Editing Geography of Tuvalu (section)

==Funafuti atoll==
===Structure of Funafuti atoll===
[[File:Funafuti bearbeitet.jpg|thumb|right|250px|Funafuti atoll]]

[[Funafuti]] [[atoll]] consists of a narrow sweep of land between {{convert|20|and|400|m|0|abbr=off}} wide, encircling a large lagoon (''Te Namo'') of about {{convert|18|km|0|abbr=in}} long and {{convert|14|km|0|abbr=in}} wide. The average depth in the Funafuti lagoon is about {{convert|20|fathom|m ft|abbr=off}}.<ref name="AC1">{{cite book |last=Coates|first=A. | title= Western Pacific Islands |year= 1970 |publisher= H.M.S.O.|pages=349}}</ref> With a surface of {{convert|275|km²|1|abbr=out}}, it is by far the largest lagoon in Tuvalu. The northern part of the lagoon has a deep basin (maximum depth recorded of 54.7 m) basin, and the southern part of the lagoon has very narrow shallow basin.<ref name="SOPAC"/> The land area of the 33 islets aggregates to {{convert|2.4|km²|1|abbr=out}}, less than one percent of the total area of the atoll.

The boreholes on [[Fongafale]] islet at the site now called ''Darwin's Drill'',<ref name="PDN">{{cite book |last1=Lal |first1=Andrick |title=South Pacific Sea Level & Climate Monitoring Project – Funafuti atoll |url=http://www.pacificdisaster.net/oip/FinalReport/Annex/3_Survey%20LDP/Survey_Diagrams_JPACE-TV.pdf |archive-url=https://web.archive.org/web/20140203011855/http://www.pacificdisaster.net/oip/FinalReport/Annex/3_Survey%20LDP/Survey_Diagrams_JPACE-TV.pdf |url-status=dead |archive-date=3 February 2014 |publisher=SPC Applied Geoscience and Technology Division (SOPAC Division of SPC) |pages=35 & 40}}</ref> are the result of drilling conducted by the [[Royal Society of London]] for the purpose of investigating the [[formation of coral reefs]] to determine whether traces of shallow water organisms could be found at depth in the [[coral]] of Pacific atolls. This investigation followed the work on [[The Structure and Distribution of Coral Reefs]] conducted by [[Charles Darwin]] in the Pacific. Drilling occurred in 1896, 1897 and 1898.<ref>{{cite news |url=http://nla.gov.au/nla.news-article17092086 |title=TO THE EDITOR OF THE HERALD |newspaper=[[The Sydney Morning Herald]] |date=11 September 1934 |access-date=20 June 2012 |page=6 |publisher=National Library of Australia}}</ref> Professor [[Edgeworth David]] of the [[University of Sydney]] was a member of the 1896 "Funafuti Coral Reef Boring Expedition of the Royal Society", under [[William Johnson Sollas|Professor William Sollas]] and lead the expedition in 1897.<ref>David, Mrs Edgeworth, ''Funafuti or Three Months on a Coral Atoll: an unscientific account of a scientific expedition'', London: John Murray, 1899</ref> However, the geologic history of atolls is more complex than Darwin (1842) and Davis (1928)<ref name="WMD1">{{cite journal| last = Davis, W.M. |title= The coral reef problem | journal = American Geographical Society Special Publication | volume = 9| issue = | pages = 1–596|date = 1928}}</ref> envisioned.<ref name="DRS">{{cite journal| last = Stoddart, D. R.|title= Theory and Reality: The Success and Failure of the Deductive Method in Coral Reef Studies–Darwin to Davis| journal = Earth Sciences History | volume = 13| issue =1 | pages = 21–34|date = 1994|doi= 10.17704/eshi.13.1.wp354u3281532021}}</ref><ref name="WRD">{{cite journal|last1= Dickinson |first1=William R. |title= Pacific Atoll Living: How Long Already and Until When?|url= https://www.geosociety.org/gsatoday/archive/19/3/pdf/i1052-5173-19-3-4.pdf|year= 2009 |journal= GSA Today |volume=19|issue=3|pages=4–10 |doi= 10.1130/GSATG35A.1 }}</ref> The survey of the atoll published in 1970 described its structure as being:

{{cquote| “[[Funafuti]] is an almost circular and conical submarine mountain 12,000 feet high, originally volcanic, and of immense geological age, much older than the relatively young and active mountains of the [[Vanuatu|New Hebrides]] and [[Solomon Islands|Solomons]]. At its base on the ocean bed it is 30 miles wide in one of the directions tested, and 28 miles wide on the other. It rises in a gentle slope which gradually steepens to a point 2,400 feet below water level, after which it rises at an angle of 80 degrees to 840 feet below water level. From this point it rises vertically, like an enormous pillar, till reaches the surface in the form of a reef enclosing a lagoon of irregular size, but of which the extremities give a measurement of 13.5 by 10.0 miles".<ref name="AC1"/>}}

===Aquifer salinization of Fongafale Islet, Funafuti===
The investigation of groundwater dynamics of [[Fongafale]] Islet, [[Funafuti]], show that [[tidal force|tidal forcing]] results in salt water contamination of the [[surficial aquifer]] during [[Perigean spring tide|spring tides]].<ref name="EAS">{{cite journal|author1=Nakada S. |author2=Yamano H. |author3=Umezawa Y. |author4=Fujita M. |author5=Watanabe M. |author6=Taniguchi M. |title= Evaluation of Aquifer Salinization in the Atoll Islands by Using Electrical Resistivity|journal=Journal of the Remote Sensing Society of Japan |volume=30 |year =2010 |pages=317–330|doi=10.11440/rssj.30.317 }}</ref> The degree of aquifer salinization depends on the specific [[topographic]] characteristics and the [[hydrologic]] controls in the sub-surface of the atoll. About half of Fongafale islet is reclaimed swamp that contains porous, highly permeable coral blocks that allow the tidal forcing of salt water.<ref name="GWD">{{Cite journal|vauthors=Nakada S, Umezawa Y, Taniguchi M, Yamano H |title= Groundwater dynamics of Fongafale Islet, Funafuti Atoll, Tuvalu |journal= Groundwater |volume= 50 |issue= 4 |date =Jul–Aug 2012 |pages=639–44 |doi= 10.1111/j.1745-6584.2011.00874.x |pmid=22035506|s2cid= 32336745 }}</ref> There was extensive swamp reclamation during World War II to create the air field that is now the [[Funafuti International Airport]]. As a consequence of the specific topographic characteristics of Fongafale, unlike other atoll islands of a similar size, Fongafale does not have a thick [[Lens (hydrology)|freshwater lens]].<ref name="GWD"/> The narrow fresh water and brackish water sheets in the sub-surface of Fongafale islet results in the [[taro]] swamps and the fresh groundwater resources of the islet being highly vulnerable to salinization resulting from the rising sea-level.<ref name="GWD"/>

In addition to the increased risk of salinized by the sea-level rise, the freshwater lens is at risk from over extraction due to the large population that now occupies Fongafale islet; the increased extraction can be exacerbated by a decrease of the rainfall recharge rate associated with the climate change.<ref name="EAS"/> Water pollution is also a chronic problem, with domestic wastewater identified as the primary pollution source.<ref name="AIW">{{cite journal| last = Fujita M., Suzuki J., Sato D., Kuwahara Y., Yokoki H., Kayanne, Y. |title= Anthropogenic impacts on water quality of the lagoonal coast of Fongafale Islet, Funafuti Atoll, Tuvalu|journal= Sustainability Science|volume= 8|issue= 3|pages= 381–390|year =2013 |url= https://link.springer.com/content/pdf/10.1007%2Fs11625-013-0204-x.pdf|doi= 10.1007/s11625-013-0204-x|s2cid= 127909606}}</ref>  Approximately 92% of households on Fongafale islet have access to septic tanks and pit toilets. However, these sanitary facilities are not built as per the design specifications or they are not suitable for the geophysical characteristics, which results in seepage into the fresh water lens and run off into coastal waters.<ref name="AIW"/>

On [[Funafuti]] and on the other islands, rainwater collected off the corrugated iron roofs of buildings is now the primary source of fresh water. On Funafuti a desalination unit that was donated by Japan in 2006 also provides fresh water.<ref name="JPDP">{{cite web|title = Japan Provides Desalination Plant to relieve Tuvalu's water problems |date =2 June 2006|url= http://www.fj.emb-japan.go.jp/pr_Japan_Provides_Desalination_Plant_to_relieve_Tuvalus_water_problems.html |publisher = Embassy of Japan in the Republic of the Fiji Islands |access-date=1 December 2011}}</ref> In response to the [[2011 Tuvalu drought|2011 drought]], Japan funded the purchase of a 100 m<sup>3</sup>/d desalination plant and two portable 10 m<sup>3</sup>/d plants as part of its Pacific Environment Community (PEC) program.<ref name="JNZ">{{cite web |title = Japan-New Zealand Aid Cooperation in response to severe water shortage in Tuvalu |date =4 November 2011|url= http://www.mofa.go.jp/announce/announce/2011/11/1104_01.html |publisher = Department of Foreign Affairs of Japan |access-date=1 December 2011}}</ref><ref name="J3">{{cite web |title = Japanese fund three desalination plants for Tuvalu |date = 17 October 2011 |url = http://www.desalination.biz/news/news_story.asp?id=6170&title=Japanese+fund+three+desalination+plants+for+Tuvalu |publisher = The International Desalination & Water Reuse Quarterly industry website |access-date = 1 December 2011 |archive-date = 7 May 2012 |archive-url = https://web.archive.org/web/20120507101412/http://www.desalination.biz/news/news_story.asp?id=6170&title=Japanese+fund+three+desalination+plants+for+Tuvalu |url-status = dead }}</ref> Aid programs from the European Union<ref name="10EDF"/><ref name="TWWSP1">{{cite web| url= http://ec.europa.eu/europeaid/documents/aap/2009/af_aap_2009_tuv.pdf |title= Tuvalu / Water, Waste and Sanitation Project (TWWSP): CRIS FED/2009/021-195, ANNEX | publisher=European Union|access-date=24 October 2011}}</ref> and Australia also provided water tanks as part of the longer-term solution for the storage of available fresh water.

===Aquifer salinization and the impact on Pulaka production===
Swamp taro (''[[Cyrtosperma merkusii]]''), known in Tuvalu as ''[[Pulaka]]'', is grown in large pits of composted soil below the water table,<ref name="GK">{{cite book|last=Koch|first=Gerd|title=The material culture of Tuvalu|publisher=Institute of Pacific Studies, [[University of the South Pacific]]|date=1983|page=46|url=https://books.google.com/books?id=w7aeiuIXVigC&pg=PA46|access-date=12 May 2010}}</ref> Pulaka has been the main source for [[carbohydrate]]s,<ref name="GK"/> it is similar to [[taro]], but "with bigger leaves and larger, coarser roots".<ref name="TARO">{{cite web |url= http://www.fao.org/WAIRdocs/x5425e/x5425e01.htm |title= Leaflet No. 1 – Revised 1992 – Taro |date= 1992 |publisher= [[Food and Agriculture Organization]] |access-date= 15 August 2012 |archive-date= 28 August 2009 |archive-url= https://web.archive.org/web/20090828014127/http://www.fao.org/Wairdocs/X5425E/x5425e01.htm |url-status= dead }}</ref>

In recent years the Tuvaluan community have raised concerns over increased salinity of the groundwater in pits that are used to cultivate pulaka.<ref name="root crop">{{cite news| url= http://www.rnzi.com/pages/news.php?op=read&id=42070 | publisher=[[Radio New Zealand]]| title= Tuvalu could lose root crop | date=17 September 2008| access-date = 10 May 2010}}</ref> Pits on all islands of Tuvalu (except [[Niulakita]]) were surveyed in 2006. [[Nukulaelae]] and [[Niutao]] each had one pit area in which salinity concentrations thought to be too high for successful swamp taro growth. However, on Fongafale in [[Funafuti]] all pits surveyed were either too saline or very marginal for swamp taro production, although a more salt tolerant species of [[taro]] (''Colocasia esculenta'') was being grown in Fongafale.<ref name="TTR">{{cite web| last = Webb| first = Dr Arthur| title = Tuvalu Technical Report: Assessment of Salinity of Groundwater in Swamp Taro (Cyrtosperma Chamissonis) "Pulaka" Pits in Tuvalu| publisher = Pacific Islands Applied Geoscience Commission, EU EDF8-SOPAC Project Report 75: Reducing Vulnerability of Pacific ACP States| date = March 2007| url = https://www.researchgate.net/publication/328175697| access-date = 2 January 2020}}</ref>

The extent of the salinization of the aquifer on Fongafale Islet is the result of both man-made changes to the [[topography]] that occurred when the air field was built in World War II by reclaiming swamp land and excavating coral rock from other parts of the islet. These topographic changes are exacerbated by the groundwater dynamics of the islet, as tidal forcing pushes salt water into the surficial aquifer during spring tides.<ref name="EAS"/>

The [[Lens (hydrology)|freshwater lens]] of each atoll is a fragile system. [[Tropical cyclone]]s and other storm events also result in wave wash over and extreme high water also occurs during spring tides. These events can result in salt water contamination of the fresh groundwater lens. Periods of low rainfall can also result in contraction of the freshwater lens as the coconut trees and other vegetation draw up the water at a greater than recharge than it can be recharged. The over extraction of ground water to supply human needs has a similar result as drought conditions.<ref name="GWD1">{{Cite journal|vauthors=Nakada S, Umezawa Y, Taniguchi M, Yamano H |title= Groundwater dynamics of Fongafale Islet, Funafuti Atoll, Tuvalu |journal= Groundwater |volume= 50 |issue= 4 |date =2012 |pages=639–44 |doi= 10.1111/j.1745-6584.2011.00874.x |pmid=22035506|s2cid= 32336745 }}</ref>