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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+、PO43-和SiO32-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-δ15NPδ13CP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-、PO43-和SiO32-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-δ15NP)未表现出随盐度的变化规律,而δ18O-NO3-δ13CP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”。
INDICATIONS OF NUTRIENTS PROCESS REVEALED BY DIURNAL VARIATIONS OF NITROGEN ISOTOPES IN THE WATERS ADJACENT TO CHANGJIANG ESTUARINE
WANG Wen-Tao1,2,3, YU Zhi-Ming1,2,3,4, SONG Xiu-Xian1,2,3,4, WU Zai-Xing1,2,3, YUAN Yong-Quan1,2,3
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+, PO43- and SiO32- 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-, δ15NP, and δ13CP 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-, PO43-, and SiO32- 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 δ13CP 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
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