Geochemistry of ohia and soil lichen, Puhimau thermal area, Hawaii

Abstract

Mercury in leaves of the ohia tree ( Metrosideros collina (Gaud.) Rock) downwind from the Puhimau thermal area (Hawaii Volcanoes National Park) exhibits a standard exponential decay-type curve, suggesting that the thermal area is acting as a point source of mercury. The impact of this probable source is detectable for about 3 km downwind. Manganese in the leaves also shows a strong decrease in concentration outward from the thermal area; and weaker, but nevertheless statistically significant, decreases were observed for barium, nickel, copper, zinc and sulfur. These last elements may be accumulating as sulfate from the thermal emissions. Accumulations of all these elements strongly suggest that the steaming ground in the thermal area is a natural source of atmospheric contamination. Selenium in the leaves is distinctly low in trees growing at the edge of the thermal area. Samples of soil lichen ( Cladonia skottsbergii Magn.) from within and without the thermal area confirm the changes seen in mercury and selenium.