Shading and Dyes

Cyanobacteria contain the photosynthetic pigment chlorophyll-a along with phycobiliproteins that allow them to use light energy more efficiently than other phytoplankton. Turbidity, stratification, and water color can influence the amount of sunlight captured by the pigments. Some planktonic cyanobacteria can regulate their buoyancy and position in the euphotic zone (depth at which 1% of the sunlight can penetrate) to maximize their sunlight-capturing ability, while benthic cyanobacteria are limited by the sunlight penetration through the entire water column. Therefore, light is the major factor determining cyanobacteria distribution in the water column or attachment to benthic substrates, followed by temperature, nutrient availability, and sheer stress associated with wave action. To reduce the amount of sunlight available for photosynthesis, dyes may be added to ponds and small lakes to physically filter sunlight with the goal of reducing cyanobacteria growth. Light-attenuating dyes do not destroy cell structure or kill cyanobacteria.

A commercial dye product can be added to the shoreline of ponds or small lakes beginning in spring and periodically during the growing season to reduce the potential for and severity of HCBs. These nontoxic dyes naturally disperse and can filter out certain light spectra, reducing light penetration and shading the water body. Dyes are available in blue, black, and other colors. Testing suggests that dyes are likely to be most effective on aquatic plants, algae, and cyanobacteria at least 2 feet below the surface (NYSFOLA 2009). Commercial dyes for this application have been available in the marketplace for decades, but there is limited published scientific demonstration of their effectiveness.

Application rates will vary by dye manufacturer, but dosing rates of commonly used dyes are in the range of 1–2 gallons of dye solution per million gallons of water (Madsen et al. 1999). After initial dye dosing, periodic re-doses are necessary to maintain the shade color and light-filtering properties and counter dye fading and dilution from inflowing water (Ludwig, Perschbacher, and Edziyie 2010).

If the pond or small lake is deeper than 2 feet and has a history of repeated cyanobacterial blooms, the dye light filtering and shading approach may be a prevention technology to consider, either alone or in conjunction with other technologies. Method practicality and costs largely hinge on the volume of the water body and the dilution caused by clear-water inflows from streams, springs, etc.; the larger the volume and dilution, the more dye you will need to add. While eutrophic waters are the most likely candidates for the approach, there are no established specific trophic state or mixing regime requirements. Using dye shading to limit photosynthesis may affect growth of some cyanobacterial species more than others, depending on light sensitivity and their relative position in the water column. As a result, you may change the species of algae and cyanobacteria that predominate (NYSFOLA 2009, Suski et al. 2018).

Floating plastic balls have been suggested as another shading option to reduce planktonic cyanobacteria, but they have not been used in HCB control (see Abridged Strategies).

Other forms of shading, especially in smaller rivers and streams, include promoting riparian vegetation canopy cover. However, there are few applied studies that show shading may be an effective management strategy (Lehmann et al. 2015, Read et al. 2014) for controlling benthic cyanobacteria in riverine systems.

PLANKTONIC	BENTHIC
EFFECTIVENESS Water body types: Pond, lake/reservoir with little to no outflow and rivers Surface area: Small Any depth Trophic state: Eutrophic Any mixing regime Water body uses: Recreation, livestock watering, irrigation	EFFECTIVENESS Water body types: Pond, lake/reservoir with little to no outflow and rivers Surface area: Small Depths greater than 2 feet Trophic state: Oligotrophic to eutrophic Any mixing regime Water body uses: Recreation, livestock watering, irrigation
NATURE OF HCB Subsurface HCBs Toxic and nontoxic HCBs Prevention strategy	NATURE OF HCB Benthic HCBs Toxic and nontoxic HCBs Prevention strategy
ADVANTAGES Unlikely carryover after bloom dissipation Low potential for adverse impacts Available and relatively inexpensive Minimal technical expertise, manpower, electricity, or specialized equipment needed for application Shading dyes are nontoxic to aquatic life when applied at recommended dosage (USEPA 2005, WA Ecology 2016)	ADVANTAGES Low potential for adverse impacts Available and relatively inexpensive Minimal technical expertise, manpower, electricity, or specialized equipment needed for application Shading dyes are nontoxic to aquatic life when applied at recommended dosage (USEPA 2005, WA Ecology 2016)
LIMITATIONS Cost-effective only for small lakes with longer residence time Inhibits photosynthesis of all algae, not just cyanobacteria Can interfere with pigment analyses used to characterize blooms (Buglewicz and Hergenrader 1977) May alter lake ecology, changing dominant plant, algae, and fish species (NYSFOLA 2009, Suski et al. 2018) Typically proprietary blends of nontoxic dyes (WA Ecology 2016); most shading products are not labeled as registered pesticides, and full chemical composition may not be given with product Limited proof of effectiveness, and blooms may return Permit may be required	LIMITATIONS Cost-effective only for small lakes with longer residence time Inhibits photosynthesis of all algae, not just cyanobacteria Low light–adapted cyanobacteria may not be affected by shading May alter lake ecology, changing dominant plant, algae, and fish species (NYSFOLA 2009, Suski et al. 2018) Typically proprietary blends of nontoxic dyes (WA Ecology 2016); most shading products are not labeled as registered pesticides, and full chemical composition may not be given with product Limited proof of effectiveness, and blooms may return Permit may be required

This aquatic growth control technology dates back at least 73 years (Eicher 1947), and commercial dye products for this purpose have been available for at least 40 years. Researchers have found that at least one shading dye does not significantly reduce visibility in water for swimmers and other recreators (Madsen et al. 1999). Dyes may be used in conjunction with other cyanobacteria preventive or control technologies such as herbicides. Perhaps most importantly, you might find that dyes have little to no effect on reducing cyanobacteria bloom frequency or severity. Some laboratory experiments and field-scale pilot studies conducted in 2- to 3-foot water depths showed that prescribed concentrations of a leading pond dye had little to no effect on algal growth rates or phytoplankton communities (Boyd, Hanapi, and Noor 1982, Ludwig, Perschbacher, and Edziyie 2010, Spencer 1984).

COST ANALYSIS

Shading with dyes has a low seasonal cost for ponds or small lakes with limited flowthrough and longer retention time.

Relative cost per growing season: Shading with dyes (light filtering)

ITEM	RELATIVE COST PER GROWING SEASON
Material	$$
Equipment	$$
Labor	$
OVERALL	$$

REGULATORY AND POLICY CONSIDERATIONS

Commercially available, nontoxic dyes are suitable for use in waters used for swimming and other recreational purposes, livestock water, irrigation, or fish consumption; however, dyes should not be applied to water that will be used for human consumption (USEPA 2020). A permit from the state herbicide or pesticide control agency may be required prior to use. Check with the state’s environmental regulatory agency before moving ahead (NYSFOLA 2009).

The dyes will impart a new and unnatural color to the water that may not be appealing to some. Furthermore, the public may view the technique as adding a manmade “chemical” to the environment to engineer the disruption of a naturally occurring, albeit undesirable, aquatic phenomenon (NYSFOLA 2009). Before applying dyes to community waters, solicit input from stakeholders to ensure that there is public consensus for intervention.

REFERENCES

Boyd, Claude E., M. Hanapi, and M. Noor. 1982. “Aquashade(R) treatment of channel catfish ponds.”  North American Journal of Fisheries Management 2 (2):193-196.

Buglewicz, Eugene G., and Gary L. Hergenrader. 1977. “The impact of artificial reduction of light on a eutrophic farm pond.”  Transactions of the Nebraska Academy of Sciences and Affiliated Societies 4.

Eicher, George. 1947. “Aniline dye in aquatic weed control.”  The Journal of Wildlife Management 11 (3):193-197. doi: https://doi.org/10.2307/3796277.

Lehmann, Katja, Andrew Singer, Michael J. Bowes, Nicola L. Ings, Dawn Field, and Thomas Bell. 2015. “16S rRNA assessment of the influence of shading on early-successional biofilms in experimental streams.”  FEMS Microbiology Ecology 91 (12):fiv129. doi: https://doi.org/10.1093/femsec/fiv129.

Ludwig, Gerald M., Peter Perschbacher, and Regina Edziyie. 2010. “The effect of the dye Aquashade® on water quality, phytoplankton, zooplankton, and sunshine bass, Morone chrysops×M. saxatilis, fingerling production in fertilized culture ponds.”  Journal of the World Aquaculture Society 41 (s1):40-48. doi: https://doi.org/10.1111/j.1749-7345.2009.00331.x.

Madsen, John D., Kurt D. Getsinger, R. Michael Stewart, John G. Skogerboe, David R. Honnell, and Chetta S. Owens. 1999. “Evaluation of transparency and light attenuation by Aquashade™.”  Lake and Reservoir Management 15 (2):142-147. doi: https://doi.org/10.1080/07438149909353958.

NYSFOLA. 2009. “Diet for a Small Lake:  The Expanded Guide to New York State Lake and Watershed Management.” New York State Federation of Lake Associations, Inc. . https://nysfola.org/diet-for-a-small-lake/.

Read, Daniel S., Michael J. Bowes, Lindsay K. Newbold, and Andrew S. Whiteley. 2014. “Weekly flow cytometric analysis of riverine phytoplankton to determine seasonal bloom dynamics.”  Environmental Science: Processes Impacts 16:594-603. doi: https://doi.org/doi.org/10.1039/C3EM00657C.

Spencer, David F. 1984. “Influence of Aquashade on growth, photosynthesis, and phosphorus uptake of microalgae.”  Journal of Aquatic Plant Management 22:80-84.

Suski, J. G., C. M. Swan, C. J. Salice, and C. F. Wahl. 2018. “Effects of pond management on biodiversity patterns and community structure of zooplankton in urban environments.” Science of the Total Environment 619-620:1441-1450. doi: https://doi.org/10.1016/j.scitotenv.2017.11.153.

USEPA. 2005. “Waste from the Production of Dyes and Pigments Listed as Hazardous EPA 530-F-05-004.” Washington, D. C. : U.S. Environmental Protection Agency. https://archive.epa.gov/epawaste/hazard/web/html/dyes-ffs.html.

USEPA. 2020. “Aquashade Registration under the Federal Insectide, Fungicide, and Rodenticide Act as Amended on July 1, 2020. USEPA Registration Number 33068-1.”

WA Ecology. 2016. “Fact Sheet for the Aquatic Plant and Algae Management NPDES General Permit.” Olympia, WA: Washington State Department of Ecology. https://ecology.wa.gov/getattachment/c514c529-657d-425e-baf7-18591e4b4577/2016APAMFactSheet.pdf.