Effects of 2,4-dichlorophenoxyacetic acid on Kentucky algae: simultaneous laboratory and field toxicity testings.

2,4-D was applied to a cove in Kentucky Lake which was highly infested with Myriophllum spicatum (Eurasian watermilfoil). Effects of 2,4-D on nontarget algal communities were monitored concurrently in the field and in laboratory microcosms for eight days. Results indicated that indirect effects of water temperature and increased nutrient concentrations due to lysis in milfoil plants may be more important in the field community dominated by Chlorophyta, Pyrrhophyta, and Bacillariophyta. 2,4-D applied at the label-recommended rate of 2 mg/L or less stimulated total community growth in both laboratory and field indicating a possible hormonal effect of 2,4-D on algae. Reduced community growth and metabolism at high laboratory concentrations of 100 mg/L and 1000 mg/L may indicate an inhibitory effect on photosynthesis and/or respiration in algae. 2,4-D altered the laboratory community structure and function in all concentrations tested. Heterotrophic taxa such as Nitzschia, Euglena, Chlamydomonas, Mallomonas, Anabaena, and Oscillatoria appeared to be least affected by 2,4-D at high concentrations. Scenedesmus, Pediastrum, Characiosiphon, Navicula, Melosira, and Fragilaria appeared to be more sensitive, even in the lowest concentrations.