Editing Algal bloom (section)

==Freshwater algal blooms==
{{Further|Eutrophication#Freshwater systems}}
[[File:Lago de coatepeque de color.jpg|thumb|Cyanobacteria activity turns [[Coatepeque Caldera]] lake into a turquoise color.]]
Freshwater algal blooms are the result of an [[Nutrient pollution|excess of nutrients]], particularly some [[phosphate]]s.<ref name="Phytoplankton Blooms: The Basics">{{cite web|last=Diersling|first=Nancy|title=Phytoplankton Blooms: The Basics|url=http://floridakeys.noaa.gov/scisummaries/wqpb.pdf |archive-url=https://web.archive.org/web/20111015162930/http://floridakeys.noaa.gov/scisummaries/wqpb.pdf |archive-date=15 October 2011 |url-status=live|publisher=NOAA | work= Florida Keys National Marine Sanctuary |access-date=26 December 2012}}</ref><ref name="Lake Scientist">{{cite web|last=Hochanadel|first=Dave|title=Limited amount of total phosphorus actually feeds algae, study finds|url=http://www.lakescientist.com/2010/limited-amount-of-total-phosphorus-actually-feeds-algae-study-finds|publisher=Lake Scientist|access-date=10 June 2012|date=10 December 2010|quote=[B]ioavailable phosphorus&nbsp;– phosphorus that can be utilized by plants and bacteria&nbsp;– is only a fraction of the total, according to Michael Brett, a UW engineering professor ...}}</ref> Excess nutrients may originate from fertilizers that are applied to land for agricultural or recreational purposes and may also originate from household cleaning products containing [[phosphorus]].<ref name="pmid249679">{{Citation |last1=Gilbert |first1=P.A. |title=The Use of Phosphate in Detergents and Possible Replacements for Phosphate |date=1 January 1978 |work=Novartis Foundation Symposia |volume=57 |pages=253–268 |editor-last=Porter |editor-first=Ruth |url=https://onlinelibrary.wiley.com/doi/10.1002/9780470720387.ch14 |access-date=18 October 2024 |edition=1 |publisher=Wiley |language=en |doi=10.1002/9780470720387.ch14 |isbn=978-0-470-66347-9 |last2=De Jong |first2=A.L. |issue=57 |pmid=249679 |editor2-last=Fitzsimons |editor2-first=David W.|url-access=subscription }}</ref>

The reduction of phosphorus inputs is required to mitigate blooms that contain cyanobacteria.<ref>{{Cite journal|last1=Higgins|first1=Scott N.|last2=Paterson|first2=Michael J.|last3=Hecky|first3=Robert E.|last4=Schindler|first4=David W.|last5=Venkiteswaran|first5=Jason J.|last6=Findlay|first6=David L.|date=September 2018|title=Biological Nitrogen Fixation Prevents the Response of a Eutrophic Lake to Reduced Loading of Nitrogen: Evidence from a 46-Year Whole-Lake Experiment|journal=Ecosystems|language=en|volume=21|issue=6|pages=1088–1100|doi=10.1007/s10021-017-0204-2|bibcode=2018Ecosy..21.1088H |s2cid=26030685|issn=1432-9840}}</ref> In lakes that are stratified in the summer, autumn turnover can release substantial quantities of bio-available phosphorus potentially triggering algal blooms as soon as sufficient photosynthetic light is available.<ref>{{cite web|url=https://www.fba.org.uk/journals/index.php/IW/article/viewFile/738/439|publisher=Freshwater Biological Association|title=Storm-triggered, increased supply of sediment-derived phosphorus to the epilimnion in a small freshwater lake|access-date=26 October 2019|date=18 November 2014|archive-url=https://web.archive.org/web/20191026222134/https://www.fba.org.uk/journals/index.php/IW/article/viewFile/738/439|archive-date=26 October 2019|url-status=dead}}</ref> Excess nutrients can enter [[Drainage basin|watershed]]s through water runoff.<ref name="phosphorus">{{cite journal|last1=Lathrop|first1=Richard C.|last2=Carpenter|first2=Stephen R.|last3=Panuska|first3=John C.|last4=Soranno|first4=Patricia A.|last5=Stow|first5=Craig A.|date=1 May 1998|title=Phosphorus loading reductions needed to control blue-green algal blooms in Lake Mendota|journal=Canadian Journal of Fisheries and Aquatic Sciences|volume=55|issue=5|pages=1169–1178|url=https://www.proquest.com/openview/6c4b981906ad8b22c3e827c9120b31b7/1?pq-origsite=gscholar |access-date=13 April 2008|doi=10.1139/cjfas-55-5-1169|url-access=subscription}}</ref> Excess [[carbon]] and [[nitrogen]] have also been suspected as causes. Presence of [[Residual Sodium Carbonate Index|residual sodium carbonate]] acts as catalyst for the algae to bloom by providing dissolved carbon dioxide for enhanced photosynthesis in the presence of nutrients.{{citation needed|date=August 2023}}

When phosphates are introduced into water systems, higher concentrations cause increased growth of algae and plants. Algae tend to grow very quickly under high nutrient availability, but each alga is short-lived, and the result is a high concentration of dead organic matter which starts to decompose. Natural decomposers present in the water begin decomposing the dead algae, consuming dissolved oxygen present in the water during the process. This can result in a sharp decrease in available dissolved oxygen for other aquatic life. Without sufficient dissolved oxygen in the water, animals and plants may die off in large numbers. This may also be known as a [[Dead zone (ecology)|dead zone]].{{citation needed|date=August 2023}}

Blooms may be observed in [[freshwater aquarium]]s when fish are overfed and excess nutrients are not absorbed by plants. These are generally harmful for fish, and the situation can be corrected by changing the water in the tank and then reducing the amount of food given.{{citation needed|date=August 2023}}

=== Natural causes of algal blooms ===
Algal blooms in freshwater systems are not always caused by human contamination and have been observed to occur naturally in both eutrophic and oligotrophic lakes. Eutrophic lakes contain an abundance of nutrients such as nitrogen and phosphates which increase the likelihood for blooms. Oligotrophic lakes don't contain much of these nutrients. Oligotrophic lakes are defined by various degrees of scarcity. The trophic state index (TSI) measures nutrients in freshwater systems and a TSI under 30 defines oligotrophic waters.<ref>{{Cite web |title=Lake Monitoring |url=https://www.nfcrwd.org/index.asp?SEC=B69A2E42-4283-4752-9A2E-9B730349E2DA&Type=B_BASIC#:~:text=Definitions:,three%20layers%20during%20the%20summer. |access-date=2024-12-09 |website=www.nfcrwd.org |language=en}}</ref> However, algal blooms in oligotrophic bodies of water have also been observed. This is a result of cyanobacteria which cause blooms in eutrophic lakes and oligotrophic lakes despite the latter containing a lack of natural and man-made nutrients.

==== Nutrient uptake and cyanobacteria ====
A cause for algal blooms in nutrient-lacking environments come in the form of nutrient uptake. Cyanobacteria have evolved to have better nutrient uptake in oligotrophic waters.<ref name=":3">{{Cite journal |last1=Cottingham |first1=Kathryn L. |last2=Ewing |first2=Holly A. |last3=Greer |first3=Meredith L. |last4=Carey |first4=Cayelan C. |last5=Weathers |first5=Kathleen C. |date=2015 |title=Cyanobacteria as biological drivers of lake nitrogen and phosphorus cycling |url=https://esajournals.onlinelibrary.wiley.com/doi/10.1890/ES14-00174.1 |journal=Ecosphere |language=en |volume=6 |issue=1 |pages=art1 |doi=10.1890/ES14-00174.1 |issn=2150-8925|hdl=10919/89390 |hdl-access=free }}</ref> Cyanobacteria utilize nitrogen and phosphates in their biological processes. Because of this, cyanobacteria are known to be important in the nitrogen and phosphate fixing cycle in oligotrophic waters.<ref name=":3" /> Cyanobacteria can fix nitrogen by accessing atmospheric nitrogen ({{chem2|N2}}) that has been dissolved into water and transforming it into nitrogen accessible to other organisms.<ref name=":3" /> This higher amount of nitrogen is then able to sustain large algae blooms in oligotrophic waters.<ref name=":4">{{Cite journal |last1=Reinl |first1=Kaitlin L. |last2=Brookes |first2=Justin D. |last3=Carey |first3=Cayelan C. |last4=Harris |first4=Ted D. |last5=Ibelings |first5=Bas W. |last6=Morales-Williams |first6=Ana M. |last7=De Senerpont Domis |first7=Lisette N. |last8=Atkins |first8=Karen S. |last9=Isles |first9=Peter D. F. |last10=Mesman |first10=Jorrit P. |last11=North |first11=Rebecca L. |last12=Rudstam |first12=Lars G. |last13=Stelzer |first13=Julio A. A. |last14=Venkiteswaran |first14=Jason J. |last15=Yokota |first15=Kiyoko |date=2021 |title=Cyanobacterial blooms in oligotrophic lakes: Shifting the high-nutrient paradigm |url=https://onlinelibrary.wiley.com/doi/full/10.1111/fwb.13791 |journal=Freshwater Biology |language=en |volume=66 |issue=9 |pages=1846–1859 |doi=10.1111/fwb.13791 |issn=1365-2427}}</ref>

Cyanobacteria are able to retain high phosphorus uptake in the absence of nutrients which help their success in oligotrophic environments. Cyanobacteria species such as ''D. lemmermannii'' are able to move between the hypolimnion which is rich in nutrients such as phosphates and the nutrient-poor metalimnion which lacks phosphates.<ref name=":4" /> This causes phosphates to be brought up to the metalimnion and give organisms an abundance of phosphates, exacerbating the likelihood for algal blooms.<ref name=":3" />

==== Upwelling of nutrients ====
Upwelling events happen when nutrients such as phosphates and nitrogen are moved from the nutrient dense hypolimnion to the nutrient poor metalimnion.<ref name=":3" /><ref name=":4" /> This happens as result of geological processes such as seasonal overturn when lake surfaces freeze or melt, prompting mixing due to changing water densities mixing up the composition of limnion layers and mixing nutrients around the system.<ref>{{Cite web |date=2024-08-09 |title=Harmful Algal Blooms |url=https://www.adkwatershed.org/harmful-algal-blooms |access-date=2024-12-09 |website=Adirondack Watershed Institute |language=en-US}}</ref> This overabundance in nutrients leads to blooms.<ref name=":4" />