Island. This has been reported to be mainly a result of salinity 
of the ground water (Fosberg, 1949)*, One seep at the edge of the 
ft/LA-A ,V-«- 
present lagoon contained 75•2 ppm'of salts almost double that of -Hi ■ 
sea water. In the case of^some* of the drier islands ,-Tbhe - i nferior 
of the island results,-in^an increase in the salinity due to the 
closed nature of the lagoon and the evaportaion of standing sea, „ . « 
tu> 'W&Mb ^S.****~XH - w - 
water seepage from shallow surfaces..- Crne possible factor of importance 
in the salinity gradients 
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dry islands would be the increase of 
salinity in the lagoon which goes hand in hand with the closing off 
of channels. One interesting case is that of Sydney Island a small 
atoll which has boon an enclosed lagoon cut off within historic time 
much like the one at Underbury. A sample of water taken from the 
lagoon water in the vicinity of islets along the NW shore evidenced 
a slainity of 166.0 pp$u nearly five times that of seawater. This 
increase in salinity may control to a great _extent the species found 
on the dry islands working "from the lAgoon to the outer beach. These 
is a suggestion that the dying Pisonia on Gardner and Sydney may be 
due to a combination of^the lack of rainfall and an increase in 
the salinity of normally tolerable levels of salinity associated 
with the lense of freshwater. One of the village wells 2.2 m. deep 
t '.'V© "Ta^jp 
on Sydney contained brackish water in .October 1964# If rainfall 
is negligible and evaporation continues over a long period the fresh 
water lens may be exhausted in some areas particularly in narrow sides 
■he*** < 
of islets and enclosed islands. Saline waters would-be' replacing these 
at levels where the roots of shrubs and trees penetrate. An ■unusually 
high salinity in waters underlying the islets would raise the salinity 
of the groundwater and may contribute to the irregular pattern of vegetation 
associations or distribution of species on dry atolls. The Pisonia groves 
of both Gardner and Sydney Islands are dying or in a state of extreme 
drought. This is a species usually identified with the more mesic sites 
of a coral atoll. It is suggested that the increased salinity of lagoon 
waters due to the enclosure of a once open lagoon may be partly responsible 
due to the raising of the salinity of the groundwater. This with the 
prevailing drought may be responsible for the apparent dying back of 
potential Pisonia groves on these islands. 
