鄱阳湖湿地沉积物N2O/N2对淹水的响应特征及机理研究

Nitrogen removal is an important process in wetlands' function of water quality purification. Whether the nitrogen removal function of wetland is healthy depends not only on the total amounts of ionic nitrogen transformed to gaseous nitrogen, but also on the ratio of two different products, i.e. N2O/N2 ratio. As a parameter representing the extent of the last phase in denitrification, N2O/N2 indicates the N2O release potential, so it is a significant parameter that should be referred to in evaluating the health of wetlands' nitrogen removal function. In wide Poyang Lake wetland where the water level fluctuation is quite frequent and of large range, the responding shifts of various physicochemical parameters and microbials' function in sediment can obviously lead to dynamical changes of N2O/N2 ratio. Therefore, Poyang Lake wetland is chosen to be the research area in this research program. Combining the long-term in-situ observation of N2O/N2 ratio in various regions under different hydrological conditions, indoor thermostatical sediment core incubation experiments and outdoor wetland system simulation research, as well as the environmental factors profile obtained with Unisense microprobe instrument, the key factors controlling N2O/N2 ratio in sediment can be analyzed. Furthermore, after the N2O reductase genome and its responding to hydrological regime shifts obtained through the molecular biological test, the mechanisms of N2O/N2 ratio responding characteristics affected by flooding events can be revealed thereby. Finally, the optimized hydrological regime that could cause the reduction of N2O/N2 in Poyang Lake wetland sediment will be discussed.

脱氮作用是湿地净化水质的重要过程。健康湿地对氮的去除作用不仅取决于湿地水体将离子氮向气态氮转化的总量，还取决于脱氮过程两种气态氮产物的比例。N2O/N2代表反硝化过程中终端反应的不完全程度，表征着N2O释放潜力的高低，是评价湿地健康脱氮功能的重要依据。鄱阳湖湿地面积广阔且水位变幅极大，淹水过程导致的环境特征及微生物功能变化必然引起沉积物N2O/N2的动态响应。本研究以鄱阳湖典型湿地为研究对象，通过野外不同区域和水情下鄱阳湖湿地沉积物N2O/N2差异的原位观测，室内沉积物柱控温实验和室外湿地池实验的模拟研究，并结合微电极系统测定的沉积物剖面环境因子进行关键控制因素分析。通过分子生物学实验鉴定沉积物中N2O还原酶基因，研究其在淹水情景下的变化特征，并以此为纽带揭示湿地沉积物N2O/N2的受控机制。综合各项研究结果，探讨有利于鄱阳湖湿地沉积物N2O/N2降低的水情特征。

对于湿地脱氮作用的评价不仅取决于湿地水体将离子氮向气态氮转化的总量，还取决于脱氮过程两种气态氮产物氧化亚氮和氮气的比例。N2O/N2代表反硝化过程中终端反应的不完全程度，表征着N2O释放潜力的高低，是评价湿地健康脱氮功能的重要依据。鄱阳湖湿地水情特征多变，淹水过程导致的环境因素变化必然引起沉积物N2O/N2的响应。本研究以鄱阳湖典型湿地为研究对象，通过野外不同区域和水情下湿地反硝化作用、N2O排放通量和N2O/N2差异的原位观测、沉积物柱淹水培养模拟研究，并结合沉积物环境因子进行关键控制因素及机制分析，探讨有利于鄱阳湖湿地沉积物N2O/N2降低的水情特征。 .通过对不同区域和类型湿地反硝化速率和N2O/N2的调查研究发现，反硝化速率在具有水力连通性的湖沼沉积物中最高，在洲滩沉积物中次之，而与大湖区连通性较弱的内湾湖沼沉积物中最低，反硝化速率与上覆水硝酸盐呈显著相关关系（p<0.01）。在几大淹水特征存在典型差异的湿地类型中，河流型湿地的N2O排放通量最高，其余依次为洲滩湿地、半封闭湖湾、蝶形湿地。N2O/N2比的分布差异也发现了同样的规律，表明长期淹水状态对于提高反硝化中的N2O还原程度，降低N2O/N2比例较为有利。.选取鄱阳湖赣江主支入湖处的典型洲滩湿地为研究对象，探讨不同淹水状态下沉积物的反硝化酶活性与N2O排放的差异。结果发现，鄱阳湖湿地沉积物DEA随着深度的增加而显著降低，反硝化作用主要发生在沉积物表层附近的区域内。非淹水区沉积物的DEA显著高于淹水区沉积物。DEA与沉积物含水率、有机质和营养盐含量均呈显著的指数拟合关系，说明这几种指标均对反硝化过程有促进作用。淹水区域沉积物的N2O排放通量较低，这可能与淹水状态使得N2O/N2降低有关。.通过沉积物柱状样淹水培养模拟实验，发现沉积物的反硝化速率经历了“适应期-快速增长期-稳定期”的不同阶段。含水率、pH随着淹水过程而升高，Eh、TOC随着淹水过程而降低，沉积物间隙水中的硝酸盐随淹水时长呈降低趋势，而氨氮呈升高趋势。淹水过程中沉积物N2O释放速率随时间呈递减趋势，N2释放速率随时间呈递增趋势，N2O/N2比例从淹水初期的1.6%降至淹水稳定期的0.1%，降低不良了反硝化产物。通过相关性分析发现沉积物N2O/N2比与含水率、pH呈显著的负相关。同时，随着硝酸盐浓度的升高，N2O/N2比也有升高趋势。