HABS-BLOCKS© Reduced Harmful Algal Bloom Activity in an in-Lake Limno-Corral Mesocosm Case Study at Grand Lake St. Marys, Ohio (USA)

HABS-BLOCKS© infused with glucose have been shown to reduce cyanobacterial populations and microcystin (MC) concentrations in laboratory mesocosm studies. An in situ limno-corral (LC) mesocosm study of HABS-BLOCKS© was conducted for two weeks during the 2025 algal bloom in Grand Lake St. Marys (GLSM) (Ohio, USA). Thirty HABS-BLOCKS© or Dummy HABS-BLOCKS© (contain no glucose) were added to three treated or three control LCs, respectively. Each LC holds approximately 1,000 L of lake water. After two weeks, cyanobacterial cell densities were 89% lower in treated compared to control LCs, and chlorophyll-a and phycocyanin concentrations averaged 80% and 77% lower, respectively. Initial MC concentrations averaged 41.4 µg/L, but treated LCs showed an average 89% reduction after two weeks. At the same time point, neither physical nor chemical parameters measured (except turbidity) were significantly different in the treated and control LCs. The treatment of GLSM water with HABS-BLOCKS© resulted in suppression of the Planktothrix population and decrease in MC concentrations. Further studies of HABS-BLOCKS© are needed to evaluate their applicability and safety.