Assessment of soil erosion on arable land using Cs measurements: a case study from Jaslovske Bohunice, Slovakia

This study was carried out to obtain a representative set of data on long-term erosion rates from a pilot area located close to the Jaslovske Bohunice village, in western Slovakia using the ¹³⁷Cs-method. The study area chosen was representative of the hilly loess cultivated areas of Slovakia. The sampling strategy was based on a multiple transect approach. Analyses of the samples for ¹³⁷Cs activity were made at the Nuclear Power Plant Research Institute, Jaslovske Bohunice. The ¹³⁷Cs-method was used to obtain long-term estimates of soil erosion in the Jaslovske Bohunice site, a representative hilly loess cultivated area of Slovakia. The estimated reference ¹³⁷Cs inventory was 2910 Bq m⁻², with a coefficient of variation of 4.3%.Examination of the ¹³⁷Cs redistribution in relation to the topography of the study area revealed that, within individual transects the ¹³⁷Cs inventories were closely related to major landforms. The ¹³⁷Cs inventories were considerably lower on the slopes than on the plateau and they were highest in the valley. However, when plotted against a selection of individual quantitative slope parameters, i.e. the S and the LS factors of the USLE or slope inclination, the correlations obtained were weak.Three conversion models, i.e. the proportional model (PM), the simplified mass balance model (MBM1) and the standard mass balance model (MBM2), from the set of models developed at Exeter University, Great Britain were selected to interpret the resulting ¹³⁷Cs measurements into soil erosion/deposition rates. The mean erosion rates estimated with the PM were 22.4, 35.6 with MBM1 and 17.3 t ha⁻¹ per year with MBM2. There was a good agreement between the average of these mean erosion rates (25.1 t ha⁻¹ per year) for the Jaslovske Bohunice site and the estimated mean soil erosion rate obtained for small erosion plots (15 t ha⁻¹ per year) for conditions similar to the study site. Nevertheless, further research on the application of the ¹³⁷Cs-method, in particular the independent validation of the results obtained, is needed. Several issues requiring further study have been highlighted.     

Soil erosion evaluation in a small basin through the use of Cs technique

Soil erosion significantly affects the most productive lands in Argentina, particularly the region called “Pampa Ondulada”. Quantification of the actual rates and patterns of soil loss is necessary for designing efficient degradation control strategies. The aim of this investigation was to gather using the ¹³⁷Cs technique a reliable set of data of erosion and sedimentation rates, in order to describe the long-term erosive landscape dynamic in a 300 ha basin representative for the “Pampa Ondulada” region of Argentina. The general topography of the basin is undulated with slopes gradients between 0 and 2.5% and slope lengths up to 800 m long. The main land use consisted in annual cropping under conventional tillage.For the soil erosion study in the basin the ¹³⁷Cs technique was used, which is based on the comparison between the ¹³⁷Cs inventories surveyed with a local reference ¹³⁷Cs profile. The sampling strategy was based on a multiple transect approach.The estimated mean soil erosion rates obtained applying Mass Balance Model 2 for the studied hillslopes ranged between −11.5 and −36 t ha⁻¹ per year and fitted the low and moderate erosion classes according to FAO. These values ranged beyond the admitted tolerance. Sedimentation was observed at the lower landscape positions probably related to changes from convex to concave slopes. The application of the ¹³⁷Cs technique in the studied basin proved to be a useful and sensible tool for assessing erosion/deposition rates. In areas with low topographic gradients like the Pampa Ondulada region, the slope length appears to be an important property for predicting spatial patterns of erosion rates.     

Terrain attributes, landform segmentation, and soil redistribution

The ¹³⁷Cs technique has greatly expanded our knowledge of the topography–soil redistribution relationship. For the technique to be useful in upscaling of process models and regional-scale conservation planning, we must be able to show that a consistent relationship exists between ¹³⁷Cs-derived soil redistribution rates and terrain attributes in a given region. In this paper, the association between ¹³⁷Cs-derived soil redistribution rates and quantitatively defined landform elements was examined at nine hummocky terrain sites in southern Saskatchewan, Canada. Shoulder (SH) elements with convex plan curvatures had the highest mean soil loss rates of 33 t ha⁻¹ yr⁻¹, followed closely by other SH and backslope (BS) elements. The erosional behavior of level elements (i.e. those with gradients less than 3°) was highly dependent on the specific dispersal area (SDA) of the element—elements with high dispersal areas were dominantly erosional (mean soil loss of 14 t ha⁻¹ yr⁻¹), whereas level elements with low dispersal areas were depositional (mean soil gain of 15 t ha⁻¹ yr⁻¹). Doubly concave footslope (FS) elements had mean soil gain of 10 t ha⁻¹ yr⁻¹. The dispersion of values across the nine sites was much greater for the depositional units than the erosional units, indicating a complex relationship between deposition and terrain attributes in the depositional units. The results clearly indicate that regional-scale patterns of soil redistribution can be developed using the ¹³⁷Cs technique.     

Assessment of soil losses on cultivated land by using the Cs technique in the Upper Yangtze River Basin of China

This paper presents the results of using the ¹³⁷Cs technique to assess soil erosion rates of both sloping cultivated land and flat terraces in the Upper Yangtze River Basin, China. The study was carried out on eighteen sloping cultivated fields and four flat terrace fields in eight counties and cities over the eastern part of the basin. The ¹³⁷Cs-reference inventory ranged from 620.5 to 2573.2 Bq/m². For the 18 sloping cultivated fields, the average ¹³⁷Cs inventory over a field ranged from 204.9 to 1847.7 Bq/m², which accounts for 15–77% of the local ¹³⁷Cs reference inventory, and the average water erosion rate ranged from 758 to 9854 t/km² per year, with erosion rates of <1000 t/km² per year in two fields; 1000–5000 t/km² per year in eight fields; and >5000 t/km² per year in eight fields. It is apparent that most of the sloping cultivated fields suffer severe or very severe soil erosion. For the four terrace fields under this study, the average ¹³⁷Cs inventory over a field ranged between 915.8 and 2675.4 Bq/m², which accounts for 97–104% of the local ¹³⁷Cs reference inventory. However, water erosion is very slight on the terrace fields and little soil is lost from the terraces. The study also indicated that the severity of soil erosion is strongly related to soil texture and slope gradient.     

Quantification of accelerated soil erosion using the environmental tracer caesium-137

The principal objective of this investigation was to quantify erosion rates for five agricultural fields in three separate study areas in Saskatchewan. The radionuclide tracer caesium-137 (¹³⁷Cs) was used to quantify net erosion and net deposition within the landscape over a 30-year period. Uneroded (native) sites were used to establish the mean background level of ¹³⁷Cs in each of the study areas. The assumption being that agricultural sites with ¹³⁷Cs areal activities greater than the native site were subject to deposition, and sites with ¹³⁷Cs less than the native control site were subject to erosion. A linear proportionality model was used to convert the loss or gain of ¹³⁷Cs to net soil erosion or deposition. Results have indicated that accelerated (anthropogenic) erosion has been commonplace on arable land in Saskatchewan, even on near-level fields (< 1.3 degrees). The net integrated sediment output from the five agricultural fields ranged from — 0.6 t th⁻¹ y⁻¹ to — 6.8 t ha⁻¹ y⁻¹ (where negative values represent erosion). What is more alarming is that between 40 and 75 per cent of all sites sampled within individual fields had erosion rates in excess of the generally accepted rate of soil formation (1.0 t ha⁻¹ y⁻¹). Also, in one highly eroded field (Crystal Springs medium sloping site) 65 per cent of the sites sampled exceeded the upper tolerable erosion rate of 11.0 t ha⁻¹ y⁻¹. These results indicate significant degradation of the non-renewable soil resource has occurred over the past 30 years and is still presently active. Land degradation by accelerated erosion would result in reductions in effective rooting depth, soil moisture holding capacity, essential nutrient stores, and would adversely effect the physical structure of the topsoil. The major reason for accelerated erosion on arable land in Saskatchewan is the practice of summer fallowing, where the field is left in a ‘bare’ state and repeatedly tilled every second or third year. During a fallow period, or prior to crop emergence during a cropping year, fields are subject to wind and water erosion. On near-level fields wind would be the dominant transport agent, while on sloping fields inter-rill and rill erosion would be the primary forces of erosion. It is suggested that the appropriate conservation farming response would be to increase application of surface mulches and possibly to decrease the frequency of summer fallowing. Without such efforts long-term sustainable agricultural production in the Prairies of Canada is considered to be a tenuous land use practice.     

The WEELS model: methods, results and limitations

Within the European Union (EU)-funded Project ‘Wind Erosion on European Light Soils’ (WEELS), a model was designed and implemented with the aim of predicting the long-term spatial distribution of wind erosion risks in terms of erosion hours and wind-induced soil loss. In order to ensure wide applicability, the model structure consists of a modular combination of different approaches and algorithms, running on available or easily collected topographic and climatological data input. Whereas the ‘WIND’, ‘WIND EROSIVITY’ and ‘SOIL MOISTURE’ modules combine factors that contribute to the temporal variations of climatic erosivity, the ‘SOIL ERODIBILITY’, ‘SURFACE ROUGHNESS’ and ‘LAND USE’ modules predict the temporal soil and vegetation cover variables that control soil erodibility. Preliminary simulations over a 29-year period for the Barnham site (UK) (1970–1998) and a 13-year period for the Grönheim site (Germany) (1981–1993) generally resulted in a higher erosion risk for the English test site, where the total mean soil loss was estimated at 1.56 t ha⁻¹ year⁻¹ and mean maximum soil loss at about 15.5 t ha⁻¹ year⁻¹. The highest rates exceeded 3 t ha⁻¹ in March, September and November. On the northern German test site, the total mean soil loss was 0.43 t ha⁻¹ year⁻¹. The highest erosion rates were predicted in April when they can exceed 2.5 t ha⁻¹. The total mean maximum soil loss at this site of about 10.0 t ha⁻¹ year⁻¹ corresponds to a loss of about 0.65 mm. Predictions based on a land use scenario for the German site revealed that the erosion risk could be reduced significantly by changing land use strategies.     

Using caesium-137 measurements to investigate soil erosion rates in western Istanbul (NW Turkey)

Buyukcekmece Reservoir, located in the western outskirts of Istanbul, is one of the major water resources of Istanbul, and supplies drinking water to about 4 million people. Erosion in the catchment of the reservoir is an important problem in terms of its longer-term sustainability for water supply. There is an urgent need to obtain reliable quantitative data regarding erosion and deposition rates within the catchment to assess the magnitude of the problem and to plan catchment management strategies. In the absence of existing data, attention has focussed on the potential for using ¹³⁷Cs measurements to provide retrospective estimates of medium-term soil erosion rates within the catchment over the past ca. 40 years. To date, the ¹³⁷Cs approach has not been used to document soil redistribution rates in Turkey and this contribution reports an attempt to confirm the viability of the approach and the results of a preliminary investigation of rates of soil loss from uncultivated areas within the catchment. The soil redistribution rates estimated using the profile distribution conversion model varied from − 16.11 (erosion) to 4.59 (deposition) t/ha/year.     

Cesium‐137‐based erosion‐rate determination of a steep mountainous region

Data on quantification of erosion rates in alpine grasslands remain scarce but are urgently needed to estimate soil degradation. We determined soil‐erosion rates based on ¹³⁷Cs in situ measurements. The method integrates soil erosion over the last 22 y (time after the Chernobyl accident). Measured erosion rates were compared with erosion rates modeled with the Universal Soil Loss Equation (USLE). The comparison was done in order to find out if the USLE is a useful tool for erosion prediction in steep mountainous grassland systems. Three different land‐use types were investigated: hayfields, pasture with dwarf shrubs, and pasture without dwarf shrubs. Our test plots are situated in the Urseren Valley (Central Switzerland) with a mean slope steepness of 37°. Mean annual soil‐erosion rates determined with ¹³⁷Cs of the investigated sites ranged between the minimum of 4.7 t ha^–1 y^–1 for pastures with dwarf shrubs to >30 t ha^–1 y^–1 at hayfields and pastures without dwarf shrubs. The determined erosion rates are 10 to 20 times higher compared to previous measurements in alpine regions. Our measurements integrated over the last 22 y, including extreme rainfall events as well as winter processes, whereas previous studies mostly reported erosion rates based on summer time and short‐term rainfall simulation experiments. These results lead to the assumption that heavy‐rainfall events as well as erosion processes during winter time and early spring do have a considerable influence on the high erosion amounts that were measured. The latter can be confirmed by photographs of damaged plots after snowmelt. Erosion rates based on the USLE are in the same order of magnitude compared to ¹³⁷Cs‐based results for the land‐use type “pasture with dwarf shrubs”. However, erosion amounts on hayfields and pasture without dwarf shrubs are underestimated by the USLE compared to ¹³⁷Cs‐based erosion rates. We assume that the underestimation is due to winter processes that cause soil erosion on sites without dwarf shrubs that is not considered by the USLE. Dwarf shrubs may possibly prevent from damage of soil erosion through winter processes. The USLE is not able to perform well on the affected sites. Thus, a first attempt was done to create an alpine factor for the USLE based on the measured data.     

Caesium-137 fallout depth distribution in different soil profiles and significance for estimating soil erosion rate

Caesium-137 (¹³⁷Cs) has been widely used for the determination of soil erosion and sediment transport rate. However, depth distribution patterns of ¹³⁷Cs in the soil profile have not been considered. As a result, the erosion rates may be over-estimated or underestimated. This paper presents the depth distribution of ¹³⁷Cs fallout in different soil profiles using published data. Three types of depth distribution functions of ¹³⁷Cs are given by using statistical regression methods, the exponential type, the peak type and the decreasing type (including uniform distribution). Relationships between ¹³⁷Cs loss and soil erosion rate are given by introducing the regression functions. The influence of depth distribution of ¹³⁷Cs on the estimation of the soil erosion rate was simulated. Simulation results showed that very different soil erosion rates could be deduced for different depth distributions when ¹³⁷Cs loss is the same, which indicates that the depth distribution pattern should be considered when soil erosion is estimated by using ¹³⁷Cs. Simulation results also suggested that it is most important to determine the depth distribution of ¹³⁷Cs near the soil surface and the annual relative loss of ¹³⁷Cs by using the depth distribution of ¹³⁷Cs as a criterion to estimate the soil erosion rate.     

Assessing soil erosion and control factors by the radiometric technique in the Boussouab catchment,Eastern Rif,Morocco

In the Eastern Rif of N Morocco, soil conservation is seriously threatened by water erosion. Large areas of soil have reached an irreversible state of degradation. In this study, the ¹³⁷Cs technique was used to quantify erosion rates and identify the main factors involved in the erosion process based on a representative catchment of the Eastern Rif. To estimate erosion rates in terms of the main factors affecting soil losses, samples were collected taking into account the lithology, slope and land use along six selected transects within the Boussouab catchment. The transects were representative of the main land uses and physiographic characteristics of that Rif sector. The reference inventory for the area was established at a stable, well preserved, matorral site (value of 4250 Bq m^− 2). All the sampling sites were eroded and ¹³⁷Cs inventories varied widely (between 245 and 3670 Bq m^− 2). The effective soil losses were also highly variable (between 5.1 and 48.8 t ha^− 1 yr^− 1). Soil losses varied with land use. The lowest average values were on matorral and fallow land (10.5 and 15.2 t ha^− 1 yr^− 1, respectively) but much higher with alfa vegetation or cereal crops (31.6 and 27.3, respectively). The highest erosion rate was on a badland transect at the more eroded part of the catchment, with rates exceeding 40 t ha^− 1 yr^− 1 and reaching a maximum of 48.8 t ha^− 1 yr^− 1.The average soil losses increased by more than 100% when the slope increased from 10° (17.7 t ha^− 1 yr^− 1) to 25° (40. 8 t ha^− 1 yr^− 1). Similar results were obtained when comparing erosion rates in soils that were covered by matorral with respect to those under cultivation. Lithology was also a key factor affecting soil loss. Soils on marls were more erodible and the average erosion rates reached 29.36 t ha^− 1 yr^− 1, which was twice as high as soils on the glacis and old fluvial terraces (average rates of 14.98 t ha^− 1 yr^− 1). The radiometric approach was very useful to quantify erosion rates and to examine the pattern of soil movement. The analysis of main erosion factors can help to promote rational soil use and establish conservation strategies in the study area.     

Use of caesium-137 data for validation of spatially distributed erosion models: the implications of tillage erosion

Validation of spatially distributed models using spatially distributed data represents a vital element in the development process; however, it is rarely undertaken. To a large extent, this reflects the problems associated with assembling erosion rate data, at appropriate temporal and spatial scales and with a suitable spatial resolution, for comparison with model results. The caesium-137 (¹³⁷Cs) technique would appear to offer considerable potential for meeting this need for data, at least for longer timescales. Nevertheless, initial attempts to use ¹³⁷Cs for model validation did not prove successful. This lack of success may be explained by the important role of tillage erosion in redistributing soil within agricultural fields and, therefore, contributing to the ¹³⁷Cs-derived soil redistribution rates. This paper examines the implications of tillage erosion for the use of ¹³⁷Cs in erosion model validation and presents an outline methodology for the use of ¹³⁷Cs in model validation. This methodology acknowledges and addresses the constraints imposed by the need to: (1) separate water and tillage erosion contributions to total soil redistribution as represented in ¹³⁷Cs derived rates; (2) account for lateral mixing of ¹³⁷Cs within fields as a result of tillage translocation; (3) simulate long-term water erosion rates using the model under evaluation if ¹³⁷Cs-derived water erosion rates are to be used in model validation. The methodology is dependent on accurate simulation of tillage erosion and tillage translocation. Therefore, as greater understanding of tillage erosion is obtained, the potential for the use of ¹³⁷Cs in water erosion model validation will increase. Caesium-137 measurements remain one of the few sources of spatially distributed erosion information and, therefore, their potential value should be exploited to the full.     

Cesium and soil carbon in a small agricultural watershed

Scientific, political, and social interests have developed recently in the concept of using agricultural soils to sequester carbon. Studies supporting this concept indicate that soil erosion and subsequent redeposition of eroded soils in the same field may establish an ecosystem disequilibrium that promotes the buildup of carbon on agricultural landscapes. The problem is to determine the patterns of soil erosion and redeposition on the landscape and to relate these to soil carbon patterns. Radioactive ¹³⁷cesium (¹³⁷Cs) can be used to estimate soil erosion patterns and, more importantly, redeposition patterns at the field level. The purpose of this study was to determine the relationship between ¹³⁷Cs, soil erosion, and soil carbon patterns on a small agricultural watershed. Profiles of soils from an upland area and soils in an adjacent riparian system were collected in 5 cm increments and the concentrations of ¹³⁷Cs and carbon were determined. ¹³⁷Cs and carbon were uniformly mixed in the upper 15–20 cm of upland soils. ¹³⁷Cs (Bq g⁻¹) and carbon (%) in the upland soils were significantly correlated (r²=0.66). Carbon content of the 0–20 cm layer was higher (1.4±0.3%) in areas of soil deposition than carbon content (1.1±0.3%) in areas of soil erosion as determined by the ¹³⁷Cs technique. These data suggest that measurements of ¹³⁷Cs in the soils can be useful for understanding carbon distribution patterns in surface soil. Carbon content of the upland soils ranged from 0.5 to 1.9% with an average of 1.2±0.4% in the 0–20 cm layer while carbon below this upper tilled layer (20–30 cm) ranged from 0.2 to 1.5% with an average of 0.5±0.3%. Total carbon was 2.66 and 3.20 kg m⁻² in the upper 20 cm and upper 30 cm of the upland soils, respectively. Carbon content of the 0–20 cm layer in the riparian system ranged from 1.1 to 67.0% with an average 11.7±17.1%. Carbon content below 20 cm ranged from 1.8 to 79.3% with an average of 18.3±17.5%. Soil carbon in the upper 20 cm of the riparian profile was 10.1 and 15.0 kg m⁻² in the upper 30 cm of the riparian profiles. This is an increase of organic carbon by a factor of 3.8 and 4.7 for the upper 20 cm and upper 30 cm of the riparian profiles, respectively, when compared to the upland soil profiles.     

Use of Cs to estimate tillage- and water-induced soil redistribution rates on agricultural land under different use and management in central-south Chile

The purpose of this research was to evaluate the applicability of conventional ¹³⁷Cs sampling and a simplified approach, for estimating medium-term tillage- and water-induced soil erosion and sedimentation rates on agricultural land in Chile. For this purpose, four study sites under contrasting land use and management were selected in central-south Chile. First, a conventional ¹³⁷Cs approach, based on grid sampling was applied, adapting a mass balance conversion model incorporating soil movement by tillage to the site specific conditions of the study region. Secondly, using the same conversion model, the feasibility of estimating soil redistribution rates from measurements of ¹³⁷Cs inventories based on composite soil samples taken along contour lines was also tested at all four sites. The redistribution rates associated with tillage and water and the total rates estimated using both methods correlated strongly at all four sites. The conventional method provides more detailed information concerning the redistribution processes operating over the landscape. The simplified method is suitable for assessing soil loss and sediment accumulation in areas exhibiting simple topography and almost similar slopes along the contour lines. Under these conditions, this method permits faster estimation of soil redistribution rates, providing the possibility of estimating soil redistribution rates over larger areas in a shorter time. In order to optimise the costs and benefits of the methods, the sampling and inventory quantification strategy must be selected according to the resolution of the required information, and the scale and complexity of the landscape relief. Higher tillage- and water-induced erosion rates were observed in the annually ploughed cropland sites than in the semi-permanent grassland sites. Subsistence managed crop and grassland sites also show greater erosion effects than the commercially managed sites. The ¹³⁷Cs methods used permit discrimination between redistribution rates observed on agricultural land under different land use and management. The ¹³⁷Cs technique must be seen as an efficient method for estimating medium-term soil redistribution rates, and for planning soil conservation and sustainable agricultural production under the climatic conditions and the soil type of the region of Chile investigated.     

137Cs tracing of the spatial patterns in soil redistribution,organic carbon and total nitrogen in the southeastern Tibetan Plateau

The southeastern Tibetan Plateau, which profoundly affects East Asia by helping to maintain the stability of climate systems, biological diversity and clean water, is one of the regions most vulnerable to water erosion, wind erosion, tillage erosion, freeze–thaw erosion and overgrazing under global climate changes and intensive human activities. Spatial variations in soil erosion in terraced farmland (TL), sloping farmland (SL) and grassland (GL) were determined by the ¹³⁷Cs tracing method and compared with spatial variations in soil organic carbon (SOC) and total nitrogen (total N). The ¹³⁷Cs concentration in the GL was higher in the 0–0.03 m soil layer than in the other soil layers due to weak migration and diffusion under low precipitation and temperature conditions, while the ¹³⁷Cs concentration in the soil layer of the SL was generally uniform in the 0–0.18 m soil layer due to tillage-induced mixing. Low ¹³⁷Cs inventories appeared at the summit and toe slope positions in the SL due to soil loss by tillage erosion and water erosion, respectively, while the highest ¹³⁷Cs inventories appeared at the middle slope positions due to soil accumulation under relatively flat landform conditions. In the GL, the ¹³⁷Cs data showed that higher soil erosion rates appeared at the summit due to freeze–thaw erosion and steep slope gradients and at the toe slope position due to wind erosion, gully erosion, freeze–thaw erosion and overgrazing. The ¹³⁷Cs inventory generally increased from upper to lower slope positions within each terrace (except the lowest terrace). The ¹³⁷Cs data along the terrace toposequence showed abrupt changes in soil erosion rates between the lower part of the upper terrace and the upper part of the immediate terrace over a short distance and net deposition on the lower and toe terraces. Hence, tillage erosion played an important role in the soil loss at the summit slope positions of each terrace, while water erosion dominantly transported soil from the upper terrace to the lower terrace and resulted in net soil deposition on the flat lower terrace. The SOC inventories showed similar spatial patterns to the ¹³⁷Cs inventories in the SL, TL and GL, and significant correlations were found between the SOC and ¹³⁷Cs inventories in these slope landscapes. The total N inventories showed similar spatial patterns to the inventories of ¹³⁷Cs and SOC, and significant correlations were also found between the total N and ¹³⁷Cs inventories in the SL, TL and GL. Therefore, ¹³⁷Cs can successfully be used for tracing soil, SOC and total N dynamics within slope landscapes in the southeastern Tibetan Plateau.     

Characterization of soil profiles in a landscape affected by long-term tillage

Soil movement by tillage redistributes soil within the profile and throughout the landscape, resulting in soil removal from convex slope positions and soil accumulation in concave slope positions. Previous investigations of the spatial variability in surface soil properties and crop yield in a glacial till landscape in west central Minnesota indicated that wheat (Triticum aestivum) yields were decreased in upper hillslope positions affected by high soil erosion loss. In the present study, soil cores were collected and characterized to indicate the effects of long-term intensive tillage on soil properties as a function of depth and tillage erosion. This study provides quantitative measures of the chemical and physical properties of soil profiles in a landscape subject to prolonged tillage erosion, and compares the properties of soil profiles in areas of differing rates of tillage erosion and an uncultivated hillslope. These comparisons emphasize the influence of soil translocation within the landscape by tillage on soil profile characteristics. Soil profiles in areas subject to soil loss by tillage erosion >20 Mg ha⁻¹ year⁻¹ were characterized by truncated profiles, a shallow depth to the C horizon (mean upper boundary 75 cm from the soil surface), a calcic subsoil and a tilled layer containing 19 g kg⁻¹ of inorganic carbon. In contrast, profiles in areas of soil accumulation by tillage >10 Mg ha⁻¹ year⁻¹ exhibited thick sola with low inorganic carbon content (mean 3 g kg⁻¹) and a large depth to the C horizon (usually >1.5 m below the soil surface). When compared to areas of soil accumulation, organic carbon, total nitrogen and Olsen-extractable phosphorus contents measured lower, whereas inorganic carbon content, pH and soil strength measured higher throughout the profile in eroded landscape positions because of the reduced soil organic matter content and the influence of calcic subsoil material. The mean surface soil organic carbon and total nitrogen contents in cultivated areas (regardless of erosion status) were less than half that measured in an uncultivated area, indicating that intensive tillage and cropping has significantly depleted the surface soil organic matter in this landscape. Prolonged intensive tillage and cropping at this site has effectively removed at least 20 cm of soil from the upper hillslope positions.     

利用137Cs示踪技术评价东北黑土侵蚀和沉积过程

Soil and water losses through erosion have been serious in the black soil region of Northeast China. Therefore, a sloping cultivated land in Songnen Plain was selected as a case study to： 1） determine the ^137Cs reference inventory in the study area; 2） calculate erosion and deposition rates of black soil on different slope locations; 3） conduct a sensitivity analysis of some model parameters; and 4） compare overall outputs using four different models. Three transects were set in the field with five slope locations for each transect, including summit, shoulder-slope, back-slope, foot-slope, and toe-slope. Field measurements and model simulation were used to estimate a bomb-derived ^137Cs reference inventory in the study area. Soil erosion and deposition rates were estimated using four ^137Cs models and percentage of ^137Cs loss/gain. The ^137Cs reference value in the study area was 2 232.8 Bq m^-2 with ^137Cs showing a clear topographic pattern, decreasing from the summit to shoulder-slope, then increasing again at the foot-slope and reaching a maximum at the toe-slope, Predicted soil redistribution rates for different slope locations varied. Among models, the Yang Model （YANG-M） overestimated erosion loss but underestimated deposition. However, the standard mass balance model （MBM1） gave predictions similar to a mass balance model incorporating soil movement by tillage （MBM2）. Sensitivity analysis of the proportion factor and distribution pattern of ^137Cs in the surface layer demonstrated the impact of ^137Cs enrichment on calculation of the soil erosion rate. Factors influencing the redistribution of fallout ^137Cs in landscape should be fully considered as calculating soil redistribution rate using ^137Cs technique.     

西班牙东南部旱作橄榄树果园水土保持措施: 植物带对土壤水分的动态影响

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.     

Evaluating gully erosion using Cs and Pb/Cs ratio in a reservoir catchment

Water erosion in the hilly areas of west China is the main process contributing to the overall sediment of the Yellow River and the Yangtze River. The impact of gully erosion in total sediment output has been mostly neglected. Our objective was to assess the sediment production and sediment sources at both the hillslope and catchment scales in the Yangjuangou reservoir catchment of the Chinese Loess Plateau, northwest China. Distribution patterns in sediment production caused by water erosion on hills and gully slopes under different land use types were assessed using the fallout ¹³⁷Cs technique. The total sediment production from the catchment was estimated by using the sediment record in a reservoir. Sediment sources and dominant water erosion processes were determined by comparing ¹³⁷Cs activities and ²¹⁰Pb/¹³⁷Cs ratios in surface soils and sub-surface soils with those of sediment deposits from the reservoir at the outlet of the catchment. Results indicated that landscape location had the most significant impact on sediment production for cultivated hillslopes, followed by the terraced hillslope, and the least for the vegetated hillslope. Sediment production increased in the following order: top>upper>lower>middle for the cultivated hillslope, and top>lower>upper>middle for the terraced hillslope. The mean value of sediment production declined by 49% for the terraced hillslope and by 80% for the vegetated hillslope compared with the cultivated hillslope. Vegetated gully slope reduced the sediment production by 38% compared with the cultivated gully slope. These data demonstrate the effectiveness of terracing and perennial vegetation cover in controlling sediment delivery at a hillslope scale. Averaged ¹³⁷Cs activities and ²¹⁰Pb/¹³⁷Cs ratios in the 0–5 cm surface soil (2.22–4.70 Bq kg⁻¹ and 20.70–22.07, respectively) and in the 5–30 cm subsoil (2.60 Bq kg⁻¹ and 28.57, respectively) on the cultivated hills and gully slopes were close to those of the deposited sediment in the reservoir (3.37 Bq kg⁻¹ and 29.08, respectively). These results suggest that the main sediment sources in the catchment were from the surface soil and subsoil on the cultivated slopes, and that gully erosion is the dominant water erosion process contributing sediment in the study area. Changes in land use types can greatly affect sediment production from gully erosion. An increase in grassland and forestland by 42%, and a corresponding decrease in farmland by 46%, reduced sediment production by 31% in the catchment.     

Establishing sediment budgets for two small lowland agricultural catchments in the UK

Sediment budgets have been established for two small (<4 km²), lowland, agricultural catchments, by using ¹³⁷Cs measurements, sediment source fingerprinting and more traditional monitoring techniques to quantify the individual components of the budget. The gross and net erosion rates for the fields on the catchment slopes were estimated using ¹³⁷Cs measurements within selected fields, which encompassed a representative range of slope angles, slope lengths and land use. These estimates were extrapolated over the entire catchment, using a simple topographically driven soil erosion model (Terrain-Based GIS, TBGIS) superimposed on a DEM, to derive catchment average gross and net erosion rates. Suspended sediment yields were measured at the catchment outlets and sediment source fingerprinting techniques were used to establish the relative contributions from the catchment surface, subsurface tile drains and eroding channel banks to the sediment yields. In-channel and wetland storage were quantified using both direct measurements and ¹³⁷Cs measurements. The sediment budgets established for the catchments highlighted the importance of subsurface tile drains as a pathway for sediment transfer, accounting for ca. 60% and 30% of the sediment output from the two catchments. Erosion from channel banks contributed ca. 10% and 6% of the sediment output from the two catchments. Although the suspended sediment yields from these catchments were considered high by UK standards (ca. 90 t km⁻² year⁻¹), the sediment delivery ratios ranged between 14% and 27%, indicating that a major proportion of the mobilised sediment was stored within the catchments. In-field and field-to-channel storage were shown to be of similar magnitude, but storage of sediment in the channel system and associated wetlands was relatively small, representing <5% of the annual suspended sediment yield.     

A preliminary assessment of the potential for using Pbex measurement to estimate soil redistribution rates on cultivated slopes in the Sichuan Hilly Basin of China

In order to assess its potential for estimating soil redistribution rates, the naturally occurring fallout radionuclide ²¹⁰Pb_ex has been used in parallel with ¹³⁷Cs, derived from the atmospheric testing of nuclear weapon testing in the 1950s to 1970s, to estimate rates of soil redistribution on a sloping field with traditional erosion control measures located near Jiajia Village, Jianyang County, in the Sichuan Hilly Basin of China. The local ²¹⁰Pb_ex reference inventory of 12,860 Bq m^− 2 is higher than those reported for many other areas of the world and may reflect the influence of cloudy weather in preventing ²¹⁰Pb released to the atmosphere across the local region moving up into the upper troposphere, where is would be more widely dispersed. The mean ²¹⁰Pb_ex and ¹³⁷Cs inventories measured in cores collected from the upper part of the field with an average slope of 10° were 8028 Bq m^− 2 and 993 Bq m^− 2, respectively, and the equivalent values for the lower part of the field, where the slopes are steeper (20°) were 11,388 Bq m^− 2 and 1299 Bq m^− 2. The pattern of post-fallout ²¹⁰Pb_ex and ¹³⁷Cs redistribution on the sloping field reflects not only the effects of water erosion and redistribution by tillage, but also the local traditional practice of “Tiaoshamiantu”, whereby sediment trapped in the ditches is returned to the fields by the farmer. The estimates of annual rates of soil loss provided by the ²¹⁰Pb_ex measurement are closely comparable with those derived from the ¹³⁷Cs measurements and are consistent with existing knowledge for the study area. The results obtained from this study confirm the potential for using ²¹⁰Pb_ex measurement to estimate soil erosion rates over medium-term timescale of 50–100 years. By combining the estimates of erosion rates provided by the ²¹⁰Pb_ex and ¹³⁷Cs measurements, the weighted mean net soil loss was estimated to be 48.7 t ha^− 1 year^− 1 from the upper subfield and 16.9 t ha^− 1 year^− 1 from the lower subfield. These rates are considerably lower than the erosion rates obtained from runoff plot measurements in the local area. It is suggested that the traditional erosion control practices and the practice of “Tiaoshamiantu” have a significant effect in reducing soil loss and conserving valuable cultivated soil on sloping fields in the Sichuan Hilly Basin.