Profundal zone
{{Lake stratification topics}}
The profundal zone is the deep zone of a lake, located below the range of effective light penetration. This is typically below the thermocline, the vertical zone in the water through which temperature drops rapidly. The temperature difference may be large enough to hamper mixing with the littoral zone in some seasons which causes a decrease in oxygen concentrations. The profundal is often defined, as the deepest, vegetation-free, and muddy zone of the lacustrine benthal.{{Cite book|url=https://portal.dnb.de/opac.htm?method=showFullRecord¤tResultId=%22118757008%22%26any¤tPosition=24|title=Die Binnengewässer Mitteleuropas. eine limnologiche Einführung|last=Thienemann|first=August|publisher=E. Schweizerbart'sche Verlagsbuchandlung|year=1925|volume=1|location=Stuttgart|language=de|trans-title=The Inland Waters of Central Europe: a Limnological Introduction|oclc=859570299|author-link=August Thienemann}} The profundal zone is often part of the aphotic zone. Sediment in the profundal zone primarily comprises silt and mud.{{Cite book|last=Dodds, Walter K. (Walter Kennedy), 1958-|title=Freshwater ecology : concepts and environmental applications of limnology|others=Whiles, Matt R.|date=15 February 2019|isbn=9780128132555|edition=Third|location=London, United Kingdom|oclc=1096190142}}
Organisms
The lack of light and oxygen in the profundal zone determines the type of biological community that can live in this region, which is distinctly different from the community in the overlying waters.{{Cite journal|last=Thienemann|first=August|author-link=August Thienemann|date=1920|title=Untersuchungen über die Beziehungen zwischen dem Sauerstoff gehalt des Wassers und der Zusammensetzung der Fauna in norddeutschen Seen|trans-title=Studies on the Relationship Between the Oxygen Content of Water and the Composition of Fauna in Northern German Lakes|journal=Archiv für Hydrobiologie|language=de|location=Stuttgart|publisher=E. Schweizerbart'sche Verlagsbuchandlung|volume=12|pages=1–65|issn=0003-9136}} The profundal macrofauna is therefore characterized by physiological and behavioural adaptations to low oxygen concentration. While benthic fauna differs between lakes, Chironomidae and Oligochaetae often dominate the benthic fauna of the profundal zone because they possess hemoglobin-like molecules to extract oxygen from poorly oxygenated water.{{cite journal|last1=Int Panis|first1=Luc|last2=Goddeeris|first2=Boudewijn|last3=Verheyen|first3=Rudolf|date=January 1996|title=On the relationship between vertical microdistribution and adaptations to oxygen stress in littoral Chironomidae (Diptera)|journal=Hydrobiologia|volume=318|issue=1–3|pages=61–67|doi=10.1007/bf00014132|s2cid=27026595}} Due to the low productivity of the profundal zone, organisms rely on detritus sinking from the photic zone. Species richness in the profundal zone is often similar to that in the limnetic zone.{{Cite journal|last1=Vadeboncoeur|first1=Yvonne|last2=McIntyre|first2=Peter B.|last3=Vander Zanden|first3=M. Jake|date=July 2011|title=Borders of Biodiversity: Life at the Edge of the World's Large Lakes|journal=BioScience|volume=61|issue=7|pages=526–537|doi=10.1525/bio.2011.61.7.7|issn=1525-3244|doi-access=free}} Microbial levels in the profundal benthos are higher than those in the littoral benthos, potentially due to a smaller average sediment particle size.{{Cite journal|last=Jones|first=J. G.|date=1980-04-01|title=Some Differences in the Microbiology of Profundal and Littoral Lake Sediments|journal=Microbiology|volume=117|issue=2|pages=285–292|doi=10.1099/00221287-117-2-285|issn=1350-0872|doi-access=free}} Benthic macroinvertebrates are believed to be regulated by top-down pressure.{{Cite journal|last1=Jyväsjärvi|first1=Jussi|last2=Immonen|first2=Hemmo|last3=Högmander|first3=Pia|last4=Högmander|first4=Harri|last5=Hämäläinen|first5=Heikki|last6=Karjalainen|first6=Juha|date=2013|title=Can lake restoration by fish removal improve the status of profundal macroinvertebrate assemblages?|journal=Freshwater Biology|language=en|volume=58|issue=6|pages=1149–1161|doi=10.1111/fwb.12115|bibcode=2013FrBio..58.1149J |issn=1365-2427}}
Nutrient cycling
Nutrient fluxes in the profundal zone are primarily driven by release from the benthos.{{Cite journal|last1=Beutel|first1=Marc W.|last2=Horne|first2=Alex J.|last3=Taylor|first3=William D.|last4=Losee|first4=Richard F.|last5=Whitney|first5=Randy D.|date=March 2008|title=Effects of oxygen and nitrate on nutrient release from profundal sediments of a large, oligo-mesotrophic reservoir, Lake Mathews, California|journal=Lake and Reservoir Management|volume=24|issue=1|pages=18–29|doi=10.1080/07438140809354047|bibcode=2008LRMan..24...18B |s2cid=85189740|issn=1040-2381}} The anoxic nature of the profundal zone drives ammonia release from benthic sediment. This can drive phytoplankton production, to the point of a phytoplankton bloom, and create toxic conditions for many organisms, particularly at a high pH. Hypolimnetic anoxia can also contribute to buildups of iron, manganese, and sulfide in the profundal zone.{{Cite journal|last=Beutel|first=Marc W.|date=December 2006|title=Inhibition of ammonia release from anoxic profundal sediments in lakes using hypolimnetic oxygenation|journal=Ecological Engineering|volume=28|issue=3|pages=271–279|doi=10.1016/j.ecoleng.2006.05.009|bibcode=2006EcEng..28..271B |issn=0925-8574}}
See also
{{Portal|Ecology|Environment|Marine Life}}
References
{{Reflist}}
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