Abstract
The effect of rainfall on the behavior of Fe, Mn, Cu, Zn, Pb, and Ti in mature soils developed on same-age volcanic bedrock in Hawaii was studied. Concentrations of the mentioned metals in total digested and weak acid-leached soil and bedrock samples were analyzed. Mass transport calculations yielded the quantity of metal enrichment or depletion in the soils relative to the bedrock. In addition, elemental mobility and the distribution between the labile and the residual fraction were examined. Based on mass transport calculations there is no significant effect of rainfall amount on the enrichment or depletion of any elements (except Cu) within soils receiving less than 570 mm/yr (4 sites). In the intermediate sites (4 sites, 930-1380 mm/yr) there is a variable effect of rainfall on all elements in the soil, but the extent of variation differs from one metal to the other. In the rainy site (2500 mm/yr) there is a large degree of enrichment or depletion of certain metals. Manganese and Zn are highly depleted and Pb is strongly enriched, whereas Fe and Cu do not show a significant mass change. Among all elements, Pb is the only one that has a continuous effect of rainfall throughout the transect. Lead is enriched in all the sites and this enrichment is well correlated with increasing rainfall. Iron is immobile in the soil, reflecting the relative stability of the Fe-rich phases and its high correlation with Ti. The mass change of Mn throughout the transect is remarkably correlated with Al (R2 = 0.87). The behavior of the trace metals Pb, Zn, and Cu in the Kohala soils is different because of the phases with which these metals are likely to be associated. Lead is probably adsorbed and coprecipated mostly with Fe oxides and hydrous oxides. Zinc is presumably associated with Mn and Al oxides and hydrous oxides and with organic matter, whereas Cu is most likely complexed by organic matter.
| Original language | English |
|---|---|
| Pages (from-to) | 3499-3511 |
| Number of pages | 13 |
| Journal | Geochimica et Cosmochimica Acta |
| Volume | 63 |
| Issue number | 21 |
| DOIs | |
| State | Published - Nov 1999 |
Bibliographical note
Funding Information:The authors thank J. D. Blum of Dartmouth College for his comments and in-depth discussions and to O. Yoffe of the Geological Survey of Israel for technical assistance. Two anonymous reviewers are thanked for helpful comments. The project was funded by a grant from the Israeli Science Foundation and by NASA’s Mission to Planet Earth program.