Dissimilatory nitrate reduction processes between the sediment-water interface in three typical wetlands of middle and lower reaches of Yangtze River

Abstract

反硝化（Denitrification，DNF）和硝酸盐异化还原为氨（Dissimilatory Nitrate Reduction to Ammonium，DNRA）是硝酸盐异养还原的2个主要途径.反硝化被认为是彻底去除水体氮负荷的主要过程；而硝酸盐异化还原为氨则将水体中的硝态氮转化为氨氮.2个过程均以硝酸盐为电子受体，并存在相互竞争关系.这2个过程的研究对理解湿地氮转化以及指导湿地氮污染修复具有重要意义.运用无扰动沉积物柱样流动培养、¹⁵NO₃^--N同位素示踪实验，并采用氨氧化-膜接口质谱仪联用（OX/MIMS）测定氨氮同位素产物的方法，对鄱阳湖碟形湖湿地、巢湖重污染河流湿地、巢湖重污染湖泊湿地3种类型湿地沉积物-水界面的硝酸盐异养还原过程进行研究，结果表明存在显著差异.3种类型湿地DNF速率的范围为（6.36±2.57）~（99.98±14.05）μmol/（m²·h），DNRA速率的范围为（0.51±0.45）~（79.82±6.08）μmol/（m²·h）.在3种类型湿地中，随着氮污染程度加重，DNF和DNRA速率均显著增加，且DNRA过程在总的硝态氮异养还原中所占的比重不断增大，说明较高的硝酸盐负荷、较高的沉积物有机质含量更有利于DNRA过程的竞争.而对反硝化方式的进一步研究发现，巢湖重污染河流、湖泊湿地主要以非耦合反硝化为主导过程，而鄱阳湖碟形湖湿地则更倾向于以硝化过程耦合控制的反硝化为主.;Denitrification(DNF) and dissimilation reduction to ammonium(DNRA) are two major pathways for the dissimilatory nitrate reduction processes. Denitrification is the dominant nitrogen loss process that removes nitrate in the water column, while DNRA reduces nitrate to ammonium which is still a biologically available form in aquatic environments. The nitrate served as electron acceptor during denitrification and DNRA processes, and the balance of two processes depends on environmental factors. The study on rates of denitrification and DNRA plays an important role in understanding the fate of nitrate and its dynamic. In this study, intact sediment cores were collected in three wetlands of Lake Poyang and Lake Chaohu. Denitrification and DNRA rates were determined by continuous-flow experiments combined with ¹⁵N isotope-tracing techniques to investigate their contributions to total nitrate reduction. The results showed that denitrification and DNRA rates ranged from (6.36±2.57) to (99.98±14.05) μmol/(m²·h) and (0.51±0.45) to (79.82±6.08) μmol/(m²·h), respectively. DNRA rates were enhanced significantly with increasing pollution degree as well as the DNRA/(DNF+DNRA) ratio, which indicates that the contribution of DNRA to total nitrate reduction in these wetlands was affected by nitrate loadings. Uncoupled nitrification-denitrification was the dominant nitrogen removal process in Lake Chaohu, and coupled denitrification was the dominant process in the Lake Poyang.