The increasing incidence and durations of Freshwater Harmful Algal Blooms (FHABs), primarily caused by potentially toxigenic cyanobacteria, threaten human health, aquatic ecosystem sustainability and economies. Successfully confronting the risks of FHABs requires cost effective and ecologically benign methods for early detection and suppression of blooms. The current study evaluated the potential of satellite-detected multispectral signals (SMSs) of phycocyanin to serve as early indicators of FHABs, and of solar-powered circulation (SPC) in surface waters to suppress FHABs.

SMS and planktonic data were collected from Crystal Lake, Des Moines, Iowa, a 25.5 ha drinking source-water reservoir where algaecides were never used, before SPC in 2005 and during SPC in 2006-2008. SMSs of phycocyanin correlated well with cyanobacterial densities until phycocyanin concentrations exceeded 145 ppb. SMSs of chlorophyll a concentrations correlated with total algal densities. Peak cyanobacterial density decreases in 2006-2008 relative to 2005 were approximately 85, 93 and 95% when absolute values were approximately 50,000, 20,000 and 15,000 cells/mL, respectively. Concentrations of green algae during SPC greatly exceeded those observed prior to SPC. Similar results were obtained from the other two reservoirs investigated.

These results indicated that SMSs of phycocyanin are sensitive indicators of the early and late stages of FHABs, and that peak stages are characterized by high SMSs of chlorophyll a. Densities of cyanobacteria trended downward during the years following SPC deployment, remaining below the World Health Organization’s Alert Level One criterion of 20,000 cells/mL after the first year. The densities of other plankton indicated healthier profiles during SPC.