Speaker(s)

H Kenneth Hudnell, PhD, SolarBee, Inc., & The University of North Carolina, Institute for the Environment, 105 Serrano Way, Chapel Hill, NC 27517

Description

The increasing incidence and durations of toxigenic FHABs threaten human and animal health, aquatic ecosystems and economies. Climate change is partially driving the increase through rising temperatures, excessive nutrient input to waterbodies during severe stormwater runoff, and water stagnation during prolonged droughts. Prolonged expenditures of $1B+/yr on watershed management failed to halt the increase. Environmentally sustainable within-waterbody management solutions are needed to suppress FHABs. The current study evaluated the efficacy of solar-powered circulation (SPC) of the epilimnion to suppress FHABs in nutrient-enriched waterbodies (Harmful Algae, 9 (2010) 208–217).

Source water managers collected planktonic data from three reservoirs before and during SPC. The reservoirs were 0.255-0.947km2, and SPC density was 1unit/0.142km2. Peak cyanobacterial cell density decreased from 300,000+cells/ml by 85, 93 and 95% during 3 consecutive years of SPC in the 1st reservoir where algaecides were never used. Chlorophyta densities increased significantly. Total nitrogen (18mg/l) and phosphorus (8mg/l) peak levels were consistent throughout the study. Nitrate (10mg/l, 6mg/l) and total phosphorus (1.3mg/l, 0.22mg/l) peak levels were consistent in the other two reservoirs. Algaecide applications of influent containing FHAB cells decreased by 85% during SPC in those reservoirs. FHABs were not experienced in the 2nd reservoir during SPC, and peak cyanobacterial densities steadily declined over 5 years. A FHAB was experienced in the 3rd reservoir shortly after SPC initiation, but not during the 2nd year when peak density was significantly below pre-SPC level. Diatom and zooplankton densities increased significantly during SPC.

These results indicated that SPC suppressed FHABs in nutrient-enriched waterbodies through a process that strengthened over time. Epilimnetic circulation suppressed FHABs by disrupting the stimulatory factor of quiescent, stagnant water. SPC avoided the need for greenhouse gas emissions from grid-power consumption, and sharply reduced dependence on chemical applications. SPC provided an environmentally sustainable, ecological approach to FHAB control.

Conference

19th Annual Southeastern Lakes Management Conference
Hawthorne Inn and Conference Center, Winston-Salem, NC, May 2010