Sinking movements of phytoplankton indicated by a simple trapping method

Sedimentation of principal phytoplankton species in Lake Constance

“…Reynolds et al (1982) concluded, that the removal of the vernal population of A. formosa in their Lund enclosures was due mainly to sedimentation. It is a commonly observed phenomenon that, with the onset of thermal stratification, the heavy diatoms are replaced by buoyant or motile algae ( Knoechel and Kalff, 1975;Reynolds, 1976aReynolds, ,1976b. In Lake Constance no marked increase of the sedimentation rate of A. formosa could be found following the onset of thermal stratification in April.…”

“…Although it is obvious that sedimentation is the ultimate fate of any particle heavier than water, there is contradictory evidence as to whether sedimentation plays a controlling role in the succession of phytoplankton. There are well documented examples for diatom populations thriving during spring overturn, which are eliminated by sedimentation after the onset of stratification (Lund, 1971;Knoechel and Kalff, 1975;Reynolds, 1976aReynolds, , 1976b. On the other hand, there is also evidence that mainly senescent populations are destined for high sedimentary losses (Eppley et al, 1967;Smayda, 1970;Reynolds, 1973).…”

Cyanobacterial dominance: The role of buoyancy regulation in dynamic lake environments

“…Given the extremes in the intensity of mixing and in underwater availability of photosynthetically active radiation (PAR) among natural lakes (see Table 1), as well as the temporal frequency of their variability (minutes to months), it becomes clear that there is no universal attribute of phytoplankton cells that is ideal under all circumstances. While motility can seem to cany obvious advantages in avoiding gravitational settlement, many non-motile planktonic organisms nevertheless remain dispersed through the vertical extent of the turbulentmixed layer; so long as the velocities of the major turbulent eddies (u) exceed, by one or more orders of magnitude, the intrinsic settling velocities of the organisms (w s ), the cells are substantially transported ("entrained"), both vertically and horizontally, within the flow (Reynolds 1984a).…”

“…Algal entrainment in turbulent flow is facilitated by the maintenance of a low value of w s relative to Denman & Gargett (1983) Imberger (1985a Harris (1978) List (1951) Reynolds (1987a) Reynolds (1987a need the velocities of the major eddies (u). bulent transport is minimal u < w s ), ag ments become dominated by the intrins behaviour.…”

“…There exist several mechanisms for the regulation of density among the gas-vacuolate cyanobacteria; each is subject to close physiological control. linking rate or negative flotation rate) among various cyanobacteria and based on literature values presented in Reynolds, 1987b Gas vacuoles comprise stacks of membranous cylinders called gas vesicles. The gas vesicles of cyanobacteria vary in length from 200 nm to 2 urn, (with mean values of between 300 and 700 nm), and in diameter between 40 and 110 nm, but show little variation within any given species (Hayes & Walsby 1986).…”