土壤植被系统及其坡面生态工程意义

坡面生态工程不同于传统的土木工程，它把植被及其对坡面不稳定的影响与侵蚀过程联系起来，这个生物学途径中的一个重要概念是“土壤植被系统”，它强调了生态工程途径的生物生态学属性，由它可推导出一定的理论假设，即土壤植被系统的若干属性和性能。这些理论实体和假设有助于对坡面生态工程科学原理的构建。

Ration Spatial Characteristics Analysis of Soil Loss Based on GIS and RUSLE in Jinzhou City

Supported by RS technology and GIS technology, the amount of soil loss and soil erosion intensity in Jinzhou City in 2010 were quantitatively evaluated by the modified RUSLE model. The characteristics of the spatial distribution of soil loss in Jinzhou City were analyzed. The results showed that the soil erosion area of Jinzhou City in 2010 was 7 284.87 km2, accounting for 70.72% of the total area of Jinzhou City. The average soil erosion modulus was 18.27 t/（hm2＆#183;a）, belonging to mild erosion. Two slope belts of 15＆#176;-25＆#176; and 6＆#176;-15＆#176; were the main soil erosion re-gions in Jinzhou City. Soil erosion in Jinzhou City was mainly concentrated in the rural residential land and the dry land, and the soil erosion amount of these two land types accounted for 60.97%of the total soil erosion amount in Jinzhou City in 2010. It was suggested that the treatment of these two land types should be strengthened and be main treatment object for soil and water conservation in future. The research could provide scientific basis for the governments to make policies about soil loss.

Effects of Three-dimensional Structure of Vegetation on Particle Size Distribution and Nutrient Content of Water-eroded Red Soil

Based on the vertical stratification type of vegetation in the 48 plots （15m×15 m） in Hetian Town, Changting County, Fujian Province, this study was conduct ed to determine the overall vegetation fractional coverage （VFC）, litter thickness, soi particle size distribution and nutrient content at different vertical level, analyze the correlations between vegetation characters and soil properties, and compare the dif ferences in the VFC, litter thickness, soil particle size distribution and nutrient con- tent among different erosion degrees and vertical structure types. The result., showed that the VFC and litter thickness were all negatively related to erosion de gree; they were positively related to soil organic matter content, total nitrogen con- tent and total phosphorus content, but not significantly correlated with soil tota potassium content. When the VFC was higher than 50% and litter thickness wa.＇ higher than 20 ram, the water and soil could be effectively conserved; and the plan litter showed better water and soil conservation effect than the upper vegetation o~ canopy layer. In the vertical structure types of different vegetations, the forest-shrub grass, forest-shrub, shrub-grass and pure grass all could promote vegetation growth improve soil structure and maintain soil fertility.

Synthesis Analysis of Soil Erosion for Three-River Headwater Region Based on GIS

In this paper,based on the common soil erosion model,the Three-River Headwaters region was select for study object. GIS methods are applied to conduct Semi-quantitative assessment for different types of soil erosion,and some results are concluded. The water erosion occurs in High Mountain and extra-high mountain of Yushu,Nangqian,Banma and Jiuzhi County in the southeast and south of the Three-River Headwaters region. The degree of erosion is prone to topography,precipitation,river and human activity. The freeze-thaw erosion mainly distributes in the northwest of the Three-River Headwaters region. The area of middle and above middle erosion degree accounts for roughly 50%.

Degradation of Soil Properties due to Erosion on Sloping Land in Southern Jiangsu Province,China

Soil erosion accelerates soil degradation. Some natural soils and cultivated soils on sloping land in southern Jiangsu Province, China were chosen to study soil degradation associated with erosion. Soil erosion intensity was investigated using the 137Cs tracer method. Soil particle-size distribution, soil organic matter (OM), total nitrogen (TN) and total phosphorus (TP) were measured, and the effects of erosion on soil physical and chemical properties were analyzed statistically using SYSTAT8.0. Results indicated that erosion intensity of cultivated soils was greater than that of the natural soils, suggesting that cultivation increased soil loss. Erosion also led to an increase of coarser soil particle proportion, especially in natural soils. In addition, silt was the primary soil particle lost due to erosion. However, in cultivated fields, coarser soil particles over time were attributed not only to soil erosion but also to mechanical eluviation as a result of farming activities. Moreover, erosion caused a decrease in soil OM, TN and TP as well as thinning of the soil layer.

Soil Conservation Measures in Rainfed Olive Orchards in South-Eastern Spain: Impacts of Plant Strips on Soil Water Dynamics

Sloping and mountainous olive production systems are widespread, occupying large parts of the Mediterranean landscape prone to water erosion. Soil erosion, runoff, and soil water content patterns over a three-year period were monitored in erosion plots on a mountainside with rainfed olive （Olea europaea cv. Picual） trees under： 1） non-tillage with barley strips of 4 m width （BS）; 2） non-tillage with native vegetation strips of 4 m width （NVS）; and 3） non-tillage without plant strips （NT）. The erosion plots, located in Lanjaron （Granada, south-eastern Spain）, on a 30% slope, were 192 m2 in area. For assessing soil water dynamics in real-time and near-continuous soil water content measurements, multisensor capacitance probes were installed in the middle of plant strips and beneath the olive tree at five soil depths （10, 20, 30, 50, and 100 cm）. The highest erosion and runoff rates were measured under NT, with a mean of 17.3 Mg ha-1 year-1 and 140.0 mm year-1, respectively, over the entire study period. The BS and NVS with respect to the NT reduced erosion by 71% and 59% and runoff by 95% and 94%, respectively. In general, greater available soil water content was found under BS than NVS and NT, especially beneath the olive tree canopies. These results supported the recommendation of non-tillage with barley strips in order to reduce erosion and to preserve soil water for trees in traditional mountainous olive-producing areas, where orchards cover vast tracts of land.

Changes in SOC and Nutrients under Intensive Tillage in Two Types of Slope Landscapes

The net effect of tillage erosion on soil properties would be associated with the spatial variation in soil constituents,and therefore plays an important role in ecological agriculture.We conducted a consecutive tillage by hoeing 15 times during a period with no rainfall in the two slope landscapes(a linear slope and complex slope) of the Yangtze Three Gorges reservoir areas,to examine the relationship between soil erosion rates and the variations in soil chemical properties and compare the effects of soil redistribution on SOC and nutrients between the linear and complex slopes.After the simulated tillage,notable changes in 137 Cs inventories of the soil occurred in the summit and toeslope positions on the linear slope,while there were significant changes in 137 Cs inventories at convex and concave positions on the complex slope.Soil profile disappeared at the summit slope boundary,with the exposure area of 16.0% and 7.6% of the experimental plot,respectively,for the linear and complex slopes due to no soil replacement.Soil organic C and nutrients were completely depleted with the disappearance of soil profiles at soil eroding zones,whereas a remarkable increase in SOC,total N and available nutrient concentrations of the post-tillage surface soil and a decrease in total nutrient concentrations(P and K) were found at depositional zones on the linear slope.For the complex slope,however,changes in SOC and nutrient concentrations of the post-tillage surface soil exhibited a patterndifferent from that on the linear slope,which showed a remarkable decrease in SOC and total nutrient concentrations but a slight increase in available nutrient concentrations after tillage in the toeslope position.Due to the gradual increase in soil depth from top to bottom of the slope,SOC and nutrient inventories in the soil profiles were significantly correlated with soil redistribution rates on both the linear and complex slopes.Tillage causes remarkable changes of soil chemical properties in the surface soil layer and soil profile,and increases SOC and nutrient inventories for the soil profile downslope in steeply sloping landscapes.

Spatial Distribution of Soil Erosion Sensitivity on the Tibet Plateau

The Tibet Plateau, occupying the main part of Qinghai-Tibet Plateau and having an average altitude of 4 500 m, has geomorphological features that are unique in the world, with soil erosion being one of the main ecological problems. Thus the main objectives of the present research were to set up an efficient and simple way of evaluating spatial distribution of soil erosion sensitivity in the Tibet Plateau as well as the responses of soil erosion to changes of natural environmental conditions, and to indicate key regions where soil erosion should be preferentially controlled. Based on the Universal Soil Loss Equation (USLE), the study applied geographic information system (GIS) technology to develop a methodological reference framework, from which soil erosion sensitivity could be evaluated. The impact of precipitation, soil, topography and vegetation on soil erosion was divided into classes of extreme sensitivity, high sensitivity, medium sensitivity, low sensitivity and no sensitivity. With the aid of GIS, the resultant map from overlaying various factors showed that soil erosion sensitivity had great discrepancy in different parts of the region. In the southeastern part of the Tibet Plateau there were mainly three classes of sensitivity, namely, extreme, high and medium sensitivity. However, the other two classes, low and no sensitivity, were dominant in the northwestern part.

An Indicator System for Assessing Soil Erosion in the Loess Plateau Gully Regions:A Case Study in the Wangdonggou Watershed,China

The Wangdonggou Watershed on the Loess Plateau in China was selected as the study area to develop a model for soil erosion assessments. Using the data collected at 20 sampling sites all tentatively selected indicators were assessed against their corresponding erosion intensity through a correlation analysis. Eight highly correlated indicators were then chosen for the soil erosion assessment. In addition, threshold limits to delineate the class size for these indicators and weights to rank them were determined. Next, a grading model incorporating the selected indicators class rating and their associated weights was developed and verified by an on site evaluation of the soil erosion intensity in the study area. Results of the verification showed that the overall accuracy of the indicator system for assessing soil erosion in the Loess Plateau gully regions could reach 85%.

Impact of soil texture and sweetpotato cropping system on soil erosion and nutrient loss in the Three Gorges Reservoir Area of the Changjiang River

This study investigated the impact of soil texture and sweetpotato cropping system on soil erosion and nutrient loss in the drought infield of the Three Gorges Reservoir Area of Changjiang River under field conditions. A factorial experiment was conducted in the study using five soil textures and two cropping systems. The lost soil during the crop season was recovered by a soil-blocking device and the dry weights for the total lost soil and its nutrient components, such as ammonium nitrogen, effective phosphorus, K^＋ and organic matter were analyzed. We found that soil texture significantly affected the dry weights of the total lost soil, effective phosphorus, K^＋, and organic matter, while sweetpotato cropping systems and interaction between soil texture and sweetpotato cropping system affected the dry weights of the total lost soil, the effective phosphorus and organic matter. Among the five soil textures tested, Da and Huang caused significantly less soil erosion and nutrient loss compared with the other three soil textures; intercropping sweetpotato with corn significantly reduced soil erosion and nutrient loss.

A Quantification of the Effects of Erosion on the Productivity of Purple Soils

Research on the effects of soil erosion on soil productivity has attracted increasing attention.Purple soil is one of the main soil types in China and plays an important role in the national economy.However,the relationship between erosion and the productivity of purple soils has not been well studied.The purpose of this research was to determine if soil depth,which is dependent on the rate of erosion,has an influence on crop yield and growth.Plot and pot experiments at different soil depths were performed.Results indicate that soils from different parental materials had different growth features and crop yields due to the differential fertility of the derived soils.The yield reduction rate increases exponentially with the depth of eroded soil(level of erosion).The yield reduction rate per unit eroded soil horizon(10 cm) is approximately 10.5% for maize and wheat.

Large-area Analysis of Soil Erosion and Landslides Induced by Rainfall: A Case of Unsaturated Shallow Deposits

Unsaturated shallow soil deposits may be affected by either superficial soil erosion or shallow landslides in adjacent or overlapping source areas and in different seasons when a different soil suction exists.The triggering analysis of both these processes is a relevant issue for the hazard analysis while the literature mostly provides specific approaches for erosion or for landslides.The paper proposes a largearea analysis for a case study of Southern Italy,consisting of unsaturated shallow deposits of loose pyroclastic(air-fall) volcanic soils that have been repeatedly affected by erosion and landslides in special seasons.For a past catastrophic event, the simulated source areas of shallow landslides are smaller than those observed in the field while the simulated eroded areas with thickness greater than 5cm are comparable with the in-situ evidences, if the analysis takes into account high rainfall intensity and a spatially variable soil cover use.More in general, the results of the paper are consistent with the previous literature and also provide a methodological contribution about the application of distinct tools over large area.The added value is that the paper shows how the combination of distinct large-area analyses may help with understanding the dominant slope instability mechanisms.Only once this goal is fully achieved, can specific physically-based analyses be confidently performed at detailed scales and for smaller specific areas.

A Participatory GIS Approach to Identify Critical Land Degradation Areas and Prioritize Soil Conservation for Mountainous Olive Groves(Case Study)

Climate change scenarios predict an increase in the frequency of heavy rainfall events in some areas. This will increase runoff and soil erosion, and reduce agricultural productivity, particularly on vulnerable mountainous agricultural lands that is already exhibiting high rates of soil erosion. Haphazard implementation of soil and water conservation （SWC） interventions on scattered fields is inefficient in reducing soil erosion. The objective of this study was to identify areas at high risk of erosion to aid the design and implementation of sustainable SWC using GIS analysis and farmers＇ participation approach. A 25 m digital elevation model （DEM） was used to derive layers of flow accumulation, slope steepness and land curvature, which were used to derive an erosion-risk （priority） map for the whole watershed. Boundaries of farmers＇ fields were mapped and verified by the community and each field was classified into high, moderate or low erosion risk. Fields with low flow accumulation （top of hill） and/or steep slope and/or convex slope were assigned high erosion risk and therefore high implementation priority. The study showed that more than 54% of the fields were classified into high erosion risk areas. Accordingly, a community-watershed plan was established, revised and approved by the community.Incentive loans to implement SWC measures were distributed to 100 farmers based on the priorities of their fields. Judged by local farmers and using 16 randomly selected fields, 90% of the targeted areas were correctly identified using the erosion risk map. After two years, the conservation measures had led to marked improvement of soil conservation. The approach is simple and easy to comprehend by the community and provides scientific basis to prioritize the implementation of SWC and to target the most degraded areas, which amplify the impact of these in reducing the vulnerability to land degradation.

Linking vegetation cover patterns to hydrological responses using two process-based pattern indices at the plot scale

Vegetation cover pattern is one of the factors controlling hydrological processes. Spatially distributed models are the primary tools previously applied to document the effect of vegetation cover patterns on runoff and soil erosion. Models provide precise estimations of runoff and sediment yields for a given vegetation cover pattern. However, difficulties in parameterization and the problematic explanation of the causes of runoff and sedimentation rates variation weaken prediction capability of these models. Landscape pattern analysis employing pattern indices based on runoff and soil erosion mechanism provides new tools for finding a solution. In this study, the vegetation cover pattern was linked with runoff and soil erosion by two previously de- veloped pattern indices, which were modified in this study, the Directional Leakiness Index （DL[） and Flowlength. Although they use different formats, both indices involve connectivity of sources ,areas （interpatch bare areas）. The indices were revised by bringing in the functional heterogeneity of the plant cover types and the landscape position. Using both artificial and field verified vegetation cover maps, observed runoff and sediment production on experiment plots, we tested the indices＇ efficiency and compared the indices with their antecedents. The results illustrate that the modified indices are more effective in indicating runoff at the plot/hillslope scale than their antecedents. However, sediment export levels are not provided by the modified indices. This can be attributed to multi-factor interaction on the hydrological process, the feedback mechanism between the hydrological function of cover patterns and threshold phenomena in hydrological processes.

Effect of Land Use on Soil Erosion and Nutrients in Dianchi Lake Watershed, China

Soil erosion and loss of soil nutrients have been a crucial environment threat in Southwest China. The land use and its impact on soil qualities continue to be highlighted. The present study was conducted to compare soil erosion under four land use types(i.e.,forestland, abandoned farmland, tillage, and grassland) and their effects on soil organic carbon(SOC), total nitrogen(TN) and total phosphorus(TP) in the Shuanglong catchment of the Dianchi Lake watershed, China. There were large variations in the erosion rate and the nutrient distributions across the four land use types. The erosion rates estimated by137 Cs averaged 2 133 t km-2year-1under tillage and abandoned farmland over the erosion rate of non-cultivated sites, and the grasslands showed a net deposition. For all sites, the nutrient contents basically decreased with the soil depth. Compared with tillage and abandoned farmland, grassland had the highest SOC and TN contents within 0–40 cm soil layer, followed by forestland. The significant correlations between137 Cs, SOC and TN were observed. The nutrient loss caused by erosion in tillage was the highest. These results suggested that grassland and forestland would be beneficial for SOC and TN sequestration over a long-term period because of their ability to reduce the loss of nutrients by soil erosion. Our study demonstrated that reduction of nutrient loss in the red soil area could be made through well-managed vegetation restoration measures.

^(137)Cs Redistribution in Thin Stony Soil of a Carbonate Rock Slope in Southwest China

The fallout radionuclide cesium-137(137 Cs) has been widely employed as a tracer for assessment of soil loss from thick uniform soils;however,few studies have been conducted on thin stony soils on slopes underlain by carbonate rocks which are widely distributed in karst areas.Information derived from 137 Cs measurement of soil samples collected along a carbonate rock slope with thin stony soil where neither soil erosion nor deposition occurred was used to investigate the characteristics of 137 Cs redistribution in a karst area of Southwest China.The results indicated that the 137 Cs inventories of the surface soil on the slope studied were much lower than that of the local 137 Cs reference inventory and the 137 Cs activities were much higher than those on slopes with thick uniform soils.The spatial distribution of 137 Cs inventories was characterized by considerable variation.The high 137 Cs depletion in the stony soil of the slope studied was mainly because a considerable proportion of the fallout input of 137 Cs could be lost with runoff and the dissolution of carbonate particles in the soil promoted the loss of 137 Cs.These demonstrated that the rates of soil loss could not be estimated from the degree of depletion of the 137 Cs inventory relative to the local reference inventory for the thin stony soil of the rocky slope underlain by carbonate rocks in the study area in the way that has been widely used in areas with thick uniform soils.

The effects of vegetation on runoff and soil loss:Multidimensional structure analysis and scale characteristics

This review summarizes the effects of vegetation on runoff and soil loss in three dimensions: vertical vegetation structures(aboveground vegetation cover, surface litter layer and underground roots), plant diversity, vegetation patterns and their scale characteristics. Quantitative relationships between vegetation factors with runoff and soil loss are described. A framework for describing relationships involving vegetation, erosion and scale is proposed. The relative importance of each vegetation dimension for various erosion processes changes across scales. With the development of erosion features(i.e., splash, interrill, rill and gully), the main factor of vertical vegetation structures in controlling runoff and soil loss changes from aboveground biomass to roots. Plant diversity levels are correlated with vertical vegetation structures and play a key role at small scales, while vegetation patterns also maintain a critical function across scales(i.e., patch, slope, catchment and basin/region). Several topics for future study are proposed in this review, such as to determine efficient vegetation architectures for ecological restoration, to consider the dynamics of vegetation patterns, and to identify the interactions involving the three dimensions of vegetation.

Relationships Between Intensity Gradation and Evolution of Soil Erosion: A Case Study of Changting in Fujian Province, China

Soil erosion gradation is a robust and objective quantitative indicator of soil erosion intensity. Recent applications of soil erosion gradation have focused on monitoring soil erosion with models or simulation of soil erosion through gradation trends. However, soil erosion simulation accuracy is generally being reduced due to the rare consideration of the relationship between soil erosion gradation and erosion evolution. In this study, we investigated different soil erosion intensity grades to demonstrate their sensitivity to types and rates of erosion. Specifically, the objective was to define the relationship between soil erosion gradation and soil erosion evolution in Changting, an undeveloped area in Fujian Province, China, for four time intervals (1975, 1990, 1999, and 2006). The time series of erosion gradation were developed by modeling analysis with integration of several erosion indicators, and the relationships between the erosion grades and evolution types and rates were quantified. Comparison of the collapsing forces with natural and restoring forces based on human activity demonstrated that there existed an obvious spatial uncertainty in the erosion evolution types, both positive and negative succession coexisted, and the evolution rates were mostly influenced by the force of policy orientation. The impacts of these driving forces were eventually reflected in the erosion intensity gradation and erosion evolution. The correlation between the negative succession rate and erosion intensity gradation was weak and showed a poor contribution to the average succession rate, while the negative correlation between the positive succession rate and erosion intensity gradation would be increasingly clear as time passed.