Regional assessment of soil erosion using the distributed model SEMMED and remotely sensed data

The soil erosion model for Mediterranean regions (SEMMED) is presented and used to produce regional maps of simulated soil loss for two Mediterranean test sites: one in southern France and one in Sicily. The model demonstrates the integrated use of (1) multi-temporal Landsat Thematic Mapper (TM) images to account for vegetation properties, (2) a digital terrain model in a GIS to account for topographical properties and to assess the transport capacity of overland flow, (3) a digital soil map to assess the spatial distribution of soil properties, and (4) a limited amount of soil physical field data. The principle drawbacks of the model are that it does not account for soil particle detachment by overland flow nor for soil surface crusting. The model is most sensitive to the initial soil moisture storage capacity and the soil detachability index. The main advantages of SEMMED are that it simulates processes at a regional scale and, where possible, it uses available data sources such as remote sensing imagery, digital elevation models (DEM) and (digital) soil databases, which usually are not available for smaller catchment areas. Using SEMMED it is possible to produce regional maps of erosion assessments, which are of more practical use in land use planning and land management than simple extrapolations from small plot experiments.     

滨海盐土遥感监测的发展趋势

重点阐述国内外滨海盐土遥感监测内容与监测技术的进展,指出尚存问题以及未来的发展趋势。近年来滨海盐土遥感监测,在空间识别上,从基于影像光谱及色相特征的目视解译向计算机自动判读逐渐演变;在盐土性质反演上,由离散样点的统计建模逐渐扩展为空间连续的智能反演;在盐渍化程度监测方面,正由单纯通过土壤理化性质表征盐渍化程度向滨海生态系统的综合监测方向发展。滨海盐土遥感监测深受水分、植被等因素的影响,还存在较大的不确定性,在反演精度、模型通用性以及数据管理上仍有很大发展空间。滨海盐土遥感监测正向时效性、动态性、智能化方向发展,建立多尺度空间的滨海盐土质量通用反演模型以及有效的海量盐土遥感数据管理机制将是未来研究发展的必然趋势。     

Relationship between soil erosion and distance to roadways in undeveloped areas of China

The presence and condition of roadways control the utilization of natural resources, which are associated with direct and indirect impacts on soil erosion in undeveloped countries. This paper addresses the relationship between soil erosion and distance to roadways in Xingguo County, an undeveloped area in Jiangxi Province of South China, for four time periods, 1958, 1975, 1982, and 2000. Soil erosion maps for each time period were interpreted using remote sensing and GIS technology for buffer zones four kilometers wide, subdivided into eight strips, each 0.5 kilometers wide, which were located alongside various types of road classes, namely trunk, town, village, and unpaved. The distribution patterns of various types of erosion were identified by GIS overlay of buffer strips and soil erosion maps. Results demonstrate that soil erosion cases found in buffer zones along both sides of trunk and town roads are the most severe, and areas with severe erosion decrease as distance from the strip to the road increases. However, moderate and slight erosion cases only have a minor relationship to the strip to road distance. There are more severe erosion cases than moderate and light erosion cases alongside village and unpaved roads, but the total area is not distinctly different from moderate and slight erosion cases, and severe erosion cases tend to decrease with an increase in the strip to road distance. Also, areas with severe erosion differentiated by time periods in the strips alongside roadways of all classes, except trunk roads, rank from highest to lowest as follows: 1975, 1958, 1982, and 2000. Notably, severe erosion areas in 1975, 1958 and 1982 are all quite extensive. Soil erosion alongside roadways of various classes is impacted jointly by historical policy, distance to roadways, and landscape. In undeveloped countries and areas, much more attention should be paid to the impacts of road construction, specifically soil erosion associated with road edge construction, and relevant measures for forest resource conservation should be formulated before initiating road construction projects.     

Conservation management decreases surface runoff and soil erosion

Conservation management practices – including agroforestry, cover cropping, no-till, reduced tillage, and residue return – have been applied for decades to control surface runoff and soil erosion, yet results have not been integrated and evaluated across cropping systems. In this study we collected data comparing agricultural production with and without conservation management strategies. We used a bootstrap resampling analysis to explore interactions between practice type, soil texture, surface runoff, and soil erosion. We then used a correlation analysis to relate changes in surface runoff and soil erosion to 13 other soil health and agronomic indicators, including soil organic carbon, soil aggregation, infiltration, porosity, subsurface leaching, and cash crop yield. Across all conservation management practices, surface runoff and erosion had respective mean decreases of 67% and 80% compared with controls. Use of cover cropping provided the largest decreases in erosion and surface runoff, thus emphasizing the importance of maintaining continuous vegetative cover on soils. Coarse- and medium-textured soils had greater decreases in both erosion and runoff than fine-textured soils. Changes in surface runoff and soil erosion under conservation management were highly correlated with soil organic carbon, aggregation, porosity, infiltration, leaching, and yield, showing that conservation practices help drive important interactions between these different facets of soil health. This study offers the first large-scale comparison of how different conservation agriculture practices reduce surface runoff and soil erosion, and at the same time provides new insight into how these interactions influence the improvement or loss of soil health.     

Contribution of phytoecological data to spatialize soil erosion: Application of the RUSLE model in the Algerian atlas

Among the models used to assess water erosion, the RUSLE model is commonly used. Policy makers can act on cover (C-factor) and conservation practice (P-factor) to reduce erosion, with less costly action on soil surface characteristics. However, the widespread use of vegetation indices such as NDVI does not allow for a proper assessment of the C-factor in drylands where stones, crusted surfaces and litter strongly influence soil protection. Two sub-factors of C, canopy cover (CC) and soil cover (SC), can be assessed from phytoecological measurements that include gravel-pebbles cover, physical mulch, annual and perennial vegetation. This paper introduces a method to calculate the C-factor from phytoecological data and, in combination with remote sensing and a geographic information system (GIS), to map it over large areas. A supervised classification, based on field phytoecological data, is applied to radiometric data from Landsat-8/OLI satellite images. Then, a C-factor value, whose SC and CC subfactors are directly derived from the phytoecological measurements, is assigned to each land cover unit. This method and RUSLE are implemented on a pilot region of 3828 km² of the Saharan Atlas, composed of rangelands and steppe formations, and intended to become an observatory. The protective effect against erosion by gravel-pebbles (50%) is more than twice that of vegetation (23%). The C-factor derived from NDVI (0.67) is higher and more evenly distributed than that combining these two contributions (0.37 on average). Finally, priorities are proposed to decision-makers by crossing the synthetic map of erosion sensitivity and a decision matrix of management priorities.     

Identification of priority areas for controlling soil erosion

Conservation prioritization is an important consideration for planning of natural resources management, allowing decison makers to implement management strategies that are more sustainable in the long-term. However, only a current erosion status or a relative index cannot exactly identify priority area for conservation. The objective of this paper is to identify conservation priorities by a specific multicriteria evaluation method. Trends in erosion risk indicate regions of increasing erosion risk and are also chosen as one of the evaluation criteria to identify the priorities based on the instability of soil erosion in the Yongding river basin. In this paper, vegetation cover, land-use, and slope gradient are used to assess erosion risk and trends in erosion risk are obtained by comparing the results of erosion risk between 2000 and 2006. Using this information, the priority conservation areas are graded into six levels. The two highest priority levels cover the regions with severe erosion or a substantial recent increase in erosion risk (4722.56 km², or 11.82% of the study area), and are recommended as erosion control regions with appropriate conservation strategies. The middle two levels cover the regions with stable erosion status or slight change, needing only minor measures. The method presented is fast and straightforward, showing good potential for successful application in other areas.     

Evaluation of soil erosion protective cover by crop residues using vegetation indices and spectral mixture analysis of multispectral and hyperspectral data

Crop residues are efficient in reducing erosion and surface water runoff on agricultural soils. Evaluating the crop residue cover fraction and its spatial distribution is important to scientists involved in the modelling of soil erosion and surface runoff, and also to authorities wishing to assess soil conservation adoption by farmers. This study focuses on the evaluation of four remote sensing techniques to estimate the cover fraction of cereal crop residues (i.e., wheat and corn) from multispectral and hyperspectral measurements. These are the Soil Adjusted Corn Residue Index (SACRI), the Crop Residue Index Multiband (CRIM), the Normalized Difference Index (NDI) and the spectral mixture analysis technique (SMA). Field campaigns that were carried out by the FLOODGEN project in Sainte-Angèle-de-Monnoir, Québec, Canada and in the Pays-de-Caux located in the Normandy region of France, allowed us to gather digital photographs, spectra and other measurements to determine the actual ground cover fraction. A linear regression analysis between results derived from Landsat-5 TM simulated field spectra and the actual ground cover fractions showed best results for the CRIM on the Ste-Angèle-de-Monnoir study site (R² = 0.96), and equally good results for the Pays-de-Caux study site (R² = 0.94). Results were not as good when SMA was applied to the same Landsat-5 TM simulated field spectra with R² values of 0.70 and 0.68 for both sites, respectively. However, results improved significantly when SMA was applied to the hyperspectral data in which case the R² values increased to 0.92 for the Sainte-Angèle-de-Monnoir site and 0.89 for the Pays-de-Caux study site. Results obtained with the NDI and SACRI from both simulated TM and hyperspectral field spectra were not conclusive.     

Interrill soil erosion as affected by tillage and residue cover

No-till cropping systems are effective in reducing soil erosion. The objective of this study was to determine whether high infiltration rates and low runoff and soil loss under long-term, no-till conditions in loessial regions of the Midwest US result from both the well-structured, porous condition of the soil and the protective cover of crop residue or primarily from residue cover. Soil loss, runoff, and infiltration were measured using a rainfall simulator on interrill erosion plots with and without residue cover on a conventional and two no-till systems in central Illinois. For both conventional till and no-till conditions, removing surface residue significantly decreased infiltration rates and increased soil loss. Tilling the no-till surface while maintaining an equal surface cover as with the no-till system slightly increased interrill erosion. Removing residue on a no-till system, however, increased soil loss significantly. A no-till soil condition without adequate residue cover will seal, crust, and erode with extremely high soil losses following surface drying.     

Simulating site-specific impacts of climate change on soil erosion and surface hydrology in southern Loess Plateau of China

Proper spatial and temporal treatments of climate change scenarios projected by General Circulation Models (GCMs) are critical to accurate assessment of climatic impacts on natural resources and ecosystems. The objective of this study was to evaluate the site-specific impacts of climate change on soil erosion and surface hydrology at the Changwu station of Shaanxi, China using a new spatiotemporal downscaling method. The Water Erosion Prediction Project (WEPP) model and climate change scenarios projected by the U.K. Hadley Centre's GCM (HadCM3) under the A2, B2, and GGa emissions scenarios were used in this study. The monthly precipitation and temperature projections were downloaded for the periods of 1900–1999 and 2010–2039 for the grid box containing the Changwu station. Univariate transfer functions were derived by matching probability distributions between station-measured and GCM-projected monthly precipitation and temperature for the 1950–1999 period. The derived functions were used to spatially downscale the GCM monthly projections of 2010–2039 in the grid box to the Changwu station. The downscaled monthly data were further disaggregated to daily weather series using a stochastic weather generator (CLIGEN). The HadCM3 projected that average annual precipitation during 2010–2039 would increase by 4 to 18% at Changwu and that frequency and intensity of large storms would also increase. Under the conventional tillage, simulated percent increases during 2010–2039, compared with the present climate, would be 49–112% for runoff and 31–167% for soil loss. However, simulated soil losses under the conservation tillage during 2010–2039 would be reduced by 39–51% compared with those under the conventional tillage in the present climate. The considerable reduction in soil loss in the conservation tillage indicates the importance of adopting conservation tillage in the region to control soil erosion under climate change.     

Repeated measurements on permanent plots using local variability sampling for monitoring soil cover

On US military installations, training activities such as vehicle use disturb ground and vegetation cover of landscapes, and increase potential rainfall runoff and soil erosion. In order to sustain training lands, soil erosion is of major concern. Thus there is a need for sampling designs to monitor degradation and recovery of land conditions. Traditionally, permanent plots are used to obtain the change of land conditions. However, the permanent plots often provide less information over time in characterizing the land conditions because of the fixed number and locations of plots. In this paper, we analyzed the sufficiency of a permanent plot sample and developed a method to improve the re-measurements of the permanent plots over time for a monitoring system of soil erosion based on spatial and temporal variability of a random function. We first applied a local variability based sampling method to generate reference samples that have sampling distances varying spatially and temporally to monitor a soil erosion relevant cover factor for an installation, Fort Riley, USA. Then, we compared a permanent sample with the reference samples annually over 13 years to determine additional sampling in the areas with high variability and temporarily suspending measurements of the permanent plots in the areas with low variability. The local variability based sampling provides estimates of local variability of the cover factor and thus is more cost-efficient than random sampling. By comparison with a reference samples, the re-measurements obtained should more accurately characterize the dynamics of the land conditions.     

The effect of urban refuse compost and different tractors tyres on soil physical properties, soil erosion and maize yield

Application of urban refuse compost to agricultural soil could help to solve municipalities' problems related to the increasing production of waste only if soil property improvement and environmental conservation can be demonstrated. The use of low-pressure tractor tyres is another proposal in modern agriculture for reducing soil compaction. This study thus aimed to detect the effects of both compost and low-pressure tractor tyres on soil loss, runoff, aggregate stability, bulk density, penetrometer resistance and maize (Zea mays L.) yield. A 3-year field experiment was carried out on a hilly (15% slope) clay loam soil in central Italy. Twelve plots (200 m² each) were monitored with tipping-pot devices for runoff and soil erosion measurement. Treatments were: compost addition (64 Mg ha⁻¹), mineral fertilisation, use of low-pressure tyres, use of traditional tyres, with three replicates, in a fully randomised block design. Compost was applied once at the beginning of the experiment. Runoff reduction due to compost ranged between 7 and 399 m³ ha⁻¹ during seasons, while soil erosion was reduced between 0.2 and 2.4 Mg ha⁻¹. Mean weight diameter (MWD) of stable aggregates, measured on wheel tracks, increased by 2.19 mm, then progressively decreased. Compost significantly increased bulk density by 0.08 Mg m⁻³ due to its inert fraction content. This effect was less evident in the second and third year, probably due to harrowing. Maize yields were slightly, but significantly, reduced in composted plots by 1.72 Mg ha⁻¹ in the third year. Low-pressure tyres significantly reduced soil loss in the third year by 1 Mg ha⁻¹. Furthermore, they did not significantly influence runoff volumes and soil structural stability. Low-pressure tyres or compost addition were singly able to prevent an increase in penetrometer resistance due to agricultural machinery traffic. Low-pressure tyres increased the maize yield during the 3 years and the difference (0.4 Mg ha⁻¹) became significant in the third year. In conclusion, results show the positive lasting effect of compost in ameliorating soil physical properties and reducing runoff and soil erosion. Low-pressure tyres appear justifiable both for the observed increase of grain production and reduction of soil compaction. This latter effect is, nevertheless, masked by compost addition which is also able to reduce penetrometer resistance. Further research is required to explain the causes of the slight inhibition of grain yield observed when compost was compared with mineral fertilisation.     

A proposed method for modelling the hydrologic response of catchments to burning with the use of remote sensing and GIS

Forest fires can have significant effects on the hydrological response of catchments, resulting in many cases in severe land degradation, flooding and soil erosion. These post-fire hazards often cause extensive damage to public and private property and urban infrastructure, thus carefully planned and designed mitigation activities are required for reducing their magnitude. This study presents a method for the quantitative estimation and mapping of post-fire erosion and runoff, which can provide the basis for the planning of these mitigation activities. Within the context of the proposed method a soil-erosion model is integrated within a GIS and remote sensing and digital cartographic data are used for estimating the model parameters before and after the passage of the fire. The model incorporates the effects of fire on the parameters that control erosion using remotely sensed estimates of the characteristics of the fire, such as the temperature and the extent. The method was implemented in four regions in Greece where severe wildfires took place during the summer of 1998. Pre- and post-fire model runs showed significant changes in runoff and erosion patterns as a result of the passage of the fire and a notable increase in the spatial variability of post-fire erosion rates. Results indicated net increases of up to 0.76 × 10^− 2 mm/h in erosion rates, although small decreases were also observed in some areas. The application of the method led to the identification of areas where erosion is expected to accelerate significantly and thus hazard-mitigation works are urgently required. The proposed method can clearly benefit from higher resolution remote-sensing data and more detailed datasets on soil properties and characteristics and is expected to provide a useful tool in planning and prioritising the works that are required for the mitigation of post-fire hazards.     

A pragmatic approach to modelling soil and water conservation measures with a catchment scale erosion model

To reduce soil erosion, soil and water conservation (SWC) methods are often used. However, no method exists to model beforehand how implementing such measures will affect erosion at catchment scale. A method was developed to simulate the effects of SWC measures with catchment scale erosion models. The method was implemented by applying the LISEM model to an agricultural catchment on the slopes of Mt. Kenya. The method consisted of a field scale calibration based on P-factors, followed by application at catchment scale. This calibration included factors such as saturated conductivity, Manning's n, roughness and slope angle. It was found that using data on P-factors, such models can be calibrated to give acceptable predictions at pixel scale. However, P-factors were also found to vary with land use type and storm size. Besides, more data on the physical effectiveness of SWC measures are needed. At catchment scale, the effect of SWC was found to be different from that at pixel scale. Most SWC were simulated to be more effective at catchment scale, indicating additional infiltration during transport through the catchment to the outlet. However, slope corrections in case of terraces were found to be less effective at this scale. Nevertheless, a simulation for current land use with current SWC measures indicated that these SWC measures decrease runoff by 28% and erosion by 60%.     

A kinematic wave based watershed model for soil erosion and sediment yield

In this study, a finite element method based soil erosion and sediment yield model has been developed for overland and stream flow. The one dimensional conservation of mass of sediment flow equation has been solved based on kinematic wave flow approximation and Galerkin's based numerical solution. Various thematic maps required for the model are prepared using Geographical Information System (GIS). Land use/Land cover is extracted from remotely sensed data. The proposed finite element based distributed model has been used for the estimation of soil erosion and sediment outflow by discretizing the watershed into small grids. The soil erosion and sediment outflow model has been developed and applied to Khadakohol watershed located in Nashik district of Maharastra state, India. Part of the available data has been used for the model calibration and the other part for model validation. The simulated results of the watershed have been compared with the observed data and found to be satisfactory.     

基于多源遥感数据的浙江省水土流失遥感监测

 通过浙江省土壤侵蚀强度判别模型,确定影响浙江省水土流失的主导因子;以TM数据和航摄1:1万DOM数据为遥感数据源,利用浙江省数字化地形图,结合样地调查,进行2009年浙江省水土流失遥感监测;以基于约束三角网技术的坡度因子提取方法、基于植被指数和像元二分模型的植被覆盖度因子提取方法以及土地利用因子提取方法,通过叠置分析实现土壤侵蚀信息提取。结果表明：浙江省水土流宍面积呈逐年减少的趋势;经过野外调査验证,研究成果准确度高。     

Developing a magnetic tracer to study soil erosion

Soil erosion is commonly measured as the quantity of sediment leaving a plot or watershed. The techniques for measuring soil erosion patterns and sediment redistribution within plots or watersheds by direct monitoring are very limited. The objective of this study was to develop a direct and non-intrusive tracer method to study the sources, patterns and rates of erosion and deposition of sediments in erosion plots. The magnetic tracer developed in this study consisted of polystyrene plastic beads embedded with a magnetic powder (magnetite). The “magnetized” beads, with a mean weight diameter of 3.2 mm and particle density of about 1.2 g cm⁻³, were uniformly mixed with soil and tested in the laboratory using simulated rainfall and inflow studies to simulate the interrill and rill components of soil erosion, respectively. In the interrill and rill experiments, the tracer was transported in the same proportion it was initially mixed with the soil. Given this fact, a magnetometer, which measures the soil's magnetic susceptibility, could be used to identify areas of deposition or detachment. The magnetic susceptibility would be increased or reduced depending on whether deposition or detachment occurs. To simulate detachment and deposition, a magnetometer was tested for different tracer concentrations and different thickness of soil containing the tracer. The magnetometer promises to be a sensitive, accurate, and useful tool to study the spatial variation of soil erosion when magnetic tracers are used.     

Implications of climate change scenarios for soil erosion potential in the USA

Atmospheric general circulation models (GCMs) project that increasing atmospheric concentrations of CO2 and other greenhouse gases May, result in global changes in temperature and precipitation over the next 40-100 years. Equilibrium climate scenarios from four GCMs run under doubled CO2 conditions were examined for their effect on the climatic potential for sheet and rill erosion in the conterminous USA. Changes in the mean annual rainfall factor (R) in the Universal Soil Loss Equation (USLE) were calculated for each cropland, pastureland and rangeland sample point in the 1987 National Resources Inventory. Projected annual precipitation changes were assumed to be from differences in either storm frequency or storm intensity. With all other USLE factors held constant these changes in R translated to changes in the sheet and rill erosion national average of +2 to +16 per cent in croplands, -2 to +10 per cent in pasturelands and -5 to +22 per cent in rangelands under the eight scenarios. Land with erosion rates above the soil loss tolerance (T) level and land classified as highly erodible (eredibility index >8) also increased slightly. the results varied from model to model, region to region and depended on the assumption of frequency versus intensity changes. These results show the range of sensitivity of soil erosion potential by water under projected climate change scenarios. However, actual changes in soil erosion could be mitigated by alterations in cropping patterns and other management practices, or possibly by increased crop growth and residue production under higher atmospheric CO2 concentrations.     

Effects of 30-year-old Aleppo pine plantations on runoff,soil erosion,and plant diversity in a semi-arid landscape in south eastern Spain

Forest management policies in Mediterranean areas have traditionally encouraged land cover changes, with the establishment of tree cover (Aleppo pine) in natural or degraded ecosystems for soil conservation purposes: to reduce soil erosion and to increase the vegetation structure. In order to evaluate the usefulness of these management policies on reduced erosion in semi-arid landscapes, we compared 5 vegetation cover types (bare soil, dry grassland, shrublands, afforested dry grasslands and afforested thorn shrublands), monitored in 15 hydrological plots (8 × 2 m), in the Ventós catchment (Alicante, SE Spain), over 4 years (1996 to 1999). Each cover type represented a different dominant patch of the vegetation mosaic on the north-facing slopes of this catchment. The results showed that runoff coefficients of vegetated plots were less than 1% of the precipitation volume; whereas runoff in denuded areas was nearly 4%. Soil losses in vegetation plots averaged 0.04 Mg ha^− 1 year^− 1 and increased 40-fold in open-land plots. The evaluation of these forest management policies, in contrast with the natural vegetation communities, suggests that: (1) thorn shrublands and dry grassland communities with vegetation cover could control runoff and sediment yield as effectively as Aleppo pine afforestation in these communities, and (2) afforestation with a pine stratum improved the stand's vertical structure resulting in pluri-stratified communities, but reduced the species richness and plant diversity in the understorey of the plantations.     

Using SPOT images and field sampling to map burn severity and vegetation factors affecting post forest fire erosion risk

Runoff and erosion rates are known to increase substantially after a major forest fire. Erosion control measures therefore need to be put into place quickly after a large fire, and determining where to locate the measures requires accurate mapping of post fire erosion risk. Burn severity can be determined from field observations, but these are costly and time consuming. Satellite imagery is an alternative to quickly map burn severity for erosion mapping purposes. Post fire erosion decreases as forest vegetation recovers and this is related to both pre fire vegetation characteristics and soil properties. The objectives of this study were to test the use of SPOT multispectral images for mapping burn severity, pre fire vegetation density, and longer term (2.5 years) vegetation recovery. Indices tested include the Normalized Burn Ratio (NBR), Normalized Difference Vegetation Index (NDVI), Differenced Normalized Burn Ratio (dNBR), and Differenced Normalized Difference Vegetation Index (dNDVI). Indices were compared to field data gathered immediately after the fire and about 2.5 years later. The multi-temporal indices (dNBR and dNDVI) were more useful for burn severity mapping in the heterogeneous forest–scrubland–vineyard environment where bedrock and vineyard surfaces were confused with burned areas when using single images (NBR and NDVI). All of the post fire indices showed traces of the fire 2.5 years later; this was confirmed using Analysis of Variance where differences in indices were related to original ground cover (pine forest, mixed forest, mostly bedrock and vineyards) and the burn scar. Pre fire vegetation cover was less successfully mapped using the NDVI according to the initial field observations. Similarly, none of the post fire indices were able to distinguish differences in N–S vegetation recovery revealed by field measurements of understory vegetation height and cover; N facing slopes had deeper finer soils and these more favourable conditions led to greater vegetation growth than on S facing slopes and topslope convexities. It is suggested that relationships between topography and soil properties can be useful for mapping both soil erodibility and post fire vegetation recovery.