Eutrophication from the nitrogen cycle:
Biogeochemical cycles are natural interconnected cycling processes of certain elemental organic living matter components as well as their biological, geological and chemical considerations. A nitrogen cycle deals with the flow of nitrogen in the environment using a process termed as nitrogen fixation.
Excess of nitrogen and phosphorous content in water bodies leads to its enrichment and thus results in an abnormally boosted growth of algae and weeds. This is called as Eutrophication. Discharge of waste water into freshwater streams and fertilizers used in agriculture are likely to be washed off from the surface and get added into water reservoirs. This is a prime factor resulting in eutrophication.
It reduces the oxygen content in water, leads to death and extinction of marine life species, increases water toxicity and thus reduces quality of usable water; forms a layer of algae over water bodies and hence the water is not exposed to sunlight, halting the cellular respiration of in-water decomposers and leading to depletion in the water oxygen level. Since exceeding amounts of nitrogen in water is decreasing our marine ecosystem balance, eutrophication due to imbalanced nitrogen cycle is an issue.