Journal of Oceanography

, Volume 71, Issue 1, pp 53–63 | Cite as

Characteristic of Si:P:N ratio in bottom water in central Suo-Nada, western Seto Inland Sea

  • Kazuo Abe
  • Mutsumi Tsujino
  • Norihisa Nakagawa
  • Katsuyuki Abo
Original Article


The nutrient composition in seawater is considered to determine the regional phytoplankton species, its composition, and its productivity. In order to examine the nutrient composition ratio in Suo-Nada, western Seto Inland Sea, where the oligotrophication process is progressing, the relationship among silicic acid [Si(OH)4], phosphate (PO4),and total dissolved inorganic nitrogen (DIN; NO3 + NO2 + NH4) in bottom water was investigated. From April through July, as stratification progressed, a stagnant water mass appeared in the bottom layer of the central part of Suo-Nada. Nutrient and apparent oxygen utilization (AOU) concentrations in this bottom water increased in this period. A plot of nutrients against AOU concentrations showed good linearity for Si(OH)4, PO4, and DIN, which suggests that increase in nutrients was accompanied by dissolved oxygen consumption due to the degradation of organic matter. The Si:P:N ratio calculated based on the increased nutrient–AOU relationship in bottom water from April through October was determined to be 25:1:9. Meanwhile, the average Si:P:N ratio existing in bottom water during the same period was 28:1:8. The two ratios obtained showed good agreement in general, although the difference between them is probably attributed to the existence of preformed fractions of each nutrient. This finding suggests that the nutrient composition ratio in bottom water generally could be regulated by the biological uptake–regeneration process from April through October in this study area, and the obtained ratio (28:1:8) is a regional characteristic with large deviation from the Redfield–Brzezinski nutrient ratio of 15:1:16.


Nutrient Regeneration Bottom water Si:P:N ratio Suo-Nada Seto Inland Sea 



The authors deeply appreciate the sampling assistance that was provided by the officers and crew of the R/V Shirafuji-Maru. The authors also express special thanks to two anonymous referees and the editor of Journal of Oceanography for kindly providing constructive comments.


  1. Abe K, Nakagawa N, Abo K, Tsujino M (2014) Dissolution of silica accompanied by oxygen consumption in the bottom layer of Japan’s central Seto Inland Sea in summer. J Oceanogr 70:267–276CrossRefGoogle Scholar
  2. Brzezinski MA (1985) The Si:C: N ratio of marine diatoms: interspecific variability and the effect of some environmental variables. J Phycol 21:347–357CrossRefGoogle Scholar
  3. Fujiwara T, Takasugi Y, Higo T (1989) Wind-induced phenomena in stratified basins. Bull Coast Oceanogr 27–1:38–46 (in Japanese with English abstract)Google Scholar
  4. Gaider RJ, La Roche J (2002) Redfield revisited: variability of C:N: P in marine microalgae and its biogeochemical basis. Eur J Phycol 37:1–17CrossRefGoogle Scholar
  5. Iwao T (2001) Fluctuation in the water quality of the coastal zone along Suo-Nada in Oita prefecture. Bull Oita Ins Mar Fish Sci 3:19–25Google Scholar
  6. Joh H, Yamochi S, Abe T, Kawai A (1984) Inorganic nutrients occurring in the oxygen-deficient bottom water of Osaka Bay. Bull Jpn Soc Sci Fish 50:1693–1700 (in Japanese with an English abstract)CrossRefGoogle Scholar
  7. Katayama S, Esaki Y, Nagamoto A (2002) Change of the water quality and plankton phase in the Buzen sea. Bull Fukuoka Fish Mar Technol Res Cent 12:67–72 (in Japanese)Google Scholar
  8. Kobayashi S, Fujiwara T (2006) Seasonal variation in intrusion depths from straight to adjoining basins in the Seto Inland Sea. Umi to Sora 82:1–11 (in Japanese with an English abstract)Google Scholar
  9. Kobayashi S, Fujiwara T, Tada M, Tsukamoto H, Toyoda T (2006) The distributions of nitrogen (N), phosphorus (P), silicon (Si) and nutrient ratios during the stratified season in the Seto Inland Sea. Oceanogr Jpn 15:207–283 (in Japanese with an English abstract)Google Scholar
  10. Montani S, Yamaguchi H, Tsutsumi H, Hamada K, Ueda A (2002) Spatial distribution of phosphorus and biological production of Suo-Sound (Western Part of the Seto Inland Sea, Japan) in summer. Bull Coast Oceanogr 39:171–179Google Scholar
  11. Nakajima S, Kanayama S, Sekimoto T, Iseki K (2010) A study on the formation mechanism of isolated cold dome and physical environment near the bottom of Suo-Nada in summer. Proc Coast Eng JSCE 66:951–955 (in Japanese with English abstract)Google Scholar
  12. Nielsen MV (1996) Growth and chemical composition of the toxic dinofragellate Gymnodinium galatheanum in relation to irradiance, temperature and salinity. Mar Ecol Prog Ser 136:205–211CrossRefGoogle Scholar
  13. Sañudo-Wilhelmy SA, Tovar-sanchez A, Fu F-X, Capone DG, Carpenter EJ, Hutchins DA (2004) The impact of surface-adsorbed phosphorus on phytoplankton Redfield stoichiometry. Nature 432:897–901CrossRefGoogle Scholar
  14. Takeoka H (2002) Progress in Seto Inland Sea research. J Oceanogr 58:93–107CrossRefGoogle Scholar
  15. Wanishi A (2007) Long-term variation of the nutrient environment in the Suo-Nada region off Yamaguchi prefecture. Bull Yamaguchi Pref Fish Res Ctr 5:1–8 (in Japanese)Google Scholar
  16. Yamamoto T (2003) The Seto Inland Sea-eutrophic or oligotrophic? Mar Poll Bull 47:37–42CrossRefGoogle Scholar
  17. Yamamoto T, Hashimoto T, Takeoka H, Sugiyama T, Matsuda O (2000) Middle layer intrusion as an important factor supporting phytoplankton productivity at a tidal front in Iyo Nada, the Seto Inland Sea. Jpn J Oceanogr 56:131–139CrossRefGoogle Scholar
  18. Yanagi T, Shiraki Y (2004) Nutrient budget of Suo-Nada during the winter. Oceanogr Jpn 13:197–205 (in Japanese with English abstract)CrossRefGoogle Scholar

Copyright information

© The Oceanographic Society of Japan and Springer Japan 2014

Authors and Affiliations

  • Kazuo Abe
    • 1
  • Mutsumi Tsujino
    • 1
  • Norihisa Nakagawa
    • 1
  • Katsuyuki Abo
    • 1
  1. 1.National Research Institute of Fisheries and Environment of Inland SeaHatsukaichiJapan

Personalised recommendations