Effect of juglone on freshwater algal growth.

Allelopathic growth inhibition of various freshwater algal species was observed upon the addition of juglone to culture medium under laboratory conditions. Juglone is a phenolic chemical compound common to most parts of the black walnut (Juglans nigra L.). Growth inhibition of all species occurred at a juglone concentration of 10(-3) M. Three of the five species were inhibited by a concentration of 10(-4) M juglone, while no inhibition occurred at 10(-5) M juglone. The results of this study indicate that juglone is less toxic to algae than fish. Therefore, the potential of juglone for aquatic management purposes is limited. Algal biomass will increase at natural juglone concentrations from 10(-8) to(-10) M due to the elimination of secondary producers. Algal biomass will decrease at natural juglone concentrations between 10(-4) and 10(-3) M. Species richness will decrease at juglone concentrations of 10(-5) and higher.