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Marine Ecology Progress Series

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MEPS 388:81-97 (2009)  -  DOI:

Nutrient limitation in Hong Kong waters inferred from comparison of nutrient ratios, bioassays and 33P turnover times

Jie Xu1,*, Kedong Yin2,5, Alvin Y. T. Ho1, Joseph H. W. Lee3, Donald M. Anderson4, Paul J. Harrison1

1Atmospheric, Marine and Coastal Environment (AMCE) Program, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR
2Key Laboratory of Tropical Marine Environmental Dynamics, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou
3Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong SAR PR
4Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
5Present address: Australian Rivers Institute, Griffith University, Nathan Campus, Brisbane, Queensland 4111, Australia

ABSTRACT: There is a need to determine the spatial and temporal dynamics of nutrient limitation to decide which nutrients should be removed during sewage treatment in Hong Kong. We compared 3 methods to assess potential or actual nutrient limitation. Ambient nutrient ratios were calculated, and nutrient enrichment bioassays were conducted, along with 33P turnover times. Comparison of nutrient ratios and bioassays demonstrated that the ambient inorganic nutrient ratios, based on the Redfield Si:N:P ratio of 16:16:1, were a rapid and effective method that could be used to predict the potentially limiting nutrient of phytoplankton biomass, except in eastern waters in summer, since the DIN:PO4 uptake ratio was occasionally below the Redfield ratio. The agreement between nutrient limitation indices of growth rate and biomass yield suggested that phytoplankton biomass and growth rate were P-limited in southern waters, with more stable conditions during summer. In contrast, a lack of agreement between these indicators showed that phytoplankton growth in potentially P-limited cases in western waters and Victoria Harbour was controlled by physical processes (e.g. strong hydrodynamic mixing and dilution). The limiting factor for phytoplankton growth varied spatially and temporally. In summer, there was a change from physical processes (e.g. the rapid dilution and possible light limitation due to strong turbulent mixing) in hydrodynamically active western waters and Victoria Harbour to P limitation, or N + P co-limitation, in southern and eastern waters with more stable conditions. In winter, phytoplankton growth was regulated by strong wind-induced vertical mixing. Hence, different seasonal sewage treatment strategies should be considered for nutrient removal.

KEY WORDS: Nutrient ratios · Nutrient enrichment bioassays · 33P turnover times · Pearl River discharge · Sewage effluent · Hong Kong · Nutrient limitation · Light availability

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Cite this article as: Xu J, Yin K, Ho AYT, Lee JHW, Anderson DM, Harrison PJ (2009) Nutrient limitation in Hong Kong waters inferred from comparison of nutrient ratios, bioassays and 33P turnover times. Mar Ecol Prog Ser 388:81-97.

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