Editing Nitrate (section)

=== Aquatic toxicity ===
[[File:Annual mean sea surface nitrate (World Ocean Atlas 2009).png|right|thumb|Sea surface nitrate from the [[World Ocean Atlas]]]]
In [[freshwater]] or [[estuary|estuarine]] systems close to land, nitrate can reach concentrations that are lethal to fish. While nitrate is much less toxic than ammonia,<ref>{{cite journal | vauthors = Romano N, Zeng C | title = Acute toxicity of sodium nitrate, potassium nitrate, and potassium chloride and their effects on the hemolymph composition and gill structure of early juvenile blue swimmer crabs(Portunus pelagicus Linnaeus, 1758) (Decapoda, Brachyura, Portunidae) | journal = Environmental Toxicology and Chemistry | volume = 26 | issue = 9 | pages = 1955–1962 | date = September 2007 | pmid = 17705664 | doi = 10.1897/07-144r.1 | bibcode = 2007EnvTC..26.1955R | s2cid = 19854591 }}</ref> levels over 30 ppm of nitrate can inhibit growth, impair the immune system and cause stress in some aquatic species.<ref>{{cite web | url=http://freshaquarium.about.com/od/watercare/a/nitrates.htm | title=Nitrates in the Aquarium | work=About.com | access-date=October 30, 2013 | author=Sharpe, Shirlie | archive-date=July 24, 2011 | archive-url=https://web.archive.org/web/20110724135608/http://freshaquarium.about.com/od/watercare/a/nitrates.htm | url-status=dead }}</ref> Nitrate toxicity remains a subject of debate.<ref>{{cite journal | vauthors = Romano N, Zeng C | title = Effects of potassium on nitrate mediated alterations of osmoregulation in marine crabs | journal = Aquatic Toxicology | volume = 85 | issue = 3 | pages = 202–208 | date = December 2007 | pmid = 17942166 | doi = 10.1016/j.aquatox.2007.09.004 | bibcode = 2007AqTox..85..202R }}</ref>

In most cases of excess nitrate concentrations in aquatic systems, the primary sources are wastewater discharges, as well as [[surface runoff]] from agricultural or [[landscape]]d areas that have received excess nitrate fertilizer. The resulting [[eutrophication]] and algae blooms result in [[Hypoxia (environmental)|anoxia]] and [[Dead zone (ecology)|dead zones]]. As a consequence, as nitrate forms a component of [[total dissolved solids]], they are widely used as an indicator of [[water quality]].