Plot-Scale Experimental Studies

چکیده تغییر غیر اصولی کاربری اراضی به ویژه اکوسیستم های طبیعی، عموما تأثیر قابل توجهی را بر ویژگیهای فیزیکی، شیمیایی و بیولوژیکی خاکها و در پی آن میزان روان آب و فرسایش خاک می گذارد. بررسی تغییرات روان آب و فرسایش خاک در پی تغییر خصوصیات خاک و شناخت متغیرهای مؤثر خاک بر وقوع آن می تواند در بهبود توصیه های مدیریتی و کمی نمودن تغییرات روان آب و فرسایش خاک مفید واقع شود. لذا این پژوهش به منظور بررسی روان آب و فرسایش خاک در خاک های تحت پوشش اراضی جنگلی و مقایسه آن با اراضی زراعی و باغ که منتج از تغییر کاربری جنگل بوده و همچنین شناسایی فاکتورهای مؤثر در روان آب و فرسایش خاک از بین متغیرهای کمی خاک در محدوده شهرستان ساری صورت گرفته است. سپس در هر یک از کاربری ها، مبادرت به اندازه گیری میزان روان آب و فرسایش خاک طی انجام شبیه سازی باران با شدت ثابت 2 میلی متر بر دقیقه، مدت زمان 15 دقیقه و نمونه برداری خاک در 15 تکرار شد. نتایج حاصله نشان داد که بیشترین و کمترین میزان روان آب به ترتیب در کاربری جنگل و باغ ایجاد شده است. همچنین مقدار فرسایش خاک در اراضی زراعی و باغ به ترتیب 76/1 و 36/1 برابر کاربری جنگل اندازه گیری شد. طبق نتایج ماتریس همبستگی درصد سیلت، رطوبت قبلی و وزن مخصوص ظاهری خاک دارای همبستگی معنی دار مثبت و درصد شن و ماده آلی دارای همبستگی معنی دار منفی با میزان روان آب می باشند. همچنین متغیرهای رس، شن و ماده آلی خاک به صورت ارتباط منفی و درصد سیلت و رطوبت قبلی خاک دارای همبستگی معنی دار مثبت با میزان فرسایش شناخته شدند. واژه های کلیدی: باران ساز، تغییر کاربری، روان آب، فرسایش خاک

1. Soil Erosion by Wind and Water: Problems and Prospects, R. Lal The Need for Improved Data Data Extrapolation Standardization of Methodology and Data Reliability Record Duration and Data Continuity Toward Standardization of Research Methods 2. Laboratory and Field Plots for Erosion Research, C. K. Mutchler, C. E. Murphree, and K. C. McGregor The Project Outline The Soil Erosion Process Small Plots Conclusions 3. Measuring Sediment Yield from River Basins, D. E. Walling Introduction Reliability of Existing Sediment Yield Data Designing Sediment Yield Monitoring Programs Additional Sources of Information on Sediment Yields 4. Rainfall Simulators for Soil Erosion Research, L. D. Meyer Characteristics of Rainfall Simulators Types of Rainfall Simulators Personnel Requirements and Related Equipment Rainfall Simulators: Asset or Burden? 5. The Revised Universal Soil Loss Equation, K. G. Renard, J. M. Laflen, and D. K. McCool R-factor K-factor L- and S-factor C-factor P-factor Comparison of RUSLE and USLE Summary 6. Modeling Soil Erosion, M. A. Nearing, L. J. Lane, and V. L. Lopes Mechanics of Erosion by Water Development of a Physically-Based Erosion Model Model Analysis Modeling on Watershed Scales Integrated Systems for Water Erosion Prediction 7. Research Progress on Soil Erosion Processes and a Basis for Soil Conservation Practices, C. W. Rose Types and Objectives of Soil Erosion Models Basic Approach to Sediment Erosion and Transport Erosion/Deposition Process Model A Simplified Erosion Process Model The Effect of Plot Length on Soil Loss per Unit Area Effect of Surface Contact Cover and Slope on Soil Loss 8. Erodibility and Erosivity, R. Lal and W. Elliot Soil Erosion Process Soil Erodibility Summary 9. Assessing Vegetative Cover and Management Effects, M. A. Stocking How Vegetative Cover and Management Work Key Areas in Crop Cover and Management Research Methodologies 10. Monitoring the Impact of Soil Erosion on Crop Productivity, F. J. Pierce and R. Lal The Need for Erosion-Productivity Research Approaches to the Problem Toward a Minimum Data Set The Erosion-Productivity MDS Model Building and Validation Summary and Conclusions 11. Wind Erosion, E. L. Skidmore Soil Erodibility by Wind Wind Erosivity Ridge Roughness Field Length Vegetative Factor A Wind Erosion Model Management Effects Conclusions 12. Methods for Investigating Basic Processes and Conditions Affecting Wind Erosion, E. L. Skidmore, L. J. Hagen, D. V. Armbrust, A. A. Durar, D. W. Fryrear, K. N. Potter, L. E. Wagner, T. M. Zobeck Wind Databases and Simulation Particle Detachment and Transport Aggregate Stability Dry Aggregate Size Distribution Surface Roughness: Shelter Angle Distribution Surface Roughness: Digitization of Pin Meter Photos Surface Crusting Loose Surface Particles Soil Wetness Canopy Structure Field Scale Wind Erosion Measurement Index

Soil erosion by water is one of the most important land degradation processes in Mediterranean environments. This process is strongly linked to problems of flooding and channel management. This article reviews existing knowledge on these topics and defines research gaps. In the framework of environmental change studies it is important to consider soil erosion at various spatial and temporal scales. Most field measurements and modelling efforts have hitherto concentrated on water erosion processes operating at the runoff plot scale. Soil erosion processes operating at other spatial scales have received much less attention in the literature. Yet, there are indications that gully and channel erosion are probably the dominant sediment sources in a variety of Mediterranean environments. Beside water erosion, other erosion processes operating within catchments, such as tillage erosion, land reshaping for land preparation (e.g., terracing) or soil quarrying can have significant impacts on soil profile truncation. Land use changes strongly affect the intensity of these processes. The conditions, position and connectivity of the runoff and sediment generating areas within catchments have a profound effect on flood characteristics within the main channels but the dynamics are not well understood. Some research has taken place into meteorological conditions producing catastrophic flooding and into development of hydrological models using catchment variables. Much less is known of the properties and effects of flood waves within channels, partly because of lack of records of these infrequent events. It is not only water but also sediment which causes destruction in floods, yet sediment is frequently ignored in channel management. The extreme conditions associated with floods in the region, the variability of flows and of flood zones, the mobility of the channels and the high sediment loads create particular challenges for channel management. Trends in land use and channel management are tending to exacerbate these problems. From this review it can be concluded that there is still an important need for process-based understanding and modelling of key soil erosion processes operating at a range of scales: i.e., from plots over hillslopes, catchments to regions. In particular, more research is needed on the linkages between upland areas which produce large volumes of runoff and sediment and channels on the other hand. Such linkages are through gullies and sedimentation zones. Monitoring and experi mental data on key soil erosion and channel processes operating within Mediterranean landscapes are crucial for the improvement of soil erosion and channel models for a range of scales. In particular, long-term monitoring of soil erosion processes and stream channel changes seems to be essential to observe the effects of infrequent torrential rain events on severe erosion, flooding and stream channel changes as well as on the transient response of Mediterranean landscapes to changes in land use and climate. Systematic collation of historical evidence of changes would be valuable. Implications of land and water use need to be examined in detail. A wide range of alternative strategies and techniques of channel and basin management must be explored and modelled. A holistic approach to management of the fluvial system is recommended.

Small portable rainfall simulators are considered a useful tool to analyze soil erosion processes in cultivated lands. European research groups in Spain (Valencia, Málaga, Lleida, Madrid and La Rioja), France (Reims) and Germany (Trier) have used different rainfall simulators (varying in drop size distribution and fall velocities, kinetic energy, plot forms and sizes, and field of application) to study soil loss, surface flow, runoff and infiltration coefficients in different experimental plots (Valencia, Montes de Málaga, Penedès, Campo Real and La Rioja in Spain, Champagne in France and Mosel-Ruwer valley in Germany). The measurements and experiments developed by these research teams give an overview of the variety of methodologies used in rainfall simulations to study the problem of soil erosion and describe the erosion features in different climatic environments, management practices and soil types. The aims of this study are: (i) to investigate where, how and why researchers from different wine-growing regions applied rainfall simulations with successful results as a tool to measure soil erosion processes; (ii) to make a qualitative comparison about the general soil erosion processes in European terroirs; (iii) to demonstrate the importance of the development of standard method for measurement of soil erosion processes in vineyards, using rainfall simulators; and (iv) and to analyze the key factors that should be taken into account to carry out rainfall simulations. The rainfall simulations in all cases allowed infiltration capacity, susceptibility of the soil to detachment and generation of sediment loads to runoff to be determined. Despite using small plots, the experiments were useful to analyze the influence of soil cover to reduce soil erosion, to make comparisons between different locations, and to evaluate the influence of different soil characteristics. The comparative analysis of the studies performed in different study areas points out the need to define an operational methodology to carry out rainfall simulations, which allows us to obtain representative and comparable results and to avoid errors in the interpretation in order to achieve comparable information about runoff and soil loss.

ABSTRACTRainfall erosivity is one of the most dynamic factors in the soil erosion process. The increase in soil erosion caused by high rainfall erosivity, and the subsequent loss of soil nutrients, can lead to reduced food production and ecosystem services. This research program under the New South Wales (NSW) Climate Change Adaptation Strategy, assesses rainfall pattern change, rainfall erosivity and erosion risk across NSW under future climate conditions. Daily rainfall erosivity and erosion risk were modelled by Revised Soil Loss Universal Equation (RUSLE) approach and compared with that driven by observed rainfall data. Future rainfall erosivity and soil erosion risk change were investigated from daily precipitation projection of the updated NSW and Australian Regional Climate Modelling (NARCliM1.5) for two future scenarios, RCP4.5 and RCP8.5, from the historical (1986–2005) to far future (2060–2079) periods. The annual average rainfall erosivity is projected to increase about 8% under RCP 4.5 and further decrease 5% under RCP 8.5 in NSW due to the predicted temperature rises. More frequent heavy rainfall events are projected to occur during summer (December–January–February), and the rainfall from these extreme rainfall events is expected to account for 51% of the total annual rainfall in the far future. NARCliM‐derived results underestimate annual rainfall erosivity compared with observation‐derived erosivity. There are greater instability (root mean squared error [RMSE]: 803.2) and erosivity uncertainty (Bias: 16%~48%) in high rainfall zones. At a monthly scale, dry months (June–July–August) are becoming drier, while wet months (December–January–February) are becoming wetter and more erosive. 67% of NSW is predicted to experience increased rainfall erosivity under RCP4.5, whereas most of NSW will shift to drought and its consequent effects under the high‐end emission scenario (RCP 8.5). To address the dual challenges of excessive wetness in coastal and north‐east NSW and increasing aridity in Western NSW, it is necessary to develop climate change adaptation management strategies based on high‐risk areas and monthly or seasonal conditions. With the emerging launch of NARCliM2.0, we anticipate further improvements of these predictions will be achieved by more accurate models and data at higher spatial and temporal resolutions.

Erosion by water on agricultural areas has been studied by USDA (SCS, ARS, FS, NRCS) since the 1930‘s, initially consisting of natural runoff plots at numerous locations in the country that provided data that culminated in the development of the Universal Soil Loss Equation (USLE) in 1965 in Agriculture Handbook 282 (Wischmeier and Smith, 1965). Rainfall simulation equipment developed by ARS scientists located at Purdue University during the early 1960‘s was used to supplement the natural rainfall plot data and provided the ability to rapidly study soil erosion processes in more controlled laboratory and field experiments. The USLE update in Agriculture Handbook 537 (Wischmeier and Smith, 1978) contained a soil erodibility nomograph, developed from the results of extensive field rainfall simulation studies across the Midwest U.S. Transitions to process-based soil erosion modeling approaches in the 1980‘s-1990‘s relied upon laboratory and field rainfall simulation experiments to study processes and develop parameterization approaches for sensitive model input parameters. The Water Erosion Prediction Project (WEPP) model solves differential equations down a slope profile, that compute changes in sediment load and detachment/deposition at discrete points (Flanagan and Nearing, 1995; Flanagan et al., 2001). Unfortunately, most data available for validation of process-based hillslope interrill/rill erosion is from natural runoff plots (USLE database) or other natural or simulated rainfall studies where soil (sediment) loss was only measured at the plot end. Newer experimental measurement techniques, equipment, and approaches are needed to allow examination of changes in sediment detachment/deposition/loads with very fine spatial resolution down a hillslope and down a rill channel. The current modeling techniques also assume either uniformly spaced rill channels down a slope profile (default is 1-m spacing), or alternately simulations can be conducted where all surface flow is assumed to be distributed at a uniform shallow depth across the entire flow width. However, in real world situations the soil conditions, landscape complexities and increases in slope lengths can result in situations where no evident rilling occurs, rill spacings change with increasing slope lengths, or surface flows converge or diverge which may result in channelized rill flows changing to broader sheet flows. These complex surface flow situations need to be accounted for in any new water erosion prediction technologies, as they can greatly affect soil detachment and deposition processes. Additionally, subsurface hydrology effects also need to be better accounted for in any new technologies. Current erosion prediction models poorly account for water moving within the soil, and how saturation conditions can weaken the soil surface and make it more susceptible to detachment. A comprehensive understanding of how subsurface water moves and can converge in fields (and may emerge to the surface) is needed in new modeling approaches that can also be linked to initiation and development of ephemeral gullies. Additionally, better understanding and modeling of the effects of subsurface drainage and controlled drainage systems on hydrology and soil erosion is required. This also highlights the needs to move to erosion prediction systems that truly represent the landscape and fields as 2-D/3-D surfaces. Current prediction technologies are largely limited to estimating soil erosion processes at points down a line to represent a rectangular area. Long-term temporal effects of various practices on soil health and soil hydrology and erosion also should be accounted for in new erosion models. Currently, baseline soil erodibility is assumed to be a constant value for a particular soil and cropping system as a function of soil texture, organic matter, and other properties. However, fields that are in long-term pasture, or long-term no-till row crop management systems along with the use of cover crops may substantially change soil organic matter, soil structure, infiltration characteristics, and erodibilities that are not currently reflected in USDA models. This presentation will explore these and other areas of research needed.

Erosion by water on agricultural areas has been studied by USDA (SCS, ARS, FS, NRCS) since the 1930‘s, initially consisting of natural runoff plots at numerous locations in the country that provided data that culminated in the development of the Universal Soil Loss Equation (USLE) in 1965 in Agriculture Handbook 282 (Wischmeier and Smith, 1965). Rainfall simulation equipment developed by ARS scientists located at Purdue University during the early 1960‘s was used to supplement the natural rainfall plot data and provided the ability to rapidly study soil erosion processes in more controlled laboratory and field experiments. The USLE update in Agriculture Handbook 537 (Wischmeier and Smith, 1978) contained a soil erodibility nomograph, developed from the results of extensive field rainfall simulation studies across the Midwest U.S. Transitions to process-based soil erosion modeling approaches in the 1980‘s-1990‘s relied upon laboratory and field rainfall simulation experiments to study processes and develop parameterization approaches for sensitive model input parameters. The Water Erosion Prediction Project (WEPP) model solves differential equations down a slope profile, that compute changes in sediment load and detachment/deposition at discrete points (Flanagan and Nearing, 1995; Flanagan et al., 2001). Unfortunately, most data available for validation of process-based hillslope interrill/rill erosion is from natural runoff plots (USLE database) or other natural or simulated rainfall studies where soil (sediment) loss was only measured at the plot end. Newer experimental measurement techniques, equipment, and approaches are needed to allow examination of changes in sediment detachment/deposition/loads with very fine spatial resolution down a hillslope and down a rill channel. The current modeling techniques also assume either uniformly spaced rill channels down a slope profile (default is 1-m spacing), or alternately simulations can be conducted where all surface flow is assumed to be distributed at a uniform shallow depth across the entire flow width. However, in real world situations the soil conditions, landscape complexities and increases in slope lengths can result in situations where no evident rilling occurs, rill spacings change with increasing slope lengths, or surface flows converge or diverge which may result in channelized rill flows changing to broader sheet flows. These complex surface flow situations need to be accounted for in any new water erosion prediction technologies, as they can greatly affect soil detachment and deposition processes. Additionally, subsurface hydrology effects also need to be better accounted for in any new technologies. Current erosion prediction models poorly account for water moving within the soil, and how saturation conditions can weaken the soil surface and make it more susceptible to detachment. A comprehensive understanding of how subsurface water moves and can converge in fields (and may emerge to the surface) is needed in new modeling approaches that can also be linked to initiation and development of ephemeral gullies. Additionally, better understanding and modeling of the effects of subsurface drainage and controlled drainage systems on hydrology and soil erosion is required. This also highlights the needs to move to erosion prediction systems that truly represent the landscape and fields as 2-D/3-D surfaces. Current prediction technologies are largely limited to estimating soil erosion processes at points down a line to represent a rectangular area. Long-term temporal effects of various practices on soil health and soil hydrology and erosion also should be accounted for in new erosion models. Currently, baseline soil erodibility is assumed to be a constant value for a particular soil and cropping system as a function of soil texture, organic matter, and other properties. However, fields that are in long-term pasture, or long-term no-till row crop management systems along with the use of cover crops may substantially change soil organic matter, soil structure, infiltration characteristics, and erodibilities that are not currently reflected in USDA models. This presentation will explore these and other areas of research needed.

High variability of soil erosion and hydrological processes in Mediterranean hillslope vineyards (Montes de Málaga, Spain)

Investigations on temporal and spatial variation of slope-scale SOC erosion and deposition

AimThe relationship between erosion and biodiversity is reciprocal. Soil organisms can both reduce soil loss, by improving porosity, and increase it, by diminishing soil stability as a result of their mixing activities. Simultaneously, soil runoff has ecological impacts on belowground communities. Despite clear research into interactions, soil erosion models do not consider biodiversity in their estimates and soil ecology has poorly investigated the effects of erosion. In order to start filling in these research gaps, we present a novel biological factor and introduce it into a well‐known soil erosion model (the revised universal soil loss equation). Furthermore, we propose insights to advance soil erosion ecology.LocationPan‐European.Time periodSimulation of present‐day conditions.Major taxa studiedEarthworms.MethodsWe present three pathways to fill in current knowledge gaps in soil biodiversity and erosion studies: (a) introducing a biological factor into soil erosion models; (b) developing plot‐scale experiments to clarify and quantify the positive/negative effects of soil organisms on erosion; (c) promoting ecological studies to assess both short‐ and long‐term effects of soil erosion on soil biota.ResultsWe develop a biological factor to be included in soil erosion modelling. Thanks to available data on earthworm diversity (richness and abundance), we generate an “earthworm factor”, incorporate it into a model of soil erosion and produce the first pan‐European maps of it.Main conclusionsNew estimates of soil loss can be generated by including biological factors in soil erosion models. At the same time, the effects of soil loss on belowground diversity require further investigation. Available data and technologies make both processes possible. We think that it is time to commit to fostering the fundamental, although complex, relationship between soil biodiversity and erosion.

Based on the momentum theorem and water-balance principle, this paper has derived the basic equations of slope runoff. Soil erosion by raindrop splash and runoff are discussed, and hillslope soil erosion processes model was established. Finally, the model was solved by numerical solution considering the common solution-determining conditions, from which not only runoff and soil erosion yield but also their processes can be obtained. The model is validated by using observation data of Soil Conservation Ecological Science & Technology Demonstration Park of Jiangxi Province. Results show that the maximum relative error between the computation and observation values of the slop runoff processes is 10％ while the maximum relative error between the computation and observation values of hillslope soil erosion processes is 9.2％. This indicates that the model is conceptually realistic reasonable and offers a feasible approach for research on soil erosion process. Key words overland flow﹒raindrop splash﹒runoff erosion﹒process﹒numerical solution

Physically based soil erosion and sediment yield models revisited

Purpose : Over the seventy years, various soil erosion modeling methods were developed in the world with different input requirements and complexity. Some of these soil erosion models have been applied in Sri Lanka covering several regions of the country at different scenarios over the past twenty years. Thus, the prime objective of this study is to compare commonly practiced GIS/ RS based soil erosion assessment models and derivation techniques of model parameters used in Sri Lanka. Research Method : Scholarly research articles, conference proceeding papers, and previously published literature on GIS/ RS based soil erosion models over the past twenty years were critically reviewed, examined, and compared to find various methodologies in the derivation of soil erosion model parameters, analysis methods, and applications with special reference to Sri Lanka. Findings : The results revealed that, in each case, the empirical soil erosion models have been applied to predict soil erosion rates in terms of rill and sheet erosion excluding gully erosion. Furthermore, soil loss at the catchment or entire country scale has been assessed in each case by using different derivation methods. The assessed soil erosion model parameters are R factor (rainfall erosivity), K factor (soil erodibility), LS factor (slope gradient), C factor (crop management factor), and P factor (support practice factor). Originality/ Value : Different derivation methods of soil erosion model parameters (R, K, LS, C, and P) were critically evaluated in order to find the most appropriate methods that can be applied in Sri Lanka in future research studies.

Abstract. Soil erosion in Alpine areas is mainly related to extreme topographic and weather conditions. Although different methods of assessing soil erosion exist, the knowledge of erosive forces of the snow cover needs more investigation in order to allow soil erosion modeling in areas where the snow lays on the ground for several months. This study aims to assess whether the RUSLE (Revised Universal Soil Loss Equation) empirical prediction model, which gives an estimation of water erosion in t ha yr−1 obtained from a combination of five factors (rainfall erosivity, soil erodibility, topography, soil cover, protection practices) can be applied to mountain areas by introducing a winter factor (W), which should account for the soil erosion occurring in winter time by the snow cover. The W factor is calculated from the ratio of Ceasium-137 (137Cs) to RUSLE erosion rates. Ceasium-137 is another possible way of assessing soil erosion rates in the field. In contrast to RUSLE, it not only provides water-induced erosion but integrates all erosion agents involved. Thus, we hypothesize that in mountain areas the difference between the two approaches is related to the soil erosion by snow. In this study we compared 137Cs-based measurement of soil redistribution and soil loss estimated with RUSLE in a mountain slope affected by avalanches, in order to assess the relative importance of winter erosion processes such as snow gliding and full-depth avalanches. Three subareas were considered: DS, avalanche defense structures, RA, release area, and TA, track area, characterized by different prevalent winter processes. The RUSLE estimates and the 137Cs redistribution gave significantly different results. The resulting ranges of W evidenced relevant differences in the role of winter erosion in the considered subareas, and the application of an avalanche simulation model corroborated these findings. Thus, the higher rates obtained with the 137Cs method confirmed the relevant role of winter soil erosion. Despite the limited sample size (11 points), the inclusion of a W factor in RUSLE seems promising for the improvement of soil erosion estimates in Alpine environments affected by snow movements.

Soil erosion processes are a type of geological hazard. They cause soil loss and sediment production, landscape dissection, and economic damage, which can, in the long term, result in land abandonment. Thus, identification of soil erosion processes is necessary for sustainable land management in an area. This study presents the potential of visual interpretation of high resolution LiDAR (light detection and ranging) imagery for direct and unambiguous identification and mapping of soil erosion processes, which was tested in the study area of the Vinodol Valley (64.57 km2), in Croatia. Eight LiDAR images were derived from the 1 m airborne LiDAR DTM (Digital Terrain Model) and were used to identify and map gully erosion, sheet erosion, and the combined effect of rill and sheet erosion, with the ultimate purpose to create a historical erosion inventory. The two-step procedure in a visual interpretation of LiDAR imagery was performed: preliminary and detailed. In the preliminary step, possibilities and limitations for unambiguous identification of the soil erosion processes were determined for representative portions of the study area, and the exclusive criteria for the accurate and precise manual delineation of different types of erosion phenomena were established. In the detailed step, the findings from the preliminary step were used to map the soil erosion phenomena in the entire studied area. Results determined the highest potential for direct identification and mapping of the gully erosion phenomena. A total of 236 gullies were identified and precisely delineated, although most of them were previously unknown, due to the lack of previous investigations on soil erosion processes in the study area. On the other hand, the used method was proven to be inapplicable for direct identification and accurate mapping of the sheet erosion. Sheet erosion, however, could have been indirectly identified on certain LiDAR imagery, based on recognition of colluvial deposits accumulated at the foot of the eroded slopes. Furthermore, the findings of this study present which of the used LiDAR imagery, and what features of the imagery used, are most effective for identification and mapping of different types of erosion processes.