Field application of biologically derived substances (BDSs: Naphthoquinone derivative) for eco-friendly mitigation of harmful cyanobacterial blooms

The naphthoquinone derivative, NQ 40, has been confirmed to be an effective algicide for controlling freshwater Microcystis blooms at the microcosm and mesocosm scales. Thus, in order to determine whether this algicide can control cyanobacterial blooms in the field, larger-scale mesocosms (50 t) and test beds (3,000 t) were tested. In the mesocosm and test-bed experiments, NQ 40 was effective and selective for algicidal activity against the target cyanobacteria ( Microcystis spp.). In addition, the algicidal activity of NQ 40 gradually increased until days 8 and 30, while the algal biomass decreased by 96.7 and 100%, respectively. Ecosystem health improved due to the algicidal effect of NQ 40. In the test-bed experiment, the Shannon–Wiener diversity index of phytoplankton was significantly enhanced and the unbalanced ecological pyramid caused by cyanobacterial blooms was restored in the NQ 40 treatment. Although a few factors (pH, dissolved oxygen, and phosphate) associated with phytoplankton abundance exhibited different patterns between the control and treatments, the dynamics of abiotic factors in the treatments generally showed similar trends to the control. Therefore, NQ 40 could be a promising eco-friendly algicidal substance for restoring freshwater ecosystems damaged by cyanobacterial blooms.