Masters Theses

Date of Award

5-1997

Degree Type

Thesis

Degree Name

Master of Science

Major

Geography

Major Professor

Carol Harden

Committee Members

Sally Horn, Ted Schmudde

Abstract

This research contributes to a growing understanding of tropical soil hydrology by calculating and describing the saturated hydraulic conductivity (Ksat) of major alluvial and residual soils located in the La Selva Biological Reserve, Costa Rica, and the Jatun Sacha Biological Reserve, Ecuador. The main goal of this study was to determine the degree to which Ksat varies between soil types within and between each of these humid tropical environments. Qay percentage and bulk density were calculated or obtained fix)m other sources for evaluation as potential influences on Ksat variation. The ring infiltrometer and auger hole methods for surface and subsurface Ksat determination were used due to their ease of use and proven reliability. Approximately five surface and subsurface Ksat samples were taken on each of the major soil types found at both reserves. Ksat varies extensively over the two humid tropical areas examined in this study. The mean Ksat values representing each major soil type on alluvial and residual soils were compared using one-way analysis of variance (ANOVA) and Mann-Whitney U tests. Results indicated that surface and subsurface Ksat values differ significantly in all cases. Ksat values calculated for surface residual soils were significantly higher than alluvial Ksat values at La Selva. La Selva’s surface residual soils yielded the highest Ksat values in this study (119.7 cm/hr), whereas Jatun Sacha’s surface residuals had the lowest Ksat values (12.1 cm/hr). Surface alluvial soils at Jatun Sacha and La Selva are very similar hydrologically (Ksat values of 27.9 cm/hr and 44.7 cm/hr respectively). R2 results indicated that a very strong positive relationship exists between the independent variables and Ksat (R2 =.89) at La Selva. In contrast, no significant relationship exists between subsurface Ksat at La Selva and the calculated values for clay percentage and bulk density (R2=.23). When compared to rainfall intensity data for each reserve, surface Ksat values exceed those of the most intense storms in almost all cases. On the other hand, subsurface Ksat is not high enough to accommodate some higher intensity storms documented over the past few years. Because most of the land within the two study areas is under a dense forest canopy, it is not exposed to the total rainfall recorded at local weather stations. Thus, Hortonian overland flow is not a realistic possibility at either reserve under natural conditions.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS