Speaker(s)

H. Kenneth Hudnell, SolarBee, Inc. & The University of North Carolina at Chapel Hill, Institute for the Environment, 105 Serrano Way, Chapel Hill, NC 27517
Bo Labisi, Palmdale Water District, 2029 E. Avenue Q, Palmdale, CA 93550
Christopher Jones, Des Moines Water Works, 408 Fleur Drive, Des Moines, IA 50321
Vic Lucero City of Thornton, Thornton, CO, 80229
Joseph Eilers, SolarBee, Inc., 1900 NE 3rd St., Suite 106-279, Bend, OR 97701

Description

The increasing incidence and durations of toxigenic Freshwater Harmful Algal Blooms (FHABs) threaten human and animal health, aquatic-ecosystem sustainability and economies. Successfully confronting the risks of FHABs requires ecologically benign and sustainable methods for bloom control. The current study evaluated the ability of solar-powered circulation (SPC) to suppress FHABs. Municipal personnel at three nutrient-enriched, source-water reservoirs collected planktonic-density data sufficient for assessing the efficacy of SPC for FHAB suppression. Peak cyanobacterial densities in Crystal Lake, a 25.5 ha reservoir where algaecides were never used, exceeded 300,000 cells/mL in 2005 prior to SPC. Peak cyanobacterial densities decreased during SPC in 2006-2008 by 85, 93 and 95%, respectively, as densities of green algae increased. Copper sulfate was applied whenever chlorophyll-a concentrations exceeded 15 ug/L in 46.5 ha Thornton Lake and 94.7 ha Lake Palmdale. Cyanobacterial densities decreased markedly during 5 years of SPC at Thornton Lake, relative to levels observed during the immediately preceding 2 years. Densities of green algae and diatoms increased during SPC as algaecide usage declined. Algaecide usage declined from 26,077 kg/yr pre-SPC to 3,992 kg in 2003 and 3,753 kg in 2004 during SPC at Lake Palmdale. Although cyanobacterial density increased during 2003, density was well below the pre-SPC level during 2004. Densities of diatoms and zooplankton increased significantly during SPC, indicting a more balanced planktonic assemblage. These results indicated that SPC suppressed FHABs through a process that strengthened over time, even as algaecide usage declined. This outcome is consistent with the literature on FHAB suppression through habitat disturbance. FHAB incidence and duration are increasing as global climate change promotes rising temperatures, lower water-flow rates with increasing drought frequency, and higher nutrient input to freshwater with more frequent flooding. SPC provides an ecologically benign and sustainable technology for FHAB control suitable for use in rural-to-metropolitan areas.

Conference

2010 Land Grant and Sea Grant National Water Conference
Hilton Head Island, SC, February 2010