Editing Eutrophication (section)

==== Decreased biodiversity ====
When an ecosystem experiences an increase in nutrients, [[primary producer]]s reap the benefits first. In aquatic ecosystems, species such as [[algae]] experience a population increase (called an [[algal bloom]]). Algal blooms limit the sunlight available to bottom-dwelling organisms and cause wide swings in the amount of dissolved oxygen in the water. Oxygen is required by all aerobically [[Respiration (physiology)|respiring]] plants and animals and it is replenished in daylight by [[photosynthesis|photosynthesizing]] plants and algae. Under eutrophic conditions, dissolved oxygen greatly increases during the day, but is greatly reduced after dark by the respiring algae and by microorganisms that feed on the increasing mass of dead algae. When dissolved oxygen levels decline to [[hypoxia (environmental)|hypoxic]] levels, fish and other [[Marine life|marine animals]] suffocate. As a result, creatures such as fish, shrimp, and especially immobile bottom dwellers die off.<ref name="Horrigan 2002">{{Cite journal|last1=Horrigan|first1=L.|last2=Lawrence|first2=R. S.|last3=Walker|first3=P.|year=2002|title=How sustainable agriculture can address the environmental and human health harms of industrial agriculture|journal=Environmental Health Perspectives|volume=110|issue=5|pages=445–456|doi=10.1289/ehp.02110445|pmc=1240832|pmid=12003747|bibcode=2002EnvHP.110..445H }}</ref> In extreme cases, [[Anaerobic organism|anaerobic]] conditions ensue, promoting growth of bacteria. Zones where this occurs are known as [[Dead zone (ecology)|dead zones]].