Euphotic zone nitrification in the California Current Ecosystem
Euphotic zone nitrification in the California Current Ecosystem
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DOI：
10.1002/lno.11348
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发表时间：
2019-10
影响因子：
4.5
通讯作者：
B. Stephens;S. Wankel;J. Beman;A. Rabines;A. Allen;L. Aluwihare
中科院分区：
文献类型：
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作者：
B. Stephens;S. Wankel;J. Beman;A. Rabines;A. Allen;L. Aluwihare
硝化作用，即微生物将铵转化为亚硝酸盐，然后再转化为硝酸盐的过程，发生在整个海洋水体中，但影响富光带 (EZ) 硝酸盐产生的环境因素仍不清楚。在这项研究中，硝酸盐中 N 和 O 同位素（分别为 δ15N 和 δ18O）的自然丰度被用于现有的模型框架中，以量化加利福尼亚洋流生态系统 (CCE) 在两个异常温暖年份中 EZ 硝化作用所贡献的硝酸盐。模型数据估计，EZ 中 6% 至 36% 的硝酸盐库源自 EZ 内硝化作用的组合步骤。 CCE 数据集发现，硝化作用对 EZ 硝酸盐的贡献与初级亚硝酸盐最大值 (PNM) 深度处的亚硝酸盐浓度 (NO2−) 呈正相关。基于这种相关性，根据加州海洋渔业合作调查 (CalCOFI) 长期调查记录的 PNM NO2− 推断，南加州洋流的 EZ 硝化作用对 EZ 硝酸盐的贡献平均为 20% ± 6%。 CalCOFI PNM NO2− 时间序列的多元线性回归分析确定了导致 NO2− 出现正偏差的两个条件。 PNM NO2− 的增强和 EZ 硝化作用的潜在增强可能与（1）根据颗粒有机碳：叶绿素比率解释，浮游植物对铵（NH4+）和 NO2− 的竞争减少，和/或（2）根据颗粒有机氮浓度解释，由于有机氮降解而增加 NH4+ 的供应（然后 NH4+ 氧化为 NO2− ）。
Nitrification, the microbial conversion of ammonium to nitrite then to nitrate, occurs throughout the oceanic water column, yet the environmental factors influencing the production of nitrate in the euphotic zone (EZ) remain unclear. In this study, the natural abundances of N and O isotopes (δ15N and δ18O, respectively) in nitrate were used in an existing model framework to quantify nitrate contributed by EZ nitrification in the California Current Ecosystem (CCE) during two anomalously warm years. Model data estimated that between 6% and 36% of the EZ nitrate reservoirs were derived from the combined steps of nitrification within the EZ. The CCE data set found nitrification contributions to EZ nitrate to be positively correlated with nitrite concentrations ( NO2− ) at the depth of the primary nitrite maximum (PNM). Building on this correlation, EZ nitrification in the southern California Current was estimated to contribute on average 20% ± 6% to EZ nitrate as inferred using the PNM NO2− of the long‐term California Cooperative Oceanic Fisheries Investigation (CalCOFI) survey record. A multiple linear regression analysis of the CalCOFI PNM NO2− time series identified two conditions that led to positive deviations in NO2− . Enhanced PNM NO2− , and potentially enhanced EZ nitrification, may be linked to (1) reduced phytoplankton competition for ammonium ( NH4+ ) and NO2− as interpreted from particulate organic carbon:chlorophyll ratios, and/or (2) to increased supply of NH4+ (and then NH4+ oxidation to NO2− ) from the degradation of organic nitrogen as interpreted from particulate organic nitrogen concentrations.