Cyanobacterial blooms
Article

Cyanobacterial blooms: causes, dangers and treatment

Accelerated by the rising temperatures due to climate change, unprecedented Cyanobacterial blooms have become a global challenge.

Cyanobacteria (blue-green algae) are one of the most common organisms on Earth. They appeared over 3.5 billion years ago, reshaping our entire biosphere. It is believed that cyanobacterial photosynthesis has enriched the early Earth’s atmosphere with Oxygen, giving rise to life as we know it.

Throughout their long history, Cyanobacteria have evolved to adapt to many geochemical and climatic changes. Modern Cyanobacteria have learned to exploit the human modifications of the aquatic environments. Nutrient over-enrichment and hydrologic alterations have dramatic effects on water ecosystems around the globe. Accelerated by the rising temperatures due to climate change, unprecedented Cyanobacterial blooms have become a global challenge.

What is Cyanobacteria?

Cyanobacteria are microorganisms that structurally resemble bacteria, but lack a nucleus and organelles. Unlike other bacteria, Cyanobacteria can conduct oxygenic photosynthesis and contain chlorophyll a.

Cyanobacteria have a remarkable capacity to adapt to global changes. They can survive high ultraviolet light, desiccation, hypersalinity, and extreme temperatures. Even for many years.

Cyanobacteria grow in freshwater lakes, streams, oceans, damp soil, moistened rocks, and more. Over billions of years of evolution, they have formed unique symbiotic associations with microorganisms, plants, seagrass, fungi, sponges, and cycads. They even live on the fur of sloths and polar bears.

Single Cyanobacteria is too small to see without a microscope, but they can grow into huge colonies, which can be seen even from space. Cyanobacterial blooms can be extremely dangerous to human health, animals, and ecosystems.

Dangers of Harmful Cyanobacterial Blooms

The expansion of Cyanobacterial Harmful Algal Blooms (CyanoHABs) has become a major concern for societies worldwide. Cyanobacteria can critically impair the safety of drinking water, as well as fishing, irrigation, and recreational value. CyanoHABs deplete the oxygen in the water, release toxins, and degrade the water quality.

Environmental impacts

Cyanobacterial blooms can severely damage the water ecosystem, causing fish and plants to suffocate and die. They compromise the water quality and safety for animals and people by releasing cyanotoxins in the water. When the Cyanobacteria in the bloom start to disintegrate, they produce bad taste and odor.

Economic impacts

CyanoHABs can bring economic losses to many business sectors. They can cause significant financial damage to the agricultural sector, fisheries, water treatment plants, tourism industry, recreational services, and real estate prices in the waterfront areas.

Health impacts of Cyanobacterial blooms

Some Cyanobacteria can release toxins called cyanotoxins, which are produced and contained within their cell. They are mostly released after the cell death or if the cells are lysed open by chemical treatment. Cyanotoxins can be very harmful to humans, animals, and the environment.

If people consume cyanotoxins, either by drinking contaminated water, inhaling it while swimming, or eating contaminated fish, it can affect their liver (hepatotoxins), their nervous system (neurotoxins), skin, and increase tumor growth (dermatoxins). There are also many reported cases of domestic and wild animal illnesses and death linked to cyanotoxins.

The cyanotoxin production depends on a combination of environmental factors. Nutrient supply rates (N, P and trace metals), light intensity, and high temperatures have a major impact. Interactions with other bacteria, viruses, and fish can also stimulate the release of cyanotoxins in water.

What causes Cyanobacterial blooms?

Anthropogenic nutrient enrichment, altered hydrologic patterns, and changes in the Earth’s climate accelerate the intensity, duration, and frequency of CyanoHABs. Extensive nutrient supply (nitrogen:N and phosphorus:P), rising atmospheric CO2 levels, and higher water temperatures intensify the Cyanobacterial growth. Vertical stratification, water residence time, and interactions with other biota are also significant factors.

Nutrient pollution feeds Cyanobacteria

Cyanobacteria are actively exploiting man-made pollution of water systems. They thrive on nutrient pollution and eutrophication. Urban, agricultural, and industrial activities increase the nutrient pollution, salinization, and eutrophication of waterways. This stimulates more frequent and persistent Cyanobacterial blooms.

Climate change exacerbates cyanobacterial blooms

Climate change is another powerful catalyst for Cyanobacterial expansion. Rising temperatures and changes in the precipitation patterns stimulate more frequent and extensive CyanoHABs. Elevated temperatures lead to an earlier onset and longer duration of thermal stratification, which makes the buoyant cyanobacteria more competitive.

The response of Cyanobacteria to the increase in temperatures strongly depends on the nutrient availability. Changes in climate alter the precipitation and biogeochemical processes that make nutrients more available for cyanobacterial blooms.

Cyanobacterial blooms accelerate climate change

CyanoHABs draw down the CO2 from the atmosphere, turning lakes into CO2 sinks.
A recent study published in Science Advances concludes that during photosynthesis, CyanoHABs also produce significant amounts of the greenhouse gas methane Substantial rates of methane production are observed under diverse conditions – light, dark, oxic, and anoxic.

This creates a positive feedback loop: higher global water temperatures stimulate more CyanoHABs, which emit more methane, which provokes more global warming.

Treatment from Cyanobacteria

CyanoHABs present significant challenges for environmental management of water bodies.
Ensuring healthy functioning of water ecosystems and safety of recreational activities requires effective management of CyanoHABs.

There are various methods to treat CyanoHABs, including physical removal, chemical procedures, biological inactivation, and ultrasonic control.

Chemical treatment

Chemical treatment is the most commonly used method, which is also the most dangerous to the environment. It involves using copper sulfate and hydrogen peroxide, which cause sudden death or lysis of Cyanobacterial cells. As a result, the release of massive amounts of cyanotoxins occurs. Chemical intervention does not resolve the core problem of CyanoHABs, as they can reappear after the treatment.

Nutrient reduction

Reducing the amount of nutrient loads entering the water systems could help limit the CyanoHAB growth. However, this requires radical changes in urban, agricultural, and industrial activities that produce the nutrient pollution. The major sources of nutrient pollution include: agriculture, aquaculture, animal farming, wastewater, storm water, fossil fuels, and households. This great variety of sources makes nutrient pollution very difficult to control as quickly and effectively as necessary.

Ultrasonic control

To avoid using harmful chemicals and achieve a fast and effective treatment, LG Sonic has developed an ultrasound technology to control algal blooms. This ultrasonic system creates a sound barrier on the top layers of the water to control the Cyanobacterial growth. Under such conditions, Cyanobacteria cannot reach the water surface, so it cannot keep growing. To maintain the ecological balance, the system does not eliminate Cyanobacteria completely. It reduces them by up to 90%. In this way, the water ecosystem can be safely restored by reducing and controlling healthy levels of Cyanobacteria.

Recommendations

Successful mitigation of CyanoHABs must rely on an in-depth understanding of the principles of aquatic ecosystem dynamics. It must be based on reliable surveillance, alerts, eco-friendly treatment methods, and adequate action plans. Inadequate mitigation of CyanoHABs can lead to extensive damage to aquatic ecosystems. This can cause significant socio-economic losses that can be even worse than the impacts of CyanoHABs.