Featured Research

from universities, journals, and other organizations

Small islands in the Pacific: Duel between freshwater and sea water

Date:
December 17, 2010
Source:
Institut de Recherche pour le Développement (IRD)
Summary:
It is said that the first refugees of climate change will come from the Pacific. In the midst of this ocean’s tropical regions are scattered 50,000 small islands, 8,000 of them inhabited. They are particularly vulnerable to the impacts of global warming. These effects include rising sea-water levels, drought and diminishing stocks of freshwater.

It is said that the first refugees of climate change will come from the Pacific. In the midst of this ocean's tropical regions are scattered 50,000 small islands, 8,000 of them inhabited. They are particularly vulnerable to the impacts of global warming. These effects include rising sea-water levels, drought and diminishing stocks of freshwater. Such water is essential for the life of the fauna and flora and for the human populations' food supplies. On the coral reef islands, freshwater occurs as underground reservoirs, as lenses in balance with the underlying sea water.

IRD scientists and their research partners have investigated the processes behind such lenses, the way they change and develops, their capacity and vulnerability. The team's geological, hydrogeological and geophysical surveys showed that the lens structure and internal processes depend strongly on the island's vegetation cover and topography. This work opens up ways towards assessing what will happen to this resource as a consequence of expected changes in the climate and sea level.

The balance between freshwater and salt water in coastal and island aquifers is unstable and the processes involved are difficult to characterize. With the objective of understanding the processes behind this lens formation on a coral island, IRD and its partners studied the structure and such parameters as the geometry of the reservoir and flow rates.

Terrain untouched by human activity

The experimental sites, islands off Noumea in the South-West lagoon of New Caledonia, are remote from any human activity. The scientists used the geophysical imaging method, electrical resistivity tomography, to study the spatial distribution of the groundwater salinity, in particular on M'Ba island, 1,500 km east of Australia. With this imaging technique the groundwater conductivity can be measured along a vertical section and hence the salinity deduced. The data collected enabled the team to characterize the shape and structure of the underground freshwater reservoir, also to assess the rain-induced groundwater recharge, using a hydrological model based on IPCC climate data including information on cyclones.

Salt concentration rises in the island's centre

Contrary to the results anticipated, this salinity proved to be intensively concentrated in the middle of the island rather than on its edges, which are the usual zones of sea water-freshwater interaction. Complementary analyses derived from a hydrogeological model have revealed the importance of vegetation cover and the island's topography in the spatial distribution of the salinity in the groundwater reservoir, located 3 or 4 m below the ground surface, and the mechanisms of this island aquifer.

Plant transpiration causes the saline water to evaporate from the roots. This process concentrates salt in the freshwater lens at the island's centre, as the plant cover is denser and longer established there. For example, a coconut palm draws up 300 L of water per day. Conversely, in the recent coastal sand dunes, the vegetation is much more sparse and the groundwater salinity remains less concentrated. Moreover, the freshwater lens recharge induced by rain is minimal in the island's centre, again owing to the density of the vegetation and the greater degree of soil development. However, it is maximal in the sand dunes near the sea. This explains an accentuation of the phenomenon, with dilution of the underground water on the island margins and concentration of salt in the central areas.

The island's morphology and internal structure also have a strong influence on the variable groundwater recharge rate along the island's transverse axis. This island was constructed by the piling-up of layers of material from sand-dominated reef formations, lying about 30 m above a complex substratum. It is geologically representative of many of the small islands or atolls in Noumea lagoon and, more generally, small coral reef islands of the Indo-Pacific region.

In conclusion, cross-validation of the geoelectrical models and the groundwater models is useful for 2D and 3D mapping of the salinity distribution of the island's groundwater aquifer. This analysis can help assess the water resources of the Pacific coral islands in the context of the search for indicators of vulnerability in the face of global climate change and bring significant evidence concerning future changes and developments in coral islands, which contributes to the survival and development of numerous terrestrial and marine species and of their inhabitants.

These investigations were conducted jointly by the teams of the research units LOCEAN (UMR IRD/Université Paris VI/CNRS/MNHN), CEREGE (UMR IRD/CNRS/Collège de France/Universités Aix-Marseille 1 and 3) and Université de la Réunion and Université d'Avignon, as part of the INTERFACE project subsidized by the French Agence Nationale de la Recherche (ANR) (programme Vulnérabilité, Milieux, Climats).


Story Source:

The above story is based on materials provided by Institut de Recherche pour le Développement (IRD). Note: Materials may be edited for content and length.


Journal Reference:

  1. Jean-Christophe Comte, Olivier Banton, Jean-Lambert Join, Guy Cabioch. Evaluation of effective groundwater recharge of freshwater lens in small islands by the combined modeling of geoelectrical data and water heads. Water Resources Research, 2010; 46 (6): W06601 DOI: 10.1029/2009WR008058

Cite This Page:

Institut de Recherche pour le Développement (IRD). "Small islands in the Pacific: Duel between freshwater and sea water." ScienceDaily. ScienceDaily, 17 December 2010. <www.sciencedaily.com/releases/2010/12/101215102434.htm>.
Institut de Recherche pour le Développement (IRD). (2010, December 17). Small islands in the Pacific: Duel between freshwater and sea water. ScienceDaily. Retrieved July 26, 2014 from www.sciencedaily.com/releases/2010/12/101215102434.htm
Institut de Recherche pour le Développement (IRD). "Small islands in the Pacific: Duel between freshwater and sea water." ScienceDaily. www.sciencedaily.com/releases/2010/12/101215102434.htm (accessed July 26, 2014).

Share This




More Earth & Climate News

Saturday, July 26, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Virginia Governor Tours Tornado Aftermath

Virginia Governor Tours Tornado Aftermath

AP (July 25, 2014) — Virginia Gov. Terry McAuliffe toured the Cherrystone Family Camping and RV Resort on the Chesapeake Bay today, a day after it was hit by a tornado. The storm claimed two lives and injured dozens of others. (July 25) Video provided by AP
Powered by NewsLook.com
Europe's Highest Train Turns 80 in French Pyrenees

Europe's Highest Train Turns 80 in French Pyrenees

AFP (July 25, 2014) — Europe's highest train, the little train of Artouste in the French Pyrenees, celebrates its 80th birthday. Duration: 01:05 Video provided by AFP
Powered by NewsLook.com
Goma Cheese Brings Whiff of New Hope to DRC

Goma Cheese Brings Whiff of New Hope to DRC

Reuters - Business Video Online (July 24, 2014) — The eastern region of the Democratic Republic of Congo, mainly known for conflict and instability, is an unlikely place for the production of fine cheese. But a farm in the village of Masisi, in North Kivu is slowly transforming perceptions of the area. Known simply as Goma cheese, the Congolese version of Dutch gouda has gained popularity through out the region. Ciara Sutton reports. Video provided by Reuters
Powered by NewsLook.com
Bill Gates: Health, Agriculture Key to Africa's Development

Bill Gates: Health, Agriculture Key to Africa's Development

AFP (July 24, 2014) — Health and agriculture development are key if African countries are to overcome poverty and grow, US software billionaire Bill Gates said Thursday, as he received an honourary degree in Ethiopia. Duration: 00:36 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins