ABSTRACT: Sinking velocities of more than 300 Nitzschia closterium aggregates were determined during roller table incubation using digital image analysis. To examine the influence of transparent exopolymer particles (TEP) on aggregate settling speed, 3 experiments with different ratios of TEP to cell volume concentration were conducted. The results showed that, for N. closterium aggregates without TEP, sinking velocity (U) was significantly related to the equivalent spherical diameter (ESD) of the aggregates, yielding U (cm s^-1) = 1.89 (ESD, cm)^0.55. The higher was the specific TEP content of an aggregate, the lower was the sinking velocity and the less pronounced was the size versus velocity relationship. Excess densities (Dr) of aggregates were derived from velocity measurements and 3-dimensional fractal dimensions (D3) of aggregates were calculated from scaling properties of Dr. Values for D3 never exceeded 2 and fit well to values of the 2-dimensional fractal dimension (D2) attained from image analysis.

KEY WORDS: Phytoplankton · Aggregates · TEP · Nitzschia closterium · Sinking velocity · Fractal dimension

Published in MEPS Vol. 182 (1999) on June 11
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1999