Place: Chippewa Lake, Medina County, Ohio, USA
Date: 5 August 2019
Set up: A 330-acre recreational water body of historical and ecological significance. Chippewa Lake is Ohio’s largest inland natural lake situated in Medina County, Ohio. This natural lake is used for fishing, canoeing, boating, and water-skiing. It includes two beaches and is surrounded by homes, a yacht club, and an upscale restaurant.
Background:
Since many years, Toxic Cyanobacterial Outbreaks (“TCOs”) have been responsible for the suspension of all activities in Chippewa Lake throughout most of the recreational season (Fig. 1). An annual short relief in toxin levels is recorded during the months of June-July. This is attributed to heavy summer rains washing into the lake, flushing the cyanobacterial scum downstream into the Chippewa Creek river, which became the source of contamination to other watersheds downstream. However, flushing out the cyanotoxins along with the floating cyanobacterial mats did not significantly affect the concentrations of planktonic and benthic cyanobacteria in the lake (“inoculum”), which shortly thereafter would initiate the growth of the next outbreak when flood season was over (Fig. 1). The higher the initial inoculum is, the faster and more aggressive will the next TCO be. Since the TCOs had never been treated in the lake, the initial cyanobacterial inoculum has been increasing from year to year, causing each bloom episode to be worse than the previous one (Fig. 1.)
The intensifying TCOs in Chippewa Lake rendered its water unusable throughout most of the year. Attempting to solve the problem, Medina County has sponsored a report in late 2018 that suggested different approaches to tackle TCOs in the Lake. Proposed solutions’ costs ranged from $500,000 to $1,500,000. The report itself had cost the county $26,000.
Objective:
The objective of the treatment in early August 2019 was to remediate a bloom surge in Chippewa Lake and prevent the expected full-blown TCO in the following months.
Treating an outbreak at its earliest stages is essential for several reasons: first, it requires a minimal algicide dose; second, it avoids a toxin-buildup in the cyanobacterial cells and their release once the bloom collapses; and lastly, it avoids an oxygen-depletion associated with the collapse of an advanced bloom and a surge in oxygen-consuming anaerobic-bacteria that feed on the dead biomass and can deplete dissolved oxygen during that process.
The treatment with Lake GuardTM Blue was applied once a surge in cyanobacterial biomass was detected in the lake, reaching an alarming level of 280,000 cells/ml (14 times the standard), corresponding with an increase in cyanotoxin levels from 0.18 ppm to 0.25 ppm over one week period. The surge in cyanobacterial levels was visible to the naked eye, with cyanobacterial mats spotted on the eastern shore of the lake, corresponding with NOAA satellite imaging taken on Aug. 3 (Fig. 6) – indicating high levels of cyanobacteria that covers over 50% of the surface of the lake.
Altogether, the lab cell count, toxin levels, satellite imaging, and visual observations corresponded with the historical trend – forecasting a major outbreak in the immediate future.
Fig. 1. Microcystin levels measured in Chippewa Lake since the Medina County Parks District initiated weekly measurements of cyanotoxins in 2016. The lake freezes between December and March. Historically, microcystin levels would increase during the months of April-June, drop during the heavy rain season in June-July, only to be followed by an intense surge from August through November. A Lake GuardTM Blue treatment was applied on August 8th, 2019 (red dotted arrow). Since the treatment, microcystin levels remained well below the warning threshold. This year was the first time in many years where the lake stayed open to the public during the peak season of August and September (confirmed as of Sep. 15, 2019).
Sampling Methods:
Measurements were taken over 9 days, at 8 am every morning, starting on Aug. 5, 2019. Samples were taken from four different sampling points. A first assessment application of ~0.9 lb/acre was applied on day 3, Aug. 7, in order to determine wind and current directions and dispersal patterns on the surface of the water. An operational application followed on Aug. 8th at a rate of 4.5 lb/acre. Results were analyzed and normalized against day 3. Pre-treatment measurements served as controls. Cyanotoxin levels, through laboratory testing, and total coverage of cyanobacterial mats on the water surface, through satellite imaging, were assessed independently by the local authorities and supported the findings of a successful treatment.
Application Method:
Lake GuardTM Blue was applied directly from a boat during the morning hours at a dose rate of ~5 lb/acre. The product, packaged in 50-lbs bags, was gravity released from the edge of a moving boat. Once the waterborne product was organized over the western perimeter of the lake (Fig. 2), it was carried by Western winds and currents that scattered the floating particles alongside cyanobacterial aggregates. The total application time of 1,500 lb Lake Guard™ Blue was less than 30 minutes. Within a few hours, no Lake GuardTM Blue particles were visible to the naked eye. Boating activity was not interrupted throughout the time of application. For precaution reasons, two beaches were closed between 8 am to 4 pm on the days of application (Aug. 7 and Aug. 8). Measurements taken two-hours post-treatment indicated negligible levels of copper ions (avg. at 0.3 ppm) in the immediate hours post-treatment, dropping below detection levels the day after.
Fig. 2. A schematic approximation of the Lake GuardTM Blue application in Chippewa Lake, 330 acres in size. The ready-to-use product was directly released from a moving boat. The product lined the western perimeter of the lake, while eastbound winds and currents carried the floating particle alongside cyanobacterial aggregations.
Results and Discussion:
Post-treatment phytoplankton assessments indicated a clear and immediate shift from dominating toxic cyanobacterial species (primarily Anabaena sp. and Planktothrix sp.) towards a healthy variety of eukaryotic green algae species including Diatoms and different Chlamidomonas-like species (Fig. 3). Interestingly, a cyanobacterium Spirulina sp. was also observed after the treatment. This strain is used as a “super-food” and is not considered toxic.
Changes in Chlorophyll-b (Chl-b) and phycocyanin (PC) levels strongly correlate with the qualitative results obtained by microscopic imaging. The lake’s ‘Resistance Factor’ to cyanobacteria, which can be assessed by the ratio between Chl-b and PC (total eukaryotic green-algal biomass vs. cyanobacterial-biomass) increased significantly by 250% (Fig. 4), indicating a clear shift in the balance of power between these two natural competitors – in favor of non-toxic species.
The trend in favor of beneficial species at the account of toxic species is in agreement with post-Lake Guard™ treatments all over the world which has demonstrated a strong correlation with the longevity of the treatment.
Moreover, the targeted efficiency with which the Lake Guard™ Blue acts in the water results in a natural increase in hydrogen peroxide (H2O2) levels in the water column, which increased significantly between days 1-4 post-treatment to a range of 0.5 mM. The presence of hydrogen peroxide in the water is attributed to the copper treatment: Copper blocks the photosynthetic electron path by binding to a component between photosystem II (PSII) and photosystem I (PSI), thus inhibiting the flow of electrons from PSII and causing the formation of singlet oxygen in the core of PSII. The singlet oxygen in PSII is then converted, enzymatically, to hydrogen peroxide. The continuous formation of the hydrogen peroxide will induce a prolonged oxidative stress that activates cell-death in cyanobacteria, but not in green-algae (Kaplan et al., 2012), further enhancing the “accuracy” and the selectivity of the targeted treatment against cyanobacteria (Helman et al., 2003; Matthijs et al., 2012; BlueGreen’s reports HERE, and HERE). This effect of allelochemical secretion from both cyanobacteria and green algae will affect distant, naïve, populations, including benthic populations (Harel et al., 2012; BlueGreen’s report HERE).
Fig. 3. Qualitative microscopic imaging. A. Pre-treatment, most of the phytoplankton captured by the microscope was of cyanobacterial species, mostly Planktothrix sp. and Anabaena sp. These toxin-producing cyanobacteria were not captured in the images taken post-treatment B. Samples taken three days post-treatment. The phytoplankton captured by microscopic imaging was mostly of beneficial green algae, mainly Diatom sp. and different Chlamydomonas-like sp. Few Spirulina sp., a nontoxic cyanobacterium, were captured by the microscopic imaging.
The amplified cycle ensued by copper treatment, namely the collapse of cyanobacterial populations after Lake Guard™ Blue treatment, followed by the prolonged oxidative stress due to the production of hydrogen peroxide, followed by a signaling cascade that results in the programmed cell death of naïve cyanobacterial populations, was observed in Chippewa Lake days after the treatment. Tens of acres of water surface were covered with a grayish-beige color of protein-based-foam (Fig. 5). This phenomenon is attributed to cyanobacterial cell-lysis and a clear indication that cyanobacterial cell-death continued progressing for days after treatment, long after copper levels were undetectable in the water (as detailed hereinafter). Members of ‘Save the Lake Coalition’ reported about the foaming phenomenon as long as two weeks after the treatment – indicating a prolonged, continuous “fight” in which cyanobacteria were ‘losing’ to high levels of eukaryotic green algae and naturally-recurring hydrogen peroxide, that were initially triggered by the treatment.
Microcystin levels remained very low post-treatment (Fig. 1), indicating that the timing of the treatment, at the early stages of the bloom-surge, was effective. The sharp decline in cyanobacterial biomass did not result in an increase in cyanotoxin-levels, confirming that the cyanobacterial cells were at their lag-phase stage, when cyanotoxin-accumulation in the cells is minimal (Wood et al., 2010). Had the treatment been applied a week or two later, during the exponential-growth phase of toxin-producing cyanobacteria, the levels of the cyanotoxins would have increased.
Fig. 4. Relative measurements for Dissolved Oxygen (DO); the ratio of total eukaryotic algal-biomass vs. cyanobacterial biomass – the ‘Resistance Factor’ (Algae vs. Cyano); Clogging potential meter; and pH. The measurements were taken daily, at 8 am, for 9 consecutive days and from different points in the lake. The initial treatment with the Lake GuardTM Blue was applied on August 7th (day 0), and the relative measurements of DO, Algae vs. Cyano, and Clog Meter were normalized to day 0. All parameters indicate a healthier post-treatment aquatic system.
The pH levels, post-treatment, dropped from pH 8.5 to pH 7.95 (Aug 9-11), a result of the reduction in overall photosynthetic activity (as a proxy to the relative decline in phytoplankton total biomass). Within 4 days (Aug. 12), pH levels rose to pH of 8.35 indicating the reinitiation of photosynthetic activity by new, predominantly non-toxic phytoplankton variety (Figs. 3 and 4).
An additional confirmation to the environmental superiority of an early-treatment comes in the form of unchanged dissolved oxygen levels before, during and after treatment – averting the risk of fish kill due to oxygen depletion (a typical outcome upon the collapse of a massive bloom).
There was no evidence for any adverse impact to either the fauna or the flora of the lake.
The clogging potential meter, which indicates the total solids in the water, improved significantly by 400% immediately after treatment (Fig. 4). This measurement serves as an additional indication to the change in populations in favor of non-toxic species: cyanobacteria are known to release significant quantities of polysaccharides into the water, which increase water viscosity, and is associated with the ‘swimmer’s itch’ nuisance. Controlling polysaccharide concentrations in the water, due to the collapse of cyanobacterial communities, breaches yet another ‘wall’ in the cyanobacterial resistance mechanism against its natural competition, further enhancing the ‘Resistance Factor’ against cyanobacteria. Breaking said network of polysaccharide production contributed to the water’s increased filterability as indicated by the clogging meter results (Fig. 4).
Fig. 5. Protein foam formation throughout the lake, day 3 post-treatment, indicating continuous bacterial cell-death and cell lysis as a result of competition with higher levels of green algae as well as the oxidative stress induced by the Lake Guard™
Blue treatment. Cyanobacteria are far more sensitive to oxidative stress than green algae, further enhancing the ‘Resistance Factor’ in favor of non-toxic species. Members of the Save the Lake Coalition continued reporting sightings of this phenomenon as late as two weeks post-treatment.
Sechi-disk measurements, on the other hand, did not change during or after the treatment, remaining at a constant ~45 cm (~18 inches) of water visibility, most likely due to high levels of tannin present in the water.
Copper ions (Cu+2) concentration in the water, sampled at 15-30 cm (6-12 inches) below water surface after 1-2 hours of the application, averaged around 0.3 ppm. The copper ion concentration in days 1-3 post-treatment was <0.00 ppm. Water alkalinity levels remained unchanged before and after treatment, at the range of 80 ppm (mg/L).
Combined, the results above indicate that the Lake Guard™ Blue treatment was selective against toxic cyanobacteria and rehabilitated the ecological ecosystem in the lake in favor of beneficial species. It supported the growth of the beneficial, nontoxic green algae, which acts as a biological buffer that prevents the cyanobacteria from reestablishing dominance in the aquatic system.
The results and analysis above were confirmed by the National Oceanic and Atmospheric Administration (NOAA) satellite imaging, showing a clear difference between pre- and post-treatment conditions. (Fig. 6).
Recent results from cyanotoxin measurements and satellite imaging, indicate to a bloom-free lake for 6 weeks in a row (and continuing) post the Lake GuardTM Blue treatment.
Fig. 6. NOAA satellite imaging shows high levels of cyanobacteria present in Chippewa Lake shortly before treatment (yellow and red pixels on Aug. 3), that were completely cleared immediately after treatment (Aug. 11 and onward, black pixels).
Conclusions:
Lake GuardTM Blue is a selective, highly targeted treatment against toxic cyanobacteria in lakes of all sizes. The simplicity and modularity of its application empower local communities, for the first time, to reclaim their water resources. They can now react, on-time, to a bloom-formation with record-low doses of algicide, reducing the environmental footprint to a minimum and preventing the subsequent formation of a toxic bloom altogether.
Targeting and eliminating, primarily, the toxic cyanobacteria, will rehabilitate the lake by allowing beneficial green algae to reclaim dominance in the ecosystem and serve as a natural buffer that prevents the next cycle of the cyanobacterial outbreak.
An application that lasted less than 30 min in a 330-acres Chippewa Lake can be easily scaled to treat lakes without any size limitation.
Six weeks after a single treatment (and counting), the residents of Chippewa Lake continue to enjoy healthy, safe conditions in their natural lake for the first time in years during peak season!
Reference List:
Harel,M., Weiss,G., Lieman-Hurwitz,J., Gun,J., Lev,O., Lebendiker,M. et al. (2012) Interactions between Scenedesmus and Microcystis may be used to clarify the role of secondary metabolites. Environmental Microbiology Reports n/a.
Helman,Y., Tchernov,D., Reinhold,L., Shibata,M., Ogawa,T., Schwarz,R. et al. (2003) Genes encoding A-type flavoproteins are essential for photoreduction of O2 in cyanobacteria. Current Biology 13: 230-235.
Kaplan,A., Harel,M., Kaplan-Levy,R.N., Hadas,O., Sukenik,A., and Dittmann,E. (2012) The languages spoken in the water body (or the biological role of cyanobacterial toxins). Frontiers in Microbiology 3.
Matthijs,H.C.P., Visser,P.M., Reeze,B., Meeuse,J., Slot,P.C., Wijn,G. et al. (2012) Selective suppression of harmful cyanobacteria in an entire lake with hydrogen peroxide. Water Research 46: 1460-1472.
Wood,S.A., Rueckert,A., Hamilton,D.P., Cary,S.C., and Dietrich,D.R. (2010) Switching toxin production on and off: intermittent microcystin synthesis in a Microcystis bloom. Environmental Microbiology Reports 3:118-24.
