水生植物塘水土界面处的碳氧调控及其对反硝化的影响机制

Hydrophyte pond is an important ecological technology in treating agricultural non-point source pollution. It was often found that different hydrophyte ponds showed obvious discrepancies in nitrogen removal efficiency in engineering practice. Aiming at this phenomenon, an assumption of "water depth and hydrophyte could arouse the change of organic matter and redox condition at water-sediment interface, and thus influence its denitrification performance" has been put forwarded. In experimental condition, the effects of some factors such as water depth, hydrophyte growth and death decay on organic matter, redox condition, nitrate flux and nitrogen removal in ecological pond system will be studied. Meanwhile, dissolved oxygen microsensor device and nitrogen isotope pairing technique will be applied to analyze the denitrification rate and nitrogen flux in the system. On this base, an enclosure experiment would be carried out to clarify the relationship between adjusting and controlling of organic matter and redox condition at water-sediment interface and the nitrogen removal efficency in hydrophyte pond, then the suitable range for adjusting and controlling organics and redox condition can be determined. Finally, a spot pilot-scale experiment would be carried out to verify the effect of hydrophyte growth and death decay on denitrification efficiency, which would supply basic foundation for the optimization design and operation controlling in hydrophyte pond.

水生植物塘是农业面源氮污染控制中的重要生态工程技术手段。在工程实践中，常常会出现不同状况塘系统脱氮效能差异明显的现象。针对这一问题，本申请课题提出"水深、水生植物造成水土界面氧化还原条件和有机碳含量发生变化，并进而影响水土界面的反硝化效能"这一假说。在实验室内受控试验条件下，采用溶解氧微电极法和氮同位素配对法解析水深、水生植物生长和衰亡腐解的碳氧调控与水土界面氧化还原条件、有机碳含量、硝酸盐通量、反硝化速率之间的相互关系；结合现场围隔试验，阐明碳氧调控与水生植物塘氮去除率的关系，从而揭示水深、水生植物对水土界面反硝化过程的内在影响机制，并确定最适于反硝化的碳氧调控范围。进一步通过现场中试试验，研究水生植物生长和衰亡腐解对塘系统脱氮效果的影响，为水生植物塘的优化设计和运行调控管理提供基础依据。

针对水生植物塘处理低碳氮比水体开展研究，研究期间依次开展了实验室小试研究、围隔实验和中试研究，得到了水生植物塘系统中水深、植物对水体pH、DO的影响，分析了水体中不同水深处的DO分布；通过对比研究得到了适于低碳氮比水体脱氮的水深条件和水生植物的类型及种植密度；研究了沉水、浮叶、挺水三种不同类型水生植物残体腐解对水质的影响，得到了具有最大C/N比释放能力的类型为挺水植物，并细致分析了典型挺水植物香蒲的腐解过程；研究了香蒲、菖蒲型水生植物塘处理低碳氮比水体的脱氮效能，分析了香蒲残体腐解强化塘系统脱氮的效能及作用机制，并对强化脱氮系统的碳氮平衡进行了测算；研究了不同类型电子供体对水培型菖蒲塘系统的氧化还原条件的影响，分析了对塘系统脱氮效能的强化作用机制，并明确了塘系统中温室气体的排放规律。通过上述研究，得到了不同自然温度段条件下不同类型电子供体（水生植物残体、无机电子供体、有机碳源）强化生态塘脱氮的工艺参数，为水生植物塘的优化设计和工程运行管理提供了基础数据。最终，通过较长时间的现场中试，研究了水生植物塘对硝酸盐污染水体的净化效果，并在植物枯萎期通过向生态塘中投加水生植物残体的方式，大幅提升了系统的脱氮性能，从而为水生植物在塘系统内部的循环利用提供了数据支撑，有利于实现强化水体反硝化和水生植物残体内部消纳循环的双重功能。