Rapid formation and sedimentation of large aggregates is predictable from coagulation rates (half-lives) of transparent exopolymer particles (TEP)

  • a Department of Chemical and Environmental Engineering, University of Arizona, Tuscon, AZ 85721, U.S.A.
  • b Marine Sciences Institute, University of California, Santa Barbara, CA 93106, U.S.A.
  • c Limnological Institute, University of Constance, D-78434 Konstanz, Germany

Abstract

Two hypotheses have been proposed to account for the precipitous formation of large, rapidly settling aggregates at the termination of phytoplankton blooms in nature; aggregation due primarily to cell-cell collisions, and aggregation resulting from the presence of abundant transparent exopolymer particles (TEP), a recently discovered class of particles formed from polysaccharides excreted by phytoplankton. The hypothesis of TEP-driven coagulation in three disparate systems, a freshwater lake, a coastal ocean, and a saltwater mesocosm was evaluated, by comparing TEP abundance to several related factors including phytoplankton concentrations, measured sediment fluxes, and abundances of large aggregates. The timing of large aggregate formation and sedimentation events was related to coagulation rates expressed in terms of particle half-lives, View the MathML source, calculated as the time for TEP or phytoplankton to decrease to half their concentration through shear coagulation. While TEP have been previously investigated only in marine systems, it is reported here that TEP also can be present in high concentrations (860 ml−1) in freshwater lakes (Lake Constance, Germany) and that high fluxes of particulate organic matter at depth coincide with the disappearance of abundant TEP from overlying waters. The half-lives of TEP in the three different systems indicate that large aggregate formation and massive sedimentation events following diatom blooms occur when the TEP half-life decreases to less than a few days. By comparing TEP and phytoplankton half-lives in these systems, it is concluded that the formation of rapidly sinking aggregates following blooms of mucous-producing diatoms is primarily controlled by concentrations of TEP, not phytoplankton.

References

    • Friedlander, 1977
    • S.K. Friedlander
    • Smoke, dust and haze: Fundamentals of aerosol behaviour

    • Wiley, NY, USA (1977)

    • Jackson and Lochmann, 1993
    • G.A. Jackson, S. Lochmann
    • Modeling coagulation of algae in marine ecosystems

    • J. Buffle, H.P. van Leeuwen (Eds.), Environmental particles, Lewis, Boca-Raton, Florida, USA (1993)

    • Kiørboe and Hansen, 1993
    • T. Kiørboe, J.L.S. Hansen
    • Phytoplankton aggregate formation: Observations of patterns and mechanisms of cell sticking and the significance of exopolymeric material

    • Journal of Plankton Research, 15 (1993), pp. 993–1018

    • Passow
    • Passow U. and A. L. Alldredge (in press) Distribution, size and bacterial colonization of transparent exopolymer particles (TEP) in the ocean. Marine Ecology Progress Series.
    • Passow and Alldredge, 1995
    • U. Passow, A.L. Alldredge
    • Aggregation of a diatom bloom in a mesocosm: The role of transparent exopolymer particles (TEP)

    • Deep-Sea Research II, 42 (1995), pp. 9–27

    • Simon et al., 1993
    • M. Simon, A. Lenhard, M.M. Tilzer
    • Bacterial production and the sinking flux of particulate organic carbon in a large and deep lake in comparison to oceanic environments

    • Marine Microbial Food Webs, 7 (1993), pp. 161–176