Speaker(s)

H Kenneth Hudnell: Vice President & Director of Science, SolarBee, Inc; Adjunct Associate Research Professor, Institute for the Environment, University of North Carolina

Description

The increasing incidence and durations of toxigenic FHABs threaten human and animal health, aquatic ecosystem sustainability and economies. FHABs, primarily caused by rapid cyanobacterial population expansions to levels above 20,000 cells/ml, often produce some of the most potent toxins known. Climate change is partially driving the increase through excessive nutrient input to water bodies during severe storm water runoff, water stagnation during prolonged droughts and rising temperatures. Eutrophication is the processes through which the flux of growth-limiting nutrients from watersheds to receiving waters stimulates FHABs. Nonpoint source nutrient inputs are estimated to be about 20 times those of point sources. Decades of U.S. policy for limiting nonpoint source inputs and eutrophication center on best management practices for soil conservation and watershed management. Both programs currently receive Federal funding of >$5 billion annually, and additional funding from state and local governments. Yet analyses of data from the U. S. Environmental Protection Agency indicates that the prevalence of eutrophication in U.S. lakes and reservoirs increased from 10-20% in 1972 to over 50% in 2009. This alarming rate of increase clearly signals the need for alternative approaches to FHAB prevention. The current study evaluated the efficacy of a within water-body management approach to FHAB suppression in nutrient-enriched waters, solar-powered circulation (SPC) of the epilimnion.

Source water managers collected planktonic data from three reservoirs before and during SPC. The reservoirs were 0.26-0.89km², and SPC density was approximately1unit/0.14 km² (35 ac). Peak cyanobacterial cell density decreased from 300,000+ cells/ml by 85, 93 and 95% during 3 consecutive years of SPC in the 1^st reservoir where algaecides were never used. Chlorophyta (nontoxigenic green algae) 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. Algaecides were regularly applied in those reservoirs when FHAB cells were observed in the influent, or chlorophyll a concentrations exceeded approximately15 ug/L. FHABs were not experienced in the 2^nd reservoir during SPC, and peak cyanobacterial densities steadily declined over 5 years. Algaecide application decreased from 1-2/mth prior to SPC to 1-2/yr during SPC as diatom densities increased. A FHAB was experienced in the 3^rd reservoir shortly after SPC initiation, but not during the 2^nd year when peak density was significantly below the pre-SPC level. Algaecide applications decreased by 85% and zooplankton densities increased significantly during SPC.

These results indicated that SPC suppressed FHABs in nutrient-enriched water bodies through a process that strengthened over time. Epilimnetic circulation suppressed FHABs by disrupting the stimulatory factor of quiescent, stagnant water. Algaecide applications declined sharply during SPC. SPC avoided greenhouse gas emissions from the grid-power consumption required by FHAB suppression through aeration. Chlorophyta, diatom and zooplankton densities increased as nutrients ascended through trophic levels of the food web during SPC, stimulating robust fisheries. SPC provided an environmentally sustainable and ecological based within water-body management solution to FHAB control.

Conference

Water and Health: Where Science Meets Policy
UNC-Chapel Hill Institute for the Environment and Water Institute, October 2010