Editing Estuary (section)

=== Effects of eutrophication on biogeochemical cycles ===
[[File:Table_of_the_Processes_in_the_Nitrogen_Cycle.jpg|thumb|Processes that nitrogen undergo in estuarine systems]]
Nitrogen is often the lead cause of [[eutrophication]] in estuaries in temperate zones.<ref>{{Cite journal |last1=Howarth |first1=Robert W. |last2=Marino |first2=Roxanne |date=2006 |title=Nitrogen as the limiting nutrient for eutrophication in coastal marine ecosystems: Evolving views over three decades |journal=Limnology and Oceanography |language=en |volume=51 |issue=1part2 |pages=364–376 |doi=10.4319/lo.2006.51.1_part_2.0364 |bibcode=2006LimOc..51..364H |s2cid=18144068 |issn=0024-3590|doi-access=free }}</ref> During a eutrophication event, biogeochemical feedback decreases the amount of available [[Silica cycle|silica]].<ref>{{Cite journal |last1=Howarth |first1=Robert |last2=Chan |first2=Francis |last3=Conley |first3=Daniel J |last4=Garnier |first4=Josette |last5=Doney |first5=Scott C |last6=Marino |first6=Roxanne |last7=Billen |first7=Gilles |date=2011 |title=Coupled biogeochemical cycles: eutrophication and hypoxia in temperate estuaries and coastal marine ecosystems |journal=Frontiers in Ecology and the Environment |language=en |volume=9 |issue=1 |pages=18–26 |doi=10.1890/100008 |hdl=1813/60819 |issn=1540-9295|doi-access=free |bibcode=2011FrEE....9...18H |hdl-access=free }}</ref> These feedbacks also increase the supply of [[Nitrogen cycle|nitrogen]] and phosphorus, creating conditions where harmful algal blooms can persist. Given the now off-balance [[nitrogen cycle]], estuaries can be driven to [[Phosphorus cycle|phosphorus]] limitation instead of nitrogen limitation. Estuaries can be severely impacted by an unbalanced phosphorus cycle, as phosphorus interacts with nitrogen and silica availability.

With an abundance of nutrients in the ecosystem, plants and algae overgrow and eventually decompose, which produce a significant amount of carbon dioxide.<ref>{{Cite journal |last1=Morales-Williams |first1=Ana M. |last2=Wanamaker |first2=Alan D. |last3=Williams |first3=Clayton J. |last4=Downing |first4=John A. |date=2021 |title=Eutrophication Drives Extreme Seasonal {{CO2}} Flux in Lake Ecosystems |url=https://link.springer.com/10.1007/s10021-020-00527-2 |journal=Ecosystems |language=en |volume=24 |issue=2 |pages=434–450 |doi=10.1007/s10021-020-00527-2 |bibcode=2021Ecosy..24..434M |s2cid=220856626 |issn=1432-9840}}</ref> While releasing {{CO2}} into the water and atmosphere, these organisms are also intaking all or nearly all of the available oxygen creating a [[Dead zone (ecology)|hypoxic]] environment and unbalanced [[oxygen cycle]].<ref>{{Cite book |last1=Selman |first1=Mindy |url=https://www.wri.org/research/eutrophication-and-hypoxia-coastal-areas |title=Eutrophication and Hypoxia in Coastal Areas |last2=Sugg |first2=Zachary |last3=Greenhalgh |first3=Suzie |date=2008 |publisher=World Resources Institute |isbn=978-1-56973-681-4 |language=en}}</ref> The excess carbon in the form of {{CO2}} can lead to low pH levels and [[ocean acidification]], which is more harmful for vulnerable coastal regions like estuaries.