User:Gros04/Trophic state index

Trophic index drivers[edit]
Both natural and anthropogenic factors can influence a lake or other water body's trophic index. A water body situated in a nutrient-rich region with high net primary productivity may be naturally eutrophic. Nutrients carried into water bodies from non-point sources such as agricultural runoff, residential fertilisers, and sewage will all increase the algal biomass, and can easily cause an oligotrophic lake to become hypereutrophic  [citation needed].

Freshwater Lakes
Although there is no absolute consensus as to which nutrients contribute the most to increasing primary productivity, phosphorus concentration is thought to be the main limiting factor in freshwater lakes. This is likely due to the prevalence of nitrogen fixing microorganisms in these systems, which can compensate for a lack of readily available fixed nitrogen.

Marine Ecosystems
In some coastal marine ecosystems, research has found nitrogen to be the key limiting nutrient, driving primary production independently of phosphorus. Nitrogen fixation cannot adequately supply these marine ecosystems, because the nitrogen fixing microbes are themselves limited by the availability of various abiotic factors like sunlight and dissolved oxygen. However, marine ecosystems are too broad a range of environments for one nutrient to limit all marine primary productivity. The limiting nutrient may vary in different marine environments according to a variety of factors like depth, distance from shore, or availability of organic matter.