Wednesday, November 15, 2006 - 8:15 AM

Spatial and Temporal Variability of Saturated Hydraulic Conductivity in Gradients of Disturbance.

Beate Zimmermann and Helmut Elsenbeer. Institute of Geoecology, Univ of Potsdam, Karl-Liebknecht St 24-25, Golm, Germany

Land-use change in the humid tropics alters soil hydraulic parameters which may change near- surface hydrologic flow paths. In southern Ecuador, the mountain rain forest ecosystem is subject to disturbances, such as shallow landslides and forest-to-pasture conversion. In both cases, rapid vegetation succession upon pasture abandonment and geomorphic stability results in a rapid recovery of land cover.

Soil saturated hydraulic conductivity (Ks) is a sensitive indicator to assess those changes regarding soil hydrology. We measured Ks in situ at soil depths of 12.5, 20, and 50 cm (n=150/depth) under landslides of different ages (0 to 30 years), under actively grazed pasture, fallows following pasture abandonment (2 to 25 years of age), and under natural forest. The results can be related to prevailing rainfall intensities to diagnose the possible occurrence of an impeding layer at a shallow soil depth. Additionally, we analyzed the data for spatial autocorrelations using geostatistical tools.

Results from the human induced disturbance regime show an enormous decrease of Ks after forest conversion to pasture at shallow soil depths, and a slow regeneration after pasture abandonment. However, the reduced permeability hardly causes an alteration of the prevailing vertical flow paths, since local rainfall intensities are predominantly low. In contrast, Ks does not differ among landslides and in comparison to the natural forest which suggests a marginal effect of landslide activity in this region on soil hydrology.

Geostatistical analyses reveal spatial autocorrelations of Ks including anisotropy for the old fallow and natural forest; variograms for pasture, a young fallow and a landslide show pure nugget effects. Hence, any spatial structure of Ks is likely to disappear under disturbed land covers and may be restored during regeneration.