Eutrophication presents as one of the most serious ecological problems of open water sources such as lakes, oceans and reservoirs. It is characterized by dense algal and plant growth owing to the enrichment by phosphorus and nitrogen nutrients needed for photosynthesis. As a result, it often contributes to the formation of extensive mats of floating plants. Examples of the plants include algal blooms, Nile cabbage and water hyacinths.
The nutrients come from animal wastes, fertilizers and sewage, which are washed by rain or irrigation into the water bodies through surface runoff. Eutrophication can also take place naturally over thousands of years as the lakes grow old and get filled with sediments.
Human activities top the list that speeds up the degree and rate of eutrophication through both point-source and non-point source discharges of the chemical nutrients (phosphates and nitrates) into water systems.
Below are a few of the sources, types, causes, effects and solutions to Eutrophication.
Sources of Eutrophication
1. Point source pollution
Pollution from contaminants that enter a waterway from a single identifiable source like stationary locations or fixed facilities.
Examples: Discharges from a sewage treatment plant or industrial plants and fish farms.
2. Non-point source pollution
Pollution from widespread, including human activities with no specific identifiable point of discharge or entry into receiving watercourses.
Examples: The nitrogen compounds leached out from fertilized agricultural lands and losses from atmospheric deposition.
Three main sources of nutrient input:
- Erosion and leaching from fertilized agricultural areas.
- Sewage from cities and industrial wastewater.
- Atmospheric deposition of nitrogen (from animal breeding and combustion gases).
Types of Eutrophication
1. Natural Eutrophication
The process of accumulation, flow and addition of nutrients to water bodies that lead to changes in the primary production and species composition of the community is called natural eutrophication. It has been occurring for millennia.
2. Cultural Eutrophication
The process that helps in speeding up natural eutrophication triggered by human activity is called cultural eutrophication. The clearing of land accelerated land runoff and more nutrients such as phosphates and nitrate are supplied to lakes and rivers, followed by coastal estuaries and bays.
Moreover, extra nutrients are also supplied by fertilizers used in farms, including fish farms, golf courses, treatment plants, and also untreated sewage.
The process of enrichment of water by nutrients can also have a natural origin i.e. natural eutrophication). However, many a time, human activities increase it dramatically (anthropogenic or cultural eutrophication).
Causes of Eutrophication
1. Fertilizers (nitrates and phosphates)
Eutrophication is predominantly caused by human actions due to their dependence on using nitrate and phosphate fertilizers. Agricultural practices and the use of fertilizers on lawns, golf courses and other fields contribute to phosphate and nitrate nutrient accumulation.
When these nutrients are washed by surface runoff into lakes, rivers, oceans and other surface waters when it rains, the hungry plankton, algae and other aquatic plant life are well fed, and their photosynthesis activity is increased. This causes a dense growth of algal blooms and plant life, such as the water hyacinths in the aquatic environments.
2. Concentrated Animal Feeding Operations
Concentrated animal feeding operations (CAFOs) are as well the main contributor of phosphorus and nitrogen nutrients responsible for eutrophication.
The concentrated animal feeding operations normally discharge high scores of the nutrients that find a way into rivers, streams, lakes and oceans where they accumulate in high concentrations, thereby plaguing the water bodies by recurring cyanobacterial and algal blooms.
3. Direct Sewage Discharge and Industrial Waste into Water Bodies
In some parts of the world, especially the developing nations, sewage water is directly discharged into water bodies such as rivers, lakes and oceans.
As a result, it introduces high amounts of chemical nutrients, thereby stimulating the dense growth of algal blooms and other aquatic plants, which threatens 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. As much as the water is treated, it can still cause the accumulation of excess nutrients, ultimately bringing about eutrophication. The direct discharge of industrial wastewater into water bodies presents similar outcomes.
Aquiculture is a technique of growing shellfish, fish and even aquatic plants (without soil) in water containing dissolved nutrients. As a highly embraced practice in recent times, it also qualifies as a top-ranking contributor to eutrophication.
If aquiculture is not properly managed, the unconsumed food particles together with the fish excretion can significantly increase the levels of nitrogen and phosphorous in the water, resulting in dense growth of microscopic floating plants.
5. Natural Events
Natural events such as floods and the natural flow of rivers and streams can also wash excess nutrients off the land into the water systems, thus causing excessive growth of algal blooms.
Also, as lakes grow old, they naturally accumulate sediments as well as phosphorus and nitrogen nutrients which contribute to the explosive growth of phytoplankton and cyanobacterial blooms.
Effects of Eutrophication
1. Abundance of Unwanted Substances
Eutrophication causes an abundance of particulate substances such as phytoplankton, zooplankton, bacteria, fungi and debris on which the turbidity and coloration of the water depend.
It increases inorganic chemicals like ammonia, nitrites, hydrogen sulfide etc. that induce the formation of harmful substances such as nitrosamines suspected of mutagenicity in the drinking water treatment plants.
2. Threatens the Survival of Fish and other Aquatic Life Forms
When aquatic ecosystems experience increased nutrients, the phytoplankton and other photosynthetic plants grow explosively, commonly known as algal blooms.
As an outcome, the algal blooms limit the amount of dissolved oxygen required for respiration by other animal and plant species in the water. Oxygen depletion happens when the algae/plant life dies and decomposes.
When the dissolved oxygen reaches hypoxic levels, the animal and plant species under the water, such as shrimp, fish and other aquatic biota suffocate to death. In extreme cases, the anaerobic conditions encourage the growth of bacteria that produces toxins that are deadly to marine mammals and birds.
The growth of phytoplankton also causes reduced light penetration into the lower depths of the water. This can bring about aquatic dead zones, loss of aquatic life, and it also lessens biodiversity.
3. Deterioration of Water Quality and Limited Access to Safe Drinking Water
Algal blooms are highly toxic, and once the water reaches the anaerobic conditions, the growth of more toxic bacterial is promoted. High organic substances give the water disagreeable odors or tastes that can be barely masked by chlorination while using as drinking water.
These substances form complex chemical compounds that not only prevent normal purification processes but deposited on the walls of the water purifier inlet tubes, accelerating corrosion and limiting the flow rate.
The consequence is an extensive deterioration of water quality and a decline in the availability of clean drinking water. The dense growth of algal blooms and photosynthetic bacteria in surface waters can also block water systems hence limiting the availability of piped water.
In this regard, toxic algal blooms have shut down numerous water supply systems across the globe. During last decade, for instance, 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.
4. Poisoning and Impact on Human Health
The cyanobacteria also referred to as dinoflagellates which generate red tide, release very powerful toxins with high poison levels in the water even at very low concentrations. The anaerobic conditions created by explosive plant growth in the water also results in the doubling of the toxic compounds.
It can also cause death in humans and animals even at the least concentration when ingested in drinking water. Besides, freshwater algal blooms can threaten livestock health. The toxic compounds can also make their way up the food chain, contributing to various negative health impacts such as cancers.
Biotoxins are linked to increased incidence of neurotoxic, paralytic and diarrhoetic shellfish poisoning in humans, which can lead to death.
The shellfish accumulate the poison in their muscles and then poison humans upon consumption. High nitrogen concentration in drinking water is associated with the ability to inhibit blood circulation in infants, a condition known as a blue baby syndrome.
5. Endangers Fishing
One of the main characteristics of eutrophication is the increased growth of minute floating plants such as algae and photosynthetic bacteria and the development of extensive and dense mats of floating plants such as Nile cabbage and water hyacinths.
Whenever this happens on a water body, fishing is endangered. It simply becomes difficult to set the fishing nets in the water, and the plants floating on water also limits the mobility of boats and other fishing vessels.
6. Degradation of Recreational Opportunities
The main problem of eutrophication is the algal blooms and other aquatic plants that float on an extensive area of the water surface. It reduces the transparency and navigation in the water, which lessens the recreational values and opportunities of the lakes, especially for boating and swimming.
Nile cabbage, algal blooms, and water hyacinth can spread over an extensive area along the shores and can sometimes float over the entire surface into the land area.
Preventive Solutions to Eutrophication
Eutrophication mainly arises from the use of nitrate and phosphate fertilizers. In a bid to address the phenomenon, composting can be used as a solution. Composting is the practice of converting organic matter such as food residues and decaying vegetation into compost manure.
The nutrients present in the compost manure are deficient in the high concentration of nitrates and phosphates that feed the algae and other microbes in water bodies.
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 nutrient limitation.
2. Reducing Pollution
Just like composting, 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 amount 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 nutrient content is reduced in the water systems, which can subsequently control eutrophication.
3. Strengthening Laws and Regulations against Non-point Pollution
Strengthening laws and regulations against non-point water source pollution can substantially control eutrophication. According to EPA, non-point pollution presents the most serious challenge in the management of nutrient entry into water systems. Controlling nutrient sources, therefore, results in decreased eutrophication.
By minimizing non-point pollution, we are essentially lessening the amount of nutrients entering the aquatic ecosystems. 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.
4. Ultrasonic Irradiation
The world is constantly seeking advanced methods for resolving some of the environmental problems. When it comes to eutrophication, the use of ultrasonic irradiation is one such mechanism that has been exploited as an alternative solution to control and manage algal blooming.
The process works by causing cavitations which produce free radicals that destroy algae cells. Research is still underway to determine the uniqueness of its use in controlling the eutrophication problem.
Curative Solutions to Eutrophication
Where water quality is already so compromised that any preventive initiative is ineffective, “curative” procedures can be implemented, such as:
- Removal and treatment of hypolimnetic water, deep water in contact with the sediments and rich in nutrients as it is in direct contact with the release source;
- Drainage of the first 10-20 cm of sediment that is subject to biological reactions and with high phosphorus concentrations;
- Oxygenation of water for reducing the negative effects of the eutrophic process and restoring the ecological condition like the absence of oxygen and toxic compounds’ formation deriving from the anaerobic metabolism;
- Chemical precipitation of phosphorous by adding iron or aluminum salts or calcium carbonate to the water, which gives rise to the precipitation of the iron, aluminum or calcium orthophosphates, thereby reducing the negative effects arising from the excessive presence of phosphorus in the sediments.