2007 Volume 68 Issue 1 Pages 29-40
Many U.S.military bases are located in the central and northern parts of Okinawa Island. A study on the river waters in such military training areas has been difficult to conduct until now. However through the Legacy Project with University of Hawaii, the authors had the opportunity to collect water samples from the central training area (CTA) in the island. The CTA is uniquely situated to gathering data on the chemical composition of unpolluted river waters, since the forest in the CTA has been designated to supplying timber and water. The purpose of the present study is to determine the chemical characteristics of river waters in the CTA.
Our results showed that the chemical composition of river water in the CTA was intermediate between those of the groundwaters in limestone areas and the river waters in silicate rock areas of Okinawa Island. This finding reflects the overall geology of the CTA and of Okinawa Island. The total concentration of chemical components supplied from the ocean as sea spray was 2.73 meq L-1, which was about 7 times larger than that of average river water throughout Japan, and accounted for over 50% of the total concentration in the rivers. The total amount of rocks chemically weathered in the CTA was almost the same as that in the northern training area (NTA) of the U.S. military. However, the amount of dissolved CaCO3 differed between the two areas due to the dissolution of limestone in the CTA. The fact that the amount of suspended sediment in the effluent was larger than the formed clay minerals in the CTA may cause serious environmental problems by eroding soil from the forest and polluting the river and ocean by the weathered soil such as red soils.
