Spatial and temporal variability of soil saturated hydraulic conductivity in gradients of disturbance

Abstract

Elektronisch veröffentlicht auf dem Publikationsserver der Universität Potsdam: http://opus.kobv. de/ubp/volltexte/2008/1640/ urn:nbn:de:kobv:517-opus-16402 [http://nbn-resolving.de/urn:nbn:de:kobv:517-opus16402] SummaryAs land-cover conversion continues to expand into ever more remote areas in the humid tropics, montane rainforests are increasingly threatened. In addition to the loss of biodiversity, land-use change potentially deteriorates regional water cycles, which may have undesirable effects for local populations such as decreased water supply during dry seasons, enhanced flooding in the rainy season, or deterioration of drinking water quality.Montane rainforests in the south Ecuadorian Andes are not only subject to man-made disturbances but also to naturally occurring landslides. I was interested in the impact of this ecosystem dynamics on a key parameter of the hydrologic cycle, the soil saturated hydraulic conductivity (synonym: permeability; Ks from here on), because it is a sensitive indicator for soil disturbances. Depending on the rainfall regime, the potential disturbance-induced decrease of Ks may become relevant for regional watersheds.My general objective was to quantify the effects of the regional natural and human disturbances on the saturated hydraulic conductivity and to describe the resulting spatialtemporal patterns. The main hypotheses were: 1) disturbances cause an apparent displacement of the less permeable soil layer towards the surface, either due to a loss of the permeable surface soil after land-sliding, or as a consequence of the surface soil compaction under cattle pastures; 2) 'recovery' from disturbance, either because of landslide re-vegetation or because of secondary succession after pasture abandonment, involves an apparent displacement of the less permeable layer back towards the original depth an 3) disturbances cause a simplification of the Ks spatial structure, i.e. the spatially dependent random variation diminishes; the subsequent recovery entails the re-establishment of the original structure.In my first study, I developed a synthesis of recent geostatistical research regarding its applicability to soil hydraulic data, including exploratory data analysis and variogram estimation techniques; I subsequently evaluated the results in terms of spatial prediction uncertainty. Concerning the exploratory data analysis, my main results were: 1) Gaussian uniand bivariate distributions of the log-transformed data; 2) the existence of significant local trends; 3) no need for robust estimation; 4) no anisotropic variation. I found partly considerable differences in covariance parameters resulting from different variogram estimation techniques, which, in the framework of spatial prediction, were mainly reflected in the spatial connectivity of the Ks-field. Ignoring the trend component and an arbitrary use of robust estimators, however, would have the most severe consequences in this respect.Regarding variogram modeling, I encouraged restricted maximum likelihood estimation becau...

Effects of Land Use and Management on SoilHydraulic Properties

“…The authors found that natural forest conversion to pasture, associated with higher degree of soil disturbance, can decrease soil surface permeability by two orders of magnitude [47]. A study by Zhou et al [4] showed that surface soil hydraulic properties were impacted by the differences in land use and soil types (Table 1), such as generally higher bulk densities and lower hydraulic conductivities for pasture and cropland compared to woodland.…”

“…Zimmermann and Elsenbeer [47] investigated several land cover types and landslides as soil forming processes and their influence on soil structural properties including soil hydraulic conductivity and soil bulk density. The authors found that natural forest conversion to pasture, associated with higher degree of soil disturbance, can decrease soil surface permeability by two orders of magnitude [47].…”

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“…Indeed, many field studies have shown that, for the same soil type, forest have higher near-surface porosity and saturated conductivity (decreasing with depth), compared to pasture or degraded forest, where conductivity profiles are more uniform (Parker and Chartres, 1983;Bormann and Klaassen, 2008;Zimmermann and Elsenbeer, 2008), and that reforestation takes at least 10 years to restore conductivity profiles (Zimmermann et al, 2006;Zimmermann and Elsenbeer, 2008).…”

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