Eutrophication is one of the most importunate environmental hazards in aquatic ecosystems, causing significant degradation of water quality and posing a substantial threat to the ecosystem's biotic components. The main environmental effects of eutrophication are a rise in suspended particles as a result of widespread macroalgal blooms, decreased biodiversity, increase in biological oxygen demand (BOD), invasion of new species, toxicity and an increase in precipitation rate, which resulted in the destruction of benthic habitat due to shade of submerged vegetation. This article will explain to you about the effects of eutrophication which will be helpful in preparing the Environment syllabus for the UPSC Civil service exam.

Effects of Eutrophication

Eutrophication- Concept

• When a body of water gets highly supplied with minerals and nutrients, plants and algae grow excessively. This is known as eutrophication or hypertrophication.
• Many lakes are naturally eutrophic, and in some situations, eutrophication progresses as the lake ages.
• Eutrophication is a term that is more commonly associated with human actions, such as the artificial introduction of plant fertilisers, which has resulted in community changes and deterioration of water quality in many freshwater systems.
• With increased human population and more extensive agricultural development, eutrophication now ranks alongside other major anthropogenic effects such as deforestation, global warming, ozone layer depletion, and large-scale environmental disturbance in terms of its potentially harmful effect on the natural ecosystem.

Effects of Eutrophication

Change in Ecosystem

• In an aquatic ecosystem, eutrophication increases primary output and affects the relative abundance, taxonomic makeup, and spatial distribution of primary producers.
• The distribution and movement of energy and biomass throughout the food web are affected by changes in resource mix and location.
• Productivity changes also affect the physico-chemical environment, which has an impact on the biota.
• The direction and strength of natural and sexual selection experienced by populations are influenced by such ecological changes.
• Furthermore, they have the potential to degrade the behavioural processes that keep species separated ecologically and reproductively.
• As a result, eutrophication of lakes frequently leads to a reduction in ecological specialisation between lakes and niches within lakes thereby changing the biodiversity as a whole.

Increase in Biological Oxygen Demand (BOD)

• Algal blooms result from eutrophication. When algae die, microorganisms begin to breakdown the organic stuff left behind.
• These bacteria require a lot of oxygen to survive.
• This raises the biological oxygen demand, or BOD, in the water body, resulting in hypoxia.
• This is inturn harmful to aquatic life.

Decreased Biodiversity

• Primary producers are the first to respond from an increase in nutrients in an ecosystem.
• Species like algae experience population growth in aquatic ecosystems (called an algal bloom).
• Algal blooms reduce the amount of sunlight available to bottom-dwelling creatures and produce large fluctuations in dissolved oxygen levels in the water.
• All aerobically respiring plants and animals require oxygen, which is provided by photosynthesizing plants and algae during the day.
• Dissolved oxygen levels rise dramatically throughout the day under eutrophic conditions, but fall dramatically after night due to respiring algae and microbes that feed on the growing mass of dead algae.
• Fish and other marine species suffocate when dissolved oxygen levels drop to hypoxic levels.
• Fish, shrimp, and especially immobile bottom dwellers die as a result of this.
• Anaerobic conditions develop in extreme cases, allowing germs to thrive. Dead zones are places where this happens.

New Species Invasion

• If a nitrogen-deficient water body is suddenly supplied with nitrogen, many other competitive species may relocate to a nitrogen-rich water body.
• These species may even out-compete the ecosystem's original occupants.
• This makes their survival at a greater risk.
• This has been observed in salt marshes in New England.
• The common carp dwells in naturally Eutrophic or Hypereutrophic environments in Europe and Asia, and has evolved to these circumstances. The success of the fish in colonising places outside of its normcommon carpal range is partly explained by the eutrophication of these areas after it was introduced.

Toxicity

• Some eutrophication-induced hazardous algal blooms are toxic to plants and animals.
• Toxic substances can work their way up the food chain and cause animal death.
• Algal blooms in freshwater can be dangerous to cattle.
• Neuro- and hepatotoxins are released when algae die or are eaten, and they can harm animals and constitute a threat to people.
• Shellfish poisoning is one example of algae toxins making their way into people.
• Shellfish (mussels, oysters) absorb biotoxins produced by algal blooms, causing these human foods to become poisonous and poisoning humans.
• Shellfish poisoning can be paralytic, neurotoxic, or diarrhoetic.
• Other marine creatures can be carriers for such toxins, like in the instance of ciguatera, where the toxin is normally accumulated by a predator fish before being poisoned by humans.

Eutrophication- Mitigation

• Eutrophication has been controlled using a range of preventive and technical solutions.
• Before being discharged into waterways, wastewater must be treated.
• Harvesting can be used to monitor nutrient recycling.
• Eutrophication can be reduced by removing nitrogen and phosphorus at the source, dividing nutrient-rich streams from receiving bodies, and diluting these components.
• When algae die and decompose, their blood should be removed.
• Algal growth can be controlled by limiting the soluble nutrients.
• Chemical precipitation of extra phosphorus is the most suitable, feasible, and effective way.
• Alum, lime, iron, and sodium aluminate are examples of precipitants.
• To eliminate nutrients, physicochemical approaches can be used.
• Phosphorus can be removed through precipitation, and nitrogen can be removed through nitrification or denitrification.
• Methods include electrodialysis, reverse osmosis, and ion exchange.
• Algae and rooted plants are killed with copper sulphate and sodium arsenite, respectively.

Conclusion

Thus eutrophication in the environmental time scale have caused plethora of harmful effects on the ecosystems. One of the primary causes of lake ecological degradation is eutrophication. Its worsening in recent decades has prompted stakeholders to explore water management and restoration alternatives, including those based on modelling techniques. We do also know that eutrophication reduces coastal ecosystems' ability to deliver vital ecosystem services including tourism, recreation, local community fish and shellfish, sportfishing, and commercial fisheries.