Eutrophication (from other Greek. Εὐτροφία - good nutrition) is the saturation of reservoirs with nutrients, accompanied by an increase in the biological productivity of water basins. Eutrophication can be the result of both the natural aging of a reservoir and anthropogenic influences . The main chemical elements contributing to eutrophication are phosphorus and nitrogen [1] [2] [3] . In some cases, the term "hypertrophization" is used.
Eutrophic reservoirs are rich in littoral and sublittoral vegetation, abundant plankton . Unbalanced eutrophication can lead to the rapid development of algae ( water bloom ) and the appearance of cyanobacteria in the water, which during the flowering period emit toxins ( alkaloids and low molecular weight peptides ) that can cause poisoning of people and animals, as well as lead to oxygen deficiency, fish and animal deaths . This process can be explained by the small penetration of sunlight into the body of the reservoir and, as a consequence, the lack of photosynthesis in nadon plants, and hence oxygen.
Content
Impact of eutrophication on the biogeocenosis of a reservoir
In a simplified form, the eutrophication process has the following basic stages:
- In the upper layer of water, the concentration of nutrients occurs, which provokes the active development of microflora (primarily phytoplankton , as well as fouling algae) in this zone and an increase in the mass of zooplankton feeding on phytoplankton. Such growth reduces the transparency of water , the depth of penetration of the sun's rays decreases, as a result of a lack of light, the death of benthic plants begins. The process of dying of bottom aquatic plants entails the death of other organisms to which these plants form a habitat or for which they are a higher link in the food chain.
- The activity of increasing the biomass of plants (especially algae) depends on the temperature regime of the upper layer of water. At night, photosynthesis does not occur in these plants, but the active process of respiration continues. In the summer, in the early hours of warm days, the oxygen content in the upper horizons of the water drops and the death of aerobic organisms inhabiting these horizons and demanding oxygen content is observed (the so-called "summer freeze" ).
- Dead organisms fall to the bottom of the reservoir and are decomposed by aerobic bacteria. However, bottom vegetation suffering from hypoxia is no longer able to provide adequate oxygen production. And if we take into account that the total bio-productivity of the eutrophic reservoir increases, an imbalance between the production and consumption of oxygen in the bottom horizons increases. The aggravated oxygen deficiency leads to the death of the demanding oxygen bottom and bottom fauna. A similar phenomenon is observed in winter in shallow closed reservoirs - the so-called. "Winter zamora" .
- In the bottom soil, devoid of oxygen, anaerobic decomposition of dead organisms occurs with the formation of such strong poisons as phenols and hydrogen sulfide, and such a powerful "greenhouse gas" (25 times superior in its effect to carbon dioxide), like methane . As a result, the eutrophication process destroys most of the species of the flora and fauna of the reservoir, almost completely destroying or transforming its ecosystems very much, and greatly degrades the sanitary and hygienic qualities of water, up to its complete unsuitability for swimming and drinking water. A pond can even become a swamp due to low oxygen levels.
Anthropogenic Eutrophication
The main anthropogenic sources of phosphorus and nitrogen: untreated wastewater (especially from livestock farms) and the flushing of fertilizers from the fields.
In many countries, the use of sodium orthophosphate in washing powders is prohibited to reduce the eutrophication of water bodies. In particular, since the beginning of the 2010s, EU countries have gradually introduced restrictions on the use of phosphates in household washing powders at the level of not more than 0.3-0.5 grams of phosphorus per wash cycle [4]
See also
- Thermification of water bodies
- Eutrophication of Lake Baikal