The impact of climate on the biogeochemical functioning of volcanic soils

• Published in: Chemical geology 2003-12, Vol.202 (3), p.195-223
• Main Authors: Chadwick, Oliver A, Gavenda, Robert T, Kelly, Eugene F, Ziegler, Karen, Olson, Carolyn G, Elliott, W.Crawford, Hendricks, David M
• Format: Article
• Language: English
• Subjects: Allophane; Andisols; Halloysite; Hawaii; Thresholds
• ISSN: 0009-2541; 1872-6836
• DOI: 10.1016/j.chemgeo.2002.09.001

Rainfall and the amount of water available to leach ions from soil are among the most important features determining mineral weathering, secondary mineral synthesis and soil chemical properties. Along an arid to humid climosequence on Kohala Mountain, Hawaii, we sampled 16 soil profiles and found that weathering and soil properties change in a nonlinear fashion with increased rainfall. The lavas are influenced by a strong rain shadow with mean annual precipitation (MAP) averaging 160 mm near the coast and rising to >3000 mm near the summit. A temperature decline from 24 to 15 °C with increasing elevation is matched by lower potential evapotranspiration (ET). A water balance model (monthly precipitation minus monthly ET) defines three broad climate zones along the sampling transect: an arid zone with moisture deficit in every month, an intermediate zone with moisture deficit during low-rainfall summer months and moisture surplus during high-rainfall winter months, and a humid zone with moisture surplus during every month. The annualized water balance can be ratioed with the integrated porosity of the top meter of soil to provide a leaching index. The index reaches 1 (total filling of the pore space on an annual basis) at about 1400 mm MAP. Index values >1 imply intense leaching conditions because of pore water replacement. In these 170 ka soils, leaching losses of soluble base cations and Si are nearly complete at index values >1, whereas only 60% of Al has been lost. At index values