Assessment of soil erosion and deposition rates in a Moroccan agricultural field using fallout 137Cs and 210Pbex

A GIS-based modified PAP/RAC model and Caesium-137 approach for water erosion assessment in the Raouz catchment, Morocco

Water erosion poses a significant environmental threat in the Mediterranean region, with pronounced impacts observed throughout Morocco. It impairs soil quality and disrupts both sediment transport and water availability. Contributing factors range from natural (climate, topography, and geology) to anthropogenic (land use, vegetation cover, and management). This study introduces an improved Priority Actions Program/Regional Activity Centre (PAP/RAC) model, enriched with GIS and the Caesium-137 (137Cs) technique, to investigate erosion within Morocco's Raouz basin. Enhanced with additional variables including soil types, slope length, rainfall erosion potential, slope orientation, soil moisture, and land surface temperature, the model transcends the classical approach, promoting granularity and precision in predictions. In addition to the comprehensive model, the 137Cs method, which discerns long-term soil erosion and redistribution, provides a dual-faceted validation, bolstering the robustness of this project's erosion risk evaluation. This study's outcomes underscore the gravity of the erosion hazard with significant soil depletion rates ranging from 8.1 to 20 t ha-1 yr-1, demonstrating the model's alignment with empirical data, affirming its utility. The modified PAP/RAC model concurs with the 137Cs data, demonstrating its usefulness for water erosion assessment and management in similar areas.

Behaviour of 137Cs and 210Pb inventory at three candidate reference sites for erosion study in the upstream Citarum watershed area, West Java, Indonesia

The fallout radionuclide (FRN) analysis needs a reference site (RS) inventory to determine erosion and sedimentation in the study area. The investigated area is in the upstream Citarum watershed, West Java, Indonesia. Twenty-seven corings and 22 scrap samples have been prepared well and measured using HPGe gamma spectroscopy. The data below the minimum detectable activity (MDA) was found for ¹³⁷Cs in RS6 cor 4 and 7 (<0.16 ± 0.08 Bq kg^-1). MDA quantification implies that the inventory below MDA eroded greater than its maximum value (76.02 tons ha^-1 a^-1). The comparison ¹³⁷Cs inventory in this study is lower than the three estimation models; however, the inventory of Mt. Papandayan is closer to the model. This study found the depth percentage of 20-30 cm using the proportion of 0-20 cm/0-30 cm ratio and predicted the portion of the existence of ¹³⁷Cs and ²¹⁰Pb_ex in the 20-30 cm in the bulk sample. The highest H₀ (142.04 kg m^-2), the relaxation length λ, and proportion of 20% of ¹³⁷Cs in 20-30 cm depth imply that ¹³⁷Cs inventory activity is possibly deeper than 30 cm. This study recommends that Mt. Papandayan could be the alternative RS for the upstream Citarum watershed.

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 forest age on soil erosion and nutrient loss in Dianchi watershed, China

Soil erosion and nutrient loss are important environmental and ecological problems in the Dianchi watershed in southwestern China. Woodlands-the primary land type in the Dianchi watershed-play an important ecological role in controlling soil and water loss. In this study, we compared soil erosion and loss of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) in woodlands of different ages, i.e., young forest, medium forest, and near-mature forest, at the Dongda River catchment in south-western Dianchi watershed. Furthermore, changes in stoichiometries in soil were analyzed. The average degree of erosion of each forest age stage was below moderate. Based on the non-arable soil erosion modulus models of ¹³⁷Cs and ²¹⁰Pb_ex, the soil erosion rates decreased gradually with the increasing forest age. The forest age affected soil nutrient distribution and loss. The losses of TOC and TP gradually decreased, while the losses of TN first increased and then decreased with the growth of forest age. TOC, TN, and TP were enriched in the topsoil. Forest age affected soil stoichiometry and soil nutrient supply level. In general, the forest can effectively reduce soil erosion and nutrient loss in the red soil area with the forest age increasing.

Soil water erosion assessment in Morocco through modeling and fingerprinting applications: A review

During the last century, a great deal of effort has been directed toward determining soil erosion rates using various methods under a wide range of climatic conditions, soil types, land uses, topography, and among others. Therefore, to better understand soil erosion studies in Morocco, a country with diverse physiography and climatic variations we undertook an analysis of national data of several soil erosion modeling and fingerprinting. The approach used for this research is a review of scientific articles, conference papers and thesis on soil erosion, focusing more on categorization of the different soil erosion models and other methods applied. The results reveal very interesting information as follows: (i) the distribution and frequency level of modeling and fingerprinting applications; the focus was on the north of the country: (Rif 32.89%, High Atlas 32.89%, Occidental Meseta 18.43% and Middle Atlas 10.53%), (ii) The (R) USLE models remain the most widely used models (51,32%) in Morocco, (iii) The support practice factor was severely lacking across the country, (iv) the highest erosion rate is concentrated in the Atlas and Rif mountains; and (v) a positive relationship between erosion rate and geological features, slope, climate, land use and cover, plus other environmental characteristics, as well as measurement and modeling conditions, and a negative relationship with the study areas size and scale. Even though the overall results show a high degree of variability, which cannot be explained by this combination of factors, but is at a minimum partly related to the experimental conditions. This overview research and database are designed to assist in the future assessment of soil erosion and to help define priorities for soil erosion research by providing a state of art for future focused and comprehensive analyses to address this issue of soil erosion in Morocco.

Modeling and Mapping of Soil Water Erosion Risks in the Srou Basin (Middle Atlas, Morocco) Using the EPM Model, GIS and Magnetic Susceptibility

The Oued Srou watershed located in the Middle Atlas Mountain of Morocco has been a subject of serious soil erosion problems due to the combination of natural factors and anthropic activities. Therefore, soil erosion hazard assessment and mapping can be handy to initiate remedial measures in the area. In this study, the improved Erosion Potential Model (EPM) integrated with GIS and remote sensing techniques is employed to map and assess the vulnerability of the Oued Srou watershed to the water erosion phenomenon and its impact on the silting of the Ahmed El Hansali dam. The results of the EPM model showed that the maximum annual soil loss rates were in the range of 5-652 m3/km2/year, with an average of 49 m3/km2/year. The delivery coefficient ratio showed that about 34433 t/year of the sediments reach the outlet of the watershed. The correlation analysis between all erosion factors revealed the following order of their importance in the water erosion control: soil sensitivity to erosion, soil protection, slope, erosive state, temperature, and rainfall. The magnetic susceptibility provided results on the evolution of soils; it showed that the most degraded soils had a high erosion rate. Generally, the stable soils not eroded showed an upward increase of magnetic susceptibility values in soil profiles; the evolution of magnetic susceptibility of degraded soils is disturbed. The magnetic susceptibility has also made it possible to highlight the source zones of sediments that reach the outlet of the watershed.

Assessment of erosion rate in a rainfed agricultural area on the Northwestern coast of Egypt using 137Cs measurements

In the present work, the use of the fallout radionuclide ¹³⁷Cs as a tracer for estimating soil redistribution rates over the past 60 years was tested in Egypt at an agricultural field with a smooth slope (0-10%) located in Ras El-Hekma on the Northwestern coast. The average annual soil erosion rate was derived from ¹³⁷Cs inventories (Bq m^-2) and by using the conversion Diffusion and Migration Model (DMM). The activity concentrations of ¹³⁷Cs with uncertainty ranging between 7.5 and 20.9% were measured using HPGe gamma spectrometry. Approximately exponential shape for the distribution of ¹³⁷Cs activity concentration was observed within the upper 20 cm of the soil profile associated with the reference site while for the study sites, the ¹³⁷Cs depth distribution profiles indicate generally an increase of activity reaching a maximum peak of ¹³⁷Cs usually at a depth of 10-15 cm followed by an abrupt exponential decrease of ¹³⁷Cs activity concentration with depth. The measured average reference inventory for this area was 697 Bq m^-2 with a coefficient of variation of 23%. This value is close to the estimated reference inventory using the conversion model, which was 744 Bq m^-2. Transect sampling strategy was adopted at the study area where three parallel transects were chosen based on the common slope. The estimated average annual erosion rate for the three transects was found to be 7.5 t ha^-1 y^-1, and sediment delivery ratio was approximately 98%, which shows the moderate vulnerability of the Ras El-Hekma area to water erosion.

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.

Depth-distributions and migration of fallout radionuclides in mountain soils from Chréa National Park (Algeria): The role of rhizospheres

The distribution and migration of artificial fallout radionuclides in natural soils has been profusely studied for assessing radioecological impacts and predicting their long-term behaviour, among other topics. Despite the standardized use of the analytical solutions of a simplified convection-diffusion equation (CDE), there are still some concerns and open questions. This work is aimed at contributing to the understanding of basic processes governing the distribution of fallout radionuclides in vegetated soils with rhizospheres. It studies ²¹⁰Pb and ¹³⁷Cs in soil cores and vegetal samples from Chréa National Park, in Algeria, along with other natural radionuclides and some major and trace elements. Results include surficial and depth distributions of radionuclide concentrations, and site and plant-specific concentration ratios (CR). Inventories of ¹³⁷Cs (3620 ± 120 Bq m^-2) and ²¹⁰Pb_exc (9000 ± 900 Bq m^-2) in soils are typical from global fallout in high precipitation areas in the Northern Hemisphere. A simple model of a polyphasic soil, including rhizospheres, provides a realistic description in the studied case, where plant roots occupy about 45% of the volume in the 0-10 cm interval, with a high porosity around rhizomes. This composite soil matrix explains the different patterns observed in the depth distribution of the studied elements. The depth-distributions of ¹³⁷Cs and ²¹⁰Pb_exc have been modelled with different approaches: i) analytical solution of the CDE with mean annual convection and large observation times; ii) as before, but with convection representing infiltration events and short observation times; iii) numerical modelling of the ¹³⁷Cs profile in the mineral phase using CDE with fast initial distributions. The three approaches fit the empirical data, but they predict different time evolutions. The approach iii) provides a more realistic description. Results are questioning the common accepted analysis and its predictive use.

The response of water flow, suspended sediment yield and erosion intensity to contemporary long-term changes in climate and land use/cover in river basins of the Middle Volga Region, European Russia

The Middle Volga Region is one of the most populated and agriculturally developed geographic regions of the East European Plain within European Russia, where noticeable changes in climate and land use/cover were observed since the 1980s and the early 1990s respectively. The long-term year-to-year (trend) variability (during mainly 1960-2016) in water flow and suspended sediment yield of 14 small and medium-size rivers in the Middle Volga Region was analyzed in the paper. It is shown that in all the studied rivers there was a statistically significant decrease (on average, by 77.2 ± 4.5%) in the intra-annual irregularity of the water flow between 1960-1979 (as a baseline period) and 2002-2016 (the period of the greatest relative climate change in the region). This decrease was caused by a statistically significant reduction in the water flow during the snowmelt period (on average, by 37.4 ± 9.8%) and by an increase in the water flow during the low-water (baseflow) seasons - during the winter months (by 145.2 ± 57.6%) and the river-ice-free period (by 94.9 ± 39.7%). The intensity of snowmelt-induced flood flow has also statistically significantly decreased (by 40.4 ± 8.2%). At the same time, a reduction in the river suspended sediment yield was more significant - by 27.9 ± 26.9 times; it was the result of great changes in soil/rill/gully erosion intensity in the region. This reduction is confirmed by an analysis of sedimentation rates within one of the small (dry valley) catchments in the north of the studied region over the past 60 years. The changes in climate (chiefly a decrease in the depth of freezing of the soil during the snowmelt period, mainly April) and land use/cover, associated basically with reduction in cultivated land area (especially in the 1990s, after the collapse of the Soviet Union), are considered to be as the main reasons for the aforementioned trends that were characteristic in general for almost the entire southern half of European Russia.

An alternative methodology to determine 210Pb activity soil profiles

Unsupported ²¹⁰Pb (Pb_exc) is generated in air and is subsequently deposited on soil surface. The Pb_exc can be used for sediment dating, soil erosion/sedimentation and air mass studies. In many cases, ²¹⁰Pb activity determination (gamma ray 46.5 keV) cannot be performed due to the lack of efficiency calibration curve, especially when radioactive patron source is not available. This work presents an alternative methodology to obtain the ²¹⁰Pb activity values, based on the activity definition and the attenuation coefficient determinations and assuming that soil samples coming from depth higher than 25 cm only contain ²¹⁰Pb generated in the soil (Pb_exc free, i.e., for those soil layers the ²¹⁰Pb activity is equal to the ²²⁶Ra activity, at secular equilibrium). The proposed methodology was evaluated using soils from La Plata region, Argentina. The same soil samples were also analyzed in a second laboratory by the conventional methodology. The obtained results indicated that the proposed procedure can be used as a good alternative in cases where a calibration sample is not available.

Assessment of soil erosion rates in a Mediterranean cultivated and uncultivated soils using fallout 137Cs

Fallout radionuclides, such as ¹³⁷Cs, have been recognized as a valuable means for studying soil erosion processes. In this study, the ¹³⁷Cs technique was used to assess soil erosion magnitude and to investigate the effectiveness of terrace cultivations in the High Atlas of Morocco, particularly, the Ourika watershed. ¹³⁷Cs depth distribution profiles were established along slope gradients associated with land use considering cereal crop, arboriculture and native forests. Along the slope gradient, depth distribution profiles highlight dissimilarities reflecting differences in land use, topographic roughness, soil particle distribution and stoniness. ¹³⁷Cs inventory decreases exponentially with depth and its penetration increases along the slope. It becomes higher at the bottom of the slope, with penetration reaching 30 cm. ¹³⁷Cs mass activity and inventory significantly decrease in cultivated terraces, compared to native forest. Although the pattern of ¹³⁷Cs gain/loss varied according to topography, soil properties and vegetation cover, showing eroding and aggrading profiles, most samples had ¹³⁷Cs values lower than the reference value, suggesting net-loss of soil as a consequence of erosion processes. The net erosion rates were estimated about 8.5 and 6.0 t ha^-1 yr^-1 in cereal crop and arboriculture agrosystems, respectively, whereas in the forest, the net erosion rate was lower at about 4.2 t ha^-1 yr^-1. Soil loss on agricultural terraces is not significantly above tolerable erosion rates for Morocco (<7 t ha^-1 yr^-1), particularly for arboriculture terraces. A strong correlation was observed between ¹³⁷Cs and both soil organic carbon and slope gradient, in uncultivated area, whereas, there was no correlation for cultivated terraces. Terraced arboriculture systems should be encouraged for better soil preservation against water erosion in the Ourika watershed.

Soil erosion and corn yield in a cultivated catchment of the Chinese Mollisol region

Evaluation of soil redistribution rates and influence on crop yield in agricultural catchments is very important information, which can provide a scientific basis for arrangement of soil and water conservation measures and sustainable crop production. In recent decades, the soil erosion has greatly aggravated in the Mollisol region of Northeast China due to unreasonable land management, which in turn has reduced crop yield. The objectives of this study were to investigate the spatial distribution of soil redistribution and the relationship between crop yield and soil redistribute at a catchment of the Chinese Mollisol region. A total of 176 soil samples were collected based on a 200 m by 200 m grid and 4 yr of corn (Zea mays L.) yields were measured. The 137Cs trace technique and Zhang Xinbao's mass balance model indicated that the soil redistribution rates ranged from -7122.25 to 5471.70 t km-2 yr-1 and averaged -830.10 t km-2 yr-1. Soil erosion dominated in the research area. The corn yields for four years ranged from 43.24 to 136.19 kg km-2 and averaged 90.42 kg km-2. The spatial distribution of soil redistribution rates and corn yield showed a similar ribbon and plaque characteristics at the catchment. An equation between corn yield and soil redistribution rates was fitted and showed that there was a significant negative correlation between corn yield and soil erosion rates, while there was no relationship between the corn yield and soil deposition rates. Therefore, effective soil and water conservation measures are urgently needed to increase crop yield and realize sustainable land-use management.

The impact of contemporary changes in climate and land use/cover on tendencies in water flow, suspended sediment yield and erosion intensity in the northeastern part of the Don River basin, SW European Russia

The basin of the Don River (the fifth longest river in Europe), located mainly in the forest-steppe and steppe landscape zones, is one of the most populated and agriculturally developed regions of the East European (Russian) Plain. Sheet, rill and gully erosion occurring chiefly in snowmelt period (March-April) and also in moderate-to-heavy-rainfalls season (chiefly May-to-September) is the main factor of present-day soil degradation within cultivated lands of this basin. Using monitoring hydrological data, it is shown, by the examples of the Khopyor River and the Medveditsa River flowing in the northeastern part of the Don River basin (SW European Russia), that suspended sediment yield of the rivers, as an objective and sufficiently accurate indicator of total erosion intensity in river basins, was reduced by 3.6-3.8 times between the 1960s-1970s and 2008-2015. This conclusion is consistent with change in sedimentation rates (using ¹³⁷Cs as a chronomarker) within one of the small catchments located in the basin of the upper reaches of the Medveditsa River. The noted dynamics in erosion intensity and suspended sediment yields took place against the background of a well-marked tendency (since the 1940s-1960s) of reduction in intra-annual unevenness of river water flow caused by a decrease in spring (snowmelt-induced, March-April) flood water flow, and by a more significant increase in water discharges during low-water-flow periods of year (winter (December-to-February) and river-ice-free period (mid-April-to-November)). These changes were accompanied by an increase in duration of spring (snowmelt-induced) flood flow with a reduction in its intensity, year-to-year anomalousness and contribution to total annual water flow of the rivers. The main reasons for all the changes noted over the last decades were climate change (a decrease in depth of soil freezing during snowmelt period caused by an increase in air temperature mainly in winter and spring months; an increase in winter thaws frequency) and human activity changes (mainly a reduction in cultivated land area, especially in the 1990s and early 2000s). The similar tendencies were identified over the last decades in other regions of the forest (south part), forest-steppe and steppe landscape zones of the East European Plain.

From floodplain to aquatic sediments: Radiogeochronological fingerprints in a sediment core from the mining impacted Sancho Reservoir (SW Spain)

The Sancho Reservoir (SW Spain) was built in 1962, about the time of maximum ¹³⁷Cs fallout, and it has been affected by acid mine drainage (AMD) particularly since the mining cease in 2001. This is a unique scenario for studying the radiogeochronological fingerprints in AMD-affected sediments deposited over the former flood plain. A sediment core sampled in 2011 was analysed for bulk density, ¹³⁷Cs, ²³⁹Pu, ²⁴⁰Pu, ²¹⁰Pb, ²²⁶Ra, ²²⁸Ra, ²³⁴Th (²³⁸U) and ⁴⁰K, and studied with various radiometric dating models. Bulk density revealed unsteady compaction and likely depositional events. The activity concentrations of ²²⁶Ra, ²²⁸Ra, ²³⁴Th (²³⁸U) and ⁴⁰K were uniform down-core, but declining overall in the upper 0-25cm, revealing changes in provenance except for ²³⁸U, which increased in the top 10cm likely due to its supply by AMD. The AMD fingerprint was also found in the ^239+240Pu/¹³⁷Cs activity ratio, which increased in the top sediment layers. The ¹³⁷Cs and ^239+240Pu profiles show well defined peaks at the same depth, with inventories being about four times higher than the expected integrated atmospheric deposition in the area. The unsupported ²¹⁰Pb (²¹⁰Pb_exc) showed a complex non-monotonic profile interrupted at several sections, particularly around the ¹³⁷Cs peak. The whole dataset cannot be interpreted in terms of continuous sedimentation processes. Based upon correlated features in the bulk density and ²¹⁰Pb_exc profiles, a series of depositional events (likely linked to peaks in the rainfall records) have been identified in the core. These events date back to the period comprised since the construction of the dam until its increase in height in 1972, which likely displaced upstream the main depositional area of riverine loads, as inferred from sediment trap data. The CRS (with a reference date) and (a piecewise) CIC models have been used for complementing and discussing the chronology.

Vertical and lateral distribution of fallout 137Cs and soil properties along representative toposequences of central Rif, Morocco

The purpose of this study is to understand and quantify the relationships between current ¹³⁷Cs inventories and the soil properties and the physiographic characteristics. A total of 36 cores were taken in seven transects with different slopes, lithology and land use. The analysis focused on the ¹³⁷Cs mass activity as well as inventories and its relationship with soil properties as grain size and organic matter. The mass activity of ¹³⁷Cs and the inventories varied between 3.6 and 63.7 Bq kg^-1 and between 521.7 and 3304.4 Bq m^-2, respectively. At uncultivated soils, high concentrations of ¹³⁷Cs are located in the top 10 cm and decreased exponentially in depth. Cultivated soils record disturbed and heterogeneous ¹³⁷Cs profiles with values of mass activity and inventories up to 38.7 Bq kg^-1 and 2510.8 Bq m^-2, respectively. The ¹³⁷Cs inventories were significantly higher in uncultivated soils (mean: 2086.9 Bq m^-2) compared to cultivated soils (mean: 1397.1 Bq m^-2). The ¹³⁷Cs mass activity showed a significant positive correlation with organic matter, silt and clay, but it was negatively correlated with sand and pH respectively. High levels of ¹³⁷Cs were found at altitudes between 500 m and 640 m a.s.l, and at slopes from 8° to 11°, as well as in dense scrub land and Fersialitic soils. A principal component analysis showed that more than 86.7% of the variance in ¹³⁷Cs mass activity was explained by the organic matter content and the land use. The results of this study provide insights into the effects of soil properties and physiographic factors on the behaviour of ¹³⁷Cs in soils of Mediterranean environments of North Africa and strengthen the reliability of this radioisotope as an erosion tracer.

Assessment of soil redistribution rates by (137)Cs and (210)Pbex in a typical Malagasy agricultural field

Soil degradation processes affect more than one-third of the Malagasy territory and are considered as the major environmental threat impacting the natural resources of the island. This innovative study reports about a pioneer test and use of radio-isotopic techniques (i.e. Cs-137 and Pb-210ex) under Madagascar agroclimatic condition to evaluate soil erosion magnitude. This preliminary investigation has been conducted in a small agricultural field situated in the eastern central highland of Madagascar, 40 km East from Antananarivo. Both anthropogenic Cs-137 and geogenic Pb-210 soil tracers provided similar results highlighting soil erosion rates reaching locally 18 t ha(-1) yr(-1,) a level almost two times higher than the sustainable soil loss rate under Madagascar agroclimatic condition. The sediment delivery ratio established with both radiotracers was above 80% indicating that most of the mobilized sediment exits the field. Assessing soil erosion rate through fallout radionuclides in Madagascar is a first step towards an efficient land and water resource management policy to optimise the effectiveness of future agricultural soil conservation practices.

Effectiveness assessment of soil conservation measures in reducing soil erosion in Baiquan County of Northeastern China by using (137)Cs techniques

Accelerated soil erosion is considered as a major land degradation process resulting in increased sediment production and sediment-associated nutrient inputs to the rivers. Over the last decade, several soil conservation programs for erosion control have been conducted throughout Northeastern China. Reliable information on soil erosion rates is an essential prerequisite to assess the effectiveness of soil conservation measures. A study was carried out in Baiquan County of Northeastern China to assess the effectiveness of soil conservation measures in reducing soil erosion using the (137)Cs tracer technique and related techniques. This study reports the use of (137)Cs measurements to quantify medium-term soil erosion rates in traditional slope farmland, contour cropping farmland and terrace farmland in the Dingjiagou catchment and the Xingsheng catchment of Baiquan County. The (137)Cs reference inventory of 2532 ± 670 Bq m(-2) was determined. Based on the principle of the (137)Cs tracer technique, soil erosion rates were estimated. The results showed that severe erosion on traditional slope farmland is the dominant soil erosion process in the area. The terrace measure reduced soil erosion rates by 16% for the entire slope. Typical net soil erosion rates are estimated to be 28.97 Mg per hectare per year for traditional slope farmland and 25.04 Mg per hectare per year for terrace farmland in the Dingjiagou catchment. In contrast to traditional slope farmland with a soil erosion rate of 34.65 Mg per hectare per year, contour cultivation reduced the soil erosion rate by 53% resulting in a soil erosion rate of 22.58 Mg per hectare per year in the Xingsheng catchment. These results indicated that soil losses can be controlled by changing tillage practices from the traditional slope farmland cultivation to the terrace or contour cultivation.