引用本文:	王文涛,俞志明,宋秀贤,吴在兴,袁涌铨.长江口邻近海域氮同位素的周日变化特征及其对营养盐过程的指示.海洋与湖沼,2020,51(4):909-918.

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长江口邻近海域氮同位素的周日变化特征及其对营养盐过程的指示
王文涛^1,2,3, 俞志明^1,2,3,4, 宋秀贤^1,2,3,4, 吴在兴^1,2,3, 袁涌铨^1,2,3
1.中国科学院海洋研究所海洋生态与环境科学重点实验室青岛 266071;2.青岛海洋科学与技术试点国家实验室海洋生态与环境科学功能实验室青岛 266237;3.中国科学院海洋大科学研究中心青岛 266071;4.中国科学院大学北京 100049

摘要:

长江口邻近海域的氮循环过程一直是近海富营养化研究领域的热点问题，然而目前较少有针对短周期的调查研究。本文调查了该区域氮、磷、硅等主要营养盐及多种形态的氮稳定同位素的在潮周期周日变化特征。结果显示，NO₃^-、NH₄⁺、PO₄^3-和SiO₃^2-的浓度范围分别为14.09—55.85、0.21—2.26、0.82—1.08和16.80—33.85μmol/L，而δ¹⁵N-NO₃^-、δ¹⁸O-NO₃^-、δ¹⁵N_P和δ¹³C_P等的分布范围分别为4.7‰—11.1‰、-2.0‰—7.8‰、-1.2‰—7.9‰和-22.9‰—-14.7‰。NO₃^-、PO₄^3-和SiO₃^2-均与盐度呈现明显的负相关特征，说明三者的主要来源为长江冲淡水；NH₄⁺则随盐度升高而浓度增加，且在底层高浓度出现时刻与高盐水团输入时刻一致，说明外海输入是该区域铵盐的主要来源。另一方面，氮稳定同位素（δ¹⁵N-NO₃^-和δ₁₅N_P）未表现出随盐度的变化规律，而δ¹⁸O-NO₃^-和δ¹³C_P则随盐度升高而增加，说明淡水输入的同位素值低于海洋水平。通过对比中、高浓度叶绿素水体中NO₃^-、15δ N-NO₃^-、δ¹⁸O-NO₃^-的变化特征可以看出，随NO₃^-浓度降低，δ¹⁵N-NO₃^-值升高，且呈现6.2‰的分馏系数，且氧同位素也随之增大，指示水体中浮游植物对硝酸盐的同化吸收作用。而另一方面，两种同位素的增加差值表现出△δ¹⁸O：△δ¹⁵N>1，说明硝酸盐在被消耗的同时还发生着补充作用。在较高盐度的水体中，发现NH₄⁺呈现出向硝酸盐的转化趋势并引起δ¹⁵N-NO₃^-降低，指示了底部明显的硝化过程，与此前的研究结果一致。本文结果以期丰富对河口区氮循环和迁移转化的认知。

关键词: 长江口邻近海域营养盐周日变化氮稳定同位素碳稳定同位素

DOI：10.11693/hyhz20191200270

分类号:P734

基金项目:国家自然科学基金青年基金，41806091号；国家重点研发计划，2016YFE0101500号；2019年度“泰山学者攀登计划”。

附件

INDICATIONS OF NUTRIENTS PROCESS REVEALED BY DIURNAL VARIATIONS OF NITROGEN ISOTOPES IN THE WATERS ADJACENT TO CHANGJIANG ESTUARINE

WANG Wen-Tao^1,2,3, YU Zhi-Ming^1,2,3,4, SONG Xiu-Xian^1,2,3,4, WU Zai-Xing^1,2,3, YUAN Yong-Quan^1,2,3

1.CAS Key Laboratory of Marine Ecology and Environmental Science, Institute of Oceanology, Chinese Academy of Science, Qingdao 266071, China;2.Laboratory of Marine Ecology and Environmental Science, Pilot National laboratory for Marine Science and Technology(Qingdao), Qingdao 266237, China;3.Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China;4.University of Chinese Academy of Sciences, Beijing 100049, China

Abstract:

The nitrogen cycles in the waters adjacent to Changjiang River estuarine have been a hotspot in the research to coastal eutrophication. However, few studies focused on the short-term changes. For enriching and expanding the knowledge of nitrogen cycles in this area, we studied the diurnal variations of nutrients, including nitrogen, phosphorus, and silicon as well as multiple nitrogen isotopes. The results show that the range of NO₃^-, NH₄⁺, PO₄^3- and SiO₃^2- concentrations ranged 14.09-55.85, 0.21-2.26, 0.82-1.08, and 16.80-33.85μmol/L, respectively, and the range of δ¹⁵N-NO₃^-, δ¹⁸O-NO₃^-, δ¹⁵N_P, and δ¹³C_P values were 4.7‰-11.1‰, -2.0‰-7.8‰, -1.2‰-7.9‰, and -22.9‰- -14.7‰, respectively. In this research, all of the NO₃^-, PO₄^3-, and SiO₃^2- displayed significantly negative correlations with salinity, indicating the main source of these three matters were Changjiang River diluted water. However, the NH₄⁺ concentrations rose with the salinity and showed high values during the high-salinity water mass appearance. It is suggested that NH₄⁺ was likely to be introduced by the ocean water. On the other hand, the nitrogen isotopes were not observed changes with salinity, while both δ¹⁸O-NO₃^- and δ¹³C_P increased with salinity, which demonstrated the values of terrestrial input were lower than the ocean input. The characteristics of NO₃^-, δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^- were analyzed in the high chl a waters. The δ¹⁵N-NO₃^- rose with the decrease in NO₃^- concentration in fractionation at 6.2‰, which indicated the nitrate assimilation of phytoplankton. Meanwhile, the δ¹⁸O-NO₃^- also rose during this process, but the increase ratio between N and O isotopes were higher than 1 (△δ¹⁸O︰△δ¹⁵N>1), suggesting that the nitrate was supplied by biological process during assimilating. In high salinity waters, the transformation trend from NH₄⁺ to NO₃^- were found, leading to the δ¹⁵N-NO₃^- decrease. This trend suggested the nitrification in the deep layers of the waters adjacent to Changjiang River estuarine, which supported the conclusions of previous research.

Key words: waters adjacent to Changjiang River estuarine nutrients diurnal variations nitrogen stable isotopes carbon stable isotopes