Editing Algal bloom (section)

=== 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" />