Land use and soil erosion in the upper reaches of the Yangtze River: some socio‐economic considerations on China's Grain‐for‐Green Programme

Soil erosion in the upper reaches of the Yangtze River in China is a major concern and the Central Government has initiated the Grain‐for‐Green Programme to convert farmland to forests and grassland to improve the environment. This paper analyses the relationship between land use and soil erosion in Zhongjiang, a typical agricultural county of Sichuan Province located in areas with severe soil erosion in the upper reaches of the Yangtze River. In our analysis, we use the ArcGIS spatial analysis module with detailed land‐use data as well as data on slope conditions and soil erosion. Our research shows that the most serious soil erosion is occurring on agricultural land with a slope of 10∼25 degrees. Both farmland and permanent crops are affected by soil erosion, with almost the same percentage of soil erosion for corresponding slope conditions. Farmland with soil erosion accounts for 86·2 per cent of the total eroded agricultural land. In the farmland with soil erosion, 22·5 per cent have a slope of < 5 degrees, 20·3 per cent have a slope of 5∼10 degrees, and 57·1 per cent have a slope of > 10 degrees. On gentle slopes with less than 5 degrees inclination, some 6 per cent of the farmland had strong (5000∼8000 t km⁻² y⁻¹) or very strong (8000∼15000 t km⁻² y⁻¹) erosion. However, on steep slopes of more than 25 degrees, strong or very strong erosion was reported for more than 42 per cent of the farmland. These numbers explain why the task of soil and water conservation should be focused on the prevention of soil erosion on farmland with steep or very steep slopes. A Feasibility Index is developed and integrated socio‐economic assessment on the feasibility of improving sloping farmland in 56 townships and towns is carried out. Finally, to ensure the success of the Grain‐for‐Green Programme, countermeasures to improve sloping farmland and control soil erosion are proposed according to the values of the Feasibility Index in the townships and towns. These include: (1) to terrace sloping farmland on a large scale and to convert farmland with a slope of over 25 degrees to forests or grassland; (2) to develop ecological agriculture combined with improving the sloping farmland and constructing prime farmland and to pay more attention to improving the technology for irrigation and cultivation techniques; and (3) to carry out soil conservation on steep‐sloping farmland using suggested techniques. In addition, improving ecosystems and the inhabited environment through yard and garden construction for households is also an effective way to prevent soil erosion. Copyright © 2006 John Wiley & Sons, Ltd.     

Spatial Estimation of Soil Erosion Risk by Land‐cover Change in the Andes OF Southern Ecuador

Ecuador has the highest deforestation rate in South America, causing large‐scale soil erosion. Inter‐Andean watersheds are especially affected by a rapid increase of the population leading to the conversion of large areas of montane forest into pasture and cropland. In this study, we estimate soil erosion risk in a small mixed land‐use watershed in the southern Andes of Ecuador. Soil loss was estimated at a spatial resolution of 30 m, using the Revised Universal Soil Loss Equation (RUSLE) where the RUSLE factors were estimated on the basis of limited public available data. Land‐cover maps for 1976, 2008 and 2040 were created assuming increasing deforestation rates over the ensuing decades. Greater erosion rates are estimated for succession areas with agricultural cropland and pasture with maximum values of 936 Mg ha⁻¹ y⁻¹, where slopes and precipitation amounts are the greatest. Under natural forest vegetation, the estimated soil erosion rates are negligible (1·5 to 40 Mg ha⁻¹ y⁻¹) even at steep slopes and higher elevations where rainfall amounts and intensities are generally higher. When the entire watershed has undergone substantial deforestation in 2040, erosion values may reach 2,021 Mg ha⁻¹ y⁻¹. Vegetation cover is the most important factor for potential soil erosion. Secondary factors are related to rainfall (R‐factor) and topography (LS factors). Although the spatial predictions of potential soil erosion have only limited meaning for erosion risk, this method provides an important screening tool for land management and assessment of land‐cover change. Copyright © 2013 John Wiley & Sons, Ltd.     

Soil erosion assessment of Lake Alemaya catchment,Ethiopia

Land degradation due to soil erosion is the major problem facing Ethiopia today. In the Lake Alemaya catchment soil erosion is caused by the intense rainfall, steep topography, and poor vegetation cover coupled with cultivation of steep lands, and inadequate conservation practices. Sediment from the catchment has affected the storage capacity of Lake Alemaya. This study has integrated the Agricultural Non‐point Source Pollution Model (AGNPS) and the technique of the Gographic Information System (GIS) to quantify soil erosion in the Lake Alemaya catchment. After application of the AGNPS, it appears that 66 per cent of the catchment has a soil erosion rate of 10 to more than 80 t ha⁻¹ y⁻¹. The annual soil loss is estimated at 31 t ha⁻¹, which is more than the permissible value of 1–16 t ha⁻¹ for different agro‐ecological zones of Ethiopia. The sediment yield of the catchment is about 10 148 ton with a delivery ratio of 6·82 per cent. Therefore, an effective management plan is needed for the conservation and rehabilitation of the catchment and to maintain the storage capacity of Lake Alemaya. Copyright © 2006 John Wiley & Sons, Ltd.     

EFFECTS OF CONVERTING FOREST TO AVOCADO ORCHARDS ON TOPSOIL PROPERTIES IN THE TRANS‐MEXICAN VOLCANIC SYSTEM,MEXICO

In the present work, land cover and land use changes between 2003 and 2008 were assessed in the Cupatitzio River sub‐basin located in the Trans‐Mexican Volcanic System and Balsas Depression in Mexico. The effects of land cover conversion from temperate forest to avocado orchards on soil properties were determined. Land cover and land use databases were built for the years 1975, 2003, and 2008 using available cartographic information and interpretation of panchromatic SPOT images for the year 2008. Additionally, soil sampling was carried out in 16 representative sites in the higher parts of the sub‐basin, where avocado plantation dynamics have caused important changes in areas covered by temperate forests. Results show that (i) temperate coniferous and tropical low deciduous forests were reduced at an annual rate of 0·9 per cent (1, 001 ha y⁻¹) between 1975 and 2008; (ii) cropland areas expanded at an annual rate of 0·7 per cent between 1975 and 2008, representing a growth of 553 ha y⁻¹; (iii) wet soil aggregate stability, mechanical resistance to penetration and nitrate (N‐NO₃) concentration in the topsoil layer of Andosols were significantly affected by land use conversion to avocado orchards. Other soil properties such as organic matter, interchangeable K, and available P showed degradation tendencies. These results suggest the importance of implementing strategies for mitigating the accelerated process of transformation and degradation of natural resources in the Cupatitzio River sub‐basin. The implementation of programs for deforestation reduction should be a priority in the restoration strategy. Copyright © 2012 John Wiley & Sons, Ltd.     

Assessment of soil erosion hazard in Kilie catchment,East Shoa,Ethiopia

This paper reports on a field study conducted in Kilie catchment, East Shoa Zone, Ethiopia to assess the rate of soil erosion by employing a soil loss prediction model (Universal Soil Loss Equation) integrated with in remote sensing and geographical information systems (RS/GIS), environment and gully measurement techniques. The final soil erosion risk map was produced after multiplication of the six factors involved in the USLE and RS/GIS. Gully measurement showed that the erosion rate is higher for the upland areas than the lowlands due to inappropriate soil and water conservation measures, free grazing by animals and conversion of hillside areas into farmlands. About 97·04 per cent of the study catchment falls within a range of 0–10 t ha⁻¹ yr⁻¹ sheet/rill erosion rate. We found that 2·17 per cent of the study area in the uplands has a soil erosion rate falling between 10 and 20 t ha⁻¹ yr⁻¹. About 0·8 per cent of the study area in the uplands is hit by severe sheet/rill erosion rate within the range of 20–60 t ha⁻¹ yr⁻¹. Gully erosion extent in the study area was evaluated through gully measurement and quantification methods. Gully density of 67 m ha⁻¹ was recorded in the catchment. The gully to plot area ratio was found to be 0·14 on average. Hence, in the upland areas, sustainable land management practices are required in order to reduce the rate of soil erosion. Copyright © 2011 John Wiley & Sons, Ltd.     

Surface runoff and soil erosion estimation using the SWAT model in the Keleta Watershed,Ethiopia

This study evaluates surface runoff generation and soil erosion rates for a small watershed (the Keleta Watershed) in the Awash River basin of Ethiopia by using the Soil and Water Assessment Tool (SWAT) model. Calibration and validation of the model was performed on monthly basis, and it could simulate surface runoff and soil erosion to a good level of accuracy. The simulated surface runoff closely matched with observed data (derived by hydrograph separation). Surface runoff generation was generally high in parts of the watershed characterized by heavy clay soils with low infiltration capacity, agricultural land use and slope gradients of over 25 per cent. The estimated soil loss rates were also realistic compared to what can be observed in the field and results from previous studies. The long‐term average soil loss was estimated at 4·3 t ha⁻¹ y⁻¹; most of the area of the watershed (∼80 per cent) was predicted to suffer from a low or moderate erosion risk (<8 t ha⁻¹ y⁻¹), and only in ∼1·2 per cent of the watershed was soil erosion estimated to exceed 12 t ha⁻¹ y⁻¹. Expectedly, estimated soil loss was significantly correlated with measured rainfall and simulated surface runoff. Based on the estimated soil loss rates, the watershed was divided into four priority categories for conservation intervention. The study demonstrates that the SWAT model provides a useful tool for soil erosion assessment from watersheds and facilitates planning for a sustainable land management in Ethiopia. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

Validating the Use of 137Cs Measurements to Derive the Slope Component of the Sediment Budget of a Small Rangeland Catchment in Southern Italy

The sediment budget is a key concept and tool for characterizing the mobilization, transfer and storage of fine sediment within a catchment. Caesium‐137 measurements can provide valuable information on gross and net erosion rates associated with sheet and rill erosion that can be used to establish the slope component of a catchment sediment budget. However, there is a need to validate the use of ¹³⁷Cs measurements for this purpose, because their reliability has sometimes been questioned. The study reported focuses on a small (3·04 ha) steepland (mean slope 37%) catchment in Southern Italy. It exploits the availability of information on the medium‐term sediment output from the catchment provided by the construction of a reservoir at its outlet in 1978 and the existence of estimates of soil redistribution rates derived from ¹³⁷Cs measurements made on 68 replicate soil cores collected from the slopes of a substantial proportion of the catchment in 2001, to validate the use of ¹³⁷Cs measurements to construct the slope component of the catchment sediment budget. An additional 50 replicate soil cores were collected from the catchment slopes for ¹³⁷Cs analysis, to complement the data already available. Nine cores collected from the area occupied by the reservoir were used to estimate the mean annual sediment input to the reservoir. In the absence of evidence that the poorly developed channel system in the catchment was either a significant sediment source or sink, it was possible to directly compare the estimate of net soil loss from the catchment slopes (7·33 Mg ha⁻¹ y⁻¹) with the estimate of sediment output from the catchment provided by the reservoir deposits (7·52 Mg ha⁻¹ y⁻¹). Taking account of the uncertainties involved, the close agreement of the two values is seen as providing a convincing validation of the use of ¹³⁷Cs measurements to both estimate soil redistribution rates and as a basis for constructing the slope component of the sediment budget of a small catchment. Copyright © 2015 John Wiley & Sons, Ltd.     

USE OF RESERVOIR DEPOSITS AND CAESIUM-137 MEASUREMENTS TO INVESTIGATE THE EROSIONAL RESPONSE OF A SMALL DRAINAGE BASIN IN THE ROLLING LOESS PLATEAU REGION OF CHINA

This paper reports the results of an investigation of the erosional response of the 3·86 km² Zhaojia Gully catchment in the rolling loess plateau region of Zichan County, Shaanxi Province, China. In the absence of direct measurements, information derived from reservoir deposits and from caesium-137 measurements on both the catchment soils and reservoir deposits was used to obtain a retrospective assessment of the longer-term (ca. 30 year) erosional response of the catchment and of the relative contributions of the rolling plateau surface and the gully areas to the sediment output from the basin. Net erosion rates on cultivated land occupying the gentle crest slopes and steeper lower slopes of the rolling plateau and the steep gully slopes were estimated to be 4500 t km⁻² year⁻¹, 8584 t km⁻² year⁻¹ and 15851 t km⁻² year⁻¹, respectively. Estimates of annual sediment yield from the study catchment based on analysis of sediment deposits in the two sediment-trap reservoirs ranged between 4627 and 32472 t km⁻² year⁻¹. Almost all the sediment transported from the catchment was contributed by 2–4 large floods each year. Measurements of the caesium-137 content of recent sediment deposits in a sediment-trap reservoir allowed the relative contributions of the total sediment yield derived from the rolling plateau and gully areas of the catchment to be estimated at 23 and 77 per cent, respectively. Analysis of the sediment deposits dating from 1973–1977 in another sediment trap reservoir allowed individual flood event couplets to be identified and indicated that the sediment associated with the first one or two floods in a season, when the soils of the plateau area were relatively dry, was derived primarily from the gully areas. The cultivated soils of the rolling plateau contributed an increased proportion of the total sediment yield during the latter stages of the flood season when the soils were wetter, and surface runoff and erosion were more widespread. Based on analysis of the caesium-137 content of the sediment deposited in this sediment-trap reservoir, the relative contributions of sediment from the rolling plateau and gully areas over the period 1973–1977 were estimated to be 21 and 79 per cent, respectively. The results obtained demonstrate the potential for using caesium-137 measurements and analysis of reservoir deposits to document the erosional response of a drainage basin. © 1997 John Wiley & Sons, Ltd.     

Carbon sequestration in soils of central Asia

Problems of frequent drought stress, low soil organic carbon (SOC) concentration, low aggregation, susceptibility to compaction, salinization and accelerated soil erosion in dry regions are accentuated by removal of crop residues, mechanical methods of seedbed preparation, summer clean fallowing and overgrazing, and excessive irrigation. The attendant soil degradation and desertification lead to depletion of SOC, decline in biomass production, eutrophication/pollution of waters and emission of greenhouse gases. Adoption of conservation agriculture, based on the use of crop residue mulch and no till farming, can conserve water, reduce soil erosion, improve soil structure, enhance SOC concentration, and reduce the rate of enrichment of atmospheric CO₂. The rate of SOC sequestration with conversion to conservation agriculture, elimination of summer fallowing and growing forages/cover crops may be 100 to 200 kg ha⁻¹ y⁻¹ in coarse‐textured soils of semiarid regions and 150 to 300 kg ha⁻¹ y⁻¹ in heavy‐textured soils of the subhumid regions. The potential of soil C sequestration in central Asia is 10 to 22 Tg C y⁻¹ (16±8 Tg C y⁻¹) for about 50 years, and it represents 20 per cent of the CO₂ emissions by fossil fuel combustion. Copyright © 2004 John Wiley & Sons, Ltd.     

Impact of land use and land cover change on environmental degradation in lake Qinghai watershed,northeast Qinghai‐Tibet Plateau

Lake Qinghai, the largest saline lake in China, covers 4234 km² (2007) with a catchment area of 29 660 km² on the northeastern margin of the Qinghai‐Tibet Plateau. The ecosystem of the lake is extremely vulnerable and sensitive to global climate change and human interference. However, little information is available on land use/cover change (LUCC) in Lake Qinghai watershed. Using a geographical information system (GIS) and remote sensing (RS), this study analysed land use and land cover change pattern in Lake Qinghai watershed between 1977 and 2004 and discussed major environmental issues in this area. LUCC analysis indicated that grassland (63 per cent) and water body (18 per cent) dominated in the watershed and the magnitude of the land use and land cover change was generally low; the percentage of the change of various land types relative to the total area was less than 1 per cent. From 1977 to 2004, cropland, sandy land, bare rock, salinized land, swampland and built‐up areas increased by 0·43, 0·35, 0·24, 0·06, 0·03 and 0·03 per cent of the total area, respectively; in contrast, water body, grassland and woodland decreased by 0·99, 0·22 and 0·05 per cent, respectively. Moreover, the area of LUCC tended to expand from places around the lake to the upper reaches of the watershed during the last three decades. The LUCC transition pattern was: woodland converted to grassland, grassland converted to cropland and water body converted to sandy land. Lake level decline and grassland degradation are major ecological and environmental problems in Lake Qinghai watershed. The level and area of the lake decreased at the rate of 6·7 cm a⁻¹ and 6·4 km² a⁻¹, respectively, between 1959 and 2007, resulting in sandy land expansion and water quality deterioration. Lake level decline and area shrinkage was mainly attributed to climate change, but grassland degradation was mainly resulted from anthropogenic activities (increasing population, overgrazing and policy). Copyright © 2008 John Wiley & Sons, Ltd.     

Reducing Sediment Connectivity Through man‐Made and Natural Sediment Sinks in the Minizr Catchment,Northwest Ethiopia

Man‐made and natural sediment sinks provide a practical means for reducing downstream reservoir sedimentation by decreasing soil erosion and enhancing the rate of sedimentation within a catchment. The Minizr catchment (20 km²) in the northwest Ethiopian highlands contains numerous man‐made soil and water conservation (SWC) structures such as soil bunds (Erken), fanya juu ridge (Cab) and micro‐trenches and natural sediment sinks such as wetlands, floodplains and grassed waterways. These sediment sinks reduce downstream sedimentation into the Koga reservoir, located at the catchment outlet, however, a large quantity of sediment is still reaching the reservoir. This study evaluates the function and effectiveness of both man‐made SWC structures and natural sediment sinks in reducing sediment export from the Minizr catchment. SWC structures and natural sediment sinks were digitized using Google Earth Imagery. Sediment pins and vertical sampling through the deposit were used to quantify the amount of deposited sediment. In addition, inflow and outflow of suspended sediment data were used to calculate the sediment‐trapping efficacies (STE) of man‐made SWC structures (soil bunds and fanya juu ridges) and natural sediment sinks. Results reveal that 144 km soil bunds and fanya juu ridges trapped 7,920 Mg y⁻¹ (55 kg m⁻¹ y⁻¹) and micro‐trenches trapped 13·26 Mg y⁻¹, each micro‐trench on average trapped 23 kg y⁻¹. The 17 ha floodplain located in the centre of the catchment trapped 9,970 Mg y⁻¹ (59 kg m⁻² y⁻¹), while a wetland with a surface area of 24 ha, located near the outlet of the catchment, trapped 8,715 Mg y⁻¹ (36 kg m⁻² y⁻¹). The STEs of soil bunds and fanya juu ridges, wetlands and floodplains were 54%, 85% and 77%, respectively. Substantial differences were observed between the STE of grassed and un‐grassed waterways at 75% and 21%, respectively. Existing man‐made and natural sediment sinks played an important role in trapping sediment, with 38% (26,600 Mg y⁻¹) of transported sediment being trapped, while 62% (43,000 Mg y⁻¹) is exported from the catchment and thus enters the Koga reservoir. Therefore, additional catchment treatment measures are required as an integrated catchment scale sediment trapping approach to help reduce sediment loads entering Koga reservoir. Moreover, to maximize the effectiveness of sediment trapping measures, avoid structural failure and ensure their sustainability, regular maintenance is needed. Copyright © 2016 John Wiley & Sons, Ltd.     

Assessment of soil erosion hazard and prioritization for treatment at the watershed level: Case study in the Chemoga watershed,Blue Nile basin,Ethiopia

Soil erosion by water is the most pressing environmental problem in Ethiopia, particularly in the Highlands where the topography is highly rugged, population pressure is high, steeplands are cultivated and rainfall is erosive. Soil conservation is critically required in these areas. The objective of this study was to assess soil erosion hazard in a typical highland watershed (the Chemoga watershed) and demonstrate that a simple erosion assessment model, the universal soil loss equation (USLE), integrated with satellite remote sensing and geographical information systems can provide useful tools for conservation decision‐making. Monthly precipitation, soil map, a 30‐m digital elevation model derived from topographic map, land‐cover map produced from supervised classification of a Land Sat image, and land use types and slope steepness were used to determine the USLE factor values. The results show that a larger part of the watershed (>58 per cent of total) suffers from a severe or very severe erosion risk (>80 t ha⁻¹ y⁻¹), mainly in the midstream and upstream parts where steeplands are cultivated or overgrazed. In about 25 per cent of the watershed, soil erosion was estimated to exceed 125 t ha⁻¹ y⁻¹. Based on the predicted soil erosion rates, the watershed was divided into six priority categories for conservation intervention and 18 micro‐watersheds were identified that may be used as planning units. Finally, the method used has yielded a fairly reliable estimation of soil loss rates and delineation of erosion‐prone areas. Hence, a similar method can be used in other watersheds to prepare conservation master plans and enable efficient use of limited resources. Copyright © 2009 John Wiley & Sons, Ltd.     

Assessment of deforestation impact on soil erosion in loess formation using 137Cs method (case study: Golestan Province,Iran)

Golestan, a province in the North-East of Iran, is characterized by high coverage of loess deposits. Since 1963, the area has experienced approximately 200,000 ha deforestation due to land-use changes in agriculture and increasing demand for wood. Approximately, 110,000 ha of the clear-cut lands are under dry-farming, mainly for wheat cropping, and about 86,000 ha have been reforested. This IAEA funded project is the first attempt to use nuclear techniques in the East of Hircanian Forest for determination of on-site impacts of deforestation due to two land-use changes (i.e. dry farming and reforestation). Practicing long-term dry-farming led to 60% soil losses with a mean rate of 2 mm per year. The net erosion rate of croplands on loess deposits in the study area was 32.27 t ha⁻¹ yr⁻¹. Reforestation, cultivation of even-aged Cypress trees since 1993, showed 13 to 60 percent effectiveness in soil conservation. Dry-farming land use resulted in the loss of 95 t ha⁻¹ soil organic carbon (SOC) stock at a mean rate of 1.7 t ha⁻¹ over 54 years. Cultivating Cypress trees successfully restored the SOC content by 100% compared with the SOC in original forests. The conversion of dry-farming lands to orchards of olive trees since 2004, brought more income for farmers but were less effective in soil conservation because of low canopy cover of olive trees. Our data provide key information and guidance for land users and decision-makers about implementing strategic and sustainable conservation practices to restore degraded land.     

Erosion predictions with the Wind Erosion Equation (WEQ) using different climatic factors

Little information is available on the performance of the Wind Erosion Equation (WEQ) for estimating wind erosion under differing climatic conditions. The objective of this study was to assess the fitting of measured and WEQ‐estimated wind erosion with different climatic C factors. Results showed that WEQ underestimated the annual wind erosion by 45 per cent when loaded with the historic C, obtained with climatic data records between 1981 and 1990. The monthly averaged C factor (monthly C, n = 12) underestimated the erosion by 29 per cent, the C factors of each one of the six studied years (annual C, n = 6) underestimated the erosion by 19 per cent, and the C factors of each one of the evaluated months (monthly C, n = 72) overestimated the erosion by 31 per cent. Precipitation explained most of C factors variability. C factors corresponding to high precipitation periods predicted low erosion amounts in no‐till (NT) and conventional tillage (CT). C factors corresponding to low precipitation periods calculated high erosion rates in CT (143 t ha⁻¹ y⁻¹) and low in NT (2·4 t ha⁻¹ y⁻¹). The historical C factor predicted no erosion in NT and 7·1 t ha⁻¹ y⁻¹ in CT. These results indicated that the WEQ should be used with variable C factors in order to assess different climatic scenarios of the semiarid Argentina. Copyright © 2007 John Wiley & Sons, Ltd.     

“MIRSED” towards an MIR approach to modelling hillslope soil erosion at the national scale

This paper reports a new methodology for assessing regional and national patterns of hillslope scale soil erosion rates in the UK using a MIR (minimum information requirement) version of WEPP (Water Erosion Prediction Project) known as MIRSED. WEPP is parameterised using a national coverage, environmental database containing topographic, soil, land management and climate variables for all hillslopes within each grid cell to be modelled. The MIRSED matrix summarises the behaviour of WEPP in a multi-dimensional parameter space, allowing results to be queried using a subset of key, spatially variable parameters to produce an averaged hillslope soil erosion response from each 1 km² grid cell. The approach is demonstrated for the Great Ouse catchment, Cambridgeshire, UK and highlights highest hillslope erosion rates of 2.2 t ha⁻¹ year⁻¹ associated with steepest slopes, erodible soils and management practices that leave the soil exposed for critical times of the year. A mean soil erosion rate of 0.4 t ha⁻¹ year⁻¹ is predicted from hillslopes across the catchment which compares well with observed data collated at different scales, using contrasting measurement techniques.     

History, origin and extent of soil erosion on Easter Island (Rapa Nui)

The isolated Easter Island (Rapa Nui) is an outstanding example of land degradation caused by land use in a sensitive ecosystem. The focus of the investigation was placed on Poike peninsula, the most eastern part of Rapa Nui. While Poike peninsula was once supplied with fertile soils, in large areas desertification takes place today. Detailed analysis of soil profiles allowed the reconstruction of the history and of causes and effects of soil erosion and gullying in the context of land use history and cultural evolution. The results of the stratigraphic analysis prove that from the beginning of human settlement around AD 300/600 until AD 1280 the agriculture on Poike peninsula was characterised by sustainable land use and a traditional type of agro-forestry. Soil erosion was not significant. At around AD 1280 the woodland on Poike, dominated by the endemic palm Jubaea sp., was cleared by slashing and burning. Intensive farming on the upper slopes of the volcanic peninsula resulted in sheet erosion lasting until the 20th century. Settlements and ceremonial places which were built around AD 1300 on downslope areas were buried soon by sediments. Agriculture ceased around AD 1400 on downslope areas as the fertile soils were completely eroded. From AD 1400 until the late 19th century sheet erosion and the accumulation of fine-layered sediments migrated upslope. On average 8.6 Mg of soil per hectare and per year were reworked by erosion (eroded and accumulated within the catchment). Gullying began on Rapa Nui with the sudden increase in the number of sheep during the early 20th century. Gullies are still developing on the island and their ongoing enlargement created extended badlands on Poike which pose a significant problem for ecological and archaeological conservation strategies. Gullying rates exceed 190 Mg ha^{− 1} y^{− 1}.     

Soil carbon sequestration in China through agricultural intensification,and restoration of degraded and desertified ecosystems

The industrial emission of carbon (C) in China in 2000 was about 1 Pg yr⁻¹, which may surpass that of the United States (1ċ84 Pg C) by 2020. China's large land area, similar in size to that of the United States, comprises 124 Mha of cropland, 400 Mha of grazing land and 134 Mha of forestland. Terrestrial C pool of China comprises about 35–60 Pg in the forest and 120–186 Pg in soils. Soil degradation is a major issue affecting 145 Mha by different degradative processes, of which 126 Mha are prone to accelerated soil erosion. Total annual loss by erosion is estimated at 5ċ5 Pg of soil and 15ċ9 Tg of soil organic carbon (SOC). Erosion‐induced emission of C into the atmosphere may be 32–64 Tg yr⁻¹. The SOC pool progressively declined from the 1930s to 1980s in soils of northern China and slightly increased in those of southern China because of change in land use. Management practices that lead to depletion of the SOC stock are cultivation of upland soils, negative nutrient balance in cropland, residue removal, and soil degradation by accelerated soil erosion and salinization and the like. Agricultural practices that enhance the SOC stock include conversion of upland to rice paddies, integrated nutrient management based on liberal use of biosolids and compost, crop rotations that return large quantities of biomass, and conservation‐effective systems. Adoption of recommended management practices can increase SOC concentration in puddled soil, red soil, loess soils, and salt‐affected soils. In addition, soil restoration has a potential to sequester SOC. Total potential of soil C sequestration in China is 105–198 Tg C yr⁻¹ of SOC and 7–138 Tg C yr⁻¹ for soil inorganic carbon (SIC). The accumulative potential of soil C sequestration of 11 Pg at an average rate of 224 Tg yr⁻¹ may be realized by 2050. Soil C sequestration potential can offset about 20 per cent of the annual industrial emissions in China. Copyright © 2002 John Wiley & Sons, Ltd.     

Combining Qualitative and Quantitative Methods for Soil Erosion Assessments: An Application in a Sloping Mediterranean Watershed,Cyprus

In arid and semi‐arid regions, water erosion is difficult to model because of highly irregular precipitation regimes and changes in vegetation cover. The application of quantitative, process‐based models at the catchment scale is often problematic because of large data requirements. Qualitative methods require less data and can be more easily performed in a relatively short time, but they are more subjective. The objective of this research is to develop an erosion assessment methodology that combines qualitative field surveys with quantitative model estimates. The qualitative World Overview of Conservation Approaches and Technologies (WOCAT) methodology is based on expert observations per mapping unit, while the Pan‐European Soil Erosion Risk Assessment (PESERA) model simulates hill slope soil loss based on land cover, soil texture, meteorological data and slope profile. This study was conducted in the 106·4‐km² Peristerona watershed in Cyprus with a mean local slope higher than 40% in the mountainous upstream area and less than 8% in the plain. Out of 68 units, PESERA and WOCAT results were in agreement in 40 units, while PESERA results were lower in 25 and higher in 3 units. Both methods identified burnt areas and complex cultivation patterns as the most degraded. The total PESERA‐based sediment yield for the watershed was 1·2 Mg ha⁻¹ y⁻¹, which fell within the range of the sediment yield measured at the check‐dam downstream (0·2–2 Mg ha⁻¹ y⁻¹). This study provides a linkage between qualitative and quantitative soil erosion methods and helps to translate the outcomes of the former into the latter, thus providing a good tool for local erosion assessment. Copyright © 2016 John Wiley & Sons, Ltd.     

Application of the caesium‐137 technique to soil degradation studies in the Southwestern Highlands of Ethiopia

Soil degradation is a serious problem in the central and northern Highlands of Ethiopia. It has been so for several decades as a result of over exploitation and mismanagement. Relocation of a portion of the population from these regions to the relatively less populated Southwestern Highlands has taken place for decades to try to address the problem. However, such mass resettlements have caused severe soil degradation problems in many destination areas in the Southwestern Highlands. The aim of this study was to assess the problem of soil degradation using the caesium‐137 isotope and to test its value for erosion study in the region. The adapted USLE was applied to compare results from the caesium‐137 isotope studies. Along a deforestation continuum, fields cultivated for various years were studied for erosion. From a reference grazing land plot, total caesium‐137 fallout of 2026 ± 176 Bq m⁻² with a CV of 24·6 per cent was recorded showing the presence of sufficient fallout to apply the technique. Erosion in cultivated fields was estimated against this reference using conversion models. Results from the Proportional Model |−13·9 ± 2·7|and the adapted USLE |12·3 ± 2·6| were not significantly different (p < 0·05), meaning the technique provides reliable results. A positive relationship was observed between severity of erosion and time of cultivation after forest clearing (R² = 0·78). The mean annual loss of soil from cultivated land, 14·9 ± 2·9 t ha⁻¹ y⁻¹, is already beyond the tolerable threshold and might exacerbate further clearing of forests for cultivation if the land is not properly managed. Copyright © 2011 John Wiley & Sons, Ltd.