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Air pollution effects: Eutrophication

What is eutrophication?

Eutrophication is a word that comes from the greek, meaning well-nourished. It is phenomenon where high concentrations of nitrogen and phosphorus (present in pollutants) are involved with water in rains, rivers or seas.

This high concentration provokes an enrichment of water by nutrient salts that cause structural changes to the ecosystem. The visual ones are massive production of algae and aquatic plants. The green coloured algae is very common in lakes and ponds, and it is only caused due to this reaction of air pollution. On the other side, the harmful ones are depletion of fish species and water deterioration.

It may not look dangerous, but eutrophication is a harmful environmental process, especially when it is empowered by human activities, which is called cultural eutrophication. The changes in the water body may depend on the usage of fertilisers, the discharge of waste water into water bodies and the reduction of its self purification capacity.

Trophic Classifications of a Water Body

The trophic or nutritional state of a water body is determined by the amount of useful nutrients dissolved on it, either if they are produced naturally or human-made. Four nutritional stages are found:

  • Oligotrophic: An oligotrophic lake or water body has low nutrient content, which means low productivity. It has high quality drinking water and it is usually found in cold environments. It facilitates life for aquatic species who need cold and well-oxygenated water.
  • Mesotrophic: It has medium level of nutrients and its productivity is also intermediate.
  • Eutrophic: It is a stage that can be produced either by humans or natural causes. At the beginning, it increases fauna and flora generation, but when vegetation growth expand massively and fauna suffers respiration and survival problems.
  • Hypereutrophic: An excessive growth of vegetation, especially seaweed, on the water surface that creates dead zones underneath. Water visibility is poor and hypereutrophic lakes are characterized for having more than 100 micrograms/liter of phosphorus and over 40 micrograms/liter of chlorophyll.

Eutrophication process: causes and effects

Despite eutrophication is a natural and biological process, it can speed up due to human activities such as:

  • Usage of fertilisers.
  • Massive production of livestock, birds and fish.
  • Treatment plants.
  • Nitrogen oxides (NOx) and sulfur oxides (SOx) emissions.

Deforestation and leaving abandoned forest and wood residues, are also main sources of eutrophication in forest lakes, cutting down water quality and causing huge environmental issues.

These causes can be divided into 3 groups: point sources where the nutrient waste travels from a particular source to water (such as wastewater effluent or untreated sewage); nonpoint sources coming from ill-defined and diffuse sources (such as runoff from abandoned mines or from pasture and range); or others.

The most important pollutants to control in order to prevent eutrophication are the mentioned phosphorus and nitrogen. According to their levels in the water body, they may provoke more or less harmful effects. For instance, some eutrophication consequences are:

  • Abundance of particulate substances such as phytoplankton, zooplankton, bacteria, fungi and debris.
  • Abundance of inorganic chemicals that can generate harmful substances in the drinking water treatment plants.
  • Abundance of organic substances that form complex chemical compounds preventing and difficulting the usual purification processes.
  • Creation of algae that gives the water disagreeables colours, odours and flavours.
  • Quality fish reduction or extinction in the affected area.
  • Toxic algae production that can drive to health problems to humans and animals at drinking it.
  • Certain algae created can produce skin irritation if bathing.
  • Reduction of oxygen concentration, especially in the deeper layers of the lake.

However, the most impactful (and weird) effect of eutrophication is the sedimentation process. At increasing its biomass, even great lakes can become solid land after some time of eutrophication due to pollution problems and massive algae formation.

Prevention of eutrophication

Since eutrophication reduction strategies are expensive and ineffective, the best way to protect an environment and its organisms is trying to prevent the phenomenon. Some of the best prevention methods for water pollution are:

  • Installing tertiary treatment systems to reduce nutrient concentrations in wastewater treatment plants.
  • Limit the production of waste water by using other practices in animal husbandry.
  • Application of effective filter ecosystems to remove nitrogen and phosphorus in the runoff water.
  • Downsizing the amount of phosphorus in detergents.
  • Fertilisation planning and slow release fertilisers usage to rationalize agricultural techniques, or changing these techniques to become organic.

Cultural eutrophication is a complex issue that can only be solved, or at least improved, by the collaboration of scientists, politicians, citizens and environmental organizations. Only together we will be able to prevent new cultural eutrophication cases and to restore some aquatic communities.

The most known law to protect and prevent water pollution in US is the Clean Water Act (CWA) of 1972, which required EPA to establish water quality criteria for the Great Lakes addressing 29 toxic pollutants with maximum levels that are safe for humans, wildlife, and aquatic life. It was first created in 1948 as The Federal Water Pollution Control Act, and over the years it has received some adjustments to improve and update it.

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