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1.
Fallout radionuclides, including lead‐210 excess (210Pbex), have been broadly and successfully used to quantify net hillslope sediment transport in agricultural, pastoral and forested landscapes but have only recently been applied in burned terrain. Quantifying post‐fire erosion is important because fires can amplify hillslope erosion, impacting terrestrial and aquatic habitat and water quality. However, we lack a basic understanding of the fate of 210Pbex in fires. To address this knowledge gap, we collected over 400 soil samples from unburned, moderately and severely burned forested sites in central Idaho. We measured soil 210Pbex content at stable reference and eroding sites and in mineral and organic soil components. At all sites, organic matter had the highest concentration of 210Pbex, representing 30% to 73% of the total activity. At the severely and moderately burned sites, 210Pbex reference inventories were lower by 58% and 41%, with about 40% less organic mass, relative to the unburned site. These results indicate that most 210Pbex in our semi‐arid, forested sites was bound to organic matter, and that a substantial portion of this lead was lost due to forest fires. These losses likely occurred through volatilization and wind transport of smoke and ash. In the moderately burned site, 210Pbex losses were more spatially variable, potentially due to spatially uneven fire intensity and effects. Despite equal percent losses of 210Pbex, lower inventories at the burned sites produced lower calculated net erosion rates relative to the unburned site. Thus, given methodological uncertainties, 210Pbex losses due to fire, and the subsequent sensitivity of calculated net erosion rates to these lower 210Pbex inventories, we suggest this method should not be used in burned terrain to calculate absolute net erosion and deposition rates. However, within a given burned site, 210Pbex inventories still provide useful information describing relative soil losses and storage across the landscape. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

2.
Infrequent, high‐magnitude events cause a disproportionate amount of sediment transport on steep hillslopes, but few quantitative data are available that capture these processes. Here we study the influence of wildfire and hillslope aspect on soil erosion in Fourmile Canyon, Colorado. This region experienced the Fourmile Fire of 2010, strong summer convective storms in 2011 and 2012, and extreme flooding in September 2013. We sampled soils shortly after these events and use fallout radionuclides to trace erosion on polar‐ and equatorial‐facing burned slopes and on a polar‐facing unburned slope. Because these radionuclides are concentrated in the upper decimeter of soil, soil inventories are sensitive to erosion by surface runoff. The polar‐facing burned slope had significantly lower cesium‐137 (137Cs) and lead‐210 (210Pb) inventories (p < 0.05) than either the polar‐facing unburned slope or equatorial‐facing burned slope. Local slope magnitude does not appear to control the erosional response to wildfire, as relatively gently sloping (~20%) polar‐facing positions were severely eroded in the most intensively burned area. Field evidence and soil profile analyses indicate up to 4 cm of local soil erosion on the polar‐facing burned slope, but radionuclide mass balance indicates that much of this was trapped nearby. Using a 137Cs‐based erosion model, we find that the burned polar‐facing slope had a net mean sediment loss of 2 mm (~1 kg m?2) over a one to three year period, which is one to two orders of magnitude higher than longer‐term erosion rates reported for this region. In this part of the Colorado Front Range, strong hillslope asymmetry controls soil moisture and vegetation; polar‐facing slopes support significantly denser pine and fir stands, which fuels more intense wildfires. We conclude that polar‐facing slopes experience the most severe surface erosion following wildfires in this region, indicating that landscape‐scale aridity can control the geomorphic response of hillslopes to wildfires. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

3.
Post‐fire runoff and erosion from wildlands has been well researched, but few studies have researched the degree of control exerted by fire on rangeland hydrology and erosion processes. Furthermore, the spatial continuity and temporal persistence of wildfire impacts on rangeland hydrology and erosion are not well understood. Small‐plot rainfall and concentrated flow simulations were applied to unburned and severely burned hillslopes to determine the spatial continuity and persistence of fire‐induced impacts on runoff and erosion by interrill and rill processes on steep sagebrush‐dominated sites. Runoff and erosion were measured immediately following and each of 3 years post‐wildfire. Spatial and temporal variability in post‐fire hydrologic and erosional responses were compared with runoff and erosion measured under unburned conditions. Results from interrill simulations indicate fire‐induced impacts were predominantly on coppice microsites and that fire influenced interrill sediment yield more than runoff. Interrill runoff was nearly unchanged by burning, but 3‐year cumulative interrill sediment yield on burned hillslopes (50 g m?2) was twice that of unburned hillslopes (25 g m?2). The greatest impact of fire was on the dynamics of runoff once overland flow began. Reduced ground cover on burned hillslopes allowed overland flow to concentrate into rills. The 3‐year cumulative runoff from concentrated flow simulations on burned hillslopes (298 l) was nearly 20 times that measured on unburned hillslopes (16 l). The 3‐year cumulative sediment yield from concentrated flow on burned and unburned hillslopes was 20 400 g m?2 and 6 g m?2 respectively. Fire effects on runoff generation and sediment were greatly reduced, but remained, 3 years post‐fire. The results indicate that the impacts of fire on runoff and erosion from severely burned steep sagebrush landscapes vary significantly by microsite and process, exhibiting seasonal fluctuation in degree, and that fire‐induced increases in runoff and erosion may require more than 3 years to return to background levels. Published in 2008 by John Wiley & Sons, Ltd.  相似文献   

4.
Nature can provide analogues for post‐mining landscapes in terms of landscape stability and also in terms of the rehabilitated structure ‘blending in’ with the surrounding undisturbed landscape. In soil‐mantled landscapes, hillslopes typically have a characteristic pro?le that has a convex upper hillslope pro?le with a concave pro?le lower down the slope. In this paper hillslope characteristic form is derived using the area–slope relationship from pre‐mining topography at two sites in Western Australia. Using this relationship, concave hillslope pro?les are constructed and compared to linear hillslopes in terms of sediment loss using the SIBERIA erosion model. It is found that concave hillslopes can reduce sediment loss by up to ?ve times that of linear slopes. Concave slopes can therefore provide an alternative method for the construction of post‐mining landscapes. An understanding of landscape geomorphological properties and the use of erosion models can greatly assist in the design of post‐mining landscapes. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

5.
A one‐dimensional uncoupled model governed by this research is a physics‐based modelling of the rainfall‐runoff induced erosion process. The presented model is composed of three parts of a three‐dimensional (3D) hillslope geometry, a nonlinear storage (kinematic wave) model for hillslope hydrological response, and an unsteady physically based surface erosion model. The 3D hillslope geometry model allows describing of the hillslope morphology by defining their plan shape and profile curvature. By changing these two topographic parameters, nine basic hillslope types are derived. The modelling of hillslope hydrological response is based on a flow continuity equation as the relation of discharge and flow depth is passed on kinematic wave approximation. The erosion model is based on a mass conservation equation for unsteady flow. The model assumes that suspended sediment does not affect flow dynamics. The model also accounts for the effect of flow depth plus loose soil depth on soil detachment. The presented model was run for two different precipitations, slope content, and length, and results were plotted for sediment detachment/deposition rate. Based on the obtained results, in hillslopes with convex and straight profile curvatures, sediment detachment only occurred in the whole length of the hillslope. However, in concave ones, sediment detachment and deposition only occurred together in hillslope. The hillslopes with straight profiles and convergent plans have the highest rate of detachment. Also, results show that most detachment rates occur in convex profile curvatures, which are about 15 times more than in straight profiles. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

6.
Fallout radionuclides (FRNs) 137Cs and 210Pb are well established as tracers of surface and sub‐surface soil erosion contributing sediment to river systems. However, without additional information, it has not been possible to distinguish sub‐surface soil erosion sources. Here, we use the FRN 7Be (half‐life 53 days) in combination with 137Cs and excess 210Pb to trace the form of erosion contributing sediment in three large river catchments in eastern Australia; the Logan River (area 3700 km2), Bowen River (9400 km2) and Mitchell River (4700 km2). We show that the combination of 137Cs, excess 210Pb and 7Be can discriminate horizontally aligned sub‐surface erosion sources (rilled and scalded hillslopes and the floors of incised drainage lines and gully ‘badland’ areas) from vertical erosion sources (channel banks and gully walls). Specifically, sub‐surface sources of sediment eroded during high rainfall and high river flow events have been distinguished by the ability of rainfall‐derived 7Be to label horizontal soil surfaces, but not vertical. Our results indicate that in the two northern catchments, erosion of horizontal sub‐surface soil sources contributed almost as much fine river sediment as vertical channel banks, and several times the contribution of hillslope topsoils. This result improves on source discrimination provided previously and indicates that in some areas erosion of hillslope soils may contribute significantly to sediment yield, but not as topsoil loss. We find that in north‐eastern Australia, scalded areas on hillslopes and incising drainage lines may be sediment sources of comparable importance to vertical channel banks. Previous studies have used the combination of 137Cs, excess 210Pb and 7Be to estimate soils losses at the hillslope scale. Here, we show that with timely and judicious sampling of soil and sediment during and immediately after high flow events 7Be measurements can augment fallout 137Cs and 210Pb to provide important erosion source information over large catchments. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

7.
Decoupling the impacts of climate and tectonics on hillslope erosion rates is a challenging problem. Hillslope erosion rates are well known to respond to changes in hillslope boundary conditions (e.g. channel incision rates) through their dependence on soil thickness, and precipitation is an important control on soil formation. Surprisingly though, compilations of hillslope denudation rates suggest little precipitation sensitivity. To isolate the effects of precipitation and boundary condition, we measured rates of soil production from bedrock and described soils on hillslopes along a semi‐arid to hyperarid precipitation gradient in northern Chile. In each climate zone, hillslopes with contrasting boundary conditions (actively incising channels versus non‐eroding landforms) were studied. Channel incision rates, which ultimately drive hillslope erosion, varied with precipitation rather than tectonic setting throughout the study area. These precipitation‐dependent incision rates are mirrored on the hillslopes, where erosion shifts from relatively fast and biologically‐driven to extremely slow and salt‐driven as precipitation decreases. Contrary to studies in humid regions, bedrock erosion rates increase with precipitation following a power law, from ～1 m Ma?1 in the hyperarid region to ～40 m Ma?1 in the semi‐arid region. The effect of boundary condition on soil thickness was observed in all climate zones (thicker soils on hillslopes with stable boundaries compared to hillslopes bounded by active channels), but the difference in bedrock erosion rates between the hillslopes within a climate region (slower erosion rates on hillslopes with stable boundaries) decreased as precipitation decreased. The biotic‐abiotic threshold also marks the precipitation rate below which bedrock erosion rates are no longer a function of soil thickness. Our work shows that hillslope processes become sensitive to precipitation as life disappears and the ability of the landscape to respond to tectonics decreases. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

8.
Most hillslope studies examining the interplay between climate and earth surface processes tend to be biased towards eroding parts of landscapes. This limitation makes it difficult to assess how entire upland landscapes, which are mosaics of eroding and depositional areas, evolve physio‐chemically as a function of climate. Here we combine new soil geochemical data and published 10Be‐derived soil production rates to estimate variations in chemical weathering across two eroding‐to‐depositional hillslopes spanning a climate gradient in southeastern Australia. At the warmer and wetter Nunnock River (NR) site, rates of total soil (–3 to –14 g m‐2 yr‐1; negative sign indicates mass loss) and saprolite (–18 to –32 g m‐2 yr‐1) chemical weathering are uniform across the hillslope transect. Alternatively, the drier hillslope at Frog's Hollow (FH) is characterized by contrasting weathering patterns in eroding soils (–30 to –53 g m‐2 yr‐1) vs. depositional soils (+91 g m‐2 yr‐1; positive sign indicates mass addition). This difference partly reflects mineral grain size sorting as a result of upslope bioturbation coupled with water‐driven soil erosion, as well as greater vegetative productivity in moister depositional soils. Both of these processes are magnified in the drier climate. The data reveal the importance of linking the erosion–deposition continuum in hillslope weathering studies in order to fully capture the coupled roles of biota and erosion in driving the physical and chemical evolution of hillslopes. Our findings also highlight the potential limitations of applying current weathering models to landscapes where particle‐sorting erosion processes are active. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

9.
Depending on the severity of the fire, forest fires may modify infiltration and soil erosion processes. Rainfall simulations were used to determine the hydrological effects of fire on Andisols in a pine forest burned by a wildfire in 2007. Six burned zones with different fire severities were compared with unburned zones. Infiltration, runoff and soil loss were analysed on slopes of 10% and 30%. Forest floor and soil properties were evaluated. Unburned zones exhibited relatively low infiltration (23 and 16 mm h?1 on 10% and 30% slope angles, respectively) and high average runoff/rainfall ratios (43% and 50% on 10% and 30% slope angles, respectively), which were associated with the extreme water repellency of the forest floor. Nonetheless, this layer seems to provide protection against raindrop impact and soil losses were found to be low (8 and 16 g m?2 h?1 for 10% and 30% slope angles, respectively). Soil cover, soil structure and water repellency were the main properties affected by the fire. The fire reduced forest floor and soil repellency, allowing rapid infiltration. Moreover, a significant decrease was noted in soil aggregate stabilities in the burned zones, which limited the infiltration rates. Consequently, no significant differences in infiltration and runoff were found between the burned and the unburned zones. The decrease in post‐fire soil cover and soil stability resulted in order‐of‐magnitude increases in erosion. Sediment rates were 15 and 31 g m?2 h?1 on the 10% and 30% slope angles, respectively, in zones affected by light fire severity. In the moderate fire severity zones, these values reached 65 and 260 g m?2 h?1 for the 10% and 30% slope angles, respectively. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

10.
The High Park Fire burned ~35 300 ha of the Colorado Front Range during June and July 2012. In the areas of most severe burn, all trees were killed and the litter and duff layers of soil were completely removed. Post‐fire erosion caused channel heads to develop well upslope from pre‐fire locations. The locations of 50 channel heads in two burned catchments were documented and the range of drainage areas contributing to these channel heads to drainage areas of unburned channel heads in the region measured previously were compared. Mean drainage area above channel heads in the burned zone decreased by more than two‐orders of magnitude relative to unburned sites. Drainage area above channel heads between the two burned catchments does not differ significantly with respect to slope, likely as a result of differences in surface roughness between the two sites following the fire. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

11.
Large wildfires can have profound and lasting impacts not only from direct consumption of vegetation but also longer-term effects such as persistent soil erosion. The 2002 Hayman Fire burned in one of the watersheds supplying water to the Denver metropolitan area; thus there was concern regarding hillslope erosion and sedimentation in the reservoirs. The efficacy of various treatments for reducing erosion was tested, including hand scarification on contour, agricultural straw mulch, wood mulch, burned controls and unburned reference plots. Simulated rill erosion experiments were used both immediately after the fire and again 10 years post fire. To better understand untreated recovery, the same experiments were applied to control plots in post-fire years 1, 2, 3 and 4, and in unburned reference plots in years 4 and 10. Results indicate that control and scarified plots produced significantly greater sediment flux rates – 1.9 and 2.8 g s−1 respectively – than the straw and wood mulch treatments – 0.9 and 1.1 g s−1 – immediately after the fire. Mulch treatments reduced runoff rate, runoff velocity, and sediment concentration and flux rate. The straw mulch cover was no longer present, whereas the wood mulch was still there in year 10. Vegetation regrowth was slow and mulch treatments provided effective cover to reduce sediment right after the fire. In post-fire year 10, there were no significant differences in sediment flux rates across treatments; it is notable, however, that the wood mulch treatment (0.09 g s−1) most closely approached the unburned condition (0.07 g s−1). The burned control plots had high sediment flux rates until post-fire year 3, when flux rates significantly decreased and were statistically no longer higher than the unburned levels from year 4 and 10. These results will inform managers of the longer-term post-fire sediment delivery rates and of the ability of post-fire emergency hillslope treatments to mitigate erosion rates. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

12.
It has generally been assumed that diffusive sediment transport on soil‐mantled hillslopes is linearly dependent on hillslope gradient. Fieldwork was done near Santa Barbara, California, to develop a sediment transport equation for bioturbation by the pocket gopher (Thomomys bottae) and to determine whether it supports linear diffusion. The route taken by the sediment is divided into two parts, a subsurface path followed by a surface path. The first is the transport of soil through the burrow to the burrow opening. The second is the discharge of sediment from the burrow opening onto the hillslope surface. The total volumetric sediment flux, as a function of hillslope gradient, is found to be: qs (cm3 cm−1 a−1) = 176(dz/dx)3 − 189(dz/dx)2 + 68(dz/dx) + 34(dz/dx)0·4. This result does not support the use of linear diffusion for hillslopes where gopher bioturbation is the dominant mode of sediment transport. A one‐dimensional hillslope evolution program was used to evolve hillslope profiles according to non‐linear and linear diffusion and to compare them to a typical hillslope. The non‐linear case more closely resembles the actual profile with a convex cap at the divide leading into a straight midslope section. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

13.
Comparison of the responses of three drainage basins burned by the Dome fire of 1996 in New Mexico is used to identify the hillslope, channel and fire characteristics that indicate a susceptibility specifically to wildfire‐related debris flow. Summer thunderstorms generated three distinct erosive responses from each of three basins. The Capulin Canyon basin showed widespread erosive sheetwash and rilling from hillslopes, and severe flooding occurred in the channel; the North Tributary basin exhibited extensive erosion of the mineral soil to a depth of 5 cm and downslope movement of up to boulder‐sized material, and at least one debris flow occurred in the channel; negligible surface runoff was observed in the South Tributary basin. The negligible surface runoff observed in the South Tributary basin is attributed to the limited extent and severity of the fire in that basin. The factors that best distinguish between debris‐flow producing and flood‐producing drainages are drainage basin morphology and lithology. A rugged drainage basin morphology, an average 12 per cent channel gradient, and steep, rough hillslopes coupled with colluvium and soil weathered from volcaniclastic and volcanic rocks promoted the generation of debris flows. A less rugged basin morphology, an average gradient of 5 per cent, and long, smooth slopes mantled with pumice promoted flooding. Flood and debris‐flow responses were produced without the presence of water‐repellent soils. The continuity and severity of the burn mosaic, the condition of the riparian vegetation, the condition of the fibrous root mat, accumulations of dry ravel and colluvial material in the channel and on hillslopes, and past debris‐flow activity, appeared to have little bearing on the distinctive responses of the basins. Published in 2000 by John Wiley & Sons, Ltd.  相似文献   

14.
Few investigations link post‐fire changes to sediment sources and erosion processes with sediment yield response at the catchment scale. This linkage is essential if downstream impacts on sediment transport after fire are to be understood in the context of fire effects across different forest environments. In this study, we quantify changing source contributions to fine sediment (<63 µm) exported from a eucalypt forest catchment (136 ha) burnt by wildfire. The study catchment is one of a pair of research catchments located in the East Kiewa River valley in southeastern Australia that have been the subject of a research program investigating wildfire effects on runoff, erosion, and catchment sediment/nutrient exports. This previous research provided the opportunity to couple insights gained from a range of measurement techniques with the application of fallout radionuclides 137Cs and 210Pbex to trace sediment sources. It was found that hillslope surface erosion dominated exports throughout the 3·5‐year post‐fire measurement period. During this time there was a pronounced decline in the proportional surface contribution from close to 100% in the first six months to 58% in the fourth year after fire. Over the study period, hillslope surface sources accounted for 93% of the fine sediment yield from the burnt catchment. The largest decline in the hillslope contribution occurred between the first and second years after fire, which corresponded with the previously reported large decline in sediment yield, breakdown of water repellency in burnt soils, substantial reduction in hillslope erodibility, and rapid surface vegetation recovery. Coupling the information on sediment sources with hillslope process measurements indicated that only a small proportion of slopes contributed sediment to the catchment outlet, with material derived from near‐channel areas dominating the post‐fire catchment sediment yield response. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

15.
Hillslopes have complex three‐dimensional shapes that are characterized by their plan shape, profile curvature of surface and bedrock, and soil depth. To investigate the stability of complex hillslopes (with different slope curvatures and plan shapes), we combine the hillslope‐storage Boussinesq (HSB) model with the infinite slope stability method. The HSB model is based on the continuity and Darcy equations expressed in terms of storage along the hillslope. Solutions of the HSB equation account explicitly for plan shape by introducing the hillslope width function and for profile curvature through the bedrock slope angle and the hillslope soil depth function. The presented model is composed of three parts: a topography model conceptualizing three‐dimensional soil mantled landscapes, a dynamic hydrology model for shallow subsurface flow and water table depth (HSB model) and an infinite slope stability method based on the Mohr–Coulomb failure law. The resulting hillslope‐storage Boussinesq stability model (HSB‐SM) is able to simulate rain‐induced shallow landsliding on hillslopes with non‐constant bedrock slope and non‐parallel plan shape. We apply the model to nine characteristic hillslope types with three different profile curvatures (concave, straight, convex) and three different plan shapes (convergent, parallel, divergent). In the presented model, the unsaturated storage has been calculated based on the unit head gradient assumption. To relax this assumption and to investigate the effect of neglecting the variations of unsaturated storage on the assessment of slope stability in the transient case, we also combine a coupled model of saturated and unsaturated storage and the infinite slope stability method. The results show that the variations of the unsaturated zone storage do not play a critical role in hillslope stability. Therefore, it can be concluded that the presented dynamic slope stability model (HSB‐SM) can be used safely for slope stability analysis on complex hillslopes. Our results show that after a certain period of rainfall the convergent hillslopes with concave and straight profiles become unstable more quickly than others, whilst divergent convex hillslopes remain stable (even after intense rainfall). In addition, the relation between subsurface flow and hillslope stability has been investigated. Our analyses show that the minimum safety factor (FS) occurs when the rate of subsurface flow is a maximum. In fact, by increasing the subsurface flow, stability decreases for all hillslope shapes. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

16.
Natural hillslopes are mostly composed of complex slope shapes, which significantly affect soil erosion. However, existing studies have mainly focused on uniform slopes to simplify complex hillslopes, and the mechanisms responsible for the influence of slope shape on soil and nutrient losses are still not well understood, especially in the application of soil improvers to reduce soil loss. To investigate the effects of slope shape and polyacrylamide (PAM) application on runoff, soil erosion and nutrient loss, this study conducted artificial field rainfall experiments involving two PAM application rates and nine slope shapes. The results indicate that the average amount of soil loss from convex slopes was 1.5 and 1.3 times greater than that from concave and uniform slopes, respectively, and the average amount of ammonia nitrogen loss and phosphate loss increased by 24.0%–58.6%. Soil and nutrient losses increased as the convexity of the convex slopes increased. For runoff, there was little difference between concave and convex slopes, but the runoff amount for both slopes was greater than that for uniform slopes. After PAM application, the soil loss decreased by more than 90%, and the nutrient loss decreased by 28.2%–68.1%. The application of PAM was most effective in reducing soil erosion and nutrient loss from convex slopes, and it is recommended to appropriately increase the PAM application rate for convex slopes. A strong linear relationship between ammonia nitrogen and phosphate concentrations and sediment concentrations was found in the runoff on slopes with no PAM application. However, this linear relationship weakened for slopes with PAM application. The findings of this study may be valuable for optimizing nonpoint source pollution management in basins.  相似文献   

17.
We examined the water balance of a forested ombrotrophic peatland and adjacent burned peatland in the boreal plain of western Canada over a 3‐year period. Complete combustion of foliage and fine branches dramatically increased shortwave radiation inputs to the peat surface while halting all tree transpiration at the burned site. End‐of‐winter snowpack was 7–25% higher at the burned site likely due to decreased ablation from the tree canopy at the unburned site. Shrub regrowth at the burned site was rapid post‐fire, and shading by the shrub canopy in the burned site approached that of the unburned site within 3 years after fire. Site‐averaged surface resistance to evaporation was not different between sites, though surface resistance in hollows was lower in the burned site. Water loss at both burned and unburned sites is largely driven by surface evaporative losses. Evaporation at the burned site marginally exceeded the sum of pre‐fire transpiration and interception at the unburned site, suggesting that evapotranspiration during the growing season was 20–40 mm greater at the burned peatland. Although the net change in water storage during the growing season was largely unchanged by fire, the lack of low‐density surface peat in the burned site appears to have decreased specific yield, leading to greater water table decline at the burned site despite similar net change in storage. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

18.
The drainage networks of catchment areas burned by wildfire were analysed at several scales. The smallest scale (1–1000 m2) representative of hillslopes, and the small scale (1000 m2 to 1 km2), representative of small catchments, were characterized by the analysis of field measurements. The large scale (1–1000 km2), representative of perennial stream networks, was derived from a 30‐m digital elevation model and analysed by computer analysis. Scaling laws used to describe large‐scale drainage networks could be extrapolated to the small scale but could not describe the smallest scale of drainage structures observed in the hillslope region. The hillslope drainage network appears to have a second‐order effect that reduces the number of order 1 and order 2 streams predicted by the large‐scale channel structure. This network comprises two spatial patterns of rills with width‐to‐depth ratios typically less than 10. One pattern is parallel rills draining nearly planar hillslope surfaces, and the other pattern is three to six converging rills draining the critical source area uphill from an order 1 channel head. The magnitude of this critical area depends on infiltration, hillslope roughness and critical shear stress for erosion of sediment, all of which can be substantially altered by wildfire. Order 1 and 2 streams were found to constitute the interface region, which is altered by a disturbance, like wildfire, from subtle unchannelized drainages in unburned catchments to incised drainages. These drainages are characterized by gullies also with width‐to‐depth ratios typically less than 10 in burned catchments. The regions (hillslope, interface and channel) had different drainage network structures to collect and transfer water and sediment. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

19.
A fundamental question in arid land management centers on understanding the long‐term effects of fire on desert ecosystems. To assess the effects of fire on surface topography, soil roughness, and vegetation, we used terrestrial (ground‐based) LiDAR to quantify the differences between burned and unburned surfaces by creating a series of high‐resolution vegetation structure and bare‐earth surface models for six sample plots in the Grand Canyon‐Parashant National Monument, Arizona. We find that 11 years following prescribed burns, mound volumes, plant heights, and soil‐surface roughness were significantly lower on burned relative to unburned plots. Results also suggest a linkage between vegetation and soil mounds, either through accretion or erosion mechanisms such as wind and/or water erosion. The biogeomorphic implications of fire‐induced changes are significant. Reduced plant cover and altered soil surfaces from fire likely influence seed residence times, inhibit seed germination and plant establishment, and affect other ecohydrological processes. Published in 2012. This article is a US Government work and is in the public domain in the USA.  相似文献   

20.
Irregular wetting, water repellency, and preferential flow are well‐documented properties of coastal sandy podzols, though little is known about the effect of fire on unsaturated zone processes in this environment. This study investigates water repellency at and below the soil surface in two coastal sandy podzols following bushfire. Water drop penetration time tests were applied to burned and unburned soils at a high dune field site in South East Queensland, Australia. It was found that the mean water drop penetration time of the burned soil was four times that of the unburned soil, but both soils were largely non‐repellent. Post‐fire repellency peaked below the surface in a patchy layer, in contrast to the laterally extensive layer reported in other studies, and high organic matter content in the soil did not appear to significantly influence repellency post‐burn. Non‐parametric statistics were used to quantify the high spatial variability in water repellency, which was ultimately insufficiently captured by atypically large (n = 1000 drop) datasets. This study confirms the presence of naturally occurring repellency and patchy infiltration in sandy soils while demonstrating that conclusively describing the influence of fire is challenging in a soil with heterogeneous infiltration characteristics. With respect to this uncertainty, it appears that fire does not increase soil water repellency such that infiltration and runoff processes due to fire‐induced water repellency would differ post‐burn.  相似文献   

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