SS3.02 Turbulence and Plankton Dynamics
Date: Wednesday, June 12, 2002
Time: 2:30:00 PM
Location: Saanich
 
KunzTJ, Aquatic Ecology, Ludwig-Maximilians-Universität, München, Germany, kunz@zi.biologie.uni-muenchen.de
 
MIXING INTENSITY AND WATER COLUMN DEPTH: HOW DO THEY AFFECT MARINE PHYTOPLANKTON BIOMASS AND ITS ABIOTIC RESOURCES?
image
Models of light-limited phytoplankton growth suggest that water column depth and mixing intensity affect the vertical distribution and biomass of phytoplankton. At low mixing intensities, algae should accumulate in the high-light environment close to the surface. At high mixing intensities, algae should be homogeneously distributed across depth and experience lower average light intensities. Consequently, depth-integrated biomass should decline with increasing mixing intensity, especially in deep water columns. I manipulated water column depth and turbulent diffusion in 16 marine field enclosures. Under near-stagnant conditions, Chl-a concentrations peaked close to the surface and declined vertically. At higher mixing intensities, moderate to low Chl-a concentrations prevailed throughout the water column and showed only slight or no vertical trends. The vertical distribution of the limiting nutrient (dissolved inorganic nitrogen) was mostly inverse to the distribution of algal biomass. Depth-integrated biomass showed no clear pattern with mixing intensity. The results confirm the prediction of algal blooms close to the surface in almost stagnant water but indicate that, under nutrient-limited conditions, depth-integrated biomass may depend less on mixing intensity than predicted for purely light-limited situations.