which depletes the oxygen levels of a body of water. It is usually related to an excess of certain nutrients, usually phosphates, which encourage the growth of large amounts of plants and algae. When these die and decay, oxygen is removed from the water, which harms the surrounding ecosystem – especially aquatic animals¹.
The Effects of Eutrophication
Eutrophication of water bodies has become a large problem throughout heavily populated parts of North America and Europe, and has a range of devastating effects. The lack of oxygen in the water can result in mass fish kills, which further pollute the water and harm the environment². It also changes the ecosystem balance. The increase in nutrients and algal blooms which often lead to eutrophication can limit the sunlight that enters the water. Even if the reduced oxygen levels in the water don’t harm them, bottom dwelling species can be affected by this reduced light¹.
It can also cause environmental conditions to become more favourable to invasive species due to the changing of the nutrient balance of the water body. A good example is the Common Carp, which is adapted to live in naturally eutrophic conditions. When the oxygen levels of a water body decrease, the carp can still function normally, even though native species will suffer³.
What is Cultural Eutrophication?
Cultural eutrophication refers to eutrophication which has been sped up or caused by human processes. Usually this occurs due to the introduction of a range of nutrients through fertilizers, chemicals, or soaps and detergents⁴. It can lead to the premature death of a body of water, and affects millions of lakes and waterways throughout the world⁵.
Causes and Effects of Cultural Eutrophication
Since cultural eutrophication is an issue caused by humans, it causes huge problems in waterways throughout the world. After heavy rainfall, the runoff usually introduces high levels of nutrients into nearby waterbodies. This often causes algal blooms, which – as explained above – destroy the biodiversity of the ecosystem.
One of the best large-scale examples of cultural eutrophication is the Gulf of Mexico. It has become a huge hypoxic zone almost devoid of marine life due to fertilizer and chemical runoff. This area reached a record size of 21,756 square kilometers in 2002. It has had huge, wide reaching effects on the local and international economy. On particularly bad years, important commercial and recreational fisheries are threatened by the hypoxic zone, and this has become a subject of debate among conservationists throughout the world⁶.
Other Examples of Cultural Eutrophication:
The Baltic Sea – The Baltic Sea contains one of the largest dead zones on the planet, averaging around 49,000 square kilometers for the last 40 years. Again, it is caused by algal blooms fueled by excess nutrients from human activities⁷.
Lake Erie – Lake Erie has long had reduced oxygen levels due to the human activities around its shores. This affects aquatic life in the area, and has had a huge impact on local fisheries since the 1950s⁶.