Anatomy of a Bloom

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What is an algal bloom? To understand that it is necessary to understand that a body of water – lake, artificial pond, reservoir – is more than just a bunch of water all in one place. Any open body of water plays host to a variety of living beings, many of which cannot be seen. The relations and interactions between these creatures create a complex biological system in even the smallest reservoir. When functioning well, the biological system is largely self-regulating, and provides the services we expect from freshwater bodies: drinking-quality water, fish stock, safe bathing and aesthetically pleasing views. However, there can be situations where the natural balance is broken, and if algal blooms are not the cause of the disruption, they will often be the result. An algal bloom is the disproportionate growth of one group of cyanobacteria, microscopic organisms commonly referred to as blue-green algae. Cyanobacteria are not in fact true algae, being classified as photosynthetic bacteria; they also proliferate much like bacteria do in other settings. The term “bloom” can be misleading; a better term would be “outbreak”. When cyanobacteria start to take over a water body, they can force aside other forms of life, monopolizing nutrients, space and ever-important sunlight. Some algal outbreaks run their course in weeks or months, leaving behind what damage they can incur in that time frame. Others will stay for longer spans, permanently changing the characteristics of the water body.

An outbreak can cause damage on several levels. At the most basic, the high load of cyanobacterial cells can harm infrastructure by biofouling; the strong shift in the food web can destroy fish populations; the blooms themselves, often visible as green, slimy scum on the surface can severely harm the aesthetic value of water bodies, harming leisure and tourism where relevant. But often the greatest damage is to water quality. The shift in biological makeup often causes a severe drop in water quality. To make matters worse, many cyanobacteria achieve their dominancy with the help of toxins – chemicals excreted to the water and deadly to many organisms, humans included. A strong toxic outbreak can render the water of an entire lake unpotable.

What causes an outbreak? What can be done about it? Our next posts will discuss these and other aspects of outbreak management.