Incorporating Allelopathic Aquatic Macrophytes for Algal Control in Carroll Creek Linear Park in Frederick, Maryland

Abstract

Algal growth in Carroll Creek is an annual problem. A group in Frederick, Maryland, Color on the Creek, installs aquatic macrophytes, including water lilies, each year in an effort to partially inhibit algal growth by blocking sunlight at the water's surface. This group does not, however, consider plants with possible allelopathic tendencies towards algae. This research collected algae directly from Carroll Creek, as well as Microcystis aeruginosa LE-3 cultured in the laboratory, and exposed them to exudates of aquatic macrophytes with known allelopathic tendencies. The macrophytes were Pistia stratiotes, (Water lettuce) Eichhornia crassipes (Water hyacinth) and Saururus cernuus L (Lizard's tail). The algae in Carroll Creek was tested for its maximum quantum yield, or photosynthetic ability, and the M aeruginosa was tested for growth inhibition, as measured by average cell density. The results of the experiments showed the exudate from water lettuce had a statistically significant (P≤0.05) allelopathic effect on the Carroll Creek algae on the last day of testing (n=6, P=0.0084). Throughout the nine days of experimentation, the maximum quantum yield during exposure to water hyacinth exudate was significantly lower (P<0.05) than the yield response of the excelsior-only control (n=9, P=0.026). None of the macrophytes had a statistically significant effect on M. aeruginosa average cell density. Further research should be done using different periods of exudate collection, as well as different concentrations of exudate, before the allelopathic effects of these macrophytes can be discounted.