Editing Floodplain (section)

==Ecology {{anchor|Ecology|Floodplain ecosystems}}==
Floodplains support diverse and productive [[ecosystems]].<ref name="IUFRO">{{cite web |last1=Kulhavy |first1=Jiri |last2=Cater |first2=Matjaz |title=Floodplain forest ecosystems |url=https://www.iufro.org/science/divisions/division-8/80000/80100/80105/ |publisher=International Union of Forest Research Organizations |access-date=15 November 2021 |archive-date=21 May 2023 |archive-url=https://web.archive.org/web/20230521212848/https://www.iufro.org/science/divisions/division-8/80000/80100/80105/ |url-status=dead }}</ref><ref name="KlimoHager2001">{{cite book |editor1-last=Klimo |editor1-first=Emil |editor2-last=Hager |editor2-first=Herbert |title=The floodplain forests in Europe : current situations and perspectives |date=2001 |publisher=Brill |location=Leiden |isbn=9789004119581 |url=https://books.google.com/books?id=nCGbpTCAeJAC&dq=klimo+hager+2001&pg=PR3 |access-date=15 November 2021}}</ref> They are characterized by considerable variability in space and time, which in turn produces some of the most species-rich of ecosystems.<ref name="WardEtal1999">{{cite journal |last1=Ward |first1=J. V. |last2=Tockner |first2=K. |last3=Schiemer |first3=F. |title=Biodiversity of floodplain river ecosystems: ecotones and connectivity1 |journal=Regulated Rivers: Research & Management |date=1999 |volume=15 |issue=1–3 |pages=125–139 |doi=10.1002/(SICI)1099-1646(199901/06)15:1/3<125::AID-RRR523>3.0.CO;2-E}}</ref> From the ecological perspective, the most distinctive aspect of floodplains is the ''flood pulse'' associated with annual floods, and so the floodplain ecosystem is defined as the part of the river valley that is regularly flooded and dried.<ref name=Bayley1995>{{cite journal |last1=Bayley |first1=Peter B. |title=Understanding Large River: Floodplain Ecosystems |journal=BioScience |date=March 1995 |volume=45 |issue=3 |pages=153–158 |doi=10.2307/1312554 |jstor=1312554}}</ref>

Floods bring in detrital material rich in nutrients and release nutrients from dry soil as it is flooded. The decomposition of terrestrial plants submerged by the floodwaters adds to the nutrient supply. The flooded [[littoral zone]] of the river (the zone closest to the river bank) provides an ideal environment for many aquatic species, so the spawning season for fish often coincides with the onset of flooding. Fish must grow quickly during the flood to survive the subsequent drop in water level. As the floodwaters recede, the littoral experiences blooms of microorganisms, while the banks of the river dry out and terrestrial plants germinate to stabilize the bank.<ref name=Bayley1995/>
[[File:Achterwehr (129456655).jpeg|thumb|268x268px|A low-lying field in [[Achterwehr]] Germany inundated by overflow from a nearby waterway.]]

The biota of floodplains has high annual growth and mortality rates, which is advantageous for the rapid colonization of large areas of the floodplain. This allows them to take advantage of shifting floodplain geometry.<ref name=Bayley1995/> For example, floodplain<ref>{{Cite journal |last1=Ferreira |first1=Leandro Valle |last2=Stohlgren |first2=Thomas J. |date=1999-09-01 |title=Effects of river level fluctuation on plant species richness, diversity, and distribution in a floodplain forest in Central Amazonia |url=https://doi.org/10.1007/s004420050893 |journal=Oecologia |volume=120 |issue=4 |pages=582–587 |doi=10.1007/s004420050893 |pmid=28308309 |bibcode=1999Oecol.120..582F |s2cid=10195707 |issn=1432-1939}}</ref> trees are fast-growing and tolerant of root disturbance. Opportunists (such as birds) are attracted to the rich food supply provided by the flood pulse.<ref name="IUFRO"/>

Floodplain ecosystems have distinct biozones. In Europe, as one moves away from the river, the successive plant communities are bank vegetation (usually annuals); sedge and reeds; willow shrubs; willow-poplar forest; oak-ash forest; and broadleaf forest. Human disturbance creates [[wet meadow]]s that replace much of the original ecosystem.<ref name="Suchara2019">{{cite journal |last1=Suchara |first1=Ivan |title=The Impact of Floods on the Structure and Functional Processes of Floodplain Ecosystems |journal=Journal of Soil and Plant Biology |date=11 January 2019 |volume=2019 |issue=1 |pages=28–44 |doi=10.33513/JSPB/1801-03|doi-broken-date=1 November 2024 |s2cid=207914841 |doi-access=free }}</ref> The biozones reflect a soil moisture and oxygen gradient that in turn corresponds to a flooding frequency gradient.<ref name="Hughes1997">{{cite journal |last1=Hughes |first1=Francine M.R. |title=Floodplain biogeomorphology |journal=Progress in Physical Geography: Earth and Environment |date=December 1997 |volume=21 |issue=4 |pages=501–529 |doi=10.1177/030913339702100402|bibcode=1997PrPG...21..501H |s2cid=220929033 }}</ref> The primeval floodplain forests of Europe were dominated by oak (60%) elm (20%) and hornbeam (13%), but human disturbance has shifted the makeup towards ash (49%) with maple increasing to 14% and oak decreasing to 25%.<ref name="KlimoHager2001"/>

Semiarid floodplains have a much lower species diversity. Species are adapted to alternating drought and flood. Extreme drying can destroy the ability of the floodplain ecosystem to shift to a healthy wet phase when flooded.<ref name="ColloffBaldwin2010">{{cite journal |last1=Colloff |first1=Matthew J. |last2=Baldwin |first2=Darren S. |title=Resilience of floodplain ecosystems in a semi-arid environment |journal=The Rangeland Journal |date=2010 |volume=32 |issue=3 |pages=305 |doi=10.1071/RJ10015}}</ref>

Floodplain forests constituted 1% of the landscape of Europe in the 1800s. Much of this has been cleared by human activity, though floodplain forests have been impacted less than other kinds of forests. This makes them important [[Refugium (population biology)|refugia]] for biodiversity.<ref name="KlimoHager2001"/><ref name="IUFRO"/> Human destruction of floodplain ecosystems is largely a result of flood control,<ref name=Bayley1995/> hydroelectric development (such as reservoirs), and conversion of floodplains to agriculture use.<ref name="KlimoHager2001"/> Transportation and waste disposal also have detrimental effects.<ref name=Bayley1995/> The result is the fragmentation of these ecosystems, resulting in loss of populations and diversity<ref name="KlimoHager2001"/> and endangering the remaining fragments of the ecosystem.<ref name="WardEtal1999"/> Flood control creates a sharper boundary between water and land than in undisturbed floodplains, reducing physical diversity.<ref name=Bayley1995/> Floodplain forests protect waterways from erosion and pollution and reduce the impact of floodwaters.<ref name="KlimoHager2001"/>

The disturbance by humans of temperate floodplain ecosystems frustrates attempts to understand their natural behavior. Tropical rivers are less impacted by humans and provide models for temperate floodplain ecosystems, which are thought to share many of their ecological attributes.<ref name=Bayley1995/>