Editing Water cycle (section)

== Related processes ==

=== Biogeochemical cycling ===
While the water cycle is itself a [[biogeochemical cycle]], flow of water over and beneath the Earth is a key component of the cycling of other biogeochemicals.<ref>{{cite web |publisher=The Environmental Literacy Council |url=http://www.enviroliteracy.org/subcategory.php/198.html |title=Biogeochemical Cycles |url-status=live |archive-url=https://web.archive.org/web/20150430133927/http://enviroliteracy.org/subcategory.php/198.html |archive-date=2015-04-30 |access-date=2006-10-24}}</ref> Runoff is responsible for almost all of the transport of eroded [[sediment]] and [[phosphorus]] from land to [[waterbody|waterbodies]].<ref>{{Cite web |url=https://enviroliteracy.org/air-climate-weather/biogeochemical-cycles/phosphorus-cycle/ |title=Phosphorus Cycle |work=The Environmental Literacy Council |access-date=2018-01-15 |url-status=live |archive-url=https://web.archive.org/web/20160820012731/http://enviroliteracy.org/air-climate-weather/biogeochemical-cycles/phosphorus-cycle/|archive-date=2016-08-20}}</ref> The [[salinity]] of the oceans is derived from [[erosion]] and transport of dissolved salts from the land. Cultural [[eutrophication]] of lakes is primarily due to phosphorus, applied in excess to [[field (agriculture)|agricultural fields]] in [[fertilizer]]s, and then transported overland and down rivers. Both runoff and groundwater flow play significant roles in transporting nitrogen from the land to waterbodies.<ref>{{cite web |publisher=Ohio State University |website=Extension Fact Sheet |url=http://ohioline.osu.edu/aex-fact/0463.html |title=Nitrogen and the Hydrologic Cycle |url-status=dead |archive-url=https://web.archive.org/web/20060901071850/http://ohioline.osu.edu/aex-fact/0463.html |archive-date=2006-09-01 |access-date=2006-10-24}}</ref> The [[dead zone (ecology)|dead zone]] at the outlet of the [[Mississippi River]] is a consequence of [[nitrate]]s from fertilizer being carried off agricultural fields and funnelled down the [[river system]] to the [[Gulf of Mexico]]. Runoff also plays a part in the [[carbon cycle]], again through the transport of eroded rock and soil.<ref>{{cite web |publisher=NASA |website=Earth Observatory |title=The Carbon Cycle |url=http://earthobservatory.nasa.gov/Library/CarbonCycle/ |url-status=dead |archive-url=https://web.archive.org/web/20060928223836/http://earthobservatory.nasa.gov/Library/CarbonCycle/ |archive-date=2006-09-28 |access-date=2006-10-24|date=2011-06-16 }}</ref>

=== Slow loss over geologic time ===
{{Main|Atmospheric escape}}

The hydrodynamic wind within the upper portion of a planet's atmosphere allows light chemical elements such as [[Hydrogen]] to move up to the [[exobase]], the lower limit of the [[exosphere]], where the gases can then reach [[escape velocity]], entering [[outer space]] without impacting other particles of gas. This type of gas loss from a planet into space is known as [[planetary wind]].<ref>{{cite web|url=http://www.astronomynotes.com/solarsys/s3.htm |author=Nick Strobel |date=June 12, 2010 |archive-date=September 17, 2010 |access-date=September 28, 2010 |archive-url=https://web.archive.org/web/20100917233236/http://astronomynotes.com/solarsys/s3.htm |title=Planetary Science |url-status=dead }}</ref> Planets with hot lower atmospheres could result in humid upper atmospheres that accelerate the loss of hydrogen.<ref name="Dvorak">{{cite book|author=Rudolf Dvořák|year=2007|url=https://books.google.com/books?id=lbIlI6gMNAYC&q=hydrodynamic+wind+planet+atmosphere&pg=PA140|title=Extrasolar Planets|publisher=Wiley-VCH|pages=139–40|isbn=978-3-527-40671-5|access-date=2009-05-05}}{{Dead link|date=August 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>