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Mckenzie Bagayas

Red on the Rise: Harmful Algal Blooms in Autumn and the Impact of Climate Change

Algal blooms usually occur during the warmer months of summer. [5] But recently, algal blooms have been occurring in a less predictable pattern. Is this a consequence of global warming? Or is this a natural phenomenon that has been occurring since time immemorial?


What are algal blooms? Algal blooms are pretty self-explanatory. ‘Algal’ refers to algae, and bloom means the development of flowers in plants. However, in this context, the bloom may refer to the increase in algae cells since algae is not a flowering plant. A more accurate algal bloom definition is as follows; an algal bloom is a phenomenon that occurs when there is an overabundance of nutrients in bodies of water which encourage the overgrowth of tiny green plants on the water’s surface. [6]


The overabundance of nutrients, primarily phosphorus, in bodies of water is referred to as eutrophication. This can occur through a variety of ways. One way would be through agricultural run-off. The phosphorus-rich fertilizer present in agricultural lands may get washed away by the rain and end up in rivers, streams, and other bodies of water. Another way would be through the leakage of sewage or wastewater. [6]


Globally, algal blooms have a huge impact on the economy. A 2019 systematic review which dealt with algal bloom data and statistics showed that digestive issues caused by this phenomenon cost, on average, $86 for mild cases, $1,015 for moderate cases, and $12, 605 for severe cases. [7]


Aside from its economic impact, algal bloom problems extend to health issues on both humans and animals. One bacterial genus that is responsible for algal blooms is the Cyanobacteria. Some species of the Cyanobacteria are capable of producing toxins that are harmful to humans. There are instances wherein the algal bloom would contain several toxin-producing Cyano-bacteria. In cases like these, each toxin-producing Cyanobacteria species would contribute their unique toxin to the algal bloom. Some of these toxins, aptly named cyanotoxins, are quite nasty.



Microcystins, cylindrospermopsin and nodularins are cyanotoxins capable of damaging the liver due to this they are called hepatotoxins as well. Anatoxin-a, anatoxin-a(s) and homoanatoxin-a are cyanotoxins that affect the nervous system negatively; they are neurotoxins. These toxins may remain in the water even after treatment and pose a risk to those who might drink it. [3]


These toxins also pose a risk to the environment and wild animals. Creatures exposed to these toxins may die off which could mess-up entire ecosystems. Even the Cyanobacteria species that do not produce harmful toxins may still pose a threat to aquatic plants and animals. Cyanobacteria algal blooms may compete with aquatic plants for nutrients. This will hamper the growth of other species of aquatic plants. Furthermore, when they would grow uncontrollably and die, they suck out the oxygen and other essential constituents needed for life, effectively killing whatever living thing that is dependent on oxygen.


How do algal blooms occur?

There are several factors that contribute to the occurrence of algal blooms. As mentioned previously, excess nutrients that wind up in bodies of water is the main contributing factor. However, besides excess nutrients, factors like temperature, sunlight, ecosystem disturbance, hydrology, and water chemistry are also contributing factors. [1][3]


The occurrence of algal blooms are still not fully understood but we have some idea as to the mechanisms behind their occurrence. [1][3]


Nutrients

The overabundance of nutrients, Phosphorus and nitrogen are the principal nutrients that are capable of causing an algal bloom. These nutrients may mix with bodies of water through a variety of ways such as through agricultural run-off, soil erosion, and sewage spills. Nutrients may come from the body of water itself. Phosphate-containing sediments may release their phosphate when the water’s dissolved oxygen concentration would plummet. [1][3]


Temperature

Algae and photosynthetic bacteria exhibit optimal growth at certain temperatures. Cyanobacteria algal blooms are more likely to occur during summer months due to the fact that these photosynthetic bacteria thrive at temperatures above 25 degrees Celsius while other types of algae do not. This grants them an edge over their competitors which would lead to their sudden explosion in numbers. [1][3]


Turbidity

Suspended particles in water would scatter or block sunlight. In the case of cyanobacteria, they thrive best when there is some amount of light blockage and scattering. Light requirements vary from algae to algae, some may prefer more sunlight while others would prefer less. With regards to this, some algae may prefer less turbid water while others would prefer high turbidity. [1][3]


Sunlight

Algae responsible for algal blooms are almost always photosynthetic. This means that they need sunlight to grow and multiply. This also means that sunlight plays an important role in the occurrence of algal blooms. Cyanobacteria have a very specific need when it comes to sunlight. Their growth would slow down when they are exposed to high-intensity sunlight for a long time. This means that the water surface is not an optimal location for their growth. However, they would grow well several inches beneath the water surface where sunlight intensity fluctuates. [1][3]


Stable conditions

This refers to the turbulence in the aquatic environment that the algae are growing in. Are they constantly being tossed around due to the water currents and wind? Or are they more or less stationary? This factor also affects turbidity which in turn affects sunlight as well. Some algae prefer constant churning while others, like the Cyanobacteria, prefer a more stable environment. During warm months, temperature differences in bodies of water may create layers. The upper warm layer becomes stable and fails to mix with the lower cooler layer. This condition is ideal for Cyanobacteria which would lead to an explosion in their numbers. [1][3]


As mentioned previously, during warmer months the water at the surface and near the surface absorbs a lot of heat. Once this happens, the water is stratified, separated into layers. The upper layer is warm and stable and the lower layer is cool. Currents that used to mix the two layers would disappear. This occurs mostly on stagnant or slow-moving waters such as those found in dams. Nutrients that would find their way in this water may sometimes sink and get trapped in the bottom layer. Throughout the warm months, the algal blooms may occur which would deplete the nutrients in the upper layer. The depletion of nutrients would prevent the growth of plants and may deter or even kill aquatic animals that rely on these nutrients. [2][4]


Finally, autumn comes and the upper layers would begin to cool. Once this happens the upper layers would begin to sink down and bring up the lower layers. In other words, mixing would occur. The nutrients that are trapped in the lower layers are introduced to the upper layers. The excess nutrients would then trigger an algal bloom in Autumn. [2][4]


Are all algal blooms harmful?

Although some algae, like some species of  Cyanobacteria,  are  capable of producing some nasty toxins, not all algal blooms are harmful. For starters, not all algal blooms are caused by toxin-producing algae. In fact, 99% of algal blooms are caused by algae that do not produce toxins. However, an algal bloom does not need to produce toxins to be damaging to the environment. When an algal bloom ends and all of the algae would start to decompose, the bacteria responsible for the decomposition process would suck out all of the oxygen in the water. This creates what is called a ‘dead zone’. Any living creature that is dependent on oxygen would suffocate in these dead zones. In areas where there are a lot of fishes living, the dead zone would cause a ‘fish-kill’. In cases wherein, the algal bloom does produce toxins, aquatic animals and land animals who would drink the toxin-filled-water may be affected negatively. Toxin-producing algal blooms are especially dangerous to humans when it occurs in drinking-water reservoirs. The routine treatment processes that the drinking-water would undergo are not capable of eliminating the toxins produced by the algae. Another situation where algal bloom would pose a threat to public health is in the occurrence of ‘Red Tide’. Wherein humans may ingest seafood that contains high levels of algae toxins. But again, harmful algal blooms constitutes only 1% of all algal bloom occurrences. [8][9]


Are algal blooms increasing?

As the debate about whether global warming is natural or man-made rages on, the world is undeniably getting warmer. Experts claim that we are progressively experiencing more and more algal blooms as a consequence of the increasing temperatures. They explained that warm temperatures would have the following effects: [5]


  • Cyanobacteria blooms would become more and more frequent as these algae prefer warm temperatures.

  • Warm temperatures would also prevent water from mixing, another condition that is favourable for the growth of Cyanobacteria.

  • Due to the increased temperatures, algal blooms would occur more often. Since algal blooms tend to absorb sunlight and heat, the water becomes warmer and encourages even more algal blooms. 


It does not stop there, global warming would also promote the increase in salinity of freshwater. As the world gets warmer, water levels would drop which would lead to an increase in dissolved-solids concen-tration including sodium chloride. The increase in salinity may reach a point wherein the freshwater would become comparable to to marine water. Once this happens, marine algae may grow in freshwater environments and cause problems. Unfortunately, this has been happening in the southern parts of the United States since 2000. [5]


As we burn more fossil fuels we release more carbon dioxide into the atmosphere. This increase in carbon dioxide is favourable for algae as they need this molecule to produce food through photosynthesis. [5]


Extreme weather patterns brought about by global warming may bring about severe droughts that are quickly followed by severe storms. These conditions would lead to the occurrence of nutrient runoff which would then encourage the occurrence of algal blooms. [5]


The warming earth would melt a lot of our ice caps which would lead to an increase in sea levels. As the sea levels increase, coastal areas are swallowed up and turn into shallow and stable coastal waters. These conditions are perfect for the growth of algae. [5]


Wrap up

Not all algal blooms are harmful. However, even those algal blooms which are caused by algae that do not produce toxins may still cause harm to the aquatic ecosystem for they may still cause ‘fish-kills’. There are a lot of factors that would come into play when it comes to the occurrence of algal blooms. Although excess nutrients is the principal factor, temperature, sunlight, turbidity and stable conditions play an important role as well. 


Algal blooms are more common in summer because the warm temperature is conducive for algal growths. However, algal blooms would still occur during autumn. Furthermore, the occurrence of algal blooms are increasing and some experts attribute this increase in frequency to the ever-increasing temperatures.


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