Cyanobacterial harmful algal blooms are becoming more prevalent issues throughout the world, threatening ecosystems, posing risks to human health, and resulting in millions of dollars in economic damage. Conventionally, treatment approaches have been chemical or physical, but these are harmful to aquatic life or inefficient, respectively, which presents the biological approach as a favorable alternative. To assess the effects of low-effort and cost-effective treatments, Hordeum vulgare, rice hull, and oak leaf litter were individually applied to Microcystis cultures and compared to two negative controls (Microcystis alone and cotton on Microcystis) and a positive control (CuSO4). This research was aimed at comparing the capabilities of these treatments on minimizing the size of cyanobacterial blooms, through optical density. It was hypothesized that Hordeum vulgare would be the most effective treatment since barley straw releases phenolic compounds. Separately, observations of the effects of these treatments on Daphnia magna populations were noted in separate cultures without Microcystis. Optical density was taken of the groups with cyanobacteria at 730 nm prior to adding treatments and repeated twice on weekly intervals. After calculating the decrease in OD, an ANOVA at alpha equals 0.05 was used to determine whether there were any significant differences between the means. The ANOVA determined that the values were not significant, as p>alpha (F(5, 37) = 1.31, p=0.283), showing that none of the treatments had significantly different effects. Thus, the hypothesis that Hordeum vulgare would be the most effective in decreasing Microcystis prevalence was not supported.

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