Eutrophication, is the artificial enrichment of a water body or aquatic system with phosphorus and nitrogen nutrients, usually with an excess amount of nutrients. This process causes an excessive growth of plants and algae and due to the biomass load, may result in oxygen depletion in the water body. For example, as a response to increased levels of nutrients, there is a great increase in phytoplankton which is called algal bloom occurs in the water body . The nutrients can become from the animal wastes, fertilizers that are often used in farming and sewage which are washed by rain or irrigation into the waterbodies through surface runoff. This will increase the nutrient level and contribute to eutrophication. Eutrophication can be divided into cultural eutrophication which is caused by human activity and natural eutrophication which is a natural process.
Cultural eutrophication is the process that speeds up natural eutrophication because of human activity. Due to the clearing of land and building of towns and cities, land runoff is accelerated and more nutrients such as phosphates and nitrate are supplied to lakes and rivers, and then to coastal estuaries and bays. Extra nutrients are also supplied by treatment plants, golf courses, fertilizers, farms and untreated sewage in many countries.
Natural eutrophication is a natural process. Eutrophication occurs in many lakes in temperate grasslands. Paleolimnologists now recognize that climate change, geology, and other external influences are critical in regulating the natural productivity of lakes. Some lakes also demonstrate the reverse process, becoming less nutrient rich with time. The main difference between natural and anthropogenic eutrophication is that the natural process is very slow, occurring on geological timescales.
Eutrophication is mainly caused by human action due to their dependence on using fertilizers. Agricultural practices and the use of fertilizers on lawns, golf courses, and other fields contribute to phosphate and nitrate nutrient accumulation. When the concentration of nutrients increases until the ground is no longer able to assimilate them, the nutrients are carried by rain into rivers and groundwater that flow into lakes or seas. The plankton, algae and other aquatic plant life are then well fed and their photosynthesis activity is increased. They grow and reproduce more rapidly, resulting in dense growth of algal blooms and plant life. This will disrupt the normal ecosystem functioning and causes many problems. (Referappendice-1)
On the other hand, eutrophication can be caused by the input of untreated sewage as well as discharge from sewage treatment plants. We can see that the sewage water is directly discharged into water bodies such as rivers, lakes, and oceans in various parts of the world, especially the developing nations. The result of this is the released of a high quantity of chemical nutrients which stimulates the disproportionate growth of algae and other aquatic plants that threaten the survival of aquatic life in many ways. Some countries may also treat the sewage water, but still discharge it into water bodies after treatment. Although the water is treated, it can still cause the accumulation of excess nutrients and lead to eutrophication. (Refer appendix-1)
Besides that, it is also caused by aquaculture. Aquaculture is a technique of growing shellfish, fish and even aquatic plants in water containing dissolved nutrients. Hence, the unconsumed food particles together with the fish excretion can significantly increase the levels of nitrogen and phosphorous in the water if aquaculture is not properly managed. This will result in the dense growth of microscopic floating plants.
Lastly, eutrophication may be caused by natural events such as floods and the natural flow of rivers and streams. The excess nutrients will be washed off from the land and flow into the water systems that causes the excessive growth of algal blooms. Also, as lakes grow old, they naturally accumulate sediments such as phosphorus and nitrogen nutrients which contribute to the explosive growth of phytoplankton and cyanobacterial blooms.
How does it happen?
Firstly, the excess nutrients are applied to the soil. Then, they get drained into the ponds, lakes, or rivers. This encourages the rapid growth of photosynthesizing organisms, especially algae. This results in a population explosion known as algal bloom. The algal bloom blocks the light of the sun from reaching the bottom of the water body. As a result, the aquatic plants beneath the algal bloom die because they cannot get sunlight to photosynthesize and this further decreases the supply of oxygen in the water. Eventually, the algal bloom dies and sinks to the bottom of the lake, decomposing microorganisms, especially aerobic bacteria, grow rapidly and use up oxygen for respiration at a fast rate. The aerobic bacteria use up oxygen faster than it can be replenished. This cause the biochemical oxygen demand (BOD) to increase resulting in the depletion of oxygen in the water. Due to the lower level of oxygen concentrations, the larger life forms, such as fish, suffocate are not able to survive.In extreme cases, if the oxygen level continues to drop until the water become completely deoxygenated, aerobic bacteria will grow and releases toxic gases that are harmful to aquatic life. This body of water can no longer support life and this process is called eutrophication. (Referappendices-2)
For aquatic plants, they need two essential nutrients to grow such as nitrogen (N) and phosphorus (P). In a healthy lake, the biochemical oxygen demand (BOD) must be low which indicates the better water quality and the nutrients must occur in small amounts for the survival of aquatic plants. Inversely, major water pollution problem will results if the nutrients are in large quantities. Too many nutrients will stimulate the rapid growth of plants and algae, clogging waterways and sometimes creating a serious algal bloom. If the situation happens, the survival of fish and other aquatic life forms will be threatened. The algal blooms that caused by the excessive nutrients in the water body will limit the amount of dissolved oxygen required for respiration by the aquatic life forms. When the algae and aquatic plants die and decompose, it will encourage the growth of detritus and oxygen deletion happens. When the dissolved oxygen reaches hypoxic levels, the animal and plant species under the water such as shrimp, fish, and other aquatic biota suffocate will die. In extreme cases, the anaerobic conditions encourage the growth of bacteria that produce toxins which are deadly to the marine mammals and birds.The growth of phytoplankton also causes the light penetration into the water to be reduced. This can bring about aquatic dead zones, loss of aquatic life and it also lessens biodiversity.(Refer Appendices-3)
Furthermore, it results in the deterioration of water quality and limited access to safe drinking water. This is because algal blooms are highly toxic and once the water reaches the anaerobic conditions, the growth of more toxic bacterial is promoted. Extensive deterioration of water quality and a decline in the availability of clean drinking water will be the consequence. Due to the dense growth of algal blooms and photosynthetic bacteria in surface waters, the water systems will be blocked and thus availability of piped water becomes limited. On this regard, toxic algal blooms have shut down numerous water supply systems across the globe. For example, in 2007, more than 2 million residents of Wuxi, China could not access piped drinking water for more than a week due to severe attack by algal blooms on Lake Taihu. (Refer Appendices-4)
Moreover, it is poisoning which will cause several negative impacts on human health and animals when ingested the water in drinking water. Even at very low concentrations, the cyanobacteria which generate red tide will release very powerful toxins with high poison levels in the water. Besides that, the toxic compound is doubled by the anaerobic conditions which created by the explosive plant growth in the water. It is harmful to humans and animals even at the least concentration when ingested in drinking water. In addition, algal blooms can threaten livestock health. For example, the first recorded incidence of animal poisoning from a blue-green algal bloom was in Lake Alexandrina, Australia in the late 1800s. (Refer appendix-5) Cattle, horses, pigs, sheep, and dogs died after drinking water covered by a scum of the blue-green algae. The major cause of deaths in animals is from liver poisoning and neurotoxicity that leads to respiratory failure. This is because the toxic compounds can make their way up the food chain, contributing to various negative health impacts such as cancers. The shellfish accumulate the poison in their muscles and then poisons humans upon consumption. Other than that, the high nitrogen concentration in drinking water will have negative effects on infants. For example, the infant will suffer blue baby syndrome. This is because the drinking water with high nitrogen concentration is associated with the ability to inhibit blood circulation in infants. Hence, the baby will take on a bluish hue because of poorly oxygenated blood resulting in blue baby syndrome.
Lastly, it endangers fishing. This is due to the increased growth of floating plants such as algae and photosynthetic bacteria which is the obstacle that limits the movement of the boat to a location and the fishing vessels. We will also have some difficulties to set the fishing nets in water because of the accumulation of floating plants on the surface of the water.
Solutions for eutrophication
Eutrophication mainly arises from the use of nitrate and phosphate fertilizers. Hence, composting can be the effective solution for eutrophication. This is because composting is a substitute for fertilizers. It is a practice of converting organic matter such as food residues and decaying vegetation into compost manure. Nutrients in the composted manure do not contain the phosphorus and nitrates that cause algae to bloom, so when there is a run-off, it does not harm the quality of water. In compost fertilizer, all the essential elements are broken down and synthesized by the plants thereby not creating the cycle of eutrophication. This method of controlling eutrophication is termed as a nutrient limitation. (Refer Appendices-6)
Other than that, limiting pollution is an easy and effective method of cutting back on the amount of nitrogen and phosphates discharged into water systems. Big manufacturing companies and municipalities ought to reduce pollution and desist from discharging waste into water systems to reduce the number of toxins and nutrients ending up in the waters that feed the algae and other microscopic organisms. If industries and municipalities can cap their waste discharge and pollution to a lower level, then the nutrient content is reduced in the water systems which can subsequently control eutrophication.
Last but not least, strengthening laws and regulations against non-point water source pollution is also a solution that can substantially control eutrophication. The number of nutrients entering the aquatic ecosystems can essentially lessen by minimizing non-point pollution. The laws should aim at enhancing high water quality standards and zero-tolerance to the non-point solution. With the support of policymakers, citizens, pollution regulatory authorities and the government, it is easy to control eutrophication.