Medium-term Soil Erosion Research Articles

Meteoric 10Be, 137Cs and 239+240Pu as Tracers of Long- and Medium-Term Soil Erosion—A Review

Isotopes of meteoric 10Be, 137Cs, 239+240Pu have been proposed as a soil redistribution tracer and applied worldwide as an alternative method to classical field-related techniques (e.g., sediment traps). Meteoric 10Be provides information about long-term soil redistribution rates (millennia), while 137Cs and 239+240Pu give medium-term rates (decades). A significant progress in developing new models and approaches for the calculation of erosion rates has been made; thus, we provide a global review (n = 59) of research articles to present these three isotopes (meteoric 10Be, 239+240Pu and 137Cs) as soil erosion markers in different environments and under different land-use types. Understanding the dynamics and behaviours of isotopes in the soil environment is crucial to determine their usefulness as soil erosion tracers; thus, we discuss the chemical–physical behaviour of meteoric 10Be, 137Cs and 239+240Pu in soils. The application of these isotopes sometimes has strong limitations, and we give suggestions on how to overcome them or how to adapt them to a given situation. This review also shows where these isotopic methods can potentially be applied in the future. A lack in knowledge about soil redistribution rates exists particularly in loess-dominated areas where the tillage system has changed or in areas with strong wind erosion.

Comparison of two methodologies used to estimate erosion rates in Mediterranean ecosystems: 137Cs and exposed tree roots

The 137Cs deposited in soil and exposed tree roots have been widely applied to estimate medium-term soil erosion rates. However, comparative studies between these methods are scarce. For this purpose, three hillsides in two Mediterranean dehesas (rangeland with disperse tree cover) were selected. Regarding the 137Cs technique, a reference site close to the study areas and with similar altitude and rainfall was selected. In order to reduce uncertainties related to the use of point soil profiles, all those collected in an area were combined to form a representative composite profile. The total inventory was 2790±50Bq/m2, and the relaxation coefficient indicated it was an undisturbed soil. The radiocaesium inventory in the study areas was 14–23% lower than in the reference area. The erosion rates for 137Cs were in the range 20.9–38.1tha−1y−1. The exposed root technique was applied to holm oak trees (age about 90years), and the erosion rates were in the range 22–34tha−1y−1. The ratio between exposed root and 137Cs techniques was 1.02±0.11 (S.D.) within the range 0.89–1.2. Both methods produced very similar results equally with respect to the mean erosion rate as well as the relative difference between the hillslope sections, i.e. displaying the same spatial variation in the study areas. As the accounting time for these two techniques is different, 50 and 90y for 137Cs and exposed roots respectively, results suggest that no change in mid-term erosion rates was implied for these areas for almost a century. The use of 137Cs and exposed roots methodology for the determination of mean erosion rates can be reproduced in other ecosystems, but a careful selection of the reference site for 137Cs is essential.

Environmental assessment of soil erosion in Inabanga watershed (Bohol, Philippines)

Analysis of soil redistribution patterns in watershed areas provides information for understanding soil erosion and deposition for implementing management practices to improve agricultural land conditions and reduce sediment loads in river systems. This paper has demonstrated the use of Cesium-137 (137Cs) in estimating retrospective medium-term soil erosion rates in selected cassava cultivated areas in Pilar, a sub-watershed within the Inabanga watershed. To estimate erosion and deposition rates and elucidate the factors affecting the soil redistribution, samples were collected from a total of ninety-eight grid intersections representative of the local land use and slope gradients in the presence or absence of soil conservation practices. A proportional model was used to deduce soil redistribution rate estimates from 137Cs inventories measured from individual soil samples. Soil measurements of 137Cs activity-generated soil erosion rate gave values of 13.15 t ha−1 year−1 in cultivated areas practicing conservation measures and 22.23 t ha−1 year−1 in those with typical upland plantation, with the former corresponding to slight erosion case and the latter to moderate erosion case. The obtained values have provided an overview of the pattern of soil redistribution in the watershed area and reflect the impact of strategic soil erosion management being applied. Interestingly, in light of recent severe meteorological events befalling the region, e.g., super typhoon Haiyan and the 7.3 magnitude earthquake, the data obtained may serve as benchmark values for 137Cs activities against which changes in the soil movement and soil redistribution pattern along the watershed areas can be evaluated.

Simulation of medium-term soil redistributions for different land use and landscape design scenarios within a vineyard landscape in Mediterranean France

Inappropriate agricultural land management practices cause irreversible soil losses in many parts of Europe. Soil degradation is predicted to increase in the next future as an effect of climate and cropping system changes. The most concerned areas are expected to be those already severely affected by erosion, as is the whole of the Mediterranean. Medium-term soil erosion models could be useful tools to analyse, understand and simulate complex interactions between geomorphic processes and human pressures for better assessment of medium-term soil redistributions associated with land use and landscape design change. The aim of this study was to compare the effects of various agricultural land uses and landscape design strategies on water and tillage erosion. The first step was to develop land use and landscape design scenarios of an agricultural Mediterranean landscape. Then, all of the scenarios were compared in terms of the soil redistribution using the LandSoil model. The results indicate that potential soil conservation associated with the adoption of sustainable land uses surpasses the potential conservation associated with certain landscape design. A detailed analysis of within-landscape soil redistributions suggests that land use is a major factor controlling sediment production, whereas landscape design is a major factor controlling hillslope connectivity.

Mound measurements — quantifying medium-term soil erosion under olive trees in Northern Jordan

Over the last few decades many quantitative erosion studies have revealed that olive orchard expansion and increased mechanization in southern European countries have led to increased soil erosion under olive trees. Consequently, these studies have suggested different methods of mitigation. In light of the 2014 European trading zone expansion to countries east and south of the Mediterranean, a further intensification of olive plantations is postulated to meet market demands. To attain first medium-term estimates of erosion in Northern Jordan and its driving factors, a new method measuring olive mounds was implemented. Seven fields with clearly erosive structures were chosen throughout the Wadi Al-Arab catchment in Northern Jordan. Topographic measurements were used to reconstruct the historical and recent surface level and calculate the volume eroded since the planting of the trees. A total of 81 bulk density measurements and 14 tree cores allowed the estimation of the soil loss in tons per hectare. The combination of modified land use map and slope information helped to identify similar olive fields with high erosive potential.Results show that the method provides medium-term quantitative estimates for averaged soil loss consistent with some existing results from similar research areas in the Mediterranean. They clearly indicate the significant potential for erosion in olive orchards with around 95±8tha−1yr−1. Tillage practice and water erosion were identified as critical erosion processes, both depending on tillage characteristics, tillage timing, and soil parent material. The investigated fields represent about 19% of the catchment's surface area and are likely to contribute to the measured yearly sediment yield that fills up the Wadi Al-Arab reservoir with sediments.

Quantifying and modelling the impact of land consolidation and field borders on soil redistribution in agricultural landscapes (1954–2009)

Soil erosion rates in cultivated areas have intensified during the last decades leading to both on and off-site problems for farmers and rural communities. Furthermore, soil redistribution processes play an important role in sediment and carbon storage within, and exports from, cultivated catchments. This study focuses on the impact of land consolidation and changes in landscape structure on medium term soil erosion and landscape morphology within a 3.7-ha field in France. The area was consolidated in 1967 and we used the Cs-137-technique to quantify soil erosion for the period (1954-2009). We measured the Cs-137 inventories of 68 soil cores sampled along transects covering the entire area and especially specific linear landforms located along both present and past field borders (i.e., lynchets and undulations landforms, respectively). These results were then confronted with the outputs of a spatially-distributed Cs-137 conversion model that simulates and discriminates soil redistribution induced by water and tillage erosion processes. Our results showed that tillage processes dominated the soil redistribution in our study area for the last 55 years and generated about 95% (i.e., 4.50 Mg.ha(-1).yr(-1)) of the total gross erosion in the field. Furthermore, we demonstrated that soil redistribution was largely affected by the presence of current and also former field borders, where hotspots areas of erosion and deposition (>20 Mg.ha(-1).yr(-1)) were concentrated. Land consolidation contributed to the acceleration of soil erosion through the conversion of depositional areas into sediment generating areas. Although the conversion model was able to reproduce the general tendencies observed in the patterns of Cs-137 inventories, the model performance was relatively poor with a r(2) of 0.20. Discrepancies were identified and associated with sampling points located along the current field borders. Our data suggests that tillage erosion processes near field boundaries cannot be described as a typical diffusive process. These processes near field boundaries should be characterised and taken into account in a future version of the model to accurately simulate rates and patterns of past soil redistribution in fragmented cultivated hillslopes. We also showed that the use of an accurate DEM resulting from LIDAR data, based on present-day topography, leads to the underestimation of soil redistribution rates by the model, especially in this landscape submitted to recent and important morphological changes. Our results have important implications for the simulation of tillage erosion processes and our understanding of soil redistribution processes in complex cultivated areas. This is of particular interest to improve our knowledge and prediction of patterns of soil physical parameters, such as carbon storage or water content, particularly sensitive to surface erosion and landscape structuration. Anglais

Mapping of erosion rates in marly badlands based on a coupling of anatomical changes in exposed roots with slope maps derived from LiDAR data

Black marls form very extensive outcrops in the Alps and constitute some of the most eroded terrains, thus causing major problems of sedimentation in artificial storage systems (e.g. reservoirs) and river systems. In the experimental catchments near Draix (France), soil erosion rates have been measured in the past at the plot scale through a detailed monitoring of surface elevation changes and at the catchment scale through continuous monitoring of sediment yield in traps at basin outlets. More recently, erosion rates have been determined by means of dendrogeomorphic techniques in three monitored catchments of the Draix basin. A total of 48 exposed roots of Scots pine have been sampled and anatomical variations in annual growth rings resulting from denudation analysed. At the plot scale, average medium-term soil erosion rates derived from exposed roots vary between 1·8 and 13·8 mm yr−1 (average: 5·9 mm yr−1) and values are significantly correlated with slope angle. The dendrogeomorphic record of point-scale soil erosion rates matches very well with soil erosion rates measured in the Draix basins. Based on the point-scale measurements and dendrogeomorphic results obtained at the point scale, a linear regression model involving slope angle was derived and coupled to high-resolution slope maps obtained from a LiDAR-generated digital elevation model so as to generate high-resolution soil erosion maps. The resulting regression model is statistically significant and average soil erosion rates obtained from the areal erosion map (5·8, 5·2 and 6·2 mm yr−1 for the Roubine, Moulin and Laval catchments, respectively) prove to be well in concert with average annual erosion rates measured in traps at the outlet of these catchments since 1985 (6·3, 4·1 and 6·4 mm yr−1). This contribution demonstrates that dendrogeomorphic analyses of roots clearly have significant potential and that they are a powerful tool for the quantification and mapping of soil erosion rates in areas where measurements of past erosion is lacking. Copyright © 2011 John Wiley & Sons, Ltd.

Estimation of soil erosion on cultivated fields on the hilly Meghalaya Plateau, North-East India

The estimation of soil erosion rates in complex subtropical agricultural systems of hilly environment is difficult and most of the traditional methods have serious limitations. The 137Cs technique allows to obtain relatively quickly retrospective medium term soil erosion results. The objective of this study was using 137Cs approach to quantify soil loss under agricultural system which develops under growing human pressure on the hilly terrain of the Meghalaya Plateau. The measured values of caesium inventory for all sampling points are between 2% and 63% of the reference value of caesium inventory. The estimated annual soil loss for sampling points located on the slope are between 29 and 79 Mg·ha−1·yr−1 in the case of an improved mass balance model. It means that soil erosion in this manually tilled agricultural area cannot be neglected.

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.

Fallout beryllium-7 as a tracer in soil erosion investigations

Recent developments in the use of the environmental radionuclides 137Cs and 210Pb for documenting medium-term soil erosion rates must be seen as an important advance. However, measurements of these radionuclides provide estimates of medium-term (i.e. ca. 45 or 100 years) soil redistribution rates and there is a need to explore the potential for using complementary radionuclides, to estimate erosion rates associated with individual events or short periods. Beryllium-7 ( 7Be, t 0.5=53 days) has the potential to fulfil these requirements. This contribution presents some preliminary results from an investigation undertaken in a field near Crediton, UK, which successfully demonstrates the potential for using 7Be as a tracer in soil erosion investigations.