*3.2.1 Eutrophication factors*

In natural lakes, there is a distinction between natural and artificial (created by humans) eutrophication. Natural eutrophication depends only on the geology of the area and the natural characteristics of the watershed. If eutrophication is related to human activity (adding a large amount of nutrients to the aquatic ecosystem), which exacerbates this natural phenomenon, these nutrients originate from point and nonpoint sources of pollution, such as phosphorus in sediments [60]. The change in land use alters the amount of nutrients in the runoff. According to studies conducted, phosphorus removed from agricultural lands is at least five times greater, and from urban areas, 10 times greater than from forest lands. Enrichment of water by nutrients exists in nature, but human activities intensify it, and this process occurs almost everywhere in the world. Three important human-related sources of nutrient input are:


The most significant cause of eutrophication is the introduction of a large amount of nutrients into the water, which causes an imbalance in the nutrient cycle and greatly increases the amount of phytoplankton biomass, ultimately leading to the growth of algae. The direct result of the increase in biomass is the high consumption of oxygen underwater [62].
