A novel method to measure particle sinking velocity in vitro, and its comparison to three other in vitro methods

Helle Ploug, Anja Terbrüggen, Anna Kaufmann, Dieter Wolf-Gladrow, and Uta Passow

Limnol. Oceanogr. Methods 8:386-393 (2010) | DOI: 10.4319/lom.2010.8.386

ABSTRACT: We introduce a novel, simple method to measure sinking velocity of particles and aggregates in roller tanks. Using this noninvasive method, it is possible to follow changes in sinking velocities on the same aggregates during time and to make paired measurements of aggregate sinking velocity and composition. Particles and aggregates are video recorded in roller tanks, and their sinking velocity is derived from the orbital trajectories. This new method is compared with three other methods (using roller tanks, a vertical flow system, and a sedimentation column), which have not previously been inter-calibrated. Agar spheres and diatom aggregates were used as model particles in all experimental systems. No method showed significantly different sinking velocities of agar spheres compared with those calculated by theory. Paired measurements showed that sinking velocities from 70 to 700 m d–1 were linearly correlated between different methods. Highest sinking velocities were measured in a sedimentation column followed by those measured in roller tanks and in the vertical flow system, respectively. The average difference of sinking velocity measured with the different methods ranged from 8% to 11% for agar spheres, and up to 20% for diatom aggregates.