Effects of the herbicide paraquat on the ecology of a reservoir

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Abstract
Summary: The application of paraquat (1.0 mg/l) to a fishing reservoir was successful in controlling the angiosperms, Potamogeton pectinatus and Myriophyllum spicatum, but a second application (0.6 mg/l) failed to control a replacement growth of the macro‐phytic alga, Chara globularis.Paraquat was quickly lost from the water after each application and was largely taken up by the sediments, never more than 6% ofthe initial dose being recorded from the macrophytes. Final analysis of the sediments indicated that about 36% of the total amount of paraquat applied to the reservoir was not recovered.Some changes in the chemistry ofthe water after the first application of paraquat were consistent with the death of the plants (e.g. alkalinity), but there was no evidence that the subsequent decay ofthe plants produced large increases in the concentrations of major nutrients in the water. Although there was no gross deoxygenation there were changes in the oxygen status of the water following the herbicide‐induced death ofthe angiosperms.Estimates of the biomass and net productivity of the macrophytes were made.