Key nitrogen biogeochemical processes revealed by the nitrogen isotopic composition of dissolved nitrate in the Changjiang River estuary, China

• Published in: Chinese journal of oceanology and limnology Vol. 32; no. 1; pp. 162 - 173
• Main Author: 于海燕 俞志明 宋秀贤 曹西华 袁涌铨 卢光远 刘丽丽
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 2014; Springer Berlin Heidelberg; Springer Nature B.V
• Subjects: Ammonium; Ammonium compounds; Assimilation; Biogeochemistry; Biological activity; Biological assimilation; Brackish; Chemical composition; Chemistry; China; dissolved inorganic nitrogen; Dissolved oxygen; Earth and Environmental Science; Earth Sciences; equations; Estuaries; Estuarine dynamics; Fractionation; Isotopes; Low temperature; Marine; Marine environment; Mineralization; mixing; Nitrates; Nitrification; Nitrogen; Oceanography; Organic nitrogen; Rayleigh equations; River mouth; River mouths; Rivers; salinity; Seasonal variation; Seasonal variations; Surface water; temperature; 中国; 同位素组成; 正相关关系; 氮库; 溶解氧浓度; 生物地球化学过程; 酸溶解; 长江口; China; INW, China, People's Rep., Changjiang Estuary; mineralization; eutrophication; nitrification; assimilation
• ISSN: 0254-4059; 2096-5508; 1993-5005; 2523-3521
• DOI: 10.1007/s00343-014-3102-x

Seasonal variations in the nitrogen isotopic composition of dissolved nitrate （δ15NO3） were investigated in the surface waters of the Changjiang River estuary in 2009 and 2010. δ15NO3 varied between -4.6‰ and 8.9%0 with changes in temperature, salinity, dissolved oxygen concentrations, and the composition of the dissolved inorganic nitrogen pool. In February, biological processes decreased because of low temperature, and the mean δ15NO3 near the river mouth was 2.4%0. In May, δ15NO3 was the highest in the surface waters among all seasons. Analysis on the conservative mixing revealed assimilation, and this finding is supported by positive relationship between Chl a and δ15NO3. The fractionation factor of assimilation was estimated to be 2.0‰ by the Rayleigh equation. Nitrification was supported based on the mixing behaviors in November 2010 and the low δ15NO3 values in May and November 2009. The high ammonium concentrations in the adjacent marine area and positive relationships between total organic nitrogen and δ15NO3 in November 2010 indicated that mineralization was taking place.