Algal Succession in Laboratory Microcosms as Affected by an Herbicide Stress

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Abstract
The effects of the herbicide, simazine, on community metabolism, chlorophylla concentrations, pigment ratios (O.D. [optical density] 430/665) and species dominance were examined over time in control systems and systems containing 0.05, 0.15 and 0.4 ppm simazine. A lag in net productivity, but larger peaks of productivity, was seen in systems receiving higher doses of herbicide. Chlorophylla concentration was inversely related to treatment level early in succession but tended to be directly correlated with treatment level late in succession. The pigment ratio showed an increase with time in all systems, although systems containing 0.4 ppm simazine lagged considerably behind. The type of successional sequence of species was affected by treatment level with Chlorella dominating at higher levels. [Control of aquatic weeds was briefly discussed.].