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Over historic time Hawai‘i's dryland forests have been largely replaced by grasslands for grazing livestock. On-going efforts have been undertaken to restore dryland forests to bring back native species and reduce erosion. The reestablishment of native ecosystems on land severely degraded by long-term alternative use requires reversal of the impacts of erosion, organic-matter loss, and soil structural damage on soil hydraulic properties. This issue is perhaps especially critical in dryland forests where the soil must facilitate native plants' optimal use of limited water. These reforestation efforts depend on restoring soil ecological function, including soil hydraulic properties. We hypothesized that reforestation...
Creosotebush (Larrea tridentata) and tarbush (Flourensia cernua) are two of the major shrub invaders of grassland in many desert areas of southern New Mexico. Soils and root systems associated with these two shrubs were studied at three sites on an alluvial fan piedmont. The soils have formed in alluvium derived from monzonite, rhyolite, and andesite, in deposits ranging in age from late Holocene to middle Pleistocene. Soil age, carbonate morphology, particle size, and landscape position were found to be major factors associated with root variability. The stage I carbonate that occurs in youngest soils has relatively little influence on root distribution because the carbonate consists only of thin coatings on sand...
Summary Heat from wildfires can produce a two-layer system composed of extremely dry soil covered by a layer of ash, which when subjected to rainfall, may produce extreme floods. To understand the soil physics controlling runoff for these initial conditions, we used a small, portable disk infiltrometer to measure two hydraulic properties: (1) near-saturated hydraulic conductivity, Kf and (2) sorptivity, S(θi), as a function of initial soil moisture content, θi, ranging from extremely dry conditions (θi < 0.02 cm3 cm−3) to near saturation. In the field and in the laboratory replicate measurements were made of ash, reference soils, soils unaffected by fire, and fire-affected soils. Each has a different degrees of...
Summary Relations between seepage flux and hydraulic properties are difficult to quantify in fluvial settings because of the difficulty in measuring these variables in situ. Tests conducted in a 1.5-m diameter by 1.5-m tall sediment-filled tank indicate that hydraulic gradient increased and hydraulic conductivity (K) decreased following the onset of downward seepage but both parameters were little changed following the onset of upward seepage. Reductions in K during downward seepage were more pronounced when surface-water current was sufficient to mobilize sediment on the bed. Averaged ratios of K determined during upward seepage to K determined during downward seepage (Kup/Kdown) through a sand-and-gravel bed increased...
Seepage rate and direction measured with a seepage metre modified for use in flowing water were greatly variable along a 300-m reach of a shallow, gravel-bed river and depended primarily on the local-scale bed topography. The median value of seepage measured at 24 locations was 24 cm/day, but seepage measured at specific sites ranged from −340 to +237 cm/day. Seepage also varied substantially over periods of hours to days and occasionally reversed direction in response to evolution of the sediment bed. Vertical hydraulic conductivity was related to seepage direction and was larger during upward seepage than during downward seepage; with differences ranging from 4 to 40% in areas of active sediment transport to more...
Electromagnetic induction (EMI) instruments provide rapid, noninvasive, and spatially dense data for characterization of soil and groundwater properties. Data from multi-frequency EMI tools can be inverted to provide quantitative electrical conductivity estimates as a function of depth. In this study, multi-frequency EMI data collected across an abandoned uranium mill site near Naturita, Colorado, USA, are inverted to produce vertical distribution of electrical conductivity (EC) across the site. The relation between measured apparent electrical conductivity (ECa) and hydraulic conductivity (K) is weak (correlation coefficient of 0.20), whereas the correlation between the depth dependent EC obtained from the inversions,...
Low-permeability sediments situated at or near the sediment-water interface can influence seepage in nearshore margins, particularly where wave energy or currents are minimal. Seepage meters were used to quantify flow across the sediment-water interface at two lakes where flow was from surface water to groundwater. Disturbance of the sediment bed substantially increased seepage through the sandy sediments of both lakes. Seepage increased by factors of 2.6 to 7.7 following bed disturbance at seven of eight measurement locations at Mirror Lake, New Hampshire, where the sediment representing the greatest restriction to flow was situated at the sediment-water interface. Although the veneer of low-permeability sediment...