What is Algal Bloom?

An example of algal bloom in a small pond.

What is an Algal Bloom?

An algal bloom is an excessive multiplication of algae population in either a salt or freshwater system. Algae are simple aquatic chlorophyll-containing photosynthetic organism that are either microscopic or large. They can pose risks to humankind, animals, and aquatic life. Algal blooms lead to the discoloration of water. Blooming occurs differently in respect to the species of algae. Moreover, there is a fixed threshold for algal blooms. Photosynthetic pigmentation of algae determines the color of flowers, it is usually green. In other cases, the algal bloom may be red, brown, or yellow depending on the pigments in algal cells.

Freshwater Algal Blooms

Freshwater algal blooms arise as a result of increased concentration of nutrients mostly phosphates. These nutrients may be from agricultural fertilizers or household detergents containing phosphorus. Presence of carbon and nitrogen in excess are also believed to accelerate algal blooms. Excess phosphates in water systems result in blooming of algae and other aquatic plants. Cyanobacteria are responsible for the blue-green color of algae (which is the dominant color of algae). Algae mature quickly but tend to have a short life. Death of algae results in the presence of dead organic matter in water which in turn lowers the amount of dissolved oxygen in the water. Reduced oxygen is due to the decay process that consumes oxygen. A decrease in dissolved oxygen results in hypoxic conditions (conditions of low oxygen levels) which in turn leads to the death of aquatic plants and animals.

Harmful Algal Blooms

Harmful algal blooms cause damage to living organisms either physically or by producing toxins. In the past, the term red tide was used to describe harmful algal bloom. The term was confusing since algae have a range of many colors and therefore terming it red was inappropriate. They are responsible for large-scale marine deaths and also shellfish poisoning. Harmful algal blooms have detrimental effects on living organisms. First, they produce toxins which cause mass deaths in fish, marine mammals, seabirds, and turtles. They can also cause disease or death among humans through ingestion of contaminated marine food. They also create physical damage to other organisms. Finally, harmful algal blooms lead to oxygen depletion in water systems. In turn this causes hypoxic conditions which are harmful to aquatic life.

Harmful algal blooms can arise either naturally depending on location or as a result of human activities. Different species of algae form a variety of harmful algal blooms depending on the environment. The coastal pollution of water by humans and an increase in water temperatures have led to the rise of harmful algal blooms. An influx of iron-rich dust from vast deserts across the globe is also believed to accelerate the growth of harmful algal blooms. Rainfall also plays a role in the growth of HABs. Other nutrients such as silica also play a role in dangerous algal bloom nourishment. A couple of measures have been suggested to combat the increased numbers of harmful algal blooms in water systems. They include treating industrial and domestic wastewater, minimizing the use of agricultural fertilizers, and reducing the amount of runoff that goes to water systems.


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