Harmful Algae 9 (2010) 208–217 Contents lists available at ScienceDirect Harmful Algae journal homepage: www.elsevier.com/locate/hal Freshwater harmful algal bloom (FHAB) suppression with solar powered circulation (SPC) H. Kenneth Hudnell a,b,*, Christopher Jones c, Bo Labisi d, Vic Lucero e, Dennis R. Hill c, Joseph Eilers a a SolarBee, Inc., 3225 Highway 22, Dickinson, ND 58601, USA b The University of North Carolina Institute for the Environment, CB # 1105, Chapel Hill, NC 27599, USA c Des Moines Water Works, 408 Fleur Drive, Des Moines, IA 50321, USA d Palmdale Water District, 2029 E. Avenue Q, Palmdale, CA 93550, USA e City of Thornton, Thornton, CO 80229, USA ARTICLE INFO ABSTRACT Article history: Freshwater harmful algal blooms (FHABs) incidence is increasing worldwide, presenting risks for human Received 22 January 2009 and animal health, aquatic-ecosystem sustainability and economic vitality. Increasing nutrient input to Received in revised form 10 October 2009 freshwater, increasing temperatures and decreasing flow rates that create quiescent or stagnant waters Accepted 19 October 2009 are primary causes of increasing incidence. Ecological approaches to FHAB control target these causes to reduce FHAB incidence without adversely impacting aquatic ecosystems. Artificial circulating increases Keywords: water flow, and is reported to suppress FHABs in the literature on habitat disturbance. This report Cyanobacteria evaluates the efficacy of a new technology, solar powered circulation (SPC), designed to create long- Harmful algal bloom distances circulation of the epilimnion (>200 m) to suppress FHABs. Three nutrient-enriched, source- Control Suppression water reservoirs periodically seeded with cyanobacteria from influent served as case studies. Utility Termination personnel systematically and consistently collected limnological data before and during SPC Artificial circulation deployment, thus enabling valid within-site comparisons. SPC units were deployed at densities of Solar powered circulation approximately 0.15 km2/unit. Pre- to post-SPC initiation changes in cyanobacterial density indicated Long-distance circulation that SPC strongly suppressed FHABs through a process that strengthened over time. Densities of green Habitat disturbance algae increased significantly during SPC at the only site where algaecides were never used, and Vertical mixing zooplankton density increased significantly at another site. Diatom densities approximately doubled Upflow following SPC initiation, although the increases were not statistically significant. Copper sulfate usage declined by 85% at one site during SPC, whereas applications declined from approximately 12/year to 1– 2/year at the other site where algaecides were used. SPC provided an effective approach to FHAB control that was ecologically benign and environmentally sustainable. ß 2009 Elsevier B.V. All rights reserved. 1. Introduction 2008). Cyanobacterial toxins, cyanotoxins, cause lethal and sub- lethal effects in humans and other organisms, and bloom Freshwater harmful algal blooms (FHABs; Hudnell, 2008) pose biomasses adversely impact aquatic biota. There is widespread serious risks for human and animal health (Hawkins et al., 1985; agreement among scientists and water quality managers that the Azevedo et al., 2008; Falconer, 2008; Hudnell, 2008a; Hudnell incidence of blooms in fresh-to-estuarine waters is increasing in et al., 2008; Pilotto, 2008; Stewart et al., 2008; Backer et al., 2008), the U.S. and worldwide (Carmichael, 2008). Every year, FHABs aquatic-ecosystem sustainability (Havens, 2008; Ibelings et al., occur where they were not observed previously, and FHAB 2008; Ibelings and Havens, 2008) and economic vitality (Steffen- durations increase. Global climate change, rising freshwater usage sen, 2008; Dodds et al., 2009). Cyanobacteria (a.k.a. blue–green demand and excessive nutrient input to freshwater are driving algae) are the predominant FHAB organism, although other much of the increase (Paerl et al., 2007; Paerl, 2008). The economic phytoplankton such as the euryhalinic chrysophyte Prymnesium costs of FHABs and eutrophication in U.S. freshwaters are parvum (a.k.a. golden algae) also causes FHABs. Dozens of conservatively estimated to be $2.2–4.6 billion annually (Dodds cyanobacterial species produce highly potent toxins (Humpage, et al., 2009). Several reports call for research to improve FHAB prevention, suppression and termination methods (Donohue et al., 2008; Dortch et al., 2008; Hudnell, 2009; Lopez et al., 2008). * Corresponding author at: SolarBee, Inc., 105 Serrano Way, Chapel Hill, NC Innovative approaches to near-term FHAB prevention and control 27517, USA. Tel.: +1 919 932 7229; fax: +1 919 967 9487. are needed to protect human health, aquatic ecosystems and E-mail address: [email protected] (H.K. Hudnell). economies (Hudnell, 2009; Hudnell and Dortch, 2008). 1568-9883/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.hal.2009.10.003 H.K. Hudnell et al. / Harmful Algae 9 (2010) 208–217 209 Approaches to FHAB control are generally classified as ecological Densities of total plankton, cyanobacteria and green algae were or chemical (Sraskraba, 1996). Ecological approaches target factors available that promote FHABs to decrease incidence, intensity and duration Phytoplankton data were available one spring-fall season pre- with ecologically benign and sustainable methods (Dortch et al., SPC 2008; Hudnell and Dortch, 2008; Hudnell, 2009). FHABs occur most Phytoplankton data were available one spring-fall season often when four stimulatory factors are present—nutrients, warmth during SPC (>20 8C),sunlight and quiescent or stagnant water(Paerl et al., 2007; Paerl, 2008; Paul, 2008). Temperature cannot be controlled in large Three sites met the criteria for inclusion as a case study. Each water bodies, and is energy intensive in smaller water bodies. site was a municipal, source-water reservoir. Operations personnel Colorants can be added to water bodies to reduce the amount of light at each site systematically collected limnological data before and available for phytoplanktonic photosynthesis, but indiscriminately during implementation of SPC for FHAB control that were sufficient inhibit beneficial and harmful algae, thereby adversely impacting to evaluate efficacy. Each utility used sampling methodology aquatic ecosystems (Spencer, 1984). Only the factors of nutrients thought best for operational purposes. The critical feature is that and quiescent or stagnant water can be targeted with ecologically sampling was consistent across time, thus enabling valid within- sustainable FHAB control methods in most cases. Nutrient input site comparisons. Comparisons of absolute values should not be reduction is essential for sustaining aquatic ecosystems from made across sites due to methodological differences and the use of freshwater to marine. However, limiting nutrient inputs often does copper sulfate at two of the three sites. not control FHABs in the near term. The implementation of nutrient input-reduction strategies is usually a long-term undertaking, and 2.2. Crystal Lake, Iowa nutrient loads already in sediment frequently stimulate FHABs when resuspended into the water column (Paerl, 2008; Perovich Crystal Lake, located in Des Moines, IA, is a water-filled gravel et al., 2008; Pieler, 2008). pit that serves as a raw-water reservoir for the adjacent Freshwater flow rates are decreasing as drought frequency and McMullen Drinking water-treatment plant. Water is continu- duration increase due to global climate change, and withdrawals ously introduced from the Raccoon River into Crystal Lake at a increase due to rising usage demand (Paul, 2008; Paerl and rate of 18.93 million L/day, and the same amount is withdrawn Huisman, 2008). Decreased flow rates create quiescent, stagnant into the water-treatment plant. Recreational activities are not waters, conditions preferred by FHABs that can be altered through allowed on the lake. Morphological characteristics are shown in hydrologic manipulations. Increasing flow rates and decreasing Table 1. water residence time can eliminate FHABs even in nutrient-rich The Raccoon River water is high in nutrients with total nitrogen freshwaters (Paerl, 2008). Artificial circulation of water bodies is an and phosphorus levels occasionally exceeding 18 mg/L and 8 mg/L, approach to FHAB control that can be implemented when flow respectively. Diversion of river water into Crystal Lake enables rates cannot be increased. The scientific basis for FHAB control microbial denitrification processes to reduce nitrogen levels for a through artificial circulation is described in the literature on mean period of 40 days prior to use. Crystal Lake regularly cyanobacterial-habitat disturbance (Reynolds et al., 1983; Stein- experienced intense cyanobacterial blooms during summers and berg, 1983; Visser and Ibelings, 1996; Donaghay and Osborn, 1997; falls that caused taste, odor and biomass problems. Copper sulfate Jungo et al., 2001; Huisman et al., 2004). Intermediate levels of or other algaecides were never applied in Crystal Lake; the utility habitat disturbance suppress FHABs and promote maximum elected to use alternative source waters during blooms because of planktonic diversity (Elliott et al., 2001). concerns about ecosystem degradation with long-term algaecide This report evaluates new solar powered circulation (SPC) usage. technology for FHAB suppression and prevention. Three case Two solar-powered SB10000 units were