It's Freakish to Know How Eutrophication Affects the Environment

Effects of eutrophication on the environment
Eutrophication is one of the biggest environmental problems caused due to modern methods of agriculture. Here is some more information about how this phenomenon affects the environment.
Did You Know
In 1976, hypoxia caused by eutrophication caused severe damage to the ecology of the New York Bight. The Benthic layer―the lowest layer―needed more than two years to return to its previous condition.
Eutrophication, in the form of its original Greek root words, means 'proper nourishment'. So, how could that possibly be a problem? The problem occurs not because of mere eu-, but hypertrophication, or too much nourishment. Eutrophication or hypertrophication is the imbalance in an aquatic habitat caused by the entry of more nutrients―particularly nitrogen and phosphor compounds―than the ecosystem can handle.

Eutrophication can be caused by both natural and man-made causes. Human activities such as agriculture and industries release their wastes into natural bodies of water. These wastes contain phosphorus and nitrogen compounds that are nutritious for plants, especially simple plants such as algae or hyacinths. Due to eutrophication, these simple plants cover extensive areas of the surface of their native water bodies. Oftentimes, they create a 'carpet' over the entire surface. While these carpets can sometimes be visually appealing due to their colorful form, they spell dire consequences to organisms living underneath. On the other hand, an ecosystem may naturally become eutrophic due to a lack of drainage or use of the nutrients.
Effects of Eutrophication on the Environment
Ecosystems are delicately balanced circles of life, and even the tiniest aberration takes a whole chunk out of the health of an ecosystem. Eutrophication drastically alters the balance of the ecosystem, bringing about radical changes in the amount of diversity of organisms living in that body of water.
Sunlight Deprivation
One of the most obvious effects of eutrophication is that sunlight can't reach the deeper levels of the water body. The omnipresent mat of algae and other similar plants, which is usually kept in check by foraging fish, hog the sunlight. Plants that depend on the sunlight penetrating deeper layers are particularly harmed, and die out. Consequently, the fish that feed on them also suffer, and so do the fish that feed on the smaller forage fish.
Eutrophic canal
Eutrophic canal
Less Variety
The previous condition leads to a smaller variation in the species surviving in the water, and an increase in the species that can exploit the conditions. Deep-dwelling algae, which can thrive in dark environment, increase massively in population, and large, sophisticated plants may die out. A change in the food naturally leads to a change in the feeder; the variation of aquatic animal species also takes a hit as a consequence of this. Some algae also secrete toxic substances, which directly contribute to reducing the population of other organisms.
Hypoxia, or the condition of having low volumes of oxygen, can be caused by eutrophication. The now-dominant algae take up the majority of the available oxygen, leaving little for the other inhabitants of the lake/river. The decay caused by sunlight deprivation also adds to hypoxia by releasing harmful substances into the water. Fish and other animals living in the lake suffer massively due to this.
Algae in lake
Eutrophic lake
Reduced Commercial Value
As a consequence of the previous condition, the amount of organic waste in the lake increases dramatically. The sediment level rises, and the water becomes much more turbid. This makes it less appealing for commercial or recreational purposes, such as swimming, boating, fishing, etc.

The algal and cyanobacterial masses may also become a nuisance for nearby citizens―not only due to the foul smell, but also by becoming breeding grounds for dangerous parasites.
Eutrophication in Terrestrial Ecosystems
Eutrophication is not limited to aquatic ecosystems, but is more commonly observed in the latter. Eutrophication of terrestrial ecosystems has similar effects as in aquatic ecosystems. Though plants need nitrates for growth, too much nitrogen is counterproductive.

Terrestrial ecosystems, such as forests and savannahs, are built around plants that have adapted to the specific levels of various nutrients in the soil in that area, which generally has low amounts of nitrogen. Nitrogen does not naturally occur in the soil, and has to be introduced via microbes or nitrogen-fixing rhizomes that convert atmospheric nitrogen into bio-available nitrate compounds. Sudden introduction of a large amount of nitrogen encourages the growth of weeds, the terrestrial equivalent of algae, and hampers the growth of naturally occurring plants, which need time to adapt to the altered soil conditions. Highly specialized ecosystems, such as bogs and meadows, are especially at risk from agricultural eutrophication.

Eutrophy has created numerous 'dead zones' around the world, i.e., areas where severely eutrophic waters are seen. Many of these are found on the US' Eastern Seaboard, the Mediterranean Sea, and the Nordic Sea. The seas around Japan and Korea also host numerous dead zones, thanks to the high amount of industrial waste created in those countries.
Eutrophication cannot be completely prevented, since fertilizers are a necessity in agriculture, but it can be reduced by a great degree. By minimizing soil runoff, much of the unwanted addition of nutrients into aquatic dump sites can be prevented. Reducing soil degradation directly results in reduced eutrophication, since more of the nutrients are utilized where they are actually needed.