Quantifying nitrate dynamics in an oligotrophic lake using Δ17O
Quantifying nitrate dynamics in an oligotrophic lake using Δ17O
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DOI：
10.5194/bg-8-687-2011
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发表时间：
2011-03
期刊：
影响因子：
4.9
通讯作者：
U. Tsunogai;S. Daita;D. Komatsu;F. Nakagawa;A. Tanaka
中科院分区：
文献类型：
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作者：
U. Tsunogai;S. Daita;D. Komatsu;F. Nakagawa;A. Tanaka
抽象。在2007年6月和8月对日本马周湖贫营养水体中硝酸盐的稳定同位素组成进行了两次测定，包括17 O异常（Δ 17 O）。然后，这些数据被用来量化硝酸盐在湖泊的地球化学动力学，通过使用大气硝酸盐的沉积速率到整个集水区的湖泊。在两次观测之间的时间段内，湖水中硝酸盐的总量从4.2 Mmol下降到2.1 Mmol，而平均Δ 17 O值保持不变，为+2.5‰。Δ 17 O值对应于大气硝酸盐与总硝酸盐的小而均匀的混合比（9.7 ± 0.8%）。这些结果表明，0.52 ± 0.34 Mmol的矿化硝酸盐通过硝化作用进入水柱，而2.6 ± 0.4 Mmol的硝酸盐同时通过同化作用从水柱中去除。湖水中溶解的硝酸盐的特征是在夏季通过同化作用迅速去除，直到几乎完全从真光层中去除，以及通过硝化作用（3.2 ± 0.3 Mmol a−1）和沉积作用（0.35 ± 0.2 Mmol a−1）持续进入湖泊，而不受季节的影响。6月硝酸盐的15 N-贫化氮同位素组成低至-6.5 ‰，这也表明湖内硝化作用是湖泊硝酸盐的主要来源，并表明湖泊及其周围的反硝化潜力很低。沉积到湖泊中的大气硝酸盐将被迅速同化，平均停留时间为1.2 ± 0.1年。此外，90%以上的被同化的硝酸盐将被同化为硝酸盐，并通过湖泊中的活性氮循环被再同化。
Abstract. The stable isotopic compositions of nitrate, including the 17O anomalies (Δ17O), were determined twice in 1 yr (June and August 2007) in the oligotrophic water column of Lake Mashu, Japan. These data were then used to quantify the geochemical dynamics of nitrate in the lake, by using the deposition rate of the atmospheric nitrate onto the entire catchment area of the lake. The total amount of nitrate in the lake water decreased from 4.2 to 2.1 Mmol during the period between the observations, while the average Δ17O values remained uniform at +2.5‰. The Δ17O values corresponded to an small and uniform mixing ratio of atmospheric nitrate to total nitrate of 9.7 ± 0.8%. These results indicate that 0.52 ± 0.34 Mmol of the remineralized nitrate was fed into the water column through nitrification, while 2.6 ± 0.4 Mmol of nitrate was simultaneously removed from the water column by assimilation, during the period between the observations. The lake water dissolved nitrate was characterized by rapid removal through assimilation during summer until it was almost completely removed from the euphotic layer, as well as continuous feeding into the lake through nitrification (3.2 ± 0.3 Mmol a−1) and deposition (0.35 ± 0.2 Mmol a−1), regardless of the seasons. The 15N-depleted nitrogen isotopic compositions of nitrate were as low as −6.5‰ in June, which also indicates that in-lake nitrification is the major source of nitrate in the lake and suggests that there is low potential for denitrification in and around the lake. Atmospheric nitrate deposited into the lake will be assimilated quickly, having a mean residence time of 1.2 ± 0.1 yr. In addition, more than 90% of the assimilated nitrate will be remineralized to nitrate and re-assimilated via active nitrogen cycling in the lake.