The Effects of Diazinon on the Growth Rates and Population Dynamics of Planktonic Algae and the Possible Uptake By Two Algal Species

Date of Graduation

Fall 1989


Master of Science in Biology



Committee Chair

Roar Irgens


The effects of various concentrations of formulation Diazinon on unialgal growth rates and freshwater population dynamics as well as the possible uptake by algal cells were studied. Comparison of standard errors from mean growth rates showed no significant inhibitory response by Chlorella pyrenoidosa-normal strain. The high temperature strain of Chlorella pyrenoidosa was significantly inhibited at 20 and 40 ppm. Selenastrum capricornutum and the blue-green alga, Synechococcus leopoliensis, were also greatly inhibited at 20 ppm. Growth of Selenastrum was completely suppressed at 40 ppm, whereas growth of Synechococcus showed a significant increase in lag phase. Results of the investigation on the population dynamics of a natural assemblage of phytoplankton revealed that as Diazinon levels increased, species diversity decreased. Complete inhibition of the blue-green component and the apparent stimulation of two green algae were also observed. A bioassay using Diazinon-exposed algal cells in Daphnia pulex cultures showed that the possible transfer of appreciable amounts of insecticide from algal cells to the Daphnia cultures was predominately responsible for the subsequent mortality rates.

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© Steven M Doggett