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Eutrophication, a term rooted in the Greek words "eutrophia" (eu = "good" and trophè = "nourishment"), refers to a condition characterized by an excessive presence of nutrients in freshwater and saltwater systems.  These nutrients, such as nitrogen, phosphorus, or sulfur, can originate from natural sources or human activities.


photo credit: OSPAR Assessment portal

When it occurs naturally, eutrophication is a gradual process where nutrients, particularly phosphorus compounds and organic matter, accumulate in water bodies. These nutrients originate from the breakdown of minerals in rocks and the activities of lichens, mosses, and fungi, which actively extract nutrients from rocks.

However, "cultural eutrophication," primarily induced by human activities, is a much faster process.

In this scenario, nutrients enter water bodies rapidly through various pollution sources, including untreated or partially treated sewage, industrial wastewater, and agricultural fertilizers.

Eutrophication often results in a conspicuous and detrimental consequence: the proliferation of algal blooms. These blooms not only impede light penetration into the water but also disrupt the delicate equilibrium of the ecosystem.
As these algae multiply, their eventual breakdown by bacteria becomes a key contributor to the depletion of oxygen in the water. This exacerbates the environmental challenges linked to eutrophication.
When oxygen levels plummet to critically low thresholds, fish and other aquatic organisms are at risk of suffocation and mortality.

Eutrophication poses a threat to native aquatic species, particularly those less capable of adapting to shifting environmental conditions. This process can also create a favourable environment for invasive species that thrive in nutrient-rich habitats.
Furthermore, the buildup of deceased organisms and organic matter on the lake or riverbed intensifies the issue, sustaining the cycle of eutrophication.


Some algae species, including cyanobacteria, produce harmful toxins, referred to as harmful algal blooms (HABs) or cyanobacterial harmful algal blooms (CyanoHABs). These toxins can have severe health implications for aquatic life and human health. People who come into contact with or consume water or seafood contaminated by these toxins can experience health problems. These may include skin rashes, gastrointestinal issues, respiratory problems, and neurological effects or death.

Canadian waterweed (Elodea canadensis).jpg
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Canadian waterweed (Elodea canadensis) is an aquatic plant native to North America.

In nutrient-rich waters, it can grow rapidly and form thick mats that block sunlight, thereby hindering the growth of other native aquatic plants. This competitive advantage can alter the natural balance of aquatic ecosystems, leading to reduced biodiversity and potential long-term ecological consequences.

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Hydrilla (Hydrilla verticillata) is an aquatic plant known for its rapid growth in nutrient-rich waters. Its dense growth can clog rivers and lakes, hinder navigation, and disrupt the natural habitats of native species. Additionally, the aggressive spread of hydrilla can result in adverse economic impacts, including increased maintenance costs for water infrastructure and reduced recreational opportunities in affected water bodies.

Zebra Mussel (Dreissena polymorpha).jpg

Dreissena polymorpha, commonly known as the Zebra Mussel, is a freshwater mollusc that has been listed by the Invasive Species Specialist Group (ISSG) of the World Conservation Union (IUCN) as one of the '100 worst invasive species.' This list highlights the environmental and ecological damage caused by invasive species worldwide, and the inclusion of the Zebra Mussel on this list underscores its significant negative impacts on aquatic ecosystems, water infrastructure, and native species in regions where it has become established.

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