Liu Chao-Rong, Zhu Jun-Yu, Li Yu-Yang, Yu Xiao-Qin, Chen Hui-Min, Yang Yan, Zhou Yong-Qiang
College of Environment Science and Engineering, China West Normal University, Nanchong 637000, China.
State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China.
Huan Jing Ke Xue. 2022 Aug 8;43(8):4118-4126. doi: 10.13227/j.hjkx.202111017.
Nitrous oxide (NO) is one of the six greenhouse gases stipulated in the Kyoto Protocol. Its greenhouse potential over the past century was 298 times that of CO, and the concentration of atmospheric NO has been continuously and rapidly increasing during the past hundred years. Shallow lakes are an important source of atmospheric NO. In order to explore the temporal and spatial changes and potential driving factors of NO emissions from eutrophic water, we conducted field observations in February (winter) and August (summer) in Lake Taihu. We used the coefficient of diffusion-headspace bottle method to trace the variability in the NO concentration[(NO)] and efflux[(NO)] from surface water bodies and explored the potential driving factors of NO emissions. The optical measurements of dissolved organic matter (DOM) are an effective approach for tracing the source and composition of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON). The migration and transformation processes of DOM also release a large amount of inorganic nitrogen, which changes the redox potential of the water column and thereby affects NO emissions. Our results showed that the variability in (NO) and (NO) in the surface waters of Lake Taihu were strongly affected by water temperature and nutrient levels. The average (NO) of the surface waters was (19.7±2.7) nmol·L, corresponding to a mean (NO) of (41.1±1.8) μmol·(m·d), and the means of both (NO) and (NO) were higher in summer than those in winter (-test, <0.01). The input and accumulation of DOM could increase the production and emission potential of NO in water bodies, as supported by both (NO) and (NO) significantly increasing with increasing level of terrestrial humic-like C1. The integration ratio of peak C to peak T : of DOM and the spectral slope results indicated that there were high inputs of terrestrial DOM in the northwestern inflowing river mouths, concurring with the high production and emission of NO found there. This suggested that the accumulation and degradation of terrestrial DOM potentially fueled the emission of NO. Our results showed that water temperature, DOM composition, and nutrient level were all important factors affecting NO emission from Lake Taihu. Long-term continuous observation can be applied to better evaluate the impact of various environmental factors on the production and emission of NO in water bodies and to help with providing scientific emission reduction plans.
一氧化二氮（N₂O）是《京都议定书》规定的六种温室气体之一。在过去的一个世纪里，其温室效应潜能是二氧化碳的298倍，并且在过去的一百年中，大气中N₂O的浓度一直在持续快速增加。浅水湖泊是大气中N₂O的一个重要来源。为了探究富营养化水体中N₂O排放的时空变化及潜在驱动因素，我们于2月（冬季）和8月（夏季）在太湖进行了实地观测。我们采用扩散-顶空瓶系数法来追踪地表水水体中N₂O浓度[（N₂O）]和通量[（N₂O）]的变化，并探究N₂O排放的潜在驱动因素。对溶解有机物（DOM）的光学测量是追踪溶解有机碳（DOC）和溶解有机氮（DON）来源及组成的有效方法。DOM的迁移和转化过程也会释放大量无机氮，这会改变水柱的氧化还原电位，从而影响N₂O排放。我们的研究结果表明，太湖表层水体中（N₂O）和（N₂O）的变化受水温及营养水平的强烈影响。表层水体的平均（N₂O）为（19.7±2.7）nmol·L，对应的平均（N₂O）为（41.1±1.8）μmol·（m²·d），且（N₂O）和（N₂O）两者的均值在夏季均高于冬季（t检验，P<0.01）。DOM的输入和积累会增加水体中N₂O的产生和排放潜能，这得到了（N₂O）和（N₂O）均随陆地类腐殖质C1水平升高而显著增加的支持。DOM的峰值C与峰值T的积分比值以及光谱斜率结果表明，在西北入湖河口有大量陆地DOM输入，这与在那里发现的高N₂O产生和排放情况一致。这表明陆地DOM的积累和降解可能推动了N₂O的排放。我们的研究结果表明，水温、DOM组成和营养水平都是影响太湖N₂O排放的重要因素。长期连续观测可用于更好地评估各种环境因素对水体中N₂O产生和排放的影响，并有助于制定科学的减排计划。
