Phytoplankton sinking rate determination: Technical and theoretical aspects, an improved methodology

An analysis of technical and theoretical problems associated with the measurement of phytoplankton sinking rates by several commonly used methods indicates that these methods are both inaccurate and imprecise. Sinking rates estimated by the discrete sample layer (DSL) method tend systematically to over-estimate the mean sinking rate of the population due to the effect of inefficient detection of cells on the bottom of the settling chamber. Sinking rates estimated using the homogeneous sample (HS) method and so-called t_0–5 technique systematically under-estimate the mean sinking rate if any cells in the population sink faster than twice the estimated average sinking rate.

A rigorous mathematical framework is developed which, in conjunction with certain modifications in settling chamber design, allows calculation of the mean sinking rate (assuming that no cells are positively buoyant) for both the DSL and HS methods. These theoretical and technical modifications permit mean sinking rates to be estimated more rapidly and with greater accuracy and precision than has been possible by previous methods.