中高纬冻融区河流N2O响应陆面非点源氮污染输出的模拟研究

Multiple studies have demonstrated that N2O emissions from various rivers respond significantly to increasing non-point source nitrogen loading. Due to the spring snow-melting and the autumn flood in the mid-high latitude freeze-thaw zone, the nitrogen pollution has the characteristics of two peaks, which has the important research significance of the rive N2O response to non-point source nitrogen pollution in cold regions. Based on the academic thoughts of “from source to sink/source”, the river N2O response to freeze-thraw and non-point source nitrogen pollution is studied in the Naoli river watershed of the Sanjiang Plain, which is in cold regions. By combining multi-sources observed river N2O and its environmental data, intensified field observations in the study area and simulations of process-based model, we aim to (1) develop a SWAT-FN2O model including modules of watershed diffuse pollution and the riverine N2O fluxes (FN2O), which is based on the water-air interface diffusion model; (2) optimize parameters of key processes in SWAT-FN2O, then figure out spatial-temporal changes in diffuse nitrogen loading and riverine N2O fluxes during the past 30 years by scenarios simulations; (3) evaluate the riverine N2O emission response to the diffuse nitrogen loading into the river and discuss the role of the river in the source/sink on the global nitrogen balance in cold regions. This study is important to further understand the transform and transport mechanisms of riverine nitrogen pollutants, which is from diffuse nitrogen in the surface land. In addition, this study is important to reduce the riverine greenhouse gas (N2O) emission and assess the climate change in cold regions.

陆面非点源氮入河量的增加，可能导致河流氧化亚氮(N2O)排放显著增加。中高纬区低温特征及非点源氮污染“冬存春出”和“秋汛输出”的双峰特征使河流N2O排放时空变异规律有别于温带及亚热带区。在当前流域水污染综合评估背景下，亟需对该区河流N2O对非点源氮污染输出的响应开展基础研究。本项目以三江平原挠力河流域为研究区，(1)基于多源河流N2O观测数据，构建河流溶存N2O回归模型，结合不同季节观测数据，运用水气界面扩散模型FN2O，揭示冻融区环境因子对河流N2O的影响及相关关系；(2)基于野外监测和室内实验数据对SWAT-FN2O耦合模型进行参数优化，揭示非点源氮输出及河流N2O年内、年际时空变异规律；(3)探究冻融区河流N2O对非点源氮污染输出的响应规律。本研究对加深冻融区非点源入河氮污染物迁移转化机理的理解具有重要理论意义，对河流温室气体减排及准确评估气候变化具有重要的实际价值。

陆面非点源氮入河量的增加，可导致河流氧化亚氮(N2O)排放显著增加。在当前流域水污染综合评估背景下，亟需对该区河流N2O对非点源氮污染输出的响应开展基础研究。本项目以三江平原挠力河流域为研究区，(1)基于多源河流N2O观测数据，构建河流溶存N2O回归模型，结合不同季节观测数据，运用水气界面扩散模型FN2O，揭示了冻融区环境因子对河流N2O的影响及相关关系;(2)基于野外监测和室内实验数据对SWAT-FN2O耦合模型进行参数优化，揭示了非点源氮输出及河流N2O年内、年际时空变异规律;(3)探究了冻融区河流N2O对非点源氮污染输出的响应规律，以及对不同水热条件下响应规律。同时，构建了基于遥感反演的水体水文水质及N2O产生与排放监测技术。本研究构建的SWAT-FN2O模型模拟的河流N2O产生量与排放量模拟精度较好，为评估流域面源N2O排放负荷的估算提供了新思路和新方法。研究发现，冻融农区河流N2O排放受到温度、传输速度、N2O溶解浓度和理论平衡浓度等季节性周期的影响，融雪和降水事件引起3-4月份河流N2O溶解浓度和气体传输速度的突然增加，但年内高峰期发生在6月份；以旱地和居住地为主的子流域，呈现出较高的河流N2O排放率，而在以林地和稻田为主的子流域，N2O排放速率相对较低。研究表明，与动态变化大气N2O浓度相比，使用恒定大气N2O浓度估算长期的河流N2O排放变化会导致河流N2O排放速率偏高，由于大气中N2O浓度的持续增加，这种高估将随着时间的推移变得越来越明显。为了克服野外观测问题，本项目进一步基于开源水文数据集、遥感云计算平台，结合贝叶斯理论及曼宁公式构建动态水文反演模型，基于实测数据探究N2O关键影响因子并构建水质遥感反演模型，再结合水-气界面N2O气体交换的半经验模型，构建基于遥感的的N2O产生与排放模型，实现快速有效的分析流域水文、水质及N2O产生与排放的时空变化。该方法为评估流域地表水体N2O排放的估算提供了新思路和新方法，对流域水体多界面氮排放评价及准确评估全球气候变化具有实际应用价值。