Long-term denudation rates of actively uplifting hillcrests in the Boso Peninsula, Japan, estimated from depth profiling of in situ-produced cosmogenic Be and Al

Depth profiling of in situ-produced cosmogenic ¹⁰Be and ²⁶Al was applied to estimate the rate of long-term denudation on actively uplifting hillcrests made of weakly consolidated sandstone in the Boso Peninsula, Japan. The nuclide concentration in the topmost meter of the hillcrest has reached an equilibrium value owing to surface denudation at 90 mm/kyr. This rate is much smaller than the regional uplift rate, and is consistent with the current isolated residual topography of the hillcrest. By considering the epoch of emergence of the sandstone hillcrests, we estimate the summit denudation rate of the adjacent mudstone hill formation to be 720 ± 110 mm/kyr.     

Degradation of unconsolidated Quaternary landforms in the western North America

One of the major goals of geomorphology is to understand the rate of landscape evolution and the constraints that erosion sets on the longevity of land surfaces. The latter has also turned out to be vital in modern applications of cosmogenic exposure dating and interpretation of lichenometric data from unconsolidated landforms. Because the effects of landform degradation have not been well documented, disagreements exist among researchers regarding the importance of degradation processes in the dating techniques applied to exposures. Here, we show that all existing qualitative data and quantitative markers of landform degradation collectively suggest considerable lowering of the surface of unconsolidated landforms over the typical life span of Quaternary moraines or fault scarps. Degradation is ubiquitous and considerable even on short time scales of hundreds of years on steeply sloping landforms. These conservative analyses are based entirely on field observations of decreasing slope angles of landforms over the typical range of ages in western North America and widely accepted modeling of landscape degradation. We found that the maximum depth of erosion on fault scarps and moraines is on average 34% of the initial height of the scarp and 25% of the final height of the moraine. Although our observations are limited to fault scarps and moraines, the results apply to any sloping unconsolidated landform in the western North America. These results invalidate the prevailing assumption of no or little surface lowering on sloping unconsolidated landforms over the Quaternary Period and affirm that accurate interpretations of lichen ages and cosmogenically dated boulder ages require keen understanding of the ever-present erosion. In our view, the most important results are twofold: 1) to show with a large data set that degradation affects universally all sloping unconsolidated landforms, and 2) to unambiguously show that even conservative estimates of the total lowering of the surface operate at time and depth scales that significantly interfere with cosmogenic exposure and lichen dating.     

Modeling impacts of erosion and deposition on soil organic carbon in the Big Creek Basin of southern Illinois

Land use land cover (LULC) plays an important role in influencing the spatial intensity of water erosion which is the primary governor of horizontal translocation of soil organic carbon (SOC). The fate of redistributed SOC through erosion remains debatable and the mineralization rate of exposed SOC protected in soil aggregates is the major focus of this argument. Cohesive spatially explicit modeling of SOC and erosion can potentially reduce some of the controversy. To this end we simulated erosion/deposition, and photosynthetic (in situ) flux of SOC in a small watershed of ~ 28.42 ha, located in the Big Creek basin of southern Illinois. The main objectives of this research were: (a) to study erosion and deposition dynamics under different LULC, (b) to examine the extent of carbon dislocation and deposition possible in the study area, and (c) to determine the net SOC accretion and reduction possible by accounting for gains through annual photosynthesis and deposition, and losses from erosion under different LULC scenarios. To fulfill our objectives, we combined GeoWEPP, an erosion/deposition process model, with CENTURY 4.0, an ecosystem model used for simulating SOC. Our results show that between 11 and 31% of the eroded soil gets deposited in the same basin depending on the LULC type, leaving the remainder to be transported downstream. Additionally, as expected, SOC flux due to erosion and deposition varies with the type of management practices. In the case of conservation management practices, the flux associated with erosion and deposition remains below 10% in comparison to in situ SOC transformations due to annual photosynthesis. However in the case of non-conservation management practices this proportion rises above 50%.     

Influence of soil, tree cover and large herbivores on field layer vegetation along a savanna landscape gradient in northern Botswana

The response of the field layer vegetation to co-varying resource availability (soil nutrients, light) and resource loss (herbivory pressure) was investigated along a landscape gradient highly influenced by elephants and smaller ungulates at the Chobe River front in Botswana. TWINSPAN classification was used to identify plant communities. Detrended Correspondence Analysis (DCA) and Canonical Correspondence Analysis (CCA) were used to explore the vegetation-environment relationships. Four plant communities were described: Panicum maximum woodland, Tribulus terrestris woodland/shrubland, Chloris virgata shrubland and Cynodon dactylon floodplain. Plant height, species richness and diversity decreased with increasing resource availability and resource loss. The species composition was mainly explained by differences in soil resources, followed by variables related to light availability (woody cover) and herbivory, and by interactions between these variables. The vegetation structure and species richness, on the other hand, followed the general theories of vegetation responses to herbivory more closely than resource related theories. The results suggest a strong interaction between resource availability and herbivory in their influence on the composition, species richness and structure of the plant communities.     

Effects of soil degradation on infiltration rates in grazed semiarid rangelands of northeastern Patagonia, Argentina

In grazed semiarid ecosystems, considerable spatial variability in soil infiltration exists as a result of vegetation and soil patchiness. Despite widespread recognition that important interactions and feedbacks occur between vegetation, runoff and erosion, currently there is only limited quantitative information on the control mechanisms that lead to differences in infiltration from different vegetation types. In this paper, we determine (i) the relationship between vegetation and soil surface characteristics and (ii) the soil infiltration rate by using rainfall simulations on runoff plots (0.60 × 1.67 m) in three plant communities of northeastern Patagonia: grass (GS), degraded grass with scattered shrubs (DGS), and degraded shrub steppes (DSS). Our results clearly indicate that vegetation and soil infiltration are closely coupled. Total infiltration was significantly higher in the GS (69.6 mm) compared with the DGS and DSS (42.9 and 28.5 mm, respectively). In the GS, soil infiltration rate declined more slowly than the others communities, reaching a terminal infiltration rate significantly greater (57.7 mm) than those of DGS and DSS (25.7 and 12.9 mm, respectively). The high rate of water losses via overland-flow may limit the possibilities for grass seedling emergence and establishment and favor the persistent dominance of shrubs.     

The response of soil erosion and sediment export to land-use change in four areas of Europe: The importance of landscape pattern

The response of erosion and sediment export to past land-use change has been studied in four agricultural areas of Europe. Three of these areas were subject to land abandonment or de-intensification and one to intensification of land-use practices. Erosion and sediment yield were modeled using the WaTEM/SEDEM model, which combines the RUSLE equation with a sediment routing algorithm. Spatial relationships between the RUSLE C-factor (i.e. land-use) and other erosion and sediment export-determining factors (slope, soil erodibility and distance to rivers) were investigated, as these account for non-linearity in the response of erosion and sediment export to land-use change.Erosion and sediment export have decreased enormously in the de-intensified areas, but slightly increased in the intensively cultivated area. The spatial pattern of land-use change in relation to other erosion and sediment export-determining factors appears to have a large impact on the response of soil erosion and sediment export to land-use change. That the drivers of abandonment of arable land and erosion coincide indicates that de-intensification leads to a more favourable landscape pattern with respect to reduction of erosion and sediment export. This mechanism applies not only within the study areas, but also among the European study areas where the process of intensification of some areas and de-intensification of others might result in an overall decrease of erosion and sediment yield through time.     

A review of runoff generation and soil erosion across scales in semiarid south-eastern Spain

Climate, lithology, soil and especially, intense land use/cover changes, make SE Spain very vulnerable to runoff generation and water erosion leading to loss of nutrients and organic matter and to infrequent but devastating floods, reservoir siltation and mass failures. This susceptibility has led to heavy economic investment and research efforts since the 1980s, making this region a worldwide reference for understanding the hydrology and geomorphology of semiarid ecosystems. Runoff and soil erosion have been intensively studied throughout the last decades in various natural ecosystems as well as in abandoned farmlands. Research has considered a wide range of methods and spatial and temporal scales. This paper reviews the methods and data describing runoff generation and water erosion, synthesising the key processes involved, rates, thresholds and controlling factors from a scale-dependent perspective. It also identifies the major gaps in current knowledge to provide recommendations for further research towards solutions that reduce the negative impacts of erosion. Research in SE Spain has contributed significantly to a better understanding of the effect of spatial and temporal scale on runoff and sediment yield measurements, and highlighted the important role of distinct erosion and sediment transport processes, hydrologic connectivity, spatial and temporal patterns of rainfall, the occurrence of extreme events and the impacts of land use changes. The most effective ways and challenges to predict runoff, soil erosion and sediment yield at the catchment scale are also discussed.     

流动沙丘干沙层厚度对土壤水分蒸发的影响

利用Micro-lysimeter对流动沙丘不同干沙层厚度下的土壤水分蒸发作了测定与分析,结果表明:当干沙层厚度发育达到5 cm以上时,流动沙丘干沙层厚度成为土壤水分蒸发的决定因素。随着干沙层厚度的增加,土壤蒸发量逐渐降低;各观测日的蒸发抑制率随着干沙层厚度的增大而增大;5 cm的干沙层对蒸发的抑制作用最大可达70.6%,30 cm的干沙层则最大可达92.38%;干沙层厚度与土壤蒸发量之间存在显著的线性关系。各气象因子以及湿沙层不同深度土壤体积含水率对土壤蒸发量的影响作用很小,相关分析均没有达到显著水平。     

Climatic influences on Holocene variations in soil erosion rates on a small hill in the Mojave Desert

A detailed study of a small hill in NE Mojave Desert in eastern California was conducted to elucidate the effect of climate on the variations in soil erosion rates through Holocene. Field surveys and sampling were carried out to obtain information on topography, geomorphology, soil and vegetation conditions, seismic refraction, sediment deposition, and hillslope processes. Integration of this information allowed reconstruction of the hill topography at the end of the Pleistocene, deduction of the evolution of the hill from the end of the Pleistocene to the present, and estimation of total soil losses resulting from various hillslope processes. The estimates are consistent with the premise that early Holocene climate change resulted in vegetation change, soil destabilization, and topographic roughening. Current, very slow, hillslope transport rates (e.g., 5 mm ky⁻¹ by rodent burrowing, a presently important transport form) appear inconsistent with the inferred total soil loss rate (31 mm ky⁻¹). Packrat midden studies imply that the NE Mojave Desert experienced enhanced monsoonal precipitation in the early Holocene, presumably accentuating soil loss. Water erosion on one slope of the hill was simulated using Water Erosion Prediction Project (WEPP), a process-based erosion model, using 4 and 6 ky of precipitation input compatible with an appropriate monsoonal climate and the present climate, respectively. The WEPP-predicted soil losses for the chosen slope were compatible with inferred soil losses. Identification of two time periods within the Holocene with distinct erosion characteristics may provide new insight into the current state of Mojave Desert landform evolution.     

Influence of soil texture on the binding energies of fine mineral dust particles potentially released by wind erosion

Models of the two aeolian processes (saltation and sandblasting) that lead to emission of fine dust particles (PM20) by wind erosion in arid and semi-arid areas have been combined to form the so-called ‘Dust Production Model’ (DPM). In this model, the size dependent binding energies of PM20 embedded within the wind-erodible loose soil aggregates or in the soil surface itself are key input parameters. Indeed, their values condition at the same time the intensity of emissions and their initial size distribution. Previous comparisons of vertical mass fluxes measured on-field with the model predictions suggest that these energies might be relatively independent of soil texture and also probably composition. Because this would greatly facilitate application of the DPM at regional or global scale, the objective of this work is to check experimentally the veracity of this result. The strategy that has been designed for this has involved selecting four natural soil samples collected in various source areas of the world and covering a wide range of textures and compositions. Then, these soil samples have been used to perform carefully controlled wind erosion simulations in a wind tunnel. During the experiments, which were carried out at different wind speeds with each soil, the horizontal flux (F_h) of saltating soil aggregates has been monitored. At the same time, number concentrations (C_i) of PM20 released by the sandblasting process were recorded in the 6 size classes of an optical size analyzer. Thus, the efficiency of the sandblasting process (defined as the ratio of C_i to F_h) could be determined for each of these size classes. Analysis of the results obtained in similar saltation conditions shows that for the four tested soils, and within the range of contents in clay and other components favoring aggregation (mostly organic matter and carbonates), the influence of soil composition and texture on binding energies of the PM20 particles within soil aggregates is at best a second order effect that can be neglected in large scale modeling of wind erosion by the DPM.     

An investigation of periglacial slope stability in relation to soil properties based on physical modelling in the geotechnical centrifuge

Results are presented from eight scaled centrifuge modelling experiments designed to investigate mass movement processes on thawing ice-rich slopes. Four pairs of simple planar slope models were constructed, one in each pair being of sufficient gradient to promote slope failure during soil thaw and the second having a gradient below the threshold for instability. Four frost susceptible soils were used, three were normally consolidated and had different clay contents (2%, 12% and 20%) and the fourth comprised the 20% clay soil, but was over consolidated prior to model testing. Modelling protocols included freezing from the surface downwards under an open hydraulic system, and thawing from the surface downwards under an enhanced gravitational field within the geotechnical centrifuge, thereby utilising scaling laws to simulate correct prototype self weight stresses during thaw. Slopes below the stability threshold gradient were subjected to between 2 and 4 cycles of freezing and thawing, simulating annual cycles. Those above the stability threshold were subjected to only one cycle, since they failed during the first thaw phase. Thermal conditions, pore water pressures, surface movements, and profiles of displacement are reported. Measured pore pressures are used in slope stability analyses based on a simple planar infinite slope model. Profiles of solifluction shear strain and mechanisms of slope failure are both shown to be sensitive to small changes in soil properties, particularly clay content and stress history. In all cases, pore pressures rose rapidly immediately following thaw, remained below the threshold for failure in low gradient models, but exceeding the threshold to trigger landslides on steeper slopes. Upward seepage of melt water away from the thaw front contributed to loss of shear strength. Mechanisms of slope failure differed between test soils, ranging from mudflow in non-cohesive silt to active layer detachment sliding in over consolidated silt–clay. During solifluction, shear strain was greatest at the surface in non-cohesive silt and decreased rapidly with depth, but in test soils containing clay, the zone of maximum shear strain was located lower in the displacement profiles.     

Simulation of soil erosion and deposition in a changing land use: A modelling approach to implement the support practice factor

Using the USPED (Unit Stream Power Erosion Deposition) model, three land use scenarios were analysed for an Italian small catchment (15 km²) of high landscape value. The upper Orme stream catchment, located in the Chianti area, 30 km south of Florence, has a long historical agriculture record. Information on land use and soil conservation practices date back to 1821, hence offering an opportunity to model impacts of land use change on erosion and deposition. For this study, a procedure that takes into account soil conservation practices and potential sediment storage is proposed. The approach was to calculate and model the flow accumulation considering rural and logging roads, location of urban areas, drainage ditches, streams, gullies and permanent sediment sinks. This calculation attempts to assess the spatial variability, especially the impact of support practices (P factor). Weather data from 1980–2003 were taken into account to calculate the R factor. However, to consider the intense pluviometric conditions in terms of the erosivity factor, the 0.75th quantile was used, while the lowest erosivity was modelled using the 0.25th quantile. Results of the USPED model simulation show that in 1821 the mean annual net erosion for the watershed was 2.8 Mg ha^− 1 y^− 1; in 1954 it was 4.2 Mg ha^− 1 y^− 1; and in 2004 it was 5.3 Mg ha^− 1 y^− 1. Conservation practices can reduce erosion processes by ≥ 20 Mg ha^− 1 y^− 1 when the 1821 practices are introduced in the present management. On the other hand, if the support practices are not considered in the model, soil erosion risk is overestimated. Field observation for the present-day simulation confirmed that erosion and associated sediment deposition predicted by the model depend, as expected, on geomorphology and land use. The model shows limitations that are mainly due to the input data. A high resolution DEM is essential for the delineation of reliable topographic potential to predict erosion and deposition especially in vineyards.     

Impact of land cover types on the soil characteristics in karst area of Chongqing

The 26 plots including natural forestland, secondary forestland, shrub-grassland, sloping cropland, artificial forest and abandoned field, were selected to discuss the impact of land cover on the soil characteristics in the three karst districts of Chongqing. The results showed that: (1) After the vegetation turned into secondary vegetation or artificial vegetation, or reclamation, soil physical properties would be degraded. In the surface-layer soil of sloping cropland, the contents of > 2 mm water-stable aggregates decreased obviously with apparent sandification. (2) The contents of soil organic matter and total nitrogen are controlled completely by vegetation type and land use intensity. The increasing trend is rather slow in the early days when over-reclamation is stopped and the land is converted to forest and pasture. (3) Herbaceous species increase and woody plants species decrease with the increase of land use intensity, therefore, the soil seed banks degrade more seriously. (4) The soil degradation index has been set up to describe the relative soil degradation degree under the conditions of different vegetation types. (5) Land cover has a significant effect on karst soil characteristics, land degradation in the karst ecosystem is essentially characterized by the different degradation of soil functions that serve as water banks, nutrient banks and soil seed banks.     

Identifying erosion hotspots and assessing communities' perspectives on the drivers,underlying causes and impacts of soil erosion in Toledo's Rio Grande Watershed: Belize

Erosion in the Rio Grande watershed of Belize, Central America results in widespread ecological impacts and significant economic costs. In this study, quantitative soil loss analysis and qualitative social surveys were integrated to identify erosion vulnerable areas or hotspots, and to analyze varying perspectives between communities near and far from erosion hotspots regarding the causes of erosion. The results of the quantitative analysis suggest that erosion hotspots are located in the upper-mid reaches of the watershed near the communities of Crique Jute, Naluum Ca, San Pedro Columbia and San Miguel. The Mann–Whitney U test identified significant difference in the ranking of erosion drivers (cattle ranching, logging, and clearing of slopes) between communities. Communities far from erosion hotspots (FEH) ranked cattle ranching and logging higher than communities near erosion hotspots as the main drivers of soil erosion (NEH and FEH, mean = 79.02, 105.92, (U) = 3055, p < 0.001 and mean = 84.9, 100.90, (U) = 3560.5 p < 0.05) respectively. On the other hand, communities near erosion hotspots (NEH) ranked clearing and planting on slopes higher than communities far from erosion hotspots as the main driver of soil erosion (NEH and FEH, mean = 107.03, 81.86, (U) = 3136.5, p < 0.001). The logistic regression model depicted that ethnicity, distance, gender, and employment were significant in explaining the data variability on the perceived implementation of erosion prevention techniques in the watershed (2LL = 208.585, X² = 49, df = 8, p < .001). This research provides significant information on the drivers, underlying causes and erosion vulnerable areas that will aid stakeholders to garner community support, develop and implement sustainable soil management practices. Moreover, the study highlights the need to implement cost-effective soil erosion prevention programs and to assess the loss of soil nutrients and agriculture productivity in the study site.     

重庆喀斯特地区土地覆被类型对土壤特征的影响

1 Introduction The karst region of Southwest China, with Guizhou Province as the center, extends across Yunnan Province, Guangxi Zhuang Autonomous Region, Sichuan Province, Chongqing, western Hunan Province, Hubei Province, and Guangdong Province, coveri…     

Arbuscular mycorrhizal fungi improve reestablishment of Leymus chinensis in bare saline-alkaline soil: Implication on vegetation restoration of extremely degraded land

Salinization and alkalinization are increasing problems in the world. Some land has been degraded to bare saline-alkaline soil where vegetation restoration is difficult because high toxic ionic content and pH are harmful to the survival of introduced plants. We grew Leymus chinensis with and without arbuscular mycorrhizal fungi (Glomus mosseae and G. geosporum) in either pots filled with soil from bare saline-alkaline land, or transplanted seedlings into field plots, to determine the influence of AM fungi on the reestablishment of this dominant grass species in bare degraded land. Association with AM fungi increased the absorption of N, P, K⁺, Ca²⁺, but decreased Mg²⁺, Na⁺ and Cl⁻ uptake under saline-alkaline stress. Therefore, higher K/Na, Ca/Na, P/Na, and P/Cl ratios were found in the inoculated plants. Plants inoculated with AM fungi accumulated significantly higher biomass, root/shoot ratio and tiller number than non-inoculated plants. AM fungi also significantly increased the survival of seedlings when they were transplanted into a bare saline-alkaline land in the field. The improvement of survival, growth and asexual reproduction of inoculated plants indicated that the plant-AM fungi mutualism could improve the reestablishment of vegetation in bare saline-alkaline soil, drive the vegetation restoration to a community dominated by original species.     

Water accumulation in soil by gravel and sand mulches: Influence of textural composition and thickness of mulch layers

The use of gravel and sand as mulch has been an indigenous farming technique for crop production for over 300 years in the semiarid loess region of northwest China. The objective of this study was to determine the influence of texture and thickness of gravel and sand mulch layers on soil water storage by field experiments. The texture experiment consists of three commonly used gravel mulch types: pebble, mixed pebble and sand, fine sand; and the thickness experiment consists of 1, 2 and 3-layers of 2 cm pebbles. Each treatment has three replications. The results indicate that gravel-sand mulches were more effective in conserving soil water, as compared with the bare soil treatment, and the mixed pebble and sand mulch was more effective to conserve soil water than the sole pebble or sand mulch. Soil water content increased with mulch thickness (the number of gravel layers), 1-layer treatment had an average soil water content of 10.85% at 0-60 cm soil layer after a rainfall of 10 mm, 2.42% and 4.92% less than the 2-layers and 3-layers treatments. From May to October in 2004, two and three layers of pebbles conserved 9.8 ± 6.6 mm and 20.0 ± 14.3 mm more water, respectively, as compared with the one layer of 2 cm pebbles at the soil depth of 0-100 cm.     

The consequences of land-cover changes on soil erosion distribution in Slovakia

Soil erosion is a complex process determined by mutual interaction of numerous factors. The aim of erosion research at regional scales is a general evaluation of the landscape susceptibility to soil erosion by water, taking into account the main factors influencing this process. One of the key factors influencing the susceptibility of a region to soil erosion is land cover. Natural as well as human-induced changes of landscape may result in both the diminishment and acceleration of soil erosion. Recent studies of land-cover changes indicate that during the last decade more than 4.11% of Slovak territory has changed. The objective of this study is to assess the influence of land-cover and crop rotation changes over the 1990–2000 period on the intensity and spatial pattern of soil erosion in Slovakia. The assessment is based on principles defined in the Universal Soil Loss Equation (USLE) modified for application at regional scale and the use of the CORINE land cover (CLC) databases for 1990 and 2000. The C factor for arable land has been refined using statistical data on the mean crop rotation and the acreage of particular agricultural crops in the districts of Slovakia. The L factor has been calculated using sample areas with parcels identified by LANDSAT TM data. The results indicate that the land-cover and crop rotation changes had a significant influence on soil erosion pattern predominately in the hilly and mountainous parts of Slovakia. The pattern of soil erosion changes exhibits high spatial variation with overall slightly decreased soil erosion risks. These changes are associated with ongoing land ownership changes, changing structure of crops, deforestation and afforestation.     

Effects of shrub removal and nitrogen addition on soil moisture in sagebrush steppe

I monitored soil moisture profiles in sagebrush steppe in SE Idaho, USA, for 6 years, a period that included four consecutive years of drought. Recharge of soil moisture was primarily the result of winter and early spring precipitation, and soil moisture declined during the spring and summer growing season. Recharge was substantially lower during drought years, and a single year of average precipitation did not restore soil moisture to pre-drought levels. Relative to control plots, there was more soil moisture on shrub removal plots and less soil moisture on nitrogen addition plots, particularly at depths of 100–180 cm. These differences suggest that in this ecosystem shrubs extract more moisture from deeper in the soil profile than perennial grasses, and that increased nitrogen availability can significantly affect soil water balance.     

山地城市土地覆盖变化对地表温度的影响

针对山地城市复杂的城市地貌和下垫面类型,本文使用TM、DEM、ETM⁺等遥感影像资料,提取了重庆市土地利用覆盖类型;借助TM、MSS等遥感数据的红外波段,反演出1988年和2000年的地表温度。分析了重庆市近十年的土地覆盖变化及其对地表温度的影响,结果表明,在1988~2000年间,研究区土地覆盖变化明显,特别是城市土地覆盖面积有显著增加。土地覆盖类型的变化会改变地表温度的空间分布,尤其是城市土地的扩展会提高地表温度。对山地、丘陵、平坝、陡坡四种耕地的地表温度进行了深入分析与研究,结果表明:山地城市土地覆盖变化引起了植被覆盖度的变化,而植被覆盖度的变化又相应地影响了地表温度的变化,植被覆盖度每下降10%,地表温度上升0.49K。