Soil Redistribution Rates Research Articles

Soil redistribution rates along the forested and cultivated steep hillslope in the mid‐Himalayas using fallout—137Cs and RUSLE model

AbstractSoil erosion emerged as a significant land degradation concern, causing serious threat to soil ecosystem services in the Himalayan region. The complex topography of the region poses limitations to the measurement of soil redistribution (erosion, transport, and deposition) rate, necessitated for the effective soil conservation planning. The study investigated soil redistribution processes over a typical complex hillslope of the mid‐Himalayan region using the fallout radionuclide (FRN)—137Cs method and Revised Universal Soil Loss Equation (RUSLE) model. It involved a comparison of 137Cs measured soil redistribution and the RUSLE model estimates, aiming to assess its correspondence over the complex hillslope. Analysis of 137Cs measurements revealed the highest net erosion (−13.2 t ha−1 year−1) at the upper hillslope with a convex shape, while sediment deposition occurred at the lower (36.9 t ha−1 year−1) and valley (32.5 t ha−1 year−1) hillslope positions with a concave shape. The RUSLE model also estimated the highest erosion on the upper hillslope (−12.3 t ha−1 year−1) but the lowest erosion at the lower (−0.88 t ha−1 year−1) and valley (−0.32 t ha−1 year−1) hillslopes, that differed with the 137Cs method. The 137Cs method provided soil redistribution rate (either net erosion or deposition), whereas RUSLE model only showed the gross erosion rate. Thus, the estimate from RUSLE corresponds only to hillslope positions with a convex and straight shapes. The distribution of 137Cs measurements has clearly revealed the influence of slope shape and steepness in governing erosion and deposition processes at the hillslope positions with convex and concave slope shapes, respectively. In addition, terraces effectively trap sediments from upslope areas. Investigation of soil erosion using 137Cs measurement along with the RUSLE model helped to validate erosion and deposition processes over the hillslope positions. The study will help to suggest suitable conservation measures for the various hillslope positions in the mid‐Himalayan region.

Plutonium isotopes can be used to model soil erosion in Kenya

Climate change poses an immediate threat to tropical soils with changes in rainfall patterns resulting in accelerated land degradation processes. To ensure the future sustainability of arable land, it is essential to improve our understanding of the factors that influence soil erosion processes. This work aimed to evaluate patterns of soil erosion using the activity of plutonium isotopes (Pu) at sites with different land use and clearance scale in the Winam Gulf catchment of Lake Victoria in Kenya. Erosion rates were modelled at potential erosive sites using the MODERN model to understand small-scale erosion processes and the effect of different management practices. The lowest soil redistribution rates for arable land were 0.10 Mg ha−1 yr−1 showing overall deposition, resulting from community-led bottom-up mitigation practices. In contrast erosion rates of 8.93 Mg ha−1 yr−1 were found in areas where steep terraces have been formed. This demonstrates the significance of community-led participation in effectively managing land degradation processes. Another key factor identified in the acceleration of soil erosion rates was the clearance of land with an increased rate of erosion over three years reported (0.45 to 0.82 Mg ha−1 yr−1) underlining the importance vegetation cover plays in limiting soil erosion processes. This novel application of fallout plutonium as a tracer, highlights its potential to inform the understanding of how soil erosion processes respond to land management, which will better support implementation of effective mitigation strategies.Graphical abstractModelling of soil erosion and deposition patterns using the MODERN model to calculate the depth of soil loss/gain.

Assessing decadal soil redistribution rates using 239+240Pu across diverse lithologies in Southeast Alaska

AbstractQuantifying soil redistribution rates, including both erosion and deposition, is critical for understanding erosion processes, landscape evolution, land management strategies, and the carbon cycle. In the Northeast Pacific coastal temperate rainforest, the interaction of perhumid climate and dense coniferous forest tends to form Spodosols which are soils characterized by a subsurface accumulation of organic matter and iron and aluminum oxides, across a range of contrasting lithologies. Deep Spodosols are frequently found on steep backslopes (up to 60%) of colluvial deposits, where shallower soils would typically be expected. We hypothesized that deep Spodosols in Southeast Alaska indicate slope stability, exhibiting negligible soil redistribution rates and stable surfaces regardless of the lithology. Our objective was to quantify soil redistribution rates for Spodosols formed on steep slopes across a range of lithologies in hilly and mountainous areas of Juneau, AK. We used 239+240Pu isotopes to quantify soil erosion and deposition rates in Spodosols formed on colluvial deposits from tonalite, slate, metavolcanic rock, and phyllite. 239+240Pu measurements revealed negligible soil redistribution rates for all studied pedons, ranging from erosion rates of 0.51 t/ha/year to deposition rates up to 0.43 t/ha/year. No difference was detected between the hill and mountain landforms, further supporting the idea that Spodosols could indicate slope stability over decadal timescales across the region. Understanding the resilience of Spodosols to erosion processes in varied lithologies and landforms on steep slopes is paramount for making informed decisions regarding sustainable land use, landslide risk mitigation, and effective carbon sequestration strategies.

137Cs radiotracer in investigating influence of hillslope positions and land use on soil erosion and soil organic carbon stock—A case study in the Himalayan region

AbstractThe topography and land use/land cover (LULC) of the hillslope play a significant influence on soil erosion because of water, which is considered as a principal factor for the reduction of soil organic carbon content. Reliable information on the impact of erosion mechanism on soil organic carbon stock (SOCS) is essential for effectively accounting for the carbon flux that influences climate change. The main objectives of this study were to determine soil erosion based on the variation of 137Cs (Radiocesium) radionuclide activity at various hillslope positions and LULC in a hilly and mountainous region of the north‐western Himalayas. Additionally, the relationship between 137Cs concentration, soil erosion rate and SOCS were examined. Fallout radionuclide‐137Cs have emerged as a suitable method for assessing soil erosion in hilly and mountainous regions where rugged topography and extreme weather events restrain the conventional soil erosion assessment. The study revealed very high soil erosion rates of 32.89 and 30.70 t ha−1 year−1 in the lower hillslope positions with cultivated fields. The lowest soil erosion was obtained with a mean of 0.47 t ha−1 year−1 from the ridge with grassland, followed by the upper hillslope (5.50 t ha−1 year−1 under deodar forest and 14.07 t ha−1 year−1 under pine forest), and the middle hillslope (1.58 t ha−1 year−1 for deodar and 7.77 t ha−1 year−1 for pine forest). The soil erosion rates differ significantly between cultivated and forested regions, and there is also a significant difference between deodar and pine forests. Moreover, a significant difference was found between topographic positions concerning 137Cs, SOCS and soil redistribution rate. This difference was more pronounced at hillslope positions with different LULC. In both disturbed (cultivated) (r2 = .111) and undisturbed (forested and grassland) (r2 = .356) soils, positive and statistically significant (p < .005) poor relationships were found between SOCS and 137Cs inventory. This indicates the presence of various factors influencing the soil organic carbon stock (SOCS) mechanism or the indirect contribution of soil erosion‐induced carbon loss. This suggests that forest cover can enhance SOCS in the soil, mitigating the adverse effects of soil erosion and climate change. Consequently, 137Cs could be effectively used to quantify the SOC stock in soil redistribution over the hillslope affected by soil erosion. Statistical analyses indicated that the 137Cs inventory, SOCS and erosion were significantly affected by various hillslope positions and LULC types.

High-resolution soil erosion mapping in croplands via Sentinel-2 bare soil imaging and a two-step classification approach

Erosion-induced lateral soil redistribution leads to spatially heterogenous soil composition, which can be captured through the distinctive spectral reflectance of soils under varying levels of erosion influence. This points to the potential of using remotely sensed soil spectra to detect severe erosion and deposition hotspots in exposed croplands and, importantly, further differentiate the intra-class spectral variability of moderate erosion that often occupies the largest proportion. Here, we aim to develop a two-step erosion classification and mapping approach based on multitemporal compositing of Sentinel-2 bare soil images of a typical agricultural region (11,500 km2) of northeast China. A random forest classifier was firstly trained against the ground-truth data derived from very high resolution (VHR) imagery in Google Earth, with an overall accuracy of 91 % that allowed for clear delineation of severe erosion and deposition areas based on their distinct topographic and spectral features particularly in the red and red-edge bands. In the second step, the remaining area of moderate erosion (60.30 %) was further differentiated using Iterative Self-Organizing cluster unsupervised classification to yield a five-class soil erosion map at 10 m spatial resolution. The accuracy of the predicted map was successfully validated by independent Caesium-137 (137Cs) and soil organic carbon observations at catchment and regional scales, as revealed by significant inter-class differences in soil redistribution rates estimated from 137Cs inventory. The severe erosion class had a soil loss rate of 5.5 mm yr−1, suggesting that previous assessments have underestimated erosion severity. The spatial accordance of crop growth with soil erosion intensity, particularly in localized settings, further highlighted the potential of bare soil imaging for mapping the spatiotemporal development of soil erosion and its response to targeted sustainable cropland management efforts.

Assessment of soil redistribution rates in a Mediterranean olive orchard in South Spain using two approaches: 239+240Pu and soil erosion modelling

Soil redistribution by water and tillage soil erosion has a profound effect on the spatial variability of soil security indicators. In this study, we assess the potential of estimating long-term soil redistribution rates across a Mediterranean olive orchard catchment using two methods: 239+240Pu and the WaTEM/SEDEM model. Additionally, we identify potential sources of uncertainty explain result discrepancies, and offer guidance for reducing uncertainty. Soil sampling points were taken both in the inter-row areas and below the tree canopies and 239+240Pu inventories were converted into soil redistribution rates using MODERN. Sediment yield data measured in the catchment outlet is used to calibrate WaTEM/SEDEM. The results show a poor agreement between both methods. In this sense, these results indicate that both methods are considerably affected by several sources of uncertainty, both inherent to the methods themselves and related to the specific conditions of the study area. The latter are mainly related to anthropogenic changes in the soil surface related to soil tillage and rill filling practices and an important past land leveling effect. Despite the discrepancies, both methods convey a similar overarching message: soil security and olive production can be highly threatened in the Mediterranean in the next decades. This study demonstrates the potential advantages of combining FRN-based estimates and model simulations and highlights the importance of selecting an appropriate study area in this type of studies and the need to recognize associated uncertainties when estimating soil redistribution rates, whether employing FRN-based or modelling methods.

Accuracy and sensitivity of soil erosion estimation using 137Cs technology: A statistical perspective

Random spatial variation of the 137Cs inventory is the principal contributor to uncertainty in soil erosion estimation using 137Cs technology. A statistically sound sampling design is imperative for obtaining reliable soil erosion estimations. The objectives of this study are to: 1) characterize the effect of sample size on the estimates of mean inventories; 2) evaluate the sensitivity of the estimated soil redistribution to sample size using a new 137Cs model; 3) compare erosion detection limits among five conversion models; and 4) assess three spatial interpolation methods. Two small watersheds were sampled in an irregular grid design, and 30 samples were taken on a reference site. A moving window scheme was used to compute the 7-point and 11-point means of 137Cs inventories. The Welch’s modified t-test was used to test the mean estimates and to compute the detection limits for the replicated samples. Five models were selected to convert 137Cs inventories to soil redistribution rates. Since most single samples without replication yielded insignificant test results, the 137Cs technique cannot be used to estimate soil erosion at a single point due to random spatial variation. With 30 reference samples, 7 replicate samples on the sampling site provided reliable estimations of 137Cs inventories and soil redistribution. The spatial patterns of the estimated 137Cs inventories and soil redistribution became more regular and systematic as sample size increased, which agreed increasingly well with topography and surface hydrology. Replicate samples can be taken from each landform element or slope position where the erosion rate is expected to be uniform. Alternatively, a systematic grid sampling scheme can be used, and the nearest neighbors can be treated as replicates to calculate moving averages. The Type I and II errors with replicated samples showed that all sampling positions should be included in calculating watershed or area mean erosion rates even though the Type I errors indicated insignificant redistribution rates for some samples. Due to the lack of spatial autocorrelation, spline and inverse distance weighting methods performed better than kriging for interpolation. Detection limits and magnitudes of soil redistribution varied substantially with conversion models, depending on their sensitivities to changes in 137Cs inventories.

Agricultural activities lead to sediment infilling of wetlandscapes in the Canadian Prairies: Assessment of contributions by tillage, water and wind erosion

Soil erosion and sediment delivery models have been increasingly employed in studies of catchment sediment dynamics in current years. These models are also used to represent the spatial interaction of soil erosion and sediment transport processes, thereby providing spatially-distributed predictions of soil redistribution rates for agricultural landscapes. It has been widely recognized that individual soil erosion processes and their interactions contribute towards total soil erosion; however, quantifying the rates and patterns of soil erosion processes and their interactions within topographically complex landscapes is challenging. Therefore, the objective of this research was to estimate and model the relative contributions of tillage, water and wind erosion towards total soil erosion in the Canadian Prairie provinces of Manitoba and Alberta using 137Cs, a fallout radionuclide tracer, and three well-established models: (i) Tillage Erosion Model (TillEM); (ii) Revised Universal Soil Loss Equation, version 2 (RUSLE2); and (iii) Single-event Wind Erosion Evaluation Program (SWEEP). The findings indicate that the patterns of 137Cs-estimated soil erosion were closely matched with the erosion pattern predicted by TillEM and suggests that tillage erosion dominates the pattern of total soil erosion on the knolls of hummocky landscapes. Additionally, soil particle size variation within the wetland catchments reflected the modeled patterns of water and tillage erosion. Furthermore, our findings confirmed that colour coefficients are useful in identifying spatial heterogeneity of soil within wetland catchments and reflect the patterns of soil loss and gains. These results indicate that water and tillage erosion, and also their interactions, are main erosion processes in the Canadian Prairie Pothole Region (PPR), but that soil movement by tillage practices has been the predominant redistribution process.

Remote sensing and nuclear techniques for high-resolution mapping and quantification of gully erosion in the highly erodible area of the Malčanska River Basin, Eastern Serbia

Gully erosion leads to the formation of deep and wide channels that increase the risk of soil loss, flooding, and water pollution. In addition, this process reduces the productivity and viability of agricultural land and natural ecosystems. Preventing gully erosion is critical for maintaining ecological balance and preserving natural resources in certain areas. This paper presents a methodology integrating remote sensing and nuclear techniques to study gully erosion. The morphometric characterization of gullies using 360-degree camera photogrammetry was introduced as a new method in erosion research. This approach aims to investigate the suitability of unmanned aerial vehicle and terrestrial photogrammetry for modeling gullies, to study the variability of erosion processes in gullies at a small scale, and to compare the differences in erosion intensity between nearby gullies. The study's objectives include identifying the effective and economical method for gullies monitoring and providing a starting point for controlling and safeguarding gullies. Mainly erosion process was detected in the studied gullies, while deposition was identified at only 2 out of 39 sampling locations. The results showed an average soil redistribution rate of 16.2 t ha−1 yr−1 and coefficients of variation of 32%, 59%, and 91% for three investigated gullies. It was determined that aerial photogrammetry methods were not practical under the conditions prevailing in the study area. Highly detailed 3D models of the gullies were created using 360-degree photogrammetry. It was confirmed that the micro-relief obtained by photogrammetric modeling is an essential contribution to erosion research. The 360-degree camera photogrammetry serves as a reliable tool for analyzing the morphology of gullies and, in perspective, tracking changes in gully systems over time or monitoring the effectiveness of the applied protection measures.

Validating plutonium-239+240 as a novel soil redistribution tracer – a comparison to measured sediment yield

Abstract. Quantifying soil redistribution rates is a global challenge addressed with direct sediment measurements (e.g. traps), models, and isotopic, geochemical, and radionuclide tracers. The isotope of plutonium, namely 239+240Pu, is a relatively new soil redistribution tracer in this challenge. Direct validation of 239+240Pu as a soil redistribution tracer is, however, still missing. We used a unique sediment yield time series in southern Italy, reaching back to the initial fallout of 239+240Pu to verify 239+240Pu as a soil redistribution tracer. Distributed soil samples (n=55) were collected in the catchment, and at undisturbed reference sites (n=22), 239+240Pu was extracted, measured with inductively coupled plasma mass spectrometry (ICP-MS), and converted to soil redistribution rates. Finally, we used a generalized additive model (GAM) to regionalize soil redistribution estimates for the catchment. For the catchment sites, mean 239+240Pu inventories were significantly reduced (16.8 ± 10.2 Bq m−2) compared to the reference inventory (40.5 ± 3.5 Bq m−2), indicating the dominance of erosion. Converting these inventory losses into soil erosion rates resulted in an average soil loss of 22.2 ± SD 7.2 t ha−1 yr−1. The uncertainties of the approach stemmed mainly from the high measurement uncertainties of some low-activity samples where samples have been bulked over depth. Therefore, we recommend taking incremental soil samples and extracting larger soil volumes (∼ 20 g). The geographic coordinates and the flow accumulation best described the spatial pattern of erosion rates in the GAM model. Using those predictors to upscale Pu-derived soil redistribution rates for the entire catchment resulted in an average on-site loss of 20.7 t ha−1 yr−1, which corresponds very well to the long-term average sediment yield of 18.7 t ha−1 yr−1 measured at the catchment outlet and to 137Cs-derived soil redistribution rates. Overall, this comparison of Pu-derived soil redistribution rates with measured sediment yield data validates 239+240Pu as a suitable retrospective soil redistribution tracer.

Combining cosmic-ray neutron sensor and fallout 137Cs to explore the connection of soil water content with soil redistribution in an agroforestry hillslope

To ensure sustainable agricultural management, there is a need not only to quantify soil erosion rates but also to obtain information on the status of soil water content and soil loss under different soil types and land uses. A clear understanding of the temporal dynamics and the soil moisture spatial variability (SMSV) will help to control soil degradation by hydrological processes. This study represents the first attempt connecting cosmic-ray neutron sensors (CRNS) with soil erosion research, a novel approach to explore the complex relationships between soil water content (SWC) and soil redistribution processes using two of the most powerful nuclear techniques, CRNS and fallout 137Cs.Our preliminary results indicate that CRNS captured soil moisture dynamics along the study toposequence and demonstrated the sensitivity of neutron sensors to investigate the effect of parent material on soil water content. The Empirical Orthogonal Function (EOF) analysis of the comprehensive data from seven CRNS surveys revealed that one dominant spatial structure (EOF1) explains 89.2% of SMSV. The soil redistribution rates estimated with 137Cs at the nine locations along the hillslope, together with local factors related to soil properties (SOC, soil depth, hydraulic conductivity) and land use showed significant correlations with EOF. This study provides strong field evidence that soil type significantly affect SMSV, highlighting the key impact on soil erosion and sedimentation rates. Nevertheless, more research is needed to investigate the specific contributions of soil properties to the spatial variability of soil moisture and their subsequent effects on soil redistribution dynamics of interest for soil management.

A comparison of 210Pbxs, 137Cs, and Pu isotopes as proxies of soil redistribution in South Spain under severe erosion conditions

PurposeThe use of fallout radionuclides as proxies for the study of soil redistribution processes in semiarid environments of Southern Spain has been restricted to 137Cs. The potential and limitations of alternative proxies such as 239+240Pu and 210Pbxs should be explored given the expected constrains imposed by the features of the study area.Materials and methodsFour soil and one sediment cores were collected in a highly eroded area to test the feasibility of these proxies under demanding conditions. The use of gamma spectrometry and ICP-MS did allow exploring the potential of 210Pbxs and Pu isotopes against the well-established tracer, 137Cs. The activity ratios 239+240Pu/137Cs were explored to evaluate the previous evolution of the sampling sites. Soil redistribution rates were estimated using the model MODERN.Results and discussionDespite all the profiles showed intense perturbation, Pu isotopes showed the highest potential thanks to higher sensitivity and sample throughput. The deviations of 239+240Pu/137Cs inventory ratios (0.012–0.158) from the global fallout average (0.026 ± 0.003) suggest that the sediment core was a deposition site involving alternate episodes of topsoil removal and incorporation from different sources. The calculated erosion rates ranged 34–43 t ha−1 year−1, being in good agreement for 137Cs and 239+240Pu. 210Pbxs was not used due to low-quality data.ConclusionsThe use of Pu as a tracer of soil redistribution processes in semiarid areas seems to be promising even under severe erosion conditions. The use of 210Pbxs is not recommended in this area due to its low concentration.Graphical

Agricultural activities lead to sediment infilling of wetlandscapes in the Canadian Prairies: Assessment of soil erosion and sedimentation fluxes

Wetlandscapes are vulnerable to land conversion and sediment infilling from upland agriculture, causing them to act as sinks for sediment deposition and putting at risk their ecosystem services. Wetlandscapes in the Canadian Prairies agroecosystems are particularly susceptible to sediment infilling because of the intensification of human activities and agricultural practices. The rising risk of soil erosion in cultivated landscapes has generated a need to estimate soil redistribution rates and soil loss monitoring tools and techniques. This research examines the effects of agricultural activities on soil loss and sedimentation rates within agricultural landscapes in the Canadian Prairies. Land and atmospheric fluxes of sediment into wetlands are quantified over the past 60 years using catchment-scale tracing (137Cs) and budgeting techniques. Findings indicate that the pattern of 137Cs erosion/deposition varies along catchment toposequences, with erosion near the top of the toposequences (the average annual soil erosion rates were found to be 1.1 kg m−2 yr−1 for Manitoba and 0.3 kg m−2 yr−1 for Alberta) and deposition within the wetland ecosystem (total deposition rates were estimated at about −3.6 kg m−2 yr-1for Manitoba and −0.9 kg m−2 yr−1 for Alberta). The sediment delivery ratios were approximately 57% and 35% in Manitoba and Alberta, respectively, indicating that a noticeable amount of the mobilized sediment exits the field. These transfers from cultivated fields into wetlands reveal that wetlandscapes in Canadian Prairies are vulnerable to sediment infilling, and soil erosion control practices are needed to achieve sustainable management of agricultural landscapes.

Using 137Cs and 210Pbex to assess soil redistribution at different temporal scales along with lithogenic radionuclides to evaluate contrasted watersheds in the Uruguayan Pampa grassland

The use of environmental radionuclides in soil monitoring has made it possible to establish erosion rates. The combined use of 137Cs and 210Pbex is a common approach for determining mean annual erosion rates retrospectively in two different time windows; 137Cs in the past 50–60 years whereas 210Pbex provide a longer period up to 100 years. However, these radionuclides have contrasting sensitive behaviors, 210Pbex is able to be more sensitive to recent redistribution events of its last period of disintegration (22.3 yr) than 137Cs, being more sensitive to the past erosion and depositional events.This work studies soil redistribution rates at different temporal scales and the variability of lithogenic radionuclides by contrasting two watersheds with different land uses. The watersheds are Arroyo del Arbolito (AAW) and Cañada del Horno (CHW), both located near the Baygorria hydroelectric dam reservoir in Uruguay. Erosion rates obtained with 137Cs and 210Pbex using the MODERN conversion model for both watersheds showed that there are no significant differences for 210Pbex estimates, which suggests that the land management practices for both watersheds in the last twenty years do not differ and the erosion rates remained the same as the earlier period. However, significant differences were found for erosion estimated by using 137Cs in CHW vs AAW (p ≤ 0.05) and cultivated vs. natural pasture (p ≤ 0.001), which indicates that the main erosion events occurred further in the past. Furthermore, these changes in erosion estimated using both isotopes coincide with changes in land use and land management, from tillage-based practices in the past to the predominance of no-tillage since the early 2000 s. This change in soil management resulted in a reduction of approximately 50% in soil loss in those cultivated areas since 1965. In AAW, 51.7% of the sampled points exceeded the tolerable erosion rate (7 Mg.ha−1.yr−1) estimated using 137Cs, whereas for 210Pbex, 37% of the sampled points exceeded this limit. For CHW, 63.6% of the sampled points exceeded the tolerable erosion limit (9 Mg.ha−1.yr−1) estimated by using 137Cs, whereas for 210Pbex, 34.2% exceeded this limit. Our results suggest that the variation of lithogenic radionuclides by erosion is dependent on soil type and erosion magnitude. This study, which describes the use of two fallout soil radiotracers, provides new insights into the impact of land use conversion on soil degradation in the Pampas grassland ecosystem.

Meteoric 10Be as a tracer of soil redistribution rates and reconstruction tool of loess–mantled soils (SW, Poland)

Loess deposits are terrestrial archives that record progressive deposition and erosion events of varying intensities. Data on long-term erosion rates are crucial for tracking changes in the stability of a loess mantle and reconstructing the evolution of loess-enriched soils. We used meteoric 10Be to i) define the factors responsible for its distribution along the profile, ii) determine long-term erosion rates in loess-enriched polygenetic soils characterised by illuviation processes, and iii) evaluate initial soil thickness and stability over time. Distribution of meteoric 10Be along the soil profiles was mainly driven by its translocation with clay particles and accumulation in the illuvial horizons. However, in some cases (loess over serpentinite), the highest meteoric 10Be content was measured in the C horizons which may be related to the longer exposure of serpentinite to meteoric 10Be deposition before the occurrence of a major loess accumulation event. The estimated long-term erosion rates greatly depend on the assumed environmental settings and were in the range of about 0.1–3 t ha−1 yr−1. Based on the soil redistribution rates, we reconstructed the removed loess layer which was from a few dm to about 3 m. The results indicate four main soil evolutionary phases: a) pre-exposure of sediments to meteoric 10Be accumulation; b) formation of thick loess mantles during the Last Glacial Maximum; c) erosion events between 21 and 11.6 ka that significantly shallowed the initial loess mantles; d) pedogenesis (with subsoil clay accumulation) in the Holocene within the thinner relicts of the former Late Pleistocene loess mantle followed by a recent and strong erosional phase due to human impact. These phases are also believed to have occurred in several other areas of Central Europe.

210Pbxs. is a viable alternative to 137Cs for tracing soil redistribution in mountain pastures affected by heterogeneous Chernobyl fallout

AbstractSoil mobilization has been investigated by means of fallout radionuclides (FRN) in a first‐order catchment of the Eastern Alps. Caesium‐137, 210Pbxs. (210Pb excess or unsupported fraction), and 241Am have been measured in soil samples collected from a pasture at about 2150 m above sea level. Combining pedological and radioactivity data, including mineral‐related radionuclides (primordial 40K and nuclides belonging to the 232Th and 238U decay chains), the distribution of FRNs, their spatial variability, vertical distribution, and relationships with pedological and topographical variables were assessed. Because of low activity concentration, it was not possible to use artificial long‐lived 241Am as a soil tracer, but preliminary results are encouraging. Inventories of 210Pbxs. and 137Cs have been converted into soil mobilization rates applying the MODERN model. Despite the gentle steepness and the absence of evident signs of erosion, the slopes of the considered catchment are affected by erosion at a rate up to 6 t ha−1 yr−1, likely related to grazing. A comparison between 210Pbxs. and 137Cs has revealed that at this site 137Cs, the most used FRN for estimating soil redistribution, is not suitable for this purpose, probably due to its irregular spatial distribution on snow‐covered ground after the Chernobyl accident. Conversely, 210Pbxs., owing to its continuous input, has provided reliable estimates of soil redistribution rates, in accordance with local morphology. The latter has in fact been related to morphometric variables in a regression model to provide an overview of soil erosion/sedimentation across the entire catchment, confirming that 210Pbxs. is a viable alternative to trace soil erosion and deposition where the Chernobyl fallout occurred on snow‐covered ground.

Assessment of soil redistribution in a typical karst catchment using 137Cs

An effective assessment of soil erosion and redistribution is a prerequisite for soil erosion control and is critical to achieving sustainable development goals. The most typical landscape in the karst region of Southwest China is found in the peak-cluster depression area, but little attention has been given to the soil redistribution here. A typical karst peak-cluster depression catchment water area in Southwest China was selected, and 137Cs technology was used to evaluate the soil redistribution rate and soil erosion process along a total transect (hillslope, depression and sinkhole) in the catchment. The results showed that the distribution of 137Cs had a high spatial variability on the total transect of the catchment (CV = 60.04%), the middle slope was the most severely eroded (highest erosion rate of 13.49 t ha−1 yr−1), and the area between the bottom slope and the depression was the primary sedimentary area on the surface in the catchment. The distribution of soil properties on the hillslope was affected by the process of soil redistribution. According to the distribution of the 137Cs soil profile, the soil profile of the hillslope was uniform, and signs of historical tillage activities were evident; the historical tillage activities of depressions were in the range of 0–20 cm depth, while the 137Cs in the sinkhole was mostly distributed in the shallow layers and decreased exponentially with depth, reflecting the depositional characteristics of noncultivated soil. In addition, this study found evidence of underground soil loss in sinkholes since the 1960s; the shallow sediment of these sinkholes mainly came from depressions, with an average deposition rate of 11.77 t ha−1 yr−1. Human disturbance and land-use change controlled recent changes in soil redistribution. The soil erosion rate of the hillslopes in catchments was extremely low (average erosion rate of 1.92 t ha−1 yr−1). The rocky desertification of hillslopes occurred before 1960; it was not a short-term contemporary process that occurred only during recent decades. This study showed that underground soil loss mainly occurred through sinkholes for a short period of time (100 years). These research results are of great significance for understanding the evolution of rocky desertification and the process of soil erosion.

Effects of cropland abandonment and afforestation on soil redistribution in a small Mediterranean mountain catchment

In slopes of Mediterranean mid-mountain areas, land use and land cover changes linked to the abandonment of cropland activity affect soil quality and degradation and soil redistribution; however, limited attention has been paid to this issue at catchment scale. This paper evaluates the effects of cropland abandonment and post-land abandonment management (through natural revegetation and afforestation) on soil redistribution rates using fallout 137Cs measurements in the Araguás catchment (0.45 km2, Central Spanish Pyrenees). A total of 52 soil core samples, distributed in a regular grid, from the first 30–40 cm and 9 sectioned reference samples were collected across the catchment and soil properties were analysed. Fallout 137Cs was measured in a 5 cm sectioned references samples and in bulk grid samples. 137Cs inventories were used to estimate soil erosion and deposition rates across the catchment. Results show that the highest erosion rates were recorded under sparsely vegetated sites in the badland area, while the lowest rates were found in the afforested area, but no significant differences were observed between the different uses and covers in soil redistribution rates likely due to a long history of human intervention through cultivation in steep slopes and afforestation practices. However, the recovery of the soil organic matter in afforested areas suggest that afforestation can reduce soil degradation at long-term scale. The information gained achieve a better understanding of soil redistribution dynamics and provide knowledge for effective land management after cropland abandonment of agroecosystems in Mediterranean mountain areas.

Microscale spatial variability of Beryllium-7 at a reference site in southwest China

Quantitative assessment of soil erosion and deposition rates using fallout radionuclides (FRNs), including Beryllium-7 (7Be), requires establishment of a reliable reference inventory i.e. the inventory of a non-eroding point. Little information, however, is currently available on the microscale spatial variability of 7Be inventory within reference sites. This is important information to inform sample design and replication, and in addition, to evaluate the uncertainty of derived soil redistribution data. In this study, soil samples were taken systematically at grid points on a 5 m × 12 m experimental reference plot with a bare soil surface, at two sampling occasions (2019 and 2021) in southwest China. 7Be activities were measured to explore the potential variability of 7Be inventory at the microscale. To determine possible causes of 7Be inventory variation, physicochemical characteristics including organic matter content (OM), pH, cation exchange capacity (CEC) and grain size compositions were analyzed at each sample location. 7Be inventories for the two periods were estimated at 211.1 ± 20.0 and 456.1 ± 43.8 Bq m−2 (mean ± 2 SEM, n = 44), with coefficients of variation of 31.4 and 31.9% for the 2019 and 2021 sampling cases, respectively. No significant correlations were observed between 7Be activity and the measured soil compositional properties, suggesting observed spatial variability is primarily a result of random variation due to rainsplash and other processes, although sampling and measuring processes may contribute some uncertainties. Using the traditional method, ca. 40 independent reference samples are required to estimate the mean 7Be inventory, i.e. to represent input across the site, with an allowable error of 10% at 95% confidence, while application of a bootstrap approach suggests that ca. 28 would be adequate under similar accuracy. Overall, results of this study emphasize that the simple assumption of uniform distribution of 7Be across the reference area needs detailed examination on a case-by-case basis, if this radionuclide is to be used effectively to assess patterns and rates of soil redistribution from field to hillslope scale.

Effect of historical land‐use change on soil erosion in a Mediterranean catchment by integrating 137Cs measurements and WaTEM/SEDEM model

AbstractSoil erosion is especially severe in areas affected by intermittent heavy rainfalls after dry periods, and human practices such as deforestation. Mediterranean mountain environments underwent conversion of rangelands into croplands during the previous centuries to increase agricultural production but this process was reversed after land abandonment in the middle of the twentieth century allowing the natural revegetation. To understand the effect of the past practices and the current agricultural management, we have combined the strength of empirical data and spatially distributed modelling in a medium‐sized catchment representative of agroforestry landscapes of NE Spain. We developed an ensemble technique composed of 137Cs‐derived soil redistribution rates as specific point values and as grid‐based setup calibration for the WaTEM/SEDEM. Thus, we overcame the point specific limitation of the 137Cs measurement and the need for calibration of spatially distributed models that allow a spatial interpretation of soil redistribution in the catchment. We implemented an automated routine model tool to increase the calculation speed and calibrate the model thus, allowing estimates of the main model parameters for simulating a variety of temporal scenarios. With this method a good fit between modelled and measured soil redistribution rates (R2 = 0.82) was obtained (Nash–Sutcliffe efficiency: 0.79). Estimates were also consistent with the previous apportions of sediment provenance obtained by the fingerprinting technique. An increase of 300% in sediment export was predicted for the past scenario when most of the catchment was cultivated, while a reduction of 40% occurred in the future scenario of land abandonment. A high influence of input resolution was found, wherein model efficiency was reduced when pixel‐size was increased. Our study demonstrates that spatially distributed models combined with 137Cs‐derived rates provide a powerful tool to understand the driving factors of erosion and delineate the hotspot areas that could suffer high erosion if submitted to certain management practices.