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By Paul Shannon
Posted on November 1, 2024
Cover Image Title: The Sun behind the trees
Cover Image by: Kai
Size: 4000 pixels x 3000 pixels
Classification: Photograph
Location: Tashkent, Uzbekistan
Year: 2024
Harmful algal blooms (HABs), otherwise referred to as “toxic algal blooms” or “blue-green algal blooms” are classified as any overabundance of algal growth exhibiting adverse impacts, whether environmental or biological. Contrary to popular belief, HABs do not consist of common green algae; rather, occurrences are often characterized by an overgrowth of toxin-bearing cyanobacterial or dinoflagellate cells (NOAA, n.d.). These toxins, known as cyanotoxins, are considered to—based on their mechanisms of action—either affect your nervous system, your endocrine and digestive systems, or your immune system, among others. Some are additionally known to be carcinogenic. Certain conventional water treatment methods, such as coagulation, sedimentation, filtration, and chlorination are able to remove low concentrations of cyanotoxins from drinking water; however, during mass bloom events, there can be issues with dissolved cyanotoxins, which may require more advanced techniques not readily available within water treatment facilities.
HABs form in eutrophic, nutrient-laden water sources, particularly warm, slow-moving bodies of water, largely because of agricultural runoff and/or sewer drainage (UNH, 2023). It’s important to note that while growths of small free-floating plants like duckweed and other filamentous strains of algae may look similar to HABs, they are not remotely similar to these blooms. HABs consist of billions of individual microscopic cells per liter of water, and should not be visible to the naked eye, nor should they appear “stringy” or hair-like.
While it is true that cyanobacteria and dinoflagellates were largely responsible for the Great Oxidation Event somewhere between 2.1 and 2.4 billion years ago (ASM, 2022), and many species aren’t even toxic, large localized buildups of these cells can form “surface scums” atop bodies of water that may appear similar to slick layers of colored paint or oil. They have also been described in the literature as possibly reminiscent of “pea soup”. These layers are known to block the sun’s rays from penetrating the surface of the water, which can prevent photosynthetic processes within its lower ecological regions. This may induce hypoxia, or a partial lack of oxygen within the water, causing virtually all affected life to—eventually—asphyxiate. This is often the primary cause of fish kill events, wherein large populations of fish die within one particular area (U.S. National Office for Harmful Algal Blooms, n.d.).
HABs have permeated water bodies worldwide for centuries, with the first recorded reports being made by Spanish explorers in the 1500s, documenting large scale fish kills off the coast of what is now Florida (NRDC, 2021), though historically, it is believed that Indigenous Americans knew of the phenomenon as well. Regardless, over the past 40 years, reports of HABs have increased significantly, and they have since become an environmental issue in every single U.S. state and virtually any coastal area in the world (Anderson et al., 2012). There is much debate within this specific field of environmental study; some attribute this increase in reports to an increasing intensity in algal bloom occurrence, caused by worsening global warming favoring algal growth (Gobler, 2020), and others have suggested that increased regional monitoring efforts are simply causing a perceived increase in intensity (Zingone et al., 2021). However, general consensus remains that as global warming continues to worsen, and global temperatures and sea levels rise, this will favor HAB formation considerably.
The most common bloom-forming genus of cyanobacteria, Microcystis, maintains more than 50 recognized morphospecies, which are themselves known to produce over 300 congeners of toxins. The most common and potentially dangerous toxin of them all, Microcystin-LR (MC-LR) is a potent liver tumor promoter and has been documented to induce microscopic cell death in as little as 20 minutes following exposure (CAEPA, 2009). Additionally, it has been shown to disrupt normal hormonal functioning of the endocrine system, filling much of the criteria required to be considered an environmental endocrine disruptor. Many toxins, however, have so far either remained undiscovered, misidentified, or under-researched, and an unintelligible number of potentially bioactive metabolites are waiting to be characterized among all genera of HABs.
Current trends show HABs may be increasing in prevalence, and yet a large proportion of the public remains unaware of harmful algal blooms as a concept. Specifically, in a 2020 study entitled Public Awareness and Concern About Harmful Algal Blooms, a survey conducted determined that 41% of American adults were unaware of the harmful effects HABs can have on humans and animals. This can pose a risk to both you and your pets—if directly exposed, effects can range from severe gastrointestinal discomfort and puking to death in as little as a few hours.
As HAB occurrence increases and more light is brought to the issue, it continues to take precedence in both the media and scientific communities. Red tides (consisting of Karenia brevis), for example, have been vehemently documented along the Gulf of Mexico and Florida coastlines, and many examples of articles can be found online detailing their description and adverse effects, as well as their regional environmental and economic impacts. Research specifically has increased recently largely due to both increased precedence and improved technologies, such as satellite imagery for monitoring and identification of potential blooms, and genetic analysis for further characterization.
Monitoring does not address the root cause of the issue, however. Simply assessing the issue and determining its implications over and over will not fix the problem. As such, many researchers are dedicating their studies to HAB mitigation, treatment, and remediation. Mitigation techniques include water column mixing, application of clay particles for phosphorus absorption, and sediment resuspension/burial; however, these three techniques have all shown mixed results. While water column mixing may impact nutrient dynamics within the water, it does nothing to address the presence of the toxic algae itself. Clay surface moderation can be effective at decreasing algal biomass; however, it may not always decrease beneath the 20-30% threshold before which significant regrowth is often observed (Yu et al., 2017). Sediment resuspension and burial has been shown to mitigate Alexandrium blooms in specific, but it has also been determined to reintroduce otherwise settled contaminants into the water, such as the very nutrients feeding bloom growth.
HAB treatment techniques are often put into one of three classifications: mechanical, chemical, and biological methods. Each has its own advantages and drawbacks. For example, most mechanical methods entail physical removal of algal biomass, and while this is an “immediate” fix, it often results in significant regrowth.
Chemical methods, however, such as application of algaecides, provide a more permanent solution, though they commonly have disadvantages. Many chemical algaecides aren’t easily biodegradable, and can bioaccumulate within ecosystems, which can cause further harm to both animal and human life. They can additionally kill beneficial bacteria found within the water, and are known to kill or otherwise affect the growth of many kinds of plants.
Biological methods are often the most effective manners of HAB treatment. However, with some of them, such as the introduction of certain kinds of weevils, there can be a period of years before any significant effects are observed. Others, however, such as phytoremediation and the application of algicidal bacteria, provide a sustainable yet immediate solution to cyanobacterial overgrowth.
Phytoremediation generally entails the application of a type of plant for the purpose of containing, extracting, or isolating contaminants within bodies of water. The common water hyacinth (E. crassipes), for example, is a phytoremediative agent by means of rhizofiltration, a method of removing contaminants from water utilizing a plant's root system. This particular plant takes nitrogen and phosphorus from the water column into its body mass, which can theoretically undo the very eutrophication that causes HABs. However, as with all treatment methods, there is a drawback—water hyacinth plants can “bloom” themselves, and form a surface scum, thus affecting the environment similarly to HABs. Moreover, as the plant takes in phosphorus and essentially starves the algae, when the cyanobacterial cells inevitably die, cell lysis may occur. This is a phenomenon wherein a cell’s membrane collapses, releasing its contents into the surrounding environment. If the algae being worked on happens to be bioactive—thus containing cyanotoxins—and cell lysis occurs, the toxins held within may be released into the environment. Subsequently, as the biological matter is decomposed by aerobic bacteria, oxygen from the environment is used up and this, in itself, can cause hypoxia due to continuously lowering dissolved oxygen levels.
There is no perfect remediation technique for the purposes of cleaning up HABs. As such, it is widely believed that the true solution of this phenomenon lies not in mitigation and remediation, but rather in prevention. This can be done by optimizing policy to prevent the initial eutrophication of that water. If you can prevent excess nutrients from entering the water to begin with, there will be no bloom developing. This is especially important during runoff conditions, when the nitrogen and phosphorus originating from applied animal manure and fertilizer on farms may be brought to nearby bodies of water.
In recent decades, steps towards prevention have been made. For example, the Harmful Algal Bloom and Hypoxia Research and Control Act of 1998 created an Inter Agency Working Group (IWG) to advance "scientific understanding and ability to detect, monitor, assess, and predict HAB and hypoxia events" (EPA, n.d.). IWG is composed of 13 different collaborating federal agencies, with the NOAA and EPA co-chairing the Group. They develop regular reports and establish plans to control or otherwise mitigate HABs, and they conduct assessments of specific events as requested. Furthermore, the CDC provides an interesting resource: the One Health Harmful Algal Bloom System (OHHABS). This is a reporting system designed to gather information regarding HABs, with the ultimate aim of preventing illness. According to the CDC, both state and territorial public health departments voluntarily report to this program. Launched in 2016, OHHABS helps to define patterns in HAB emergence, protect American water systems, and communicate with and educate the public in exposure prevention.
Additionally, as of May 2019, according to the Environmental Working Group, thirty U.S. states either publish 1) an advisory for beaches in the presence of HABS or 2) a map of harmful algal blooms. Many U.S. states maintain some form of an Algal Bloom Report Form, where you can submit suspicious bodies of water near human traffic for further analysis.
Canada has implemented similar measures for prevention. For instance, the Harmful Algal Bloom and Hypoxia Research and Control Amendments Act of 2013 provides the federal government with the ability to provide funds for mitigation of algal blooms that are "considered to be of national significance". Action plans have been established as well, such as the Canada-Ontario Lake Erie Action Plan, which identifies 120+ actions to reduce the influx of phosphorus that enters Lake Erie. Measures such as improving wastewater treatment, encouraging sustainable farming practices, and wetland conservation are included, and should soon become commonplace throughout the world.
References
Anderson, D. M., Cembella, A. D., & Hallegraeff, G. M. (2012). Progress in understanding harmful algal blooms: Paradigm shifts and new technologies for research, monitoring, and management. Annual Review of Marine Science, 4(1), 143-176. https://doi.org/10.1146/annurev-marine-120308-081121
California Environmental Protection Agency. (2009). Microcystins: A Brief Overview of Their Toxicity and Effects, With Special Reference to Fish, Wildlife, and Livestock. https://oehha.ca.gov/media/downloads/ecotoxicology/document/microcystin031209.pdf
Canada could take inspiration from U.S. environmental policy preventing algal blooms. (2019, March 11). International Institute for Sustainable Development. https://www.iisd.org/articles/us-policy-algal-blooms
Freshwater Harmful Algal Blooms 101. (2019, August 28). Be a Force for the Future | NRDC. Retrieved September 15, 2024, from https://www.nrdc.org/stories/freshwater-harmful-algal-blooms-101
Gobler, C. J. (2020). Climate change and harmful algal blooms: Insights and perspective. Harmful Algae, 91, 101731. https://doi.org/10.1016/j.hal.2019.101731
The Great Oxidation Event: How Cyanobacteria changed life. (2022, February 18). ASM.org. https://asm.org/articles/2022/february/the-great-oxidation-event-how-cyanobacteria-change
NOAA, Ohio State University, & Ohio Department of Health. (n.d.). Harmful Algal Blooms in Ohio Waters: What is this stuff? [Algal bloom fact sheet]. https://cees.indianapolis.iu.edu/doc/2010osg-habpanelweb.pdf
U.S. National Office for Harmful Algal Blooms. (n.d.). Fish kills – Harmful algal blooms. Harmful Algal Blooms. Retrieved September 15, 2024, from https://hab.whoi.edu/impacts/impacts-wildlife/fish-kills/
UNH. (2023, November 22). Causes of harmful algal blooms: Understanding the factors behind the phenomenon. College of Life Sciences and Agriculture. https://colsa.unh.edu/blog/2023/11/causes-harmful-algal-blooms-understanding-factors-behind-phenomenon
Yu, Z., Song, X., Cao, X., & Liu, Y. (2017). Mitigation of harmful algal blooms using modified clays: Theory, mechanisms, and applications. Harmful Algae, 69, 48-64. https://doi.org/10.1016/j.hal.2017.09.004
[Writing Editor: Anonymous]
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