Controlling factors of seasonal variation in the nitrogen isotope ratio of nitrate in a eutrophic coastal environment
Controlling factors of seasonal variation in the nitrogen isotope ratio of nitrate in a eutrophic coastal environment
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DOI：
10.1016/j.ecss.2009.08.006
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发表时间：
2009-11
影响因子：
2.8
通讯作者：
R. Sugimoto;A. Kasai;T. Miyajima;K. Fujita
中科院分区：
文献类型：
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作者：
R. Sugimoto;A. Kasai;T. Miyajima;K. Fujita
研究了日本温带富营养化海湾中NO3−（δ NNO 315）氮稳定同位素比值的季节变化。随着温度、溶解氧浓度和溶解无机氮（DIN）池组成的变化，δ NNO 315的变化范围沿着从−10.4 ‰到9.3‰。全年，δ NNO 315分别与NO3−浓度和分数呈指数和线性正相关。δ NNO 315的最小值出现在DIN中NO3−含量较低的春季和秋季，而最大值出现在DIN中NO3−含量较高的夏季。这些结果表明，硝化作用是决定δ NNO 315变化的主要过程。春季和秋季的δ NNO 315最小值表明，低水温和短停留时间等水文特性抑制了硝化细菌的活性。硝化作用的氮同位素区分度（εnit）估计为−15至−25‰，这与之前实验室对海洋硝化菌的估计相似或略高。此外，海湾中心一年多的同位素结果表明，大部分NO3-是通过水柱中的原位硝化作用再生的。这意味着大量的再生氮将导致伊势湾的富营养化。
Seasonal changes in the nitrogen stable isotope ratio of NO3−(δNNO315) were investigated in a temperate eutrophic coastal embayment in Japan. Wide variation of δNNO315 from −10.4 to 9.3‰ was found along with changes in temperature, dissolved oxygen concentrations, and the composition of the dissolved inorganic nitrogen (DIN) pool. Throughout the year, δNNO315 showed positive exponential and linear relationships with NO3−concentrations and fractions, respectively. The minima of δNNO315 were observed in spring and autumn when the NO3−fraction in DIN was small, while the maximum was in summer when the NO3−fraction was large. These results indicate that nitrification was the dominant process that determined δNNO315 variation. The δNNO315 minima in spring and autumn suggested that hydrographic properties, such as low water temperature and short residence time of the water, suppressed the nitrifying bacterial activity in these seasons. An apparent nitrogen isotope discrimination (εnit) by nitrification was estimated as −15 to −25‰, which is similar to or slightly higher than previous laboratory estimates of marine nitrifiers. Furthermore, isotope results at the bay center over a year suggest that most of the NO3−was regenerated by in situ nitrification in the water-column. This implies that large amounts of regenerated nitrogen would lead the eutrophication in Ise Bay.