Phytoplankton development and turbulent mixing in Lake Kinneret (1992-1996) |
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Authors: | Berman, Tom Shteinman, Boris |
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Affiliation: | Israel Oceanographic & Limnological Research, Yigal Allon Kinneret Limnological Laboratory PO Box 345, Tiberias, 14102, Israel |
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Abstract: | We have utilized data from a recently developed three-dimensionalvelocity fluctuation meter to compute the dissipation of turbulentkinetic energies (TKE) and the intensity of turbulent mixingin horizontal and vertical planes in the pelagic, epilimnicwater of Lake Kinneret, Israel. These characteristics of wind-inducedturbulent movement have been monitored from January 1992 throughDecember 1996. The turbulence parameters were strongly correlatedto wind energy inputs, calculated daily as 5 day cumulativeinputs. There have been dramatic changes in the annual and seasonaldevelopment of phytoplankton, together with unusually high levelsof primary production in this lake since 1994. We observed differentpatterns of vertical and horizontal turbulent movement and ofTKE dissipation rates during the years when unusualphytoplankton development occurred (19941996) comparedto normal years (1992, 1993). The first appearanceof the filamentous cyanobacterium Aphanizomenon in this lakein AugustSeptember 1994 coincided with a period of markedlylower rates of TKE dispersion and a shift from vertical to horizontaldominance of the turbulent eddy spins. The absence of a regularwinter-spring bloom of the dinoflagellate, Peridinium, in 1996occurred when dissipation rates of TKE were extremely high,while record high amounts of dinoflagellates (1994, 1995) appearedwhen dissipation rates were very low. Correlations were shownbetween phytoplankton parameters (chlorophyll, primary productionand the ratio of primary production to chlorophyll) and boththe dissipation rate of TKE and the intensity of water turbulentmixing in the vertical plane. We suggest that the changes inthe turbulence climate of Lake Kinneret were animportant factor in determining shifts in phytoplankton successionand the population composition of the algal assemblage. |
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