Algal blooms are rapid growths or gatherings of algae in aquatic systems like lakes, rivers, or oceans. Depending on the algae, such blooms can cause red, brown, or blue pigmentation in the water.
Although some blooms may be non-harmful, others grow harmful toxins that are dangerous to aquatic species, animals, and even people. These blooms are referred to as harmful algal blooms (HABs).
Causes of Algal Blooms
Agriculture and sewage nutrient pollution
Excess nutrients, particularly nitrogen and phosphorus, are one of the primary causes of algal blooms. These nutrients are usually derived from- agricultural runoff that includes fertilizers and manure, poorly treated or untreated sewage, and detergents that find their way into water bodies.
Once these nutrients flow into rivers and lakes, they serve as food for algae, causing rapid algal growth.
Climate Change and Increasing Water Temperatures
Climate change is an important factor causing algal blooms. Warmer temperatures can accelerate algal growth, and decrease water mixing, resulting in stagnant conditions that are perfect for algae. It also prolong the algal growing season. With increasing global temperatures, more intense and frequent blooms are being reported globally.
Natural Events
Certain algal blooms are naturally caused by upwelling, which brings nutrient-rich water from the deep ocean to the surface, and seasonal fluctuations, such as spring or summer, during which light, temperature, and nutrients are optimally suited to support the growth of algae. But even naturally occurring blooms may become toxic when coupled with anthropogenic activities raising nutrient levels.
Types of Algal Blooms
Algal blooms are broadly classified according to the impact on the environment, aquatic organisms, and human health. Not all harmful algal blooms are toxic, but even the non-toxic ones are disturbing to aquatic environments when they come in massive amounts.
Harmful Algal Blooms (HABs)
Harmful Algal Blooms (HABs) are initiated by specific species of algae, which are toxigenic. They can have effects on aquatic animals, land animals, and human beings. In aquatic ecosystems, HABs are commonly linked with “red tides” because they tint water reddish-brown. HAB toxins can become stored in shellfish, rendering them inedible. In freshwater, blue-green algae are most commonly implicated in toxic blooms that can cause fish kills, animal illness, and even liver damage or neurological illness in humans exposed to the water. HABs also cause oxygen depletion, producing “dead zones” where water life finds it difficult to survive.
Non-Toxic Algal Blooms
Not all algal blooms are toxic. Some consist of non-toxic species that still bloom excessively under favorable conditions. Although they do not directly pose a health threat, they can severely lower water clarity and shade the water, which inhibits photosynthesis in aquatic plants. When these algae die, their decomposition depletes dissolved oxygen from the water, resulting in hypoxic environments that can kill fish and other aquatic life. Additionally, the decomposition of massive blooms tends to produce bad odors and render water bodies uninhabitable for recreational purposes.
Effects of Algal Blooms
Algal blooms- both toxic and non-toxic may have far-reaching effects that extend across ecosystems, economies, and human health.
Ecological Impacts
Dead zones and loss of biodiversity– As algal blooms die and decompose; the process consumes a huge amount of oxygen dissolved in the water. This leads to hypoxia or low-oxygen conditions, resulting in “dead zones” where hardly any aquatic species can live. The decreased oxygen level causes death among fish, crustaceans, and other sea creatures, destroying food webs and lowering biodiversity. Additionally, shading by dense algal mats prevents sunlight from reaching it, weakening submerged aquatic vegetation critical to the stability of the ecosystem.
Economic Impacts
Fisheries and Tourism– Algal blooms may ruin economies based on fishing, aquaculture, and tourism. Toxins in seafood may result in seafood harvesting bans, greatly affecting fishermen’s livelihoods. In recreational water use areas, blooms usually result in beach closings and warnings, keeping tourists away. Management and clean-up costs, as well as lost income from affected industries, may be great.
Human Health Hazards
Toxins and water safety- One of the scariest effects of toxic algal blooms (HABs) is the danger they inflict on human health. Some algae, especially cyanobacteria (blue-green algae) and dinoflagellates secrete highly toxic compounds that can pollute freshwater and marine ecosystems. These toxins- microcystins, saxitoxins, and domoic acid have the potential to impact human health by a variety of routes such as consuming tainted water, eating seafood that has accumulated the toxins, or even bathing in contaminated waters.
Consumption of contaminated water or seafood can result in symptoms varying from diarrhea, vomiting, and nausea to severe effects such as liver injury, paralysis, or neurological disturbances. Exposure through the skin to toxic blooms can result in rashes or allergic skin reactions, whereas inhalation of particulate matter, particularly in and around water during a bloom, can result in respiratory irritation and difficulty breathing.
Treatment plants can have a difficult time eliminating these toxins, particularly at the time of large-scale blooms. Thus, upon the presence of algal toxins, health authorities issue public health advisories so that people cannot use the water for drinking, cooking, or even recreational uses. Repeated exposure, though at a low level, is a new area of focus in public health studies because it may be related to long-term health impacts.
Recent Cases of Harmful Algal Blooms
Harmful algal blooms have been reported worldwide with increased frequency over the past decade, signaling the increased importance of this environmental concern. These instances show the far-reaching effects of HABs on wildlife, ecosystems, and human health.
Sea Lion Poisoning along California’s Coast
A significant case was reported along the Californian coast, where numerous sea lions were reported to be disoriented, ill, or deceased. The findings indicated that the animals had been exposed to elevated concentrations of domoic acid, a neurotoxin that marine diatoms, particularly Pseudo Nietzsche, secrete. Sea lions, being the carnivorous mammals they are, consume the toxin indirectly when their diet includes feed containing contaminated algae.
Domoic acid affects the central nervous system, causing symptoms like confusion, tremors, seizures, and in some instances, death. During this outbreak, several marine mammals were discovered stranded on beaches, displaying erratic behavior and extreme neurological distress. Marine rescue facilities were inundated with cases and posted public warnings to avoid beach areas by beachgoers and pets.
This event is an example of how algal toxins bioaccumulate via the food web and cause wide-scale wildlife mortality. It is also an example of the imperative to create early warning systems and monitoring programs for detecting harmful blooms and safeguarding marine life and human communities dependent on these systems.
Red Tide Events in Florida
Florida regularly suffers from harmful algal blooms due to Karenia brevis, a marine dinoflagellate that is the cause of “red tide” events. The blooms color the water reddish-brown because of the dense population of algal cells and yield brevetoxins, which are toxic to marine life and humans.
Florida’s red tides have produced huge fish kills, killed sea turtles, manatees, and dolphins, and severely disrupted native ecosystems. Red tides can become airborne via sea spray, resulting in respiratory irritation in beachgoers, especially those with asthma or other medical conditions. In addition, eating contaminated shellfish can result in neurotoxic shellfish poisoning in human beings.
Economically, red tides impact Florida’s tourism and fishing industries, causing beach closures, declining seafood sales, and economic losses to coastal communities. Despite attempts to monitor and manage these blooms, their frequency and intensity seem to be on the rise, which may be attributed to climate change and nutrient runoff.
Elephant deaths linked to toxic Algae in Botswana
In 2020, Botswana suffered a mysterious and tragic die-off of more than 300 elephants in the Okavango Delta. Following extensive research, experts concluded that cyanobacterial neurotoxins were the probable reason. The toxins were created by the blue-green algae in the waterholes frequented by elephants and other animals.
The elephants died suddenly, according to reports, with some falling face-first- a symptom of quick neurological collapse. The event was of international concern, not only because of the magnitude but also because of the implications for conservation and ecosystem well-being.
The Botswana example illustrates how climatic shifts, like extended drought and increased temperatures, can make it possible for the development of harmful algae even in isolated, freshwater ecosystems. It also points to the necessity for international watchfulness in observing water quality and protecting wildlife from the hidden threat of algal blooms.
Monitoring and Managing Algal Blooms
Successful management of algal blooms is dependent on early detection, real-time monitoring, and coordinated response systems. Satellite imaging, water quality sensors, and laboratory analysis are used to monitor nutrient levels, temperature, and certain algal species.
Government agencies, environmental organizations, and research institutions frequently collaborate to develop forecasting models that are able to predict where and when blooms are likely to happen. The models use environmental information like rainfall, nutrient runoff, and water temperature.
Public notices are important to guarantee water safety during blooms. Temporary beach closures, shellfish harvesting grounds, or even water treatment plants might be required in some instances to safeguard public health. Long-term research and monitoring infrastructure investment is essential to reduce the harm inflicted by algal blooms.
Preventive Measures of Algal Blooms
Prevention of algal blooms requires addressing their causes, primarily nutrient pollution and climate conditions. Some key measures include:
Better agricultural practices: Farmers can use sustainable methods such as controlled application of fertilizers, buffer strips, and crop rotation to decrease runoff into adjacent water bodies.
Wastewater management: Augmenting sewage treatment facilities to lower nutrient loads- such as nitrogen and phosphorus prevents algae growth.
Urban planning and green infrastructure: Developing green space and wetlands within urban areas can screen stormwater and restrict nutrient outflow to rivers and lakes.
Public awareness campaigns: Educating people on the use of fertilizers responsibly and conserving water can promote anticipatory behavior.
Climate Mitigation: Curbing greenhouse gas emissions and enhancing climate resilience are longer-term but necessary measures to lower the incidence of conditions favorable to blooms such as warm, stagnant waters.
Conclusion
Algal blooms are a multifaceted environmental problem with wide-ranging implications. Although some blooms are natural and harmless, others, especially harmful algal blooms (HABs), are serious threats to aquatic ecosystems, human health, and regional economies. Human activities, such as climate change, have amplified the frequency and intensity of these occurrences.
High-profile events, ranging from California sea lion poisonings to Botswana elephant mortality, demonstrate the worldwide extent of the issue. Controlling and mitigating against algal blooms needs a concerted effort, involving scientific study, effective monitoring, policy measures, and public assistance.
As climatic patterns persist in changing and pressures on water resources by people continue to expand, dealing with algal blooms must remain a global environmental agenda item.
References
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- Weston, P. (2024, November 29). ‘Climate-induced poisoning’: 350 elephants probably killed by toxic water. The Guardian. https://www.theguardian.com/environment/2024/nov/29/mystery-mass-die-off-deaths-elephants-toxic-water-botswana
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