Journal of Tropical Oceanography ›› 2016, Vol. 35 ›› Issue (5): 38-47.doi: 10.11978/2015130CSTR: 32234.14.2015130

• Marine Biology • Previous Articles     Next Articles

Nitrogen fixation and its contribution of nitrogen to primary production in the surface waters of the northeastern South China Sea during October 2014

LIU Jiaxing1, 2, 3, ZHOU Linbin1, 2, LI Gang1, 2, TAN Yehui1, 2, LIU Huajian1, 2, 3, ZHAO Chunyu1, 2, 3, KE Zhixin1, 2, LI Jiajun1, 2, 3, JIANG Xin1, 2, 3   

  1. 1. Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;; 2. Guangdong Provincial Key Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;; 3. University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2015-10-22 Online:2016-08-29 Published:2016-09-22
  • Contact: Corresponding author: TAN Yehui. E-mail: tanyh@scsio.ac.cn
  • Supported by:
    Foundation item: National Science Foundation of China (41130855 and 41276162); Strategic Priority Research Program of the Chinese Academy of Sciences (XDA11020200); Special Fund for Agro-scientific Research in the Public Interest (201403008); National Project of Basic Sciences and Technology of China (2012FY112400 and 2013FY111200) and Science and Technology Planning Project of Guangdong Province (2014B030301064)

Abstract: Biological N2 fixation rate and primary productivity in surface seawater were measured using 15N and 14C tracer assays, respectively, at 28 stations in the northeastern South China Sea during October 2014. Combined with variables including temperature and salinity, dissolved nutrients and chlorophyll a, the spatial distribution of N2 fixation rate, and the nitrogen contribution of N2 fixation to primary production were discussed. Our results showed that the highest rate (3475 nmolN·m-3·h-1) was observed at a Pearl River plume-affected station, where substantial filamentous Trichodesmium colonies apparent to naked eyes occurred. The highest rate was about two or three orders of magnitude higher than those observed at other stations, where N2 fixation rates ranged from 4 to 213 nmolN·m-3·h-1 with an average of 77±54 nmolN·m-3·h-1 (n=27) were detected. The lowest N2 fixation rate was observed in the Taiwan Bank and its adjacent seawaters influenced by the China Coastal Current. There was a significant negative correlation between N2 fixation rate and surface seawater temperature in the inshore waters (bottom depth <100 m; R=0.68, p<0.05). Higher seawater temperature, higher phosphate concentration and lower nitrate plus nitrite concentration may contribute to the higher N2 fixation rate at the stations influenced by the Pearl River plume, while lower seawater temperature and salinity may result in the lower N2 fixation rate in the Taiwan Bank and its adjacent inshore seawaters influenced by the China Coastal Current. The primary productivity (14.19-0.17 mgC·m-3·h-1) decreased from the inshore area to the open waters. N2 fixation could meet 0.08% to 9.30% (3.90%±3.10% on average, n=28) of the nitrogen demand by primary production and the contribution percentage increased from the inshore area toward the open waters. In addition, the contribution percentage significantly increased when the surface temperature was higher than 26℃. Our results indicated that nitrogen fixation and primary production could be regulated by physical processes such as the Pearl River plume and China Coastal Current in the northeastern South China Sea in autumn.

Key words: nitrogen fixation rate, primary production, contribution, autumn, northeastern South China Sea