湖泊沉积物硝酸盐异化还原为铵与反硝化过程的偶联作用及其对藻类演替的影响

The coupling of the denitrification and dissimilatory nitrate reduction to ammonium (DNRA) process (with the same substrate and the similar induction factors but totally different ecological function) in sediments of lake, makes an important impact on the regulation of nitrogen loading and algal succession. This study will combine a systematic analysis of the relationship between DNRA, denitrification rate and various physicochemical factors in sediments of lakes in Wuhan city and Lake Chaohu with different eutrophic level. The composition of bacterial communities involved in denitrification and DNRA process will also be studied. Furthermore, the key environmental factors regulating the denitrification and DNRA process will be screened. Through laboratory simulation and field mesocosm experiments, the weight proportion, scope and threshold of the key factor will be determined. Then we will put forward the coupling mechanism of denitrification and DNRA process, and evaluate the contribution percentage of denitrification and DNRA process to nitrogen loading. On this basis, the effect of the change of nitrogen form and content resulting from the denitrification and DNRA process on algal succession (between N2-fixing cyanobacteria and non-N2-fixing cyanobacteria) will be studied and discussed. Finally, we will outline the relationship between physicochemical factors, denitrification and DNRA process, nitrogen loading and algal succession. In a word, this project is expected to provide the more basic data about DNRA, and important support for the development of nitrogen loading estimation and nitrogen removal or retention technologies through regulating the denitrification and DNRA, and also a new possible explanation for algal succession.

湖泊沉积物反硝化与硝酸盐异化还原为铵（简称DNRA）过程作用底物和诱发条件较为相似但结果迥然不同，两个过程的偶联对氮负荷的调控和藻类演替均可产生重要影响。本项目以武汉市湖泊和巢湖为对象，系统分析不同类型湖泊或湖区沉积物中反硝化和DNRA速率与理化因子的关系，辨析参与反硝化和DNRA过程的细菌群落组成，筛选调控反硝化和DNRA过程的关键因子。结合室内和野外模拟验证关键调控因子的权重、作用范围与阈值，提出反硝化和DNRA过程的偶联机制，据此估算两个过程对氮负荷的调控贡献。在此基础上，探讨基于反硝化与DNRA作用的氮形态和含量改变对水华藻类演替（固氮蓝藻与非固氮蓝藻）的影响，勾勒出理化因子、反硝化和DNRA过程、氮负荷与藻类演替之间的对应关系。本项目有望提供更多DNRA过程的基础数据，并为沉积物氮负荷估算和氮的去除或保留等相关技术的研发提供重要支撑，同时为水华藻类演替提供新的解释。

硝酸盐异化还原为铵（DNRA）和反硝化是硝酸盐异化还原分化的两个过程，弄清影响两个过程分化的关键调控因素不仅有助于了解其对氮素水平的调控作用和藻类演替的影响，而且对底泥修复和污水处理过程中脱氮功能的提升起到重要的指导作用。本项目首先以长江中下游湖泊、水库、池塘开展大尺度调查（30余个水体、超200个样点），发现有机碳的分解能力和碳氮比是硝酸盐异化还原过程分化的关键指标，较高的有机碳分解能力和碳氮比更能促进DNRA功能超过反硝化作用。而在硫元素较高的区域，碳硫比代替碳氮比更能直接影响硝酸盐异化还原过程的分化。同时，有机碳组分氧烷基碳（主要来源于藻类）更易诱导DNRA过程，从而增强氮的保留。在此过程中，DNRA功能主要由数量更少的DNRA细菌行使。随后，选择固氮与非固氮蓝藻水华演替的水体进行密集调查，并结合室内和野外模拟试验，验证本项目的科学假设：固氮蓝藻水华衰亡后诱发DNRA过程占优，促使水体铵态氮富集，这有利于非固氮蓝藻水华的发生，而非固氮蓝藻水华衰亡后激发反硝化过程脱氮，引发水体中氮的缺乏，进而有助于固氮蓝藻水华的发生。最后，由于硝酸盐异化还原过程的分化直接决定氮的去除或保留，故开展了底泥修复材料和污水处理基质方面的研发工作，重点突破材料筛选、剂量确定、效果评估、模型构建、生产工艺等研发内容，并发现有机碳的可持续性分解、有机碳的多元化、有机碳的量不宜过多等因素可显著提升反硝化作用且限制DNRA过程，并以此为基础最终研制出底泥原位修复专用材料和污水处理特殊基质等产品，以期最大程度地实现脱氮功能且避免DNRA过程。研发的产品在室内模拟、原位围隔、中试等不同规模条件下进行验证和评估，结果表明产品的各项指标均明显高于国内外类似产品，目前正在进行推广应用。总体来说，本项目按计划进展顺利，完成项目规定的研究内容和目标并有所延伸，且开发相关产品进行推广应用，在氮素的转化方面具有重要的理论和实践意义。