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 ecosystems and economies. Successfully confronting the risks of FHABs requires ecologically benign and environmentally sustainable methods for bloom suppression. The current study evaluated the ability of solar-powered circulation (SPC) of the epilimnion to suppress FHABs.

A survey of water body managers indicated that municipal personnel at three eutrophic source-water reservoirs collected planktonic-density data sufficient for assessing the efficacy of SPC for FHAB control. Cell density data were collected from Crystal Lake, a 25.5 ha reservoir where algaecides were never used, before SPC in 2005 and during 2006-2008 after two SPC units were deployed. Peak cyanobacterial cell densities prior to SPC exceeded 300,000 cells/mL. Density decreases in 2006-2008 were approximately 85, 93 and 95%, respectively. Green algal densities increased during SPC. Personnel at the other two reservoirs, 46.5 ha Thornton Lake and 94.7 ha Lake Palmdale, routinely applied copper sulfate whenever chlorophyll a concentrations exceeded approximately15 ug/L. Thornton Lake cyanobacterial densities exceeded 100 units/mL on nine occasions during 2001 and 2002, prior to the deployment of three SPC units. After deployment through 2007, cyanobacteria density exceeded 100 cells/mL once, and 50 units/mL on three occasions. Densities of green algae and diatoms increased during SPC, presumably due to decreased FHABs and algaecide usage. 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 peak cyanobacterial density increased during 2003, the peak density of approximately 500 cells/mL in 2004 was well below the pre-SPC level of 2,100 cells/mL observed during 2002. 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 evidence that SPC suppresses FHABs is consistent with the scientific literature indicating that quiescent, stagnant water is a stimulatory factor for FHABs, and the literature on FHAB suppression through habitat disturbance. SPC provides an ecologically benign and environmentally sustainable approach to FHAB control.

Conference

SETAC North America 30th Annual Meeting
New Orleans, LA, November 2009