Response of Cyanobacterial Blooms to Floating Islands of Native Aquatic Macrophytes in Large-Scale Mesocosms

Cost-effective, non-destructive remediation and prevention techniques for Cyanobacterial Harmful Algal Blooms (CyanoHABs) are needed to help mitigate their negative impacts on human, animal, and ecosystem health. Many aquatic macrophytes produce allelochemicals that inhibit the growth of cyanobacteria. Floating islands stocked with allelopathic macrophytes could offer a natural, environmentally friendly way of improving water quality and reducing CyanoHAB severity. We tested the ability of three native Kansas macrophytes (Sagittaria latifolia, Ludwigia peploides, and Heteranthera multiflora) deployed in single-species, floating islands to reduce cyanobacteria blooms in large-scale (3,000 gallon) experimental mesocosms. We created cyanobacterial blooms before deploying the islands, then compared phytoplankton community structures and water properties (physical and chemical) before and after the floating islands were added. The addition of the macrophytes did not significantly change the phytoplankton communities or reduce phytoplankton densities in the mesocosms. The addition of macrophytes did not result in meaningful improvement in water quality, except for a decrease in water column total phosphorus in the H. multiflora treatment. In our study, we deployed a relatively small number of plants compared to other studies, which may have contributed to the lack of allelopathic effectiveness of our floating island treatments. We provide suggestions to future researchers and resource managers that could improve the effectiveness of floating island treatments. This study is a first step to assessing the potential of using native allelopathic macrophytes as an ecological solution to add to the CyanoHAB mitigation toolkit.