Phosphorus limitation of primary productivity during the spring-summer blooms in Sagami Bay, Japan

Abstract

In coastal regions of Sagami Bay, Japan, we examined the nutrient limitations of primary productivity of phytoplankton blooms during spring to summer 2000, using 2 approaches; (1) dissolved nutrient concentrations and ratios, and (2) bioassay experiments. During the study period, maximum concentration of nitrate + nitrite (19.2 µM) and silicate (31.2 µM) were measured on July 10 after heavy rainfalls, where the supplies of nitrate, nitrite and silicate to the coastal regions primarily related to the increase in freshwater discharge by precipitation. However, such relationships were not found regarding the phosphate concentration. Chlorophyll (Chl) a concentration increased after the increase in freshwater discharge and Chl a peaks over 10 mg m -3 were observed 5 times. Phosphate concentration observed at the depth of the 5 Chl a peaks was low enough to indicate probable P limitation based on criteria of nutrient concentrations and ratios. Bioassay experiments were carried out 12 times, every 8 d from May 1 to July 28. Primary productivities following nitrate and silicate additions showed no response compared to the controls. However, phosphate additions in the post-bloom period caused a significant increase in the primary productivity. On May 25, the primary productivity increased 51% relative to the control. These results suggest that phytoplankton productivity was limited by phosphate during the spring-summer blooms, and that phosphate availability in the Sagami Bay is an important factor in the termination of the blooms.KEY WORDS: Bioassay · Coastal ecosystem · Nutrient · P limitation · Phytoplankton bloom · Primary productivity Resale or republication not permitted without written consent of the publisher

Diatoms control nutrient cycles in a temperate, wave‐dominated estuary (southeast Australia)

“…Only one site had a DIN : DIP ratio slightly below 22 (site 14: 19). P limitation was indicated at DIP concentrations of ,0.2 mmol L 21 (Dortch and Whitledge 1992;Fujiki et al 2004) and at concentrations of ,0.1 mmol L 21 (Justić et al 1995). Therefore, P limitation is indicated based on DIP concentrations throughout the main basin and in Erowal Bay regardless of which threshold value is used.…”

“…Therefore, P limitation is indicated based on DIP concentrations throughout the main basin and in Erowal Bay regardless of which threshold value is used. DIN : DIP ratios of .20 (Fujiki et al 2004), .22 (Justić et al 1995), and $30 (Dortch and Whitledge 1992) have been used as a second criteria for P limitation. Since six out of 10 sites exceed a ratio of 30 and another three sites exceed a ratio of 22, the DIN : DIP ratio additionally indicates P limitation for primary production.…”

Characteristics of Horizontal Community Distribution and Nutrient Limitation on Growth Rate of Phytoplankton during a Winter in Gwangyang Bay, Korea

“…식물플랑크톤의 영양염 제한 인자를 검토하는 방법으로 는 영양염 구성 성분비, Mesocosm 실험, Bio-assay 등이 있다 (Brzezinski 1985;Fisher et al 1992;Fujiki et al 2004;Taylor et al 1995). …”

In situ observation of phytoplankton productivity by an underwater profiling buoy system: use of fast repetition rate fluorometry

“…Sagami Bay is strongly influenced by the Kuroshio Current, which runs along the eastern coast of Japan. Oligotrophic oceanic waters mix with eutrophic riverine waters in the bay, and rich blooms of diatoms or dinoflagellates are often observed from April to June (Nakata 1985, Fujiki et al 2004. Measurements with the profiling buoy system were made at 10:00 h daily from 15 April to 10 May 2005.…”