High Erosion Risk Research Articles

Relative importance of organic carbon, land use and moisture conditions for the aggregate stability of post-glacial clay soils

Erosion and colloidal particle loss from cultivated clay soils in cool humid climate pose a risk to soil productivity and surface water quality. To enhance soil management practices that effectively reduce clay soil erosion, we need to understand the interrelations between the key variables on which clay soil aggregate structure depend. The objective of our study was to quantify the relative importance of OC content, land use and soil wetness, for the aggregate stability of post-glacial clay soils. We estimated the potential effect of five different land uses (cereal cropping with variable tillage and crop rotation, permanent grassland and forest as a control) on clay soil aggregate stability as measured by the percentage of water-stable aggregates (WSA% of 2–5mm fraction) and colloid detachment (turbidity, NTU%), after controlling for the differences in organic carbon content (OC%) and Clay%/OC% ratio between the land uses through covariance analysis. Further, we assessed how aggregate structure in differently managed soils with different OC% tolerates the varying moisture conditions. The higher OC% was reflected in all cultivated soils by increased aggregate stability, implying that OC inputs may positively affect soil structure even in low additions. When compared at equal OC%, the mean WSA% was lower in cereal cropping than in soils under forest or permanent grass, clearly showing the negative effect of tillage frequency on the aggregate stability. The detachment of colloidal particles from aggregates was higher in soils with a high Clay%/OC% ratio, and thus the Clay%/OC% ratio may offer an easily measurable indicator for the risk of clay dispersion, and thereby soil erosion and the export of particle-bound nutrients from cultivated fields. When compared at an equal Clay%/OC% ratio, colloid detachment from aggregates representing cereal fields was two- to threefold as compared to permanent grassland. Cultivated soils with less than 4–6% OC were very sensitive to waterlogging, highlighting the role of proper drainage in erosion control. The results demonstrate that an increase in OC content and proper drainage would help to improve the aggregate stability of cultivated clay soils in cool humid climate, but the effective improvement of the present situation would require drastically reduced soil disturbances for areas with the highest erosion risk.

Identification of areas vulnerable to soil erosion risk in India using GIS methods

Abstract. This paper attempts to provide information for policymakers and soil conservation planners in the form of district-wise soil erosion risk (SER) maps prepared for the state of Telangana, India. The SER values for each district were computed by extracting the information on grid-wise soil erosion and soil loss tolerance limit values existing on the country-scale in a GIS environment. The objectives of the study were to (i) identify the areas of the state with a high erosion risk, and (ii) identify areas with an urgent need of conservation measures. The results reveal that around 69 % of the state has a negligible risk of soil erosion above the tolerance limits, and does not call for immediate soil conservation measures. The remaining area (2.17 M ha) requires conservation planning. Four districts, viz. Adilabad, Warangal, Khammam, and Karimnagar are the most risk-prone with more than one-quarter of their total geographical areas showing net positive SER values. In order to obtain a clearer picture and categorize the districts based on their extent of vulnerability, weighted erosion risk values were computed. Adilabad, Warangal, and Khammam were identified as the worst-affected districts in terms of soil erosion, and therefore are in need of immediate attention of natural resource conservation.

Dinitrogen fixation by the legume cover crop Pueraria phaseoloides and transfer of fixed N to Hevea brasiliensis—Impact on tree growth and vulnerability to drought

Rubber tree plantations (Hevea brasiliensis) are expanding into marginal areas with low soil fertility and long dry seasons with a high risk of soil erosion and drought damage to trees. Introducing an N2-fixing legume cover crop in rubber plantations may reduce runoff and soil erosion as well as increasing the availability of nutrients but may also increase competition for water. This study quantified the effect of the legume cover crop Pueraria phaseoloides on N, P and K nutrition, water status and growth of young rubber trees (three years old in 2007) over a four year period (2007–2010). The plantation was located on a toposequence with a range of soil depths and water storage capacities in northeast Thailand.The legume aboveground biomass production and its nutrient content and decomposition rate were measured and the N2 fixation was estimated using the abundance of 15N (δ15N) in the legume. Measurements were taken of the tree stem girth and height and tree leaf predawn water potential, nutrient content and greenness. The transfer of N2 fixed by the cover crop to the trees was estimated using δ15N in the tree leaves.The annual biomass production of the legume was 8Mgha−1 year−1 and the N accumulation by the legume was 250kg N ha−1 year−1. The natural abundance method applied to the aboveground components of the legume gave N2 fixation rates varying from 85 to 93% depending on the year. The leaf δ15N was similar in the three non-legumes (H. brasiliensis, Vetiveria zizanioides and Praxelis clematidea) used as reference plants for estimating the N2 fixation. The higher level of N and the much lower leaf δ15N values for the rubber trees intercropped with P. phaseoloides, compared to rubber trees growing without a legume cover crop, showed that there was a relatively high transfer of fixed N from the legume to the trees, varying from 39% to 46% of tree leaf N depending on the year. Neither N2 fixation nor N transfer varied significantly along the toposequence. At the bottom of the toposequence, both the nutrient (N, P and K) and water status of trees was significantly improved with the legume cover crop, doubling the tree girth at seven years of age (tree girth: 28cm, tree height: 700cm). However, at the top of the toposequence with low water storage capacity, the legume cover crop improved tree nutrition and growth but reduced the trees' ability to survive intense drought.These results raise concern about the resilience to drought of the rubber tree/P. phaseoloides system, since the positive effect of the legume on rubber tree nutrition and growth may increase the risk of water stress and tree mortality. With future changes in climate, an increasing number of areas will be concerned by the question of optimizing the tradeoff between N inputs and water availability.

Soil erosion risk mapping using RUSLE model on jhargram sub-division at West Bengal in India

An appraisal of spatial and quantitative information on soil erosion is a major challenge for human sustainability. The present study demonstrates the prognostic modeling capabilities of geo-spatial technology based on soil erosion potential model to assess the effects of implementing land use changes within sub-tropical region in India. The Revised Universal Soil Loss Equation (RUSLE) integrated with geo-spatial technology was used to produce predictive soil erosion map. Rainfall pattern, soil type, topography, crop system and management practices and geo-spatial data were used to predict the soil erosion model. Results shows 74.77 % of the study area is marked as low potential zone for soil erosion, whereas 5.58 % (>10 t h−1 year−1) is very high erosion risk zone. The present information may help recognizing areas that are vulnerable to soil loss and the proposed method will be used for generalized planning and assessment purposes for supervision and preserve the soil erosion.

An Approach for Simulating Soil Loss from an Agro-Ecosystem Using Multi-Agent Simulation: A Case Study for Semi-Arid Ghana

Soil loss is not limited to change from forest or woodland to other land uses/covers. It may occur when there is agricultural land-use/cover modification or conversion. Soil loss may influence loss of carbon from the soil, hence implication on greenhouse gas emission. Changing land use could be considered actually or potentially successful in adapting to climate change, or may be considered maladaptation if it creates environmental degradation. In semi-arid northern Ghana, changing agricultural practices have been identified amongst other climate variability and climate change adaptation measures. Similarly, some of the policies aimed at improving farm household resilience toward climate change impact might necessitate land use change. The heterogeneity of farm household (agents) cannot be ignored when addressing land use/cover change issues, especially when livelihood is dependent on land. This paper therefore presents an approach for simulating soil loss from an agro-ecosystem using multi-agent simulation (MAS). We adapted a universal soil loss equation as a soil loss sub-model in the Vea-LUDAS model (a MAS model). Furthermore, for a 20-year simulation period, we presented the impact of agricultural land-use adaptation strategy (maize cultivation credit i.e., maize credit scenario) on soil loss and compared it with the baseline scenario i.e., business-as-usual. Adoption of maize as influenced by maize cultivation credit significantly influenced agricultural land-use change in the study area. Although there was no significant difference in the soil loss under the tested scenarios, the incorporation of human decision-making in a temporal manner allowed us to view patterns that cannot be seen in single step modeling. The study shows that opening up cropland on soil with a high erosion risk has implications for soil loss. Hence, effective measures should be put in place to prevent the opening up of lands that have high erosion risk.

Risk assessment of post-wildfire hydrological response in semiarid basins: the effects of varying rainfall representations in the KINEROS2/AGWA model

Representation of precipitation is one of the most difficult aspects of modelling post-fire runoff and erosion and also one of the most sensitive input parameters to rainfall-runoff models. The impact of post-fire convective rainstorms, especially in semiarid watersheds, depends on the overlap between locations of high-intensity rainfall and areas of high-severity burns. One of the most useful applications of models in post-fire situations is risk assessment to quantify peak flow and identify areas at high risk of flooding and erosion. This study used the KINEROS2/AGWA model to compare several spatial and temporal rainfall representations of post-fire rainfall-runoff events to determine the effect of differing representations on modelled peak flow and determine at-risk locations within a watershed. Post-fire rainfall-runoff events at Zion National Park in Utah and Bandelier National Monument in New Mexico were modelled. Representations considered included both uniform and Soil Conservation Service Type II hyetographs, applying rain over the entire watershed and applying rain only on the burned area, and varying rainfall both temporally and spatially according to radar data. Results showed that rainfall representation greatly affected modelled peak flow, but did not significantly alter the model’s predictions for high-risk locations. This has important implications for post-fire assessments before a flood-inducing rainfall event, or for post-storm assessments in areas with low-gauge density or lack of radar data due to mountain beam blockage.

A high-resolution map of direct and indirect connectivity of erosion risk areas to surface waters in Switzerland—A risk assessment tool for planning and policy-making

Off-site effects of soil erosion are becoming increasingly important, particularly the pollution of surface waters. In order to develop environmentally efficient and cost effective mitigation options it is essential to identify areas that bear both a high erosion risk and high connectivity to surface waters. This paper introduces a simple risk assessment tool that allows the delineation of potential critical source areas (CSA) of sediment input into surface waters concerning the agricultural areas of Switzerland. The basis are the erosion risk map with a 2m resolution (ERM2) and the drainage network, which is extended by drained roads, farm tracks, and slope depressions. The probability of hydrological and sedimentological connectivity is assessed by combining soil erosion risk and extended drainage network with flow distance calculation. A GIS-environment with multiple-flow accumulation algorithms is used for routing runoff generation and flow pathways. The result is a high resolution connectivity map of the agricultural area of Switzerland (888,050ha). Fifty-five percent of the computed agricultural area is potentially connected with surface waters, 45% is not connected. Surprisingly, the larger part of 34% (62% of the connected area) is indirectly connected with surface waters through drained roads, and only 21% are directly connected. The reason is the topographic complexity and patchiness of the landscape due to a dense road and drainage network. A total of 24% of the connected area and 13% of the computed agricultural area, respectively, are rated with a high connectivity probability. On these CSA an adapted land use is recommended, supported by vegetated buffer strips preventing sediment load. Even areas that are far away from open water bodies can be indirectly connected and need to be included in planning of mitigation measures. Thus, the connectivity map presented is an important decision-making tool for policy-makers and extension services. The map is published on the web and thus available for application.

Estimation of soil erosion risk within an important agricultural sub-watershed in Bursa, Turkey, in relation to rapid urbanization.

This paper integrates the Revised Universal Soil Loss Equation (RUSLE) with a GIS model to investigate the spatial distribution of annual soil loss and identify areas of soil erosion risk in the Uluabat sub-watershed, an important agricultural site in Bursa Province, Turkey. The total soil loss from water erosion was 473,274 Mg year(-1). Accordingly, 60.3% of the surveyed area was classified into a very low erosion risk class while 25.7% was found to be in high and severe erosion risk classes. Soil loss had a close relationship with land use and topography. The most severe erosion risk typically occurs on ridges and steep slopes where agriculture, degraded forest, and shrubs are the main land uses and cover types. Another goal of this study was to use GIS to reveal the multi-year urbanization status caused by rapid urbanization that constitutes another soil erosion risk in this area. Urbanization has increased by 57.7% and the most areal change was determined in class I lands at a rate of 80% over 25 years. Urbanization was identified as one of the causes of excessive soil loss in the study area.

Risk assessment of soil erosion by application of remote sensing and GIS in Yanshan Reservoir catchment, China

Soil erosion is considered to be a serious problem for environmental sustainability. Healthy and stable soils are crucial for human well-being, providing important ecosystem functions and services. There is a need for a simple and practical approach which estimates and maps soil erosion risk that uses available information as input data to facilitate water and soil conservation. In this work, we developed a predictive approach to estimating the soil erosion risk of the Yanshan Reservoir catchment, which combines remote sensing information, geographic information system spatial analysis technology and a soil erosion risk assessment model. Three dominating factors affecting soil erosion were considered: vegetation coverage, topographic slope and land use. The soil erosion risk was divided into six levels: slight, light, moderate, intense, severe and extremely severe. The slight and light erosion risk accounted for about 83 % of the watershed and was prominent in cultivated land areas, while areas with relatively higher erosion risk were on steep slopes. This approach pointed to inappropriate land use and development as a source of increased risk of soil erosion of the Yanshan Reservoir catchment. Compared with field survey data, the soil erosion modeling approach was shown to have a high accuracy. Therefore, this model could be used to estimate and map soil erosion intensity and distribution at the catchment scale, and could provide useful information for managers and planners to make land management and conservation decisions.

A Water Yield‐Oriented Practical Approach for Multifunctional Forest Management and its Application in Dryland Regions of China

AbstractMountainous forest areas are vitally important for water supply in dryland regions which suffer from high erosion risk and severe water shortage. Massive afforestation, mainly for erosion control, may reduce the water yield and threaten local water supply security. Moreover, many over‐dense forests due to a strict logging ban policy have produced remarkably negative impacts for both forests (e.g., low timber quality, restricted natural regeneration, and high stand instability) and water yield. To satisfy the rapidly increasing demands on water supply and other services, a practical approach for managing forest stands in a multifunctional way, which particularly addresses water yielding, is urgently required. For this purpose, we integrated the existing knowledge and experience, designed an “ideal” stand structure to represent multifunctional forest (MFF) and determined its key parameters (a ground coverage of >0.7, a canopy density around 0.7, and an H/DBH ratio (tree height [m] to the diameter at breast height [cm]) of <0.7). Moreover, a decision process for MFF stand management was recommended as: (1) investigating the site quality; (2) identifying the site‐specific main forest functions; (3) quantifying the stand structure; (4) diagnosing the stand structure by comparing with the “ideal” one; and (5) arranging the functions/structure‐oriented management measures. In this way, the water‐yielding function can be improved and meanwhile other forest functions can be promoted.

Dynamics of Runoff and Suspended Sediment Transport in a Highly Erodible Catchment on the Chinese Loess Plateau

AbstractRunoff is the key factor to understand the land degradation causing high risk of soil erosion and can reduce the water available for human societies and ecosystems. The dynamics of runoff and suspended sediment transport are not completely understood. In this study, we examined the trends, breaking point and regime changes for the runoff and sediment load at different temporal scales using 50 years of continuous observational data from a highly erodible sub‐catchment with an area of 7,325 km2 in the Beiluo River basin on the Loess Plateau, China. At the annual scale, the runoff and sediment load declined significantly (p < 0·05) with decreasing rates of −0·23 mm y−1 and −164·9 Mg km−2 y−1, respectively. Abrupt changes in the runoff and sediment load series were detected between 1979 and 1999; thus, the data were divided into intervals of 1960–1979, 1980–1999 and 2000–2009. The flow duration curve analysis indicated increasing low‐flow values and decreasing daily runoff and sediment discharge peaks, which suggested that soil and water conservation measures reduced the volume of runoff and the sediment load. This led to a more uniform runoff regime. At the flood event scale, we investigated the relationship between runoff and the suspended sediment load based on 123 flood events, which showed clearly that the magnitude and frequency of hyper‐concentrated sediment flows decreased in 2000–2009 compared with 1960–1999. The annual erosive rainfall exhibited non‐significant changes throughout the entire study period. We conclude that soil and water conservation measures (e.g. afforestation, grassing, terraces and check dams) have played major roles in the changes in runoff and the sediment load in the Beiluo River catchment. Copyright © 2015 John Wiley & Sons, Ltd.

Intravesical midurethral sling mesh erosion secondary to transvaginal mesh reconstructive surgery

Abstract Objective We sought to evaluate the feasibility and the outcomes of correcting the intravesical mesh erosion after secondary mesh augmented pelvic reconstructive surgery pervaginally. Methods We evaluated a case of mesh erosion following midurethral sling that occurred 4 years after secondary mesh surgery. Prior to second surgery, ultrasound and cystoscopy examination were performed to exclude mesh complication. Serial examinations during follow-up after the operation were uneventful until the patient presented 4 years after the second surgery with a history of dysuria and hematuria. Cystoscopy examination discovered intravesical mesh erosion 4 years after the secondary surgery. Removal of the midurethral sling mesh erosion and bladder repaired were done vaginally. Results The patient was still symptom free and continent 1 year following tape excision. Urodynamic evaluation 6 months post-tape excision was also normal. Conclusion Repeated vaginal reconstructive surgery may jeopardize a primary mesh or sling, and pose a high risk of mesh erosion, which may be delayed for several years. Removal of the mesh erosion and bladder repair are feasible pervaginally with good outcome.

Decadal Trends of Soil Loss and Runoff in the Koga Catchment, Northwestern Ethiopia

AbstractThis study used the physically based distributed Annualized Agricultural Non‐Point Source model to simulate decadal trends in soil loss and runoff with changes in land use/cover in the 98·4 km2 upper part of the Koga catchment. The study indicated that soil loss in the study area has increased from 17 Mg ha−1 y−1 in 1957 to 25 Mg ha−1 y−1 in 2010 because of a decrease in the amount of woody vegetation cover. We found that over the past 50 years, high risk erosion areas with soil loss greater than 35 Mg ha−1 y−1 covered, on average, 41% of the study area, while these same areas contributed, on average, 78% of the soil loss from the study area. Twenty one percent of the study area has been in the high risk erosion category throughout all the years since 1957. The total amount of soil loss from the study area varied with changes in the amount of woody vegetation cover. Other factors such as landforms and soil type also affected the amount of soil erosion. Whereas most of the high erosion areas were found in the upper part of the catchment, most of the high runoff areas were found in the lower part of the catchment, indicating that the amount of soil erosion is not directly related to runoff volume in the study area. Crop fields contributed to most of the soil loss in the study area. Copyright © 2015 John Wiley & Sons, Ltd.

Evaluation of soil erosion risk for watershed management in Shenmu watershed, central Taiwan using USLE model parameters

This study compiles the latest regional topographic data from field investigation and remote-sensing images to recalculate parameters of the universal soil loss equation (USLE) model of the Shenmu watershed; also to compensate for reduced accuracy of this model on small-scale slopes, this study incorporates soil erosion pin data which were collected periodically to measure the extent of soil erosion. Firstly, this study utilized the USLE model and soil erosion pin data to compare the soil erosion potential of the Chushui and Aiyuzi subwatersheds and concluded that soil erosion drastically increased if accumulated rainfall exceeded 200 mm; also, erosion depths were greater in the Aiyuzi subwatershed while estimated total erosion volume was higher in the Chushui subwatershed; this was attributed to the larger area of Chushui subwatershed and based on field measurements which supported the results of the USLE model. Secondly, this study utilized modified USLE model to compare the extreme event erosion resulting from typhoon Morakot which revealed that high rainfall intensity and long-duration rainfall events can generate large volume non-point sources of sediment that is estimated to far exceed 7–10 times of the annual soil erosion. Thirdly, this study related the C parameter of the USLE model to the existing land use in the Shenmu watershed using current, real data. Finally, this study established a post-typhoon Morakot soil erosion risk map composed of five categories of risk which was compared with post-event land cover to suggest high-erosion risk zones that may require further monitoring, remediation, and engineering measures to limit soil loss.

Transmission and storage properties of a tropical loamy sand soil as influenced by organic-based and inorganic fertilizers

Short-term effect of organic and inorganic amendments on soil physical quality (SPQ) is marked when dealing with tropical soils which are naturally exposed to a high risk of water erosion. This study assessed the suitability of Tithonia diversifolia (Mexican Sunflower) when incorporated as green manure (GM) and also composted with poultry manure (PM) and other organic-based and inorganic fertilizers to improve some hydraulic properties of an Alfisol subject to excessive drainage. Treatments applied include fresh T. diversifolia (GM), PM, T. diversifolia composted with PM, organo-mineral fertilizers (OMF), neem fertilizer (NF), inorganic fertilizer (20-10-10 NPK), and control in a randomized complete block design and replicated four times. Soil samples were collected at 0–20 cm depth to determine near steady-state infiltration rates (Is), sorptivity, transmissivity, saturated hydraulic conductivity (Ks), macroporosity (MacP), microporosity (MicP), air capacity (AC), and relative water capacity (RWC). The Is rates were significantly (P ≤ 0.05) reduced to optimum range with the addition of the organic fertilizers over very high value (128.7 cm hr−1) observed for control. Whereas, Ks was enhanced in the order: GM > compost (CP) > NF > inorganic fertilizer > control > organo-mineral fertilizer > PM. Sorptivity and transmissivity were highest in control and inorganic fertilizer plots, indicating that the addition of organic fertilizers lowered these parameters while MacP, MicP, AC, and RWC were generally increased with the addition of organic-based and inorganic fertilizers. Specifically, NF increased MicP by 34% over control. Values for RWC which were within the optimum range (0.60–0.70) were only obtained with NF (0.74), OMF (0.72), NPK (0.70), and GM (0.60). The SPQ parameters assessed in this study were enhanced by the addition of fresh T. diversifolia applied as GM and CP compared to other treatments. Therefore, T. diversifolia usually burned by farmers should instead be incorporated into the soil as manure.

Influence of tillage intensity and nitrogen placement on nitrogen uptake and yield in strip-tilled white cabbage (Brassica oleracea convar. capitata var. alba)

Field grown vegetables with wide row spacing would likely benefit from the conservation tillage practice, strip-tillage, with regards to minimizing soil erosion or increasing soil moisture contents, but there are only few studies for strip-tilled vegetables at present. For this reason, a 2-year field experiment was performed in South West Germany to investigate the effect of strip-tillage under broadcast and placed nitrogen application on nitrogen availability and yield of white cabbage (Brassica oleracea convar. capitata var. alba). The treatments were fall strip-tillage (ST), intensive strip-tillage with tillage both in fall and spring (STi; all of them with broadcast nitrogen fertilization) and intensive strip-tillage with band-placed nitrogen (STi_pN). In 2013, a fifth treatment was added, which was ST additional sowing of Phacelia (Phacelia tannacetifolia) as a cover crop (ST_Phac). A conventional tillage treatment (MP; moldboard plowing) was used as the control. No significant differences in soil mineral nitrogen (SMN) were detected in spring (20±5kgNha−1) and at harvest time (5±0.9kgNha−1) between the MP and all strip-tillage treatments from 0–90cm soil depth, except for significantly lower SMN contents in ST_Phac in spring 2013 (5kgNha−1). During the growing period, the SMN contents in strip-tillage treatments tended to be higher than in the MP control. Results of nitrogen content in plants, N-uptake, and nitrogen use efficiency (NUE) showed higher values under ST compared to the more intensive strip-tillage treatments (STi and STi_pN). The cabbage yield ranged between 65tha−1 (MP) and 74tha−1 (ST) in 2012 and 50tha−1 (STi_pN) and 58tha−1 (MP) in 2013. The fall strip-tillage treatment (ST) seems to be as effective as the conventional moldboard plowing for white cabbage in terms of N availability and yield. These results could be used to apply or improve strip-till systems with respect to other similar vegetables, which are (i) exposed to high erosion risk because of the wide row spaces and (ii) which are dependent on high N demand for adequate growth.

Evidence of Strong Land Degradation by Wind Erosion as a Result of Rainfed Cropping in the Algerian Steppe: A Case Study at Laghouat

AbstractIn Algeria, overgrazing has long threatened the sustainable use of the nearly 20 million hectares of steppe lands. More recently, governmental policies favouring extensive rainfed cereal cropping in the steppe region have increased anthropic pressure on this fragile environment. Low rainfall, weak crop development and sandy soils lead to a high risk of wind erosion, yet no studies have been carried out in this region to this date to quantify the effect of steppe conversion on wind erosion. A 1·3‐ha field in the central steppe of Algeria (Laghouat) was converted to cropland (Hordeum Vulgare L.) and equipped with a weather station and Big Spring Number Eight sand straps to monitor climate‐related parameters and sediment fluxes over a 25‐month period. Threshold wind velocities (3·6 m height) varied between 6 and 7 m s−1 with a weak seasonal variation. More than 70% of the saltation‐producing winds originated from the NW. For these winds, a soil loss of 155 Mg ha−1 was measured. Half of the sediment loss occurred during a single, 12‐day period. Deposition of 26·5 Mg ha−1 was observed for SW winds. The measured erosion rates by far exceeded all norms of tolerable soil loss, indicating that rainfed cereal cropping is a highly unsustainable form of land use in the steppe region around Laghouat. National agricultural policies should be revised to take this into account. © 2014 The Authors. Land Degradation and Development published by John Wiley & Sons, Ltd.

Searching for a downward spiral? Soil erosion risk, agro-forest landscape and socioeconomic conditions in Italian local communities

Soil erosion is a common form of land degradation in Europe concentrating on sloping rural areas. Consequences of soil erosion include the alteration of the long-term balance between ecosystem functioning and socio-ecological systems. Although it was hypothesized that rural areas with specific environmental (soil, climate, vegetation) and territorial attributes (economic marginality and poor accessibility) are more exposed to soil erosion risk, less information are available on the spatial link with various socio-spatial, productive, cultural and political attributes of local communities, spanning from unemployment to subsidence agriculture, from quality of life to water management, from poverty to economic backwardness. Taken together, these factors may trigger a downward spiral leading to land degradation. The present study explores, on a municipal scale in Italy, the spatial relationship between an index of soil erosion risk and 133 indicators describing six research domains. Exploratory data analysis based on non-parametric inference, principal components analysis and hierarchical clustering was carried out with the aim to profile municipalities exposed to high risk of soil erosion and to identify a restricted number of factors possibly determining a downward spiral towards soil erosion and land degradation. Results indicate that the socioeconomic profile of risky areas in Italy is characterized by specific rural development attributes and defined productive structure and socio-spatial characteristics representing a possible target for mitigation policies. Multi-factor studies investigating the influence of the local socioeconomic context on soil erosion may contribute to improve the effectiveness of national soil conservation strategies.

Short and medium-term effects of a wildfire and two emergency stabilization treatments on the availability of macronutrients and trace elements in topsoil

In NW Spain, a European region with very high fire incidence and erosion risks, the effects on soils of a medium-to-high severity wildfire and two emergency stabilization techniques were studied. In burned plots (control, BS; seeded with cereal, BSS; straw mulched, BSM) and adjacent unburned plots (US), the topsoil (0–2cm) pH and thirteen NH4Ac–DTPA extractable elements were evaluated at t=0, 4, 8 and 12months after the fire. Compared to US, fire increased by 0.3–0.5units the soil pH which decrease slowly over time, but remaining significantly higher at t=12 (BS, BSM, BSS>US). Ammonium nitrogen (N) levels were higher (p<0.05) in burned plots than in US, difference decreasing progressively from 48-fold (t=0) to 25-fold (t=12). Although no significant effect of fire was immediately observed, the extractable sodium (Na) and potassium (K) were higher (p<0.05) in burned plots than in US at t=4 and t=8, probably due to cation leaching from the overlying ash. Fire did not modify the extractable magnesium (Mg), but at t=0 the extractable calcium (Ca) and phosphorous (P) were transiently and significantly higher in burned plots than in US. Extractable aluminum (Al), iron (Fe), copper (Cu), cobalt (Co) and zinc (Zn) were lower and manganese (Mn) was higher in burned plots than in US. Neither seeding nor mulching significantly modified the topsoil concentrations of the elements considered. The PCA revealed that BS, BSM and BSS became more similar to US over the study period due to a rapid decrease in extractable Ca and Mg and a slow decrease in extractable Mn and NH4+–N. At t=12, the most notable differences between burned plots and US were in the concentrations of extractable Al and Zn. Data suggest that at least another 4–8months will be required for full recovery of the burned plots to unburned conditions.

Landscape dynamic characteristics using satellite data for a mountainous watershed of Abha, Kingdom of Saudi Arabia

The changes in land use/land cover (LULC) play a major role in the study of various aspects of environmental issues. Land use is the results of various socioeconomic activities taking place at various urban and regional setups. In this paper, landscape dynamic characteristics are investigated by using remote sensing and geographic information system in mountainous watershed of Abha, Saudi Arabia. Land use classes were mapped and assessed from a time series of maps of year 2000–2010. The LULC transformations were also analyzed according to elevation and slope. Assessment of the data shows that LULC had undergone substantial changes in this semi-arid mountainous watershed from 2000 to 2010. During this period, the sparse vegetation and water bodies decreased from 48.47 to 39.31 km2 and 0.30 to 0.11 km2, respectively, whereas build-up area increased from 17.02 to 36.36 km2. The area under water bodies has reduced due to construction activities, disturbance in drainage network, and sedimentation in the watershed. The areas having high altitudes were exposed to changes in landscape characteristic. In the regions having lower altitude (1,950–2,350), an agricultural land has decreased, whereas build-up land has increased. As a result of rough structure, only small flat areas, located in this sections and valley channels, may be used as build-up land. Slope gradient had also an influence on the distribution of LULC. The assessment of land use and land cover type distribution by slope category provided the baseline for the implementation of the nationwide land conservation policy of conversion of agricultural land to forestland in order to control high soil erosion risk. The changes in land use and land cover in the studied watershed were mainly controlled by human factors (land management, construction, and population pressure) rather than natural factors.