In situ microcosms of a winter plankton community were exposed for 21 d to 0 0, 0 1, 0 5 and 1 0 mg/L of the herbicide simazine, approximating persistent levels found after application in other systems Physical-chemical parameters, phytoplankton, bacteria and zooplankton were quantified
Simazine induced decreases in dissolved oxygen and pH, but induced increases in nitrate and am monia levels compared to control microcosms Phytoplankton were differentially affected by simazine Sensitive taxa included Trachelomonas, Glenodinium and diatoms Others, such as Dinobryon and small coccoids, were not significantly affected Bacteria data were variable and did not exhibit changes related to phytoplankton densities or simazine
Rotifers dominated the zooplankton and were also differentially affected by simazine The dominant species, Kellicottia bostomensis, exhibited a positive response to simazine, as did Keratella cochlearis, due to lesser mortality in higher concentrations of simazine Polyarthra vulgaris was unaffected, but Synchaeta pectinata was impaired by simazine at day 21 Zooplankton (primarily rotifers) may have fed on heterotrophic cells more than on autotrophic cells, and may have been more closely associated with the detrital food chain than the autotrophic food chain
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