Air Pollution: Harmful Algal Blooms' Unseen Cause

Harmful algal blooms (HABs) are a growing concern for scientists and environmentalists alike, as they can have detrimental effects on aquatic ecosystems, including people, animals, and plants. HABs occur when toxin-producing algae grow excessively in bodies of water, causing negative impacts such as water discolouration, unpleasant odours, and even toxicity that can lead to illnesses in humans and animals. While the immediate health effects of HABs are known, long-term consequences are still being investigated. Nutrient pollution, particularly from excess nitrogen and phosphorus, is a significant contributor to HABs, as it provides favourable conditions for rapid algae growth. These blooms can also create dead zones where aquatic life cannot survive due to depleted oxygen levels. As a result, understanding and preventing HABs are crucial for maintaining the health of both ecosystems and human populations.

Point source pollution

The US Environmental Protection Agency (EPA) defines point source pollution as "any single identifiable source of pollution from which pollutants are discharged, such as a pipe, ditch, ship or factory smokestack". Point source pollution is easy to identify and comes from a single place. It is the opposite of non-point source pollution, which is harder to identify and address as it comes from many places at once.

Factories and power plants are common sources of point-source pollution, affecting both air and water. Smokestacks may emit carbon monoxide, heavy metals, sulfur dioxide, nitrogen dioxide, and particulate matter (small particles) into the air. Oil refineries, paper mills, and auto plants that use water for manufacturing often discharge effluent—wastewater containing harmful chemical pollutants—into rivers, lakes, or the ocean. Municipal wastewater treatment plants are another common source of point-source pollution, as they can introduce nutrients and harmful microbes into waterways. Nutrients can cause a rampant growth of algae in water.

Large farms that raise livestock, such as cows, pigs, and chickens, are other sources of point-source pollution. These farms are known as concentrated animal feeding operations (CAFOs). If they do not treat their animals' waste, these substances can enter nearby water bodies as raw sewage, significantly increasing the level and rate of pollution.

To control point-source discharges, the Clean Water Act established the National Pollutant Discharge Elimination System (NPDES). Under the NPDES program, factories, sewage treatment plants, and other point sources must obtain a permit from the state and EPA before discharging waste or effluents into any body of water. Prior to discharge, the latest technologies must be used to treat effluents and reduce pollutants.

Eutrophication

The occurrence of HABs is influenced by various physical and chemical factors, including the ratio of nitrogen to phosphorus, organic nutrient supply, temperature, and light attenuation. The precise drivers of toxin production in HABs are still being actively researched. Eutrophication and HABs are significant issues for many freshwater and coastal marine ecosystems, and their management is a complex task requiring the collective efforts of scientists, policymakers, and citizens.

Climate change

The effects of climate change, such as stronger vertical temperature stratification, sea level rise, changes in coastal upwelling, and increased carbon dioxide levels, can exacerbate the occurrence and impact of HABs. Additionally, climate change-induced rainfall can increase runoff, contributing to the spread of HABs.

Furthermore, the increase in water temperature caused by climate change can enhance the competitive fitness of HAB taxa. This can lead to a dominance of certain algal species, disrupting the natural balance of aquatic ecosystems. Warmer temperatures also contribute to the longer persistence of HABs, increasing their potential to cause harm to the environment and human health.

Toxin production

Harmful algal blooms (HABs) are rapid and massive expansions of cellular populations such as cyanobacteria, diatoms, and dinoflagellates in aquatic ecosystems. While not all algal blooms produce toxins, dozens of HAB species do, and these toxins can be harmful or even fatal to humans, livestock, wildlife, marine animals, and other life forms.

The precise drivers of toxin production are still being actively researched. However, it is known that factors such as the ratio of nitrogen to phosphorus, organic nutrient supply, temperature, and light attenuation play important and interconnected roles in determining HAB composition and toxin production. For example, warmer temperatures caused by climate change can favor HAB taxa and improve their competitive fitness. Intense storms, another consequence of climate change, create pulses of nutrient runoff, which can promote excessive fertilization (eutrophication) of both flowing and non-flowing waters. Point source pollution, such as discharges from wastewater treatment plants, concentrated animal feeding operations, and stormwater associated with industrial activity, can also be high in nitrogen and phosphorus, contributing to eutrophication.

The toxins produced by HABs can have severe impacts on human and animal health. Exposure to these toxins can occur through various routes, including oral exposure from ingestion of contaminated water, inhalation, dermal exposure through direct contact with contaminated water, and consumption of contaminated seafood, especially shellfish. Shellfish and other filter-feeding organisms accumulate toxins from the algae, and these toxins may then accumulate higher in the food web. Some algal toxins, such as brevetoxins, can even become airborne in sea spray, causing respiratory distress in coastal populations.

It is important to note that HAB organisms occur naturally. However, human activities, such as agricultural runoff, inadequate wastewater treatment, and road runoff, have exacerbated the problem by contributing to excessive eutrophication of many water bodies. The increase in HABs and their associated toxin production has led to significant economic losses and negative impacts on aquatic ecosystem sustainability and economic vitality.

Cyanobacteria

The growth of cyanobacteria is also influenced by climate change, including global warming and rising CO2 concentrations. Warmer temperatures lead to water stratification, allowing buoyant cyanobacteria to float upwards and access sunlight for photosynthesis more easily than non-buoyant algae. Cyanobacteria can also absorb light energy, further increasing water temperatures and creating a positive feedback loop that favours their growth over that of eukaryotic algae.

The occurrence of toxic cyanobacterial blooms is a serious global issue that requires proper environmental management. While chemical interventions can be used to control blooms, they do not resolve the core problem and may have negative ecological impacts. Reducing nutrient loading entering water systems is crucial for limiting cyanobacterial growth, but it requires significant changes in urban, agricultural, and industrial activities.

To address the challenges posed by cyanobacterial blooms, it is essential to have a comprehensive understanding of aquatic ecosystem dynamics and reliable surveillance and treatment methods. The socio-economic impacts of inadequate mitigation can be significant, highlighting the urgency of effective management strategies.

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