State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Biomedical Omics Center, Korea Basic Science Institute, Cheongju 28119, South Korea.
Sci Total Environ. 2020 Jun 20;722:138005. doi: 10.1016/j.scitotenv.2020.138005. Epub 2020 Mar 16.
Lakes actively transform nitrogen (N) and emit disproportionately large amounts of NO relative to their surface area. Studies have investigated the relative importance of denitrification or nitrification on NO emissions; however, the linkage between NO efflux and dissolved organic nitrogen (DON) and carbon (DOC) remains largely unknown. Long-term (2012-2017) seasonal field observations and a series of degradation experiments were used to unravel how DON composition impacts NO emissions from Lake Taihu, China. In the northwestern part of the lake, large riverine inflow and high NO emissions occur in all seasons (24.6 ± 25.2 μmol m d), coincident with high levels of terrestrial DON and DOC here. The degradation of labile DON and DOC likely enhanced ammonification as supported by the correlations between NH-N and DON, DOC, a(350), and terrestrial humic-like C3. The area with large riverine inputs in the northwestern part of the lake was characterized by low DO which may enhance incomplete aerobic nitrification and incomplete denitrification, both leading to NO production. Twenty days laboratory experiments indicated greater NO production in the northwest inflow samples (NO on day 20: 120.9 nmol L and 17.3 nmol L for bio- and photo-degradation samples, respectively) compared with the central lake samples (NO on day 20: 20.3 nmol L and 12.3 nmol L for bio- and photo-degradation samples, respectively), despite both having low Chl-a. Our DON and DOC degradation experiments confirmed the occurrence of ammonification along with consumption of NH-N and thereafter NO-N. Our results collectively suggest that terrestrial DON fueled ammonification, enhanced nitrification and incomplete denitrification, and thereby became an important contributor to the NO efflux from Lake Taihu.
湖泊积极地转化氮（N），并相对于其表面积不成比例地大量排放 NO。已有研究调查了反硝化或硝化作用对 NO 排放的相对重要性；然而，NO 通量与溶解有机氮（DON）和碳（DOC）之间的联系在很大程度上仍不清楚。本研究采用长期（2012-2017 年）季节性野外观测和一系列降解实验，以揭示太湖 DON 组成如何影响其 NO 排放。在湖泊的西北部，大量的河流流入和高 NO 排放发生在所有季节（24.6±25.2 μmol m d），与这里高浓度的陆源 DON 和 DOC 相一致。易降解 DON 和 DOC 的降解可能增强了氨化作用，这得到了 NH-N 与 DON、DOC、a(350)和陆源腐殖质样 C3 之间的相关性的支持。湖泊西北部河流输入量大的区域特征是低 DO，这可能会增强不完全好氧硝化和不完全反硝化作用，这两种作用都会导致 NO 的产生。20 天的实验室实验表明，西北入流样品中的 NO 产生量更大（生物和光降解样品在第 20 天的 NO 分别为 120.9 和 17.3 nmol L），而湖心区样品的 NO 产生量较低（生物和光降解样品在第 20 天的 NO 分别为 20.3 和 12.3 nmol L），尽管这两个区域的 Chl-a 都较低。我们的 DON 和 DOC 降解实验证实了氨化作用的发生，以及 NH-N 的消耗和随后的 NO-N 的消耗。我们的结果共同表明，陆源 DON 促进了氨化作用、硝化作用和不完全反硝化作用，从而成为太湖 NO 排放的一个重要贡献者。
