Journal
CONTINENTAL SHELF RESEARCH
Volume 60, Issue -, Pages 104-112Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.csr.2013.04.017
Keywords
Alkaline phosphatase activity; Phosphate stress; Microphytoplankton; Changjiang discharge; Coastal upwelling; East China Sea
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Funding
- R.O.C. National Science Council [NSC101-2611-M-019-016, NSC101-2313-B-019-006]
- Center of Excellence for the Oceans, National Taiwan Ocean University
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The status of summer microphytoplankton phosphorus stress in the East China Sea (ECS) was evaluated by alkaline phosphatase activity (APA) and the maximum quantum efficiency of photosynthesis (F-v/F-m). During the study period in 2005-2008, values of APA ranged 0.19-1414 pmol PO43- (mu g Chl. a)(-1) min(-1) and those of F-v/F-m ranged 0.22-0.57. In general, low APA and high F-v/F-m, occurred in the coastal zone as well as in the Changjiang (Yangtze River) plume, and high APA occurred in the mid-shelf region of the northern ECS. Based on regression analyses of APA and F-v/F-m, 2 mixing series that influenced the microphytoplankton phosphorus status were identified. Changjiang discharge with high nutrient concentrations and a high dissolved N:P ratio marked the starting point of the plume-driven mixing series. Along this mixing series, the river discharge gradually mixed with offshore waters, and microphytoplankton produced high APA values when the phosphate concentration dropped below 0.2 mu mol P L-1. Coastal upwelling was observed to initiate a unique upwelling-driven mixing series in summer. As upwelled water mixed across the continental shelf, the utilization of nutrients caused low F-v/F-m values without a corresponding increase in the APA. The area of microphytoplankton showing symptoms of phosphorus stress in summer varied from year to year, and was closely related to the size of Changjiang plume and the strength of coastal upwelling. (C) 2013 Elsevier Ltd. All rights reserved.
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