水域中硝化作用與氧化亞氮的產生:亞熱帶深水水庫與長江口擴散舌研究案例;The nitrification and N2O production in aquatic environment: case studies in a subtropical deep reservoir and Chang Jiang River plume

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Title:	水域中硝化作用與氧化亞氮的產生:亞熱帶深水水庫與長江口擴散舌研究案例;The nitrification and N2O production in aquatic environment: case studies in a subtropical deep reservoir and Chang Jiang River plume
Authors:	蕭淞云;Hsiao,Sun-Yun
Contributors:	國際研究生博士學位學程
Keywords:	硝化作用;氧化亞氮;穩定同位素示蹤劑;懸浮顆粒;沉降顆粒;水庫;河口擴散舌;鐵錳氧化物;nitrification;nitrous oxide;stable isotope tracer;suspended particles;sinking particles;reservoirs;river plume;Fe/Mn oxide
Date:	2014-10-14
Issue Date:	2014-11-24 15:42:22 (UTC+8)
Publisher:	國立中央大學
Abstract:	硝化作用是氮循環中一個重要的中間過程，它將氨氧化為亞硝酸或硝酸，並產生氧化亞氮為副產物。它被認為是水域環境中溫室氣體氧化亞氮(N2O)的主要產生過程。氧化亞氮是第三大人為溫室氣體，自從上個世紀大量使用化學合成的肥料後，大氣中的氧化亞氮濃度便開始顯著升高。這些過量的氮留在土壤中或沖刷至水域環境中，便有可能經由硝化作用轉變為氧化亞氮。另一個在水域中自上個世紀以來因人類活動而增加的特徵便是懸浮顆粒物。本論文以穩定同位素示蹤劑法量測硝化作用速率，並探討懸浮顆粒於硝化作用及 N2O 生成的影響。在副熱帶與中營養化的翡翠水庫發現硝化作用速率與 N2O 皆主要分布於無光層，但銨在該處卻很少。沉降顆粒補集器(sediment trap)的結果顯示在冷季與颱風季時顆粒沉降通量較高，這些快速沉降顆粒物使是由於上游集水區的強降雨帶來並在水庫中型成混濁的中層流(interflow)現象。這些顆粒物上的有機物直接注入無光層可能作為畏光的硝化作用微生物的基質，促進了硝化作用速率以及 N2O 的累積。在長江口擴散舌區，同步量測的群聚呼吸率與硝化速率結果顯示在中等鹽度區域硝化作用需要的氧氣甚至比群聚呼吸率還高。而懸浮顆粒物上的鐵錳含量發現足以提供硝化作用所需的氧化劑，同時也發現其含量與硝化速率高度相關，顯示鐵錳氧化物可能代替氧氣作為硝化作用的氧化劑。此外，N2O 的產生速率也發現在最混濁的河口區高於其他區域。以上結果顯示水域中因強降雨或土壤侵蝕而增加的懸浮顆粒可以促進硝化作用並可能增加 N2O 的產生，進而加速全球暖化。 ;Nitrification is an important intermediate process in nitrogen cycle that oxidizes ammonia to nitrite and/or nitrate and produces N2O as byproduct. Currently, nitrification has been recognized as the major source of N2O, which is regarded as one of the main greenhouse gases. Since 19th century, excessive use of chemical synthesized nitrogenous fertilizer has elevated the total amount of nitrogen in environments. The excess nitrogen remained in soil and leached into aquatic environments may be transformed to N2O through nitrification. In addition, the enhanced soil erosion can elevate the suspended particles in aquatic environments. In this dissertation we determined the rate of nitrification (NR) in turbid environments by the stable isotope tracer method to investigate the role of suspended particles on nitrification and N2O production. In the subtropical mesotrophic Feitsui Reservoir, high NR and N2O were recorded in the aphotic zone where rare ammonium and high particle sinking flux occurred. These fast-sinking particles in the aphotic zone was dominantly brought from the turbid interflows induced by heavy precipitation during cold season and typhoon periods. The light-sensitive nitrifying microorganisms may utilize the remineralized organics on those particles as substrate source for nitrification and also N2O production. In Chang Jiang River plume, simultaneous measurement of NR and community respiration rate (CR) revealed that the oxygen demand of nitrification was greater than that of community respiration. However, the amounts of reactive Fe/Mn oxide of suspended particles seemed enough to support oxidant demand of nitrification. Meanwhile, the reactive Fe/Mn was significantly positive correlated to NR, indicating that the reactive Fe/Mn may serve as an alternative electron acceptor in nitrification. Moreover, the production rate of N2O from ammonium in the turbid river mouth is significantly higher than that in other relatively clear regions. The results suggested that the elevated suspended particles in aquatic environment due to soil erosion may enhance nitrification and also N2O production. Consequently, the increasing N2O may potentially accelerate the global warming.
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