POSTER: Microcystis Growth Suppression- Laboratory Study of Three Chemical Treatment Methods
Research Mentor: Dr. Hidetoshi Urakawa
Additional Authors: Julia Davis, Taylor Hancock, Michael Kratz, Haruka Urakawa, Hidetoshi Urakawa
Abstract:
Harmful algal blooms of the toxin-producing cyanobacterium Microcystis aeruginosa have become a growing problem for southwest Florida freshwater bodies. Recently a 2018 bloom in the Caloosahatchee River and a 2016 bloom in Lake Okeechobee both led to the declaration of a state of emergency. Current long-term mitigation efforts such as nutrient reduction do not protect against the immediate risk these blooms pose for residents and wildlife, many short-term chemical spraying methods can cause harm through biomagnification of toxic chemicals and increased toxin release upon application. Hydrogen peroxide and L-lysine have shown promising results in selectively inhibiting the growth of M. aeruginosa and are more ecologically friendly due to fast degradation in water or biological enhancement of non-target organisms, respectively. We further explored three chemical treatment methods for the rapid suppression of M. aeruginosa, the use of amino acid L-lysine, hydrogen peroxide and combined treatments of both chemicals, which have never been tested before. Two M. aeruginosa strains, NIES-90 and FD4, were initially examined. The two L-lysine treatments 3 mg/L and 8 mg/L yielded significant concentration-dependent growth inhibition ranging from 43-94% when compared to controls. The two hydrogen peroxide treatments 16.7 mg/L and 33.3mg/L resulted in similar growth inhibition ranging from 40-89%. The combined treatments 3 mg/L L-lysine: 16.7 mg/L hydrogen peroxide and 8 mg/L L-lysine: 33.3 mg/L HP resulted in 82-99% decline of growth. Five more M. aeruginosa strains which vary in ecological adaptions such as toxin-production and colony formation were also used to assess variability in treatment sensitivity. Other abundant algae found in southwest Florida water bodies were also tested and found largely to be less sensitive compared to M. aeruginosa. Results of toxicity trials were then used to determine treatment concentrations for application in a mesocosm study. Water and natural phytoplankton communities from the Calo osahatchee River were pumped into mesocosms for a 7-day treatment observation. All three treatment applications led to reduced cyanobacterial populations when compared to controls.