The literal meaning of the eutrophication is “well-nourished”. But this term brings a negative connotation when it is studied in the field of ecology and environmental sciences. Eutrophication is a situation in which an excessive growth of organisms on the surface of an aquatic body is observed due to the presence of an excessive amount of nutrients and chemicals containing minerals (phosphorus and nitrogen). This condition is an environmental hazard as it disrupts the natural course of aquatic life and the ecosystem. A very common example is algal blooms. This is the superfluous growth of algae on the water surface. This happens due to the enrichment of water which promotes the growth of algae. These algae which keep on covering the water surface due to prolific growth blocks sunlight from entering into the water. As we know that there plants underwater too, those plants also absorb light energy coming from the sun and utilize it to carry out photosynthesis. This allows them to produce oxygen which gets dissolved in water. This dissolved oxygen is used by fishes and aquatic animals so that they can live and carry out cellular respiration just like terrestrial animals. But when algae block sunlight, this situation renders those aquatic plants unable to produce oxygen. Due to lack of oxygen first, the aquatic plants die, then the aquatic animals which are dependent on the dissolved oxygen, they die. The death of living organisms under the water causes other complications, which lead to the death of the whole aquatic community.
Progression and Mechanism of Eutrophication
Eutrophication leads to excessive growth of algae and phytoplankton on the water surface. This growth happens due to the enrichment of a water body. This enrichment increases the overall nutrient concentration of the water. The nutrient which plays a major role in the process of eutrophication is phosphorus. This element is present in fertilizers because plants need phosphorus for growth. However, phosphorus not only increases the growth of plants but it also increases the growth of other green organisms (photosynthesis capable organisms) like algae. When these organisms (algae and phytoplankton) grow on the surface of water bodies they inhibit the sunlight from reaching the bottom of the water body. This leads to inhibition of photosynthesis in aquatic plants which produce oxygen as a by-product of photosynthesis. It is a learned fact that the majority of life is sustained on this planet due to oxygen. The marine animals utilize the oxygen which is produced by the marine plants. This dissolved oxygen is as essential for marine life as it is for terrestrial life. When the oxygen levels decrease marine animals start to die. The dead marine animals and plants are then decomposed by bacteria present in water. As we know that the process of decomposition also requires oxygen, the level of oxygen in water further decreases. This causes a condition which is termed as hypoxia. Decomposition further releases nutrients in the water which in turn favors the growth of algae present on the surface.
Similarly, when algae and phytoplankton die, they are decomposed by saprotrophic bacteria. These bacteria utilize the left oxygen to decompose algae and release nutrients. The algae, however, are present on the surface can utilize the oxygen present in the air and keeps growing. And the marine ecosystem is annihilated and is replaced by anaerobic bacteria. Such bacteria produce toxins that make the water poisonous and harmful for terrestrial animals.
Types of Eutrophication
While studying it, one can observe that eutrophication exists in two ways.
- Natural Eutrophication
- Anthropogenic/cultural Eutrophication
If we study ecology, we come to realize that there is a natural flow of nutrients in the environment. Nutrients are present in free or compound form in the environment. These nutrients are fixed and utilized by organisms and when they die, saprotrophic organisms (bacteria and fungi) break down the dead matter and release nutrients back into the environment. There is another notable process that plays a role in eutrophication. This process is the natural flow of water. Water bodies are often on a lower level, and when water flows it washes the nutrients along with it into the water bodies. These nutrients cause to increase in the normal nutrient concentration which leads to enrichment of that particular water body. This phenomenon leads to eutrophication. And natural growth of algae can be observed on the surface of the water. However, this is a natural course and flow of nutrient and it is a very slow process. Natural eutrophication is not hazardous, but it can cause fluctuations in the balance of the ecosystem.
This eutrophication is caused as a result of activities done by man. It is an effect of human behavior on the environment. The course and progression of this eutrophication are a lot faster than natural eutrophication and it is hazardous. This is so hazardous that it is ruled out as water pollution. How human life is causing eutrophication is explained below.
Human Activities and Eutrophication
In this era of modernization, man is in constant search of fulfilling his disproportionate needs at cost of natural habitat. To make the crops grow faster and produce better yield, we have created fertilizers. So, we can feed the inordinate masses of people. In order to accommodate this growing population, we have cleared natural prairies and meadows to make colonies. We are constantly expanding cities by eradicating forests. All of these activities have consequences. Theses consequences are explained below:
Fertilizers and Detergents
The main components of fertilizers are nutrients that are specifically required by plants to grow. These include Phosphorus, Nitrogen, and Magnesium. However, the nutrients which cause eutrophication are phosphorus and nitrogen. Dominantly, phosphorus causes more complications as compared to nitrogen. Phosphorus is present in fertilizers and detergents in the form of phosphates. And it is easier for plants to uptake phosphorus in bound form as compare to free form. Phosphates also can leach into the soil by dissolving in water. However, when the agricultural land is profusely the remains of fertilizers are washed into the water bodies. The same thing happens when detergents. We often think of sewage as a trivial matter and most of the wastes form houses are drained into local water bodies. The detergents present in the wastes being drained into the water bodies from houses not only pollute water but also enrich it with nutrients which causes eutrophication.
Phosphates and nitrates can leach into the soil. When water rushes on the ground it always carries the soil with it. This phenomenon is known as soil erosion. However, where there are tree there is less soil erosion. This is because the roots of the trees adhere to the soil, providing stability and strength to the ground. Due to deforestation soil erosion is becoming common and due to this soil containing minerals gets eroded and it is washed into water bodies resulting in eutrophication as well as congestion.
Eutrophication in different types of water bodies
All water bodies, no matter the size are susceptible to eutrophication because algae and phytoplankton grow at a very high rate, jeopardizing other living organisms by competing for food, oxygen, and sunlight.
Eutrophication in Rivers and Lakes
Rivers and lakes are vast and tremendous water bodies. Nevertheless, their sizes do not make them immune to eutrophication. As lakes and rivers are large, they have more surface area to allow light from the sun to serve the aquatic life. But eutrophication is a fast-paced biological mechanism it still negatively affect the habitat present under the water. Looking in history humans used to make settlements near water sources. This fact makes it easier to understand why there are rivers and big lakes near big cities. Life is always attracted to water some organisms live close to some inside it. Rivers and lakes are also rich in biodiversity. But this makes it even sadder that most of the waste material is being dumped and drained into these rivers and lakes. These wastes are composed of phosphate-containing detergents and fertilizers. Which causes algal blooms on a mass level. This is a major cause of the death marine ecosystem. And due to the hypoxic environment, harmful anaerobes also grow in the water. This causes water toxicity. This water not only proves to be harmful to animals, but it also does damage to human health. As water seeps into the underground water sources. The villages and small towns outside the city built on these lakes and rivers also suffer due to the mismanagement of big cities.
Consequences and effects of Eutrophication
Life is dependent on water and it cannot exist without it. The animals on the land obtain water from the water bodies available to them. The eutrophication in water causes many complexities not only for aquatic animals but also for the animals on land. Moreover, eutrophication does not only happens in water, it is also present in the soil. The soil eutrophication is caused when the wastes containing nitrates and phosphates seep into the soil. This situation occurs when wastes containing phosphates and nitrates are drained on open land and there is no water body at a lower level. This allows the wastes to stay on land and seep deep into the soil. Due to this many other species of plants which are favored by enriched environment grow fast. Such a plant gives rise to competition for the natural species of the land. This situation results in many ecological complexities. And the land effected by soil eutrophication does not remain cultivatable.
Ecological and Economic Effects of Eutrophication
Due to water and soil eutrophication every year we face many losses. Eutrophication of soil not only ruins the quality of land, but it also makes it a problem to cultivate anything on it. Due to the enrichment of soil with phosphorus and nitrogen, many weeds that are favored by the higher concentration of nitrates and phosphates start to grow. It costs extra labor to remove them. Eutrophication makes water hazy and unclear. This affects transportation through water bodies. Eutrophication fishes and other aquatic life, which is a source of food for a lot of human beings, gets depleted. Due to this many fishermen suffer. There is a high chance that land or water that is a victim of eutrophication produces toxic plants. It is also known that water-rich bacteria often contain pathogenic bacteria which lead to diseases like Tetanus, cholera, and jaundice.
The ecosystem suffers a great deal due to eutrophication. On land, which is suffering from eutrophication, there is an excessive amount of unwanted plants. These plants start growing on their own and disturb the balanced ecosystem. Some animals feed on a certain plant, and when they disappear from the land it becomes natural that either the dependent animals migrate to another source or die of hunger. This causes biodiversity reduction and imbalance in the ecosystem. In water when algae cover up the surface of the water it causes the death of aquatic plants and animals down below. When they are decomposed by bacteria the oxygen level decreases. Sometimes oxygen drops to such extreme levels that it creates dead zones where there are just dead organisms that are not even getting decomposed due to anoxia. This situation causes a loss in marine biodiversity.
Eutrophication is not only a condition of water, but it also occurs in soil. This is predominantly caused by human activities. However, a little eutrophication occurs naturally too. Eutrophication algae and phytoplankton profusely grow on the surface of the water causing blockage of sunlight, resulting in inhibition of photosynthesis which is carried out by aquatic plants. This lowers the dissolved oxygen level in the water, and this results in hypoxia. This causes the death of aquatic animals which are dependent on them for oxygen. The dead organisms, under the water, are decomposed by bacteria that consume oxygen. This further depletes the oxygen. When oxygen levels are depleted to extreme level dead zones are created in the water. This causes loss of biodiversity in the marine ecosystem. Eutrophication also makes water harbor many pathogenic bacteria which causes diseases and eutrophication also leads to the production of harmful and toxic plants which cause serious damage to animals, human beings, ecosystems, and the economy.
- Chislock, M.F.; Doster, E.; Zitomer, R.A.; Wilson, A.E. (2013). “Eutrophication: Causes, Consequences, and Controls in Aquatic Ecosystems”. Nature Education Knowledge. 4 (4): 10. Retrieved 10 March 2018.
- Schindler, David and Vallentyne, John R. (2004) Over fertilization of the World’s Freshwaters and Estuaries, University of Alberta Press, p. 1, ISBN 0-88864-484-1
- Khan, M. Nasir and Mohammad, F. (2014 ) “Eutrophication of Lakes” in A. A. Ansari, S. S. Gill (eds.), Eutrophication: Challenges and Solutions; Volume II of Eutrophication: Causes, Consequences and Control, Springer Science+Business Media Dordrecht. doi:10.1007/978-94-007-7814-6_5. ISBN 978-94-007-7814-6.
- Khan, Fareed A.; Ansari, Abid Ali (2005). “Eutrophication: An Ecological Vision”. Botanical Review. 71 (4): 449–482. doi:10.1663/0006-8101(2005)071[0449:EAEV]2.0.CO;2. JSTOR 4354503.