PARENT SESSION
Oral Session #76: Ecosystem Ecology: Larger scale processes, geomorphology, soils.
Presiding: W. Straw
Thursday, August 8. 9:00 AM to 11:30 AM. Gila Meeting Room, TCC.

Effects of soil development on hydrological properties and flow paths in the Hawaiian Islands.

Lohse, Kathleen^*,1, ¹ University of California, Berkeley, Berkeley, CA

ABSTRACT- A chronosequence of soils in the Hawaiian archipeligo provides a unique opportunity to examine how water movement through the soil profile changes with soil development in a humid tropical environment. Detailed hydrological studies were conducted at the extreme end of a chronosequence of soils in the Hawaiian Islands as a part of a larger study evaluating hydrologic losses of nitrogen (N) under elevated N supply. I determined in-situ soil-water retention, soil hydraulic conductivity, and flow path characteristics on a 300 year old Andisol (Thurston) and 4.1 million year old Oxisol (Kokee) both supporting native montane tropical forest. I found that surface and subsurface soils drained rapidly at Thurston but observed significant differences in surface and subsurface soil-water retention and conductivity at Kokee. A simulated rainfall experiment with deuterium isotope tracer showed that highly conductive surface soils over an impeding subsurface layer at Kokee resulted in a perched water table and lateral flow along the permeability contrast. Across the soil age gradient, soil anisotropy and the probability of lateral flow increased as soil saturated hydraulic conductivity in subsurface soils declined. The findings from this study demonstrate that soil development can dramatically alter the rate and direction of water flow which have important implications for interpreting mass balance studies and may provide insights into the evolution of storm runoff mechanisms.

KEY WORDS: soil development, Hawaii, hydrological properties