构筑根孔湿地土壤氧化还原形态特征的形成机制及其与污染净化的关系

Oxidation-reduction (redox) reactions are the most important and interesting chemical reaction that occur in aquic/hydric soils, and are central to major element cycling, to many sorption processes, to trace element mobility and toxicity, to most remediation schemes, and to life itself. Compared with natural wetlands, the redox reactions processes in constructed wetlands are more quick, intense and diverse. A large quantity of soil "microsites" exist for the occurrence of these reactions. The accompanying specific redoximorphic features (RMFs) form around these soil microsites. Relatively more effort had been put on the soil RMFs in (semi-) natural hydric soils at home and abroad. However, the formation mechanisms of RMFs were less studied in constructed wetlands. As yet to our best knowledge we have not found any report about RMFs in a constructed wetland with constructed root channels which were formed by artificially buried plant straws. This project will select the plant-bed/ditch systems in constructed root channel wetlands as study objects. A series of methods and techniques will be adopted including profile checking and reduced scale representation of RMFs and macropores with grid positioning, soil micromorphology, platinum electrode construction for in situ redox potential measurements with reference electrode and voltmeter, Rhizon soil moisture samplers - an excellent pore water sampler, dissolved greenhouse gas sampling and determination, delta 15N natural tracer and other tracer technology including brilliant blue FCF as a dye tracer and halide ion (Cl-, Br-, I-) as a solute-transport monitor, control and simulation experiments based on orthogonal test design and so on. Through continuous researches of four years, the following objectives are expected to achieve, (1) to reveal the formation mechanisms of RMFs in the soil phase and sediment phase of constructed wetlands; (2) to verify the main redox reactions occurring in constructed wetlands; (3) to characterize the roles of RMFs in the water quality improvement of constructed wetlands; (4) to probe into the inhibiting mechanism of constructed root channel wetland on greenhouse gases production and emissions. This project study might obtain some breakthroughs in the purification mechanisms of wetlands constructed root channels. It would provide scientific evidence for deeply exploring the oxidation-reduction reactions processes occurring in constructed wetlands and promoting the large-scale engineering application of constructed root channel technology.

氧化还原作用是渍水土壤中最重要的反应。与自然湿地相比，人工湿地内部氧化还原反应过程更剧烈，存在着大量的反应"微区"，并伴随其特有的氧化还原形态特征（RMFs）。国内外已针对（半）天然水成土壤RMFs开展了较大量研究。然而，有关人工湿地RMFs形成机理的研究甚少，未见埋植秸秆形成根孔的湿地RMFs报道。项目选择构筑根孔湿地植物床-沟壕系统为对象，采用方格法剖面清查、土壤微形态、氧化还原电位原位探针法、孔隙水原位采集、溶存气体测定、delta 15N自然丰度法等示踪技术、模拟控制试验等方法手段，通过连续4年的研究，探明人工湿地土壤和沉积物相RMFs的形成机制，求证人工湿地中发生的主要氧化还原反应，表征人工湿地RMFs在水质净化中所扮演的角色，剖析构筑根孔湿地的温室气体减排作用机制。本研究有望在湿地根孔净化机理方面获得突破，为深入揭示湿地氧化还原反应过程和工程推广应用方面提供科学依据。

湿地系统中的氧化还原反应过程和调控机制一直是研究热点和难点。有关人工湿地氧化还原形态特征形成机理的研究甚少，未见埋植秸秆形成根孔的湿地中氧化还原形态特征报道。本基金项目围绕构筑根孔湿地氧化还原状况变化与物质迁移转化的梯度和热区效应开展研究，旨在揭示构筑根孔湿地运行初期在湿地水文情势的激发下岸边带芦苇根际土壤中氧化还原状况的变化特征，氧化还原形态特征的形成机制，及其与各类污染物净化之间的关系。主要研究内容包括：湿地岸边带土壤氧化还原形态特征的表征和形成机制，人工湿地中发生的主要氧化还原反应及其影响因素，氧化还原状况变化在水质净化过程中所扮演的角色，构筑根孔湿地的温室气体减排机制，岸边带芦苇根际土壤氨氮吸附过程与机制和微生物群落结构特征，植物床-沟壕系统对源水藻类的捕获效应，构筑根孔湿地夏季浮游植物群落结构及水质指征，根孔湿地对典型污染物重金属、多环芳烃的累积作用机制等。发现：不同氧化还原形态特征在构筑根孔湿地已初步形成，人造根孔周围土壤为氧化还原贫化区，自然根孔周围为氧化还原新生体；根孔净化区是氧化还原的剧烈交替区域，根孔净化区的植物床-沟壕系统是界面反应最为强烈的区域，在此发生着微生物群落结构的水平迁移和活性增强效应，土壤酶活性的交叠变化和底物响应，氮磷等营养元素的迁移转化，藻类的捕获和降解效应，以及重金属和多环芳烃等难降解和持久性物质的富集和持留。发现源水有机质的性质在冬季经湿地净化后发生了显著变化，其可生化性的增强主要是在植物床-沟壕系统中完成的；通过对植物床-沟壕系统进行形态优化改进，可以显著增强其界面反应梯度和氨氧化微生物的反应活性；构筑根孔湿地能够有效地减排或避免温室气体的产生。本研究为人们认识构筑根孔湿地氧化还原状况变化与物质迁移转化的梯度和热区效应提供参考依据，为构筑根孔湿地的推广应用提供技术支撑。