的迁移转化进行预测。. 以洞庭湖澧水和沅水演替带为对象，研究湖泊湿地所共同面临的富营养化环境问题。建立了湿地演替带Eh变化剖面，丰富了湿地演替带Eh系列量测数据资料,得出了Eh变化特征。结合土壤和地下水理化特性，揭示了氮在演替带中迁移转化的主要途径与驱动因子。建立HYDRUS-3D模型预测氮在演替带内的迁移转化及浓度分布，并开展了部分延伸性工作，对污染防治和水环境保护具有重要意义。