Showing papers in "Catena in 2013"

Effects of biochar on soil properties and erosion potential in a highly weathered soil

Abstract: Highly weathered soils in humid Asia are characterized by low soil fertility and high soil erosion potential. This study evaluates the influences of biochar made from the waste wood of white lead trees ( Leucaena leucocephala (Lam.) de Wit) on the physicochemical and biological properties of long-term cultivated, acidic Ultisol. This study used three application rates (0%, 2.5%, and 5% (wt/wt)) of the biochar with an incubation time of 105 d for all cases. Soils were collected at 21 d, 42 d, 63 d, 84 d and 105 d during the incubation period to evaluate changes in soil properties over time. A simulated rainfall event (80 mm h − 1 ) was performed to estimate soil loss for all treatments at the end of the incubation time. Experimental results indicate that applying biochar improved the physicochemical and biological properties of the highly weathered soils, including significant increases in soil pH from 3.9 to 5.1, cation exchange capacity from 7.41 to 10.8 cmol (+) kg − 1 , base cation percentage from 6.40 to 26.0%, and microbial biomass carbon (MBC) from 835 to 1262 mg kg − 1 . Compared with the control (i.e., no biochar), biochar application decreased bulk density from 1.4 to 1.1 Mg m − 3 , increased K sat by 1.8 times and increased the mean weight diameter (MWD) of soil aggregates from 2.6 cm to 4.0 cm. Incorporating biochar into the soil significantly reduced soil loss by 50% and 64% at 2.5% and 5% application rates, respectively, compared with the control. The formation of macroaggregates in the biochar-amended soils is the critical factor to improve soil erosion potential. Based on these results, a 5% application rate of biochar is considered as suitable for highly weathered soil because this application rate efficiently improves soil physiochemical properties and reduces soil loss.

Soil erosion and surface runoff on different vegetation covers and slope gradients: A field experiment in Southern Shaanxi Province, China

Abstract: The southern of the Shaanxi Province in central China is a region of great magnitude for water conservation. Long term anthropogenic interference in terms of deforestation and inappropriate land use has dramatically accelerated soil erosion in this region. A field experiment in the Shangnan County using 33 small erosion plots of 7 m2 in size was carried out to determine and compare the soil loss and surface runoff from five vegetation covers and three levels of slope gradient (> 10°–≤ 20°, > 20°–≤ 30°, and > 30°). The five vegetation covers embraced the most frequent rural land-use forms in the study area: farmlands including horticulture (tea plantation with peanut as an intercrop) and agriculture (maize in a winter-wheat–summer-maize rotation) activities, grasslands that have developed on abandoned farmlands, and forestlands including low and high forests (Chinese cork-oak coppices and pine plantations, respectively). The change in the runoff among the vegetation covers and slope gradients was high but not as significantly pronounced as for the change in the soil loss. Results showed that the slope gradient has an impact on the runoff and soil loss: the greater the slope gradient the higher the potential for runoff and soil loss. In addition, results exhibited that the rate of erosion is substantially affected by changes in vegetation cover. Farmlands generated the highest runoff and soil loss, whereas the tea plantations at slopes > 30° were most susceptible to erosion. Grasslands had less runoff and soil loss than farmlands. Forestlands provided evidence for their suitability for soil and water conservation in the study area, as negligible soil-losses in comparison to the other vegetation covers were generated.

Vegetation cover reduces erosion and enhances soil organic carbon in a vineyard in the central Spain

Abstract: Land degradation, and soil and nutrient loss, are significant environmental problems in semi-arid agricultural environments in the Mediterranean Basin. One land use that is particularly associated with the highest rates of erosion in Spain is extensive vineyards. We examined the effectiveness of two cover crops for improving soil physical properties and reducing erosion in a vineyard located in the Henares River basin southeast of Madrid, Spain. We assessed erosion from three replicate plots of 2 m 2 each with three treatments that comprised: traditional tillage, permanent cover of Brachypodium distachyon and spring-mown crop of Secale cereale . Erosion plots under traditional tillage yielded substantially more erosion (5.88 t ha − 1 yr − 1 ) than Brachypodium (0.78 t ha − 1 yr − 1 ) or Secale (1.27 t ha − 1 yr − 1 ). While the concentration of SOC in sediments was greater for the cover crops, the mass-corrected loss of SOC was greater under tillage (0.06 t ha − 1 yr − 1 ) than under Brachypodium or Secale (0.02 t ha − 1 yr − 1 ). Root biomass was two- to four-times greater under the vegetation treatments. Our measure of aggregate stability for the tillage treatment remained between 7.9 and 5.4 drops over the four years of study and values for both cover crops exceeded that for Tillage by the end of the second year. The vegetation cover treatments increased SOC by 1.2% and intrapedal SOC by 10–60% compared with Tillage. By the end of the study, steady-state infiltration in the cover treatments was 45% greater than that under tillage, with the largest increase under Brachypodium . We attribute the greater infiltration on cover treatments to a greater abundance of larger pores on vegetated compared with tilled plots. Our study reinforces the notion that there are considerable benefits of using cover crops in rainfed vineyards, not only for prevention of soil erosion, but to enhance soil condition and potentially reduce the heavy reliance on industrial fertilisers.

Biochar from water hyacinth (Eichornia crassipes) and its impact on soil biological activity

Abstract: Biochar is a useful material for carbon storage in soils. In this report, we explored conversion of water hyacinth (Eichornia crassipes) to biochar as a sustainable weed management strategy, as it also has potential for improving soil quality. Eichornia biomass samples were carbonised with limited supply of air in a muffle furnace at varied temperature (200 to 500 °C) and residence time (30 to 120 min). The biochar yield decreased with temperature and time, but biochar carbon stability increased with temperature. The optimum condition for obtaining maximum stable carbon in Eichornia biochar (EBC) is 300–350 °C temperature with 30–40 min residence time. TGA and FTIR studies showed that EBC has increased aromaticity and carbon stability compared to the starting biomass. Impact of the EBC on soil quality was studied using a red soil, from Dhanbad, India. Soil biochemical properties (dehydrogenase, fluorescein hydrolases, catalase, respiration, active microbial biomass) and maize seedling growth were used to investigate the effects of biochar addition to the soil. Maize seedling vigour index increased from 1.0 at control to 1.61 in 20 g/kg EBC treatment. The maximum increase in soil enzymes like acid phosphatase activity (+ 32%), alkaline phosphatase activity (+ 22.8%), and fluorescein hydrolases activity (50%) occurred at the EBC dose of 20 g/kg. EBC significantly enhanced the soil biological activity particularly the active microbial biomass which has increased by 3 times and soil respiration by 1.9 times. The study shows that the waste Eichornia weed could be gainfully utilised as a soil quality amendment material by converting it to EBC.

Rainfall erosivity in Brazil: A review

Abstract: article i nfo In this paper, we review the erosivity studies conducted in Brazil to verify the quality and representativeness of the results generated and to provide a greater understanding of the rainfall erosivity (R factor) in Brazil. We searched the ISI Web of Science, Scopus, SciELO, and Google Scholar databases and in recent theses and dissertations to obtain the following information: latitude, longitude, city, states, length of record (years), altitude, precipitation, R factor, equations calculated and respective determination coefficient (R 2 ). We found 35 studies in Brazil that used pluviographic rainfall data to calculate the rainfall erosivity. These studies were concentrated in the cities of the south and southeast regions (~60% of all the cities studied in Brazil) with a few studies in other regions, mainly in the north. The annual rainfall erosivity in Brazil ranged from 1672 to 22,452 MJ mm ha −1 h −1 yr −1 . The lowest values were found in the northeast region, and the highest values were found in the north region. The rainfall erosivity tends to increase from east to west, particularly in the northern part of the country. In Brazil, there are 73 regression equations to calculate erosivity. These equations can be useful to map rainfall erosivity for the entire country. To this end, techniques already established in Brazil may be used for the interpolation of rainfall erosivity, such as geostatistics and artificial neural networks.

European small portable rainfall simulators: A comparison of rainfall characteristics

Abstract: Small-scale portable rainfall simulators are an essential research tool for investigating the process dynamics of soil erosion and surface hydrology. There is no standardisation of rainfall simulation and such rainfall simulators differ in design, rainfall intensities, rain spectra and research questions,which impede drawing a meaningful comparison between results. Nevertheless, these data become progressively important for soil erosion assessment and therefore, the basis for decision-makers in application-oriented erosion protection. The artificially generated rainfall of the simulators used at the Universities Basel, La Rioja, Malaga, Trier, Tubingen, Valencia, Wageningen, Zaragoza, and at different CSIC (Spanish Scientific Research Council) institutes (Almeria, Cordoba, Granada, Murcia and Zaragoza) was measured with the same methods (Laser Precipitation Monitor for drop spectra and rain collectors for spatial distribution). Data are very beneficial for improvements of simulators and comparison of simulators and results. Furthermore, they can be used for comparative studies, e.g. with measured natural rainfall spectra. A broad range of rainfall data was measured (e.g. intensity: 37–360 mm h−1; Christiansen Coefficient for spatial rainfall distribution: 61–98%; median volumetric drop diameter: 0.375–6.5 mm; mean kinetic energy expenditure: 25–1322 J m−2 h−1;meankinetic energy per unit area and unit depth of rainfall: 0.77–50 J m−2 mm−1). Similarities among the simulators could be found e.g. concerning drop size distributions (maximum drop numbers are reached within the smallest drop classes b1 mm) and low fall velocities of bigger drops due to a general physical restriction. The comparison represents a good data-base for improvements and provides a consistent picture of the different parameters of the simulators that were tested.

Post-fire mulching for runoff and erosion mitigation Part I: Effectiveness at reducing hillslope erosion rates

Abstract: article i nfo Mulch treatments often are used to mitigate post-fire increases in runoff and erosion rates but the comparative effectiveness of various mulches is not well established. The ability of mulch treatments to reduce sediment yields from natural rainfall and resulting overland flow was measured using hillslope plots on areas burned at high severity following four wildfires in the western United States. Wheat straw mulch, wood strand mulch, and hydromulch were evaluated along with untreated control plots on multiple fires for 4 to 7 years after burn- ing. Needle cast from fire-killed conifer trees was evaluated in an area of moderate burn severity at one fire, and seeding with genetically native seed was tested, with and without hydromulch, at another fire. Rainfall, ground cover, and soil water repellency were measured in each treatment site at all 4 fires. Mean sediment yields on the control plots ranged from 0.3 to 7.5 Mg ha −1 in the first post-fire year, from 0.03 to 0.6 Mg ha −1 in the second, and from 0 to 0.4 Mg ha

Effects of rainfall intensity, underlying surface and slope gradient on soil infiltration under simulated rainfall experiments

Abstract: Knowledge of infiltration patterns and process is very important in understanding and managing slope hydrological processes, crop irrigation, soil erosion, and so on. This paper describes a study in which simulated rainfall events were used to study the effects of various factors (vegetation cover, rainfall intensity, and slope angle) on the soil moisture increase after rainfall and the infiltration recharge coefficient. Soils hosting three different plants (purple medic, PM; spring wheat, SW; and ryegrass, RS) were considered, along with bare soil (BL). These soil surfaces were tested with four different slopes (8.8, 17.6, 26.8 and 36.4%) and subjected to five different rainfall intensities (0.5.0.75, 1.0, 1.5 and 2.0 mm min(-1)). The following key results were obtained: (1) The water distribution in BL boxes differed significantly from that in boxes with vegetation cover, but all boxes with vegetation cover exhibited similar distributions. Vegetation cover significantly increased the depth of the wetting front: under very similar conditions, the wetting front in the RS box reached a depth of more than 35 cm, while that in the BL box reached only 25 cm. (2) Vegetation cover (especially ryegrass) yielded a greater soil moisture increase than did bare land. The overall average soil moisture increase for RS boxes was 36.7 +/- 5.1 mm, about twice than that of BL (3) The water storage after rain across the whole soil profile initially increased and then decreased as the rainfall intensity rose. No differences in the average soil water content increase were found between various rainfall intensities. (4) As the slope increased from 8.8% to 36.4%, the water storage increase initially rose but then fell sharply. There were significant differences (p = 0.05) between the water storage increases for gradual slopes (8.8 and 17.6%) and steep slopes (26.8 and 3.4%). (5) The recharge coefficient increased with increasing vegetation cover but decreased with increasing rainfall intensity, slope gradient, and initial soil water content. The average value for boxes with vegetation cover was 1.5 times that for BL boxes. The vegetation cover was the most important factor in determining the recharge coefficient. (C) 2012 Elsevier B.V. All rights reserved.

Impact of mulching on soil and water dynamics under intermittent simulated rainfall

Abstract: Application of crop residues to soil is a common management practice for soil erosion control and for improving rainfall infiltration. Runoff generation, sediment transport and soil water storage are complex phenomena, involving several interdependent processes. Antecedent moisture conditions, rainfall patterns, and soil cover play an important role in the detachment and transport of soil particles and infiltration. This study aimed to investigate in laboratory the effect of distinct mulch densities on runoff and sediment transport, by using multiple step intermittent rainfall events. Laboratory experiments were conducted using a soil flume and rainfall simulator with three soil cover treatments: 1) bare soil; 2) low mulch cover, 2 t/ha density; and 3) high mulch cover, 4 t/ha density. Experiments comprised a sequence of five different rainfall events in an intermittent way, i.e., three uniform patterns with increasing rainfall intensities, one advanced pattern and one delayed pattern. The laboratory experiments described in this work clearly show that mulching strongly affects infiltration, soil moisture, surface runoff and erosion. Intermittency and characteristics of sequential rainfall events also influenced these processes. Experimental results showed that mulch covers of 2 t/ha and 4 t/ha caused reductions of, respectively, 21% and 51% in the runoff peak. High mulch cover rates resulted in a significant increase in soil moisture. Additionally, soil temperature was more optimally regulated under a mulch cover density of 4 t/ha.

Predicting runoff and sediment connectivity and soil erosion by water for different land use scenarios in the Spanish Pre-Pyrenees

Abstract: Overland flow connectivity and runoff and sediment trap effectiveness are currently the cutting edge topics in soil erosion research. The effect of agricultural terraces, irrigation channels and trails on runoff and soil erosion modelling at catchment scale is still a remaining research question. In this study we run the index of connectivity of Borselli et al. (2008) and a modified version of the revised Morgan, Morgan and Finney (RMMF) model to predict the hydrological connectivity and the rates of soil erosion under four different scenarios of land uses and land abandonment. This goal is achieved by using geographic information systems (GIS) in the Estanque de Arriba catchment (74 ha; Spanish Pre-Pyrenees) where 83 soil samples were collected. The different maps of hydrological connectivity were used to create runoff and sediment trap effectiveness masks that were included in the assessment of the effective cumulative runoff. The results showed that the index of connectivity was very high in the irrigation channels and walls of the agricultural terraces for the past and current scenarios. The runoff and sediment connectivity of the catchment from the hillsides to the lake decreased with an increasing vegetation cover and a decreasing number of linear landscape elements. The connectivity decreased from the past to the current scenario and from the current to the future scenario with vegetation recovery in the abandoned fields. The vegetation factor appeared to be more important than the disappearance of the agricultural terraces and channels to explain the changes in the connectivity at catchment scale. Random changes in the IC values appeared between the current and the future scenario without vegetation recovery in some parts of the catchment and were related to the mathematical procedure of the model that combines the upslope and downslope components at each pixel. This information is of special relevance in areas disturbed by humans and those with complex topography. The average erosion rates ranged between 1.5 and 3.7 Mg ha− 1 year− 1 for the different land use scenarios decreasing with the increase of the vegetation recovery in the abandoned fields. A significant percentage of the study area will suffer more erosion in the early stage of future land abandonment with an increasing volume of overland flow in the fields at the bottom of the catchment whereas soil erosion will decrease significantly after long-term land abandonment with vegetation recovery. Further research is proposed to better account the changes that happen in the soil and vegetation parameters at the early stages of land abandonment. The results of this study suggest that current active systems could be stabilized by trapping and retaining eroded sediment by increasing the vegetation cover and preserving the agricultural terraces.

Responses of soil moisture in different land cover types to rainfall events in a re-vegetation catchment area of the Loess Plateau, China

Abstract: Implementation of the Grain-for-Green project has resulted in significantly increased vegetative cover on the Loess Plateau of China during the past few decades. The plant communities influence soil moisture recharge and usage processes, particularly the input process, which is directly related to transformation of the limited precipitation into available soil water in the semi-arid Loess Plateau. A study to measure soil moisture dynamics of typical land cover types associated with precipitation events was conducted in a re-vegetated catchment area. Smart probes were inserted at 6 different depths below the ground surface under grass (Andropogon), subshrub (Artemisia scoparia), shrub (Spiraea pubescens), tree (Robinia pseudoacacia), and crop (Zea mays) vegetation to record volumetric soil moisture at 10-minute intervals for a period of 60 days during the growing season in 2011. The advance of the wetting front and total accumulated infiltrated water were measured. The rainfall events were sporadic with widely different intensities, and the soil moisture was replenished mainly by 3-4 heavy precipitation events during July and August. The mean soil moisture content profiles of the 5 vegetation types can be ordered as crop>grass>subshrub>tree>shrub and this relationship displayed time stability. The different land cover types clearly influenced the water infiltration and water input amounts in the re-vegetated area. The subshrub site showed the highest total infiltration amount (164 mm) with precipitation (227 mm) during the study period. The grass site had an infiltration amount of 156 mm. The tree site had a total precipitation of 154 mm and an infiltration amount of 97 mm. The infiltration amount was 136 mm for the shrub site and was the lowest (83 mm) for the crop site. Natural grasses displayed a rapid infiltration rate and the wetting front was able to reach a greater depth. (c) 2012 Elsevier B.V. All rights reserved.

Sediment accretion and organic carbon burial relative to sea-level rise and storm events in two mangrove forests in Everglades National Park

Abstract: The goal of this investigation was to examine how sediment accretion and organic carbon (OC) burial rates in mangrove forests respond to climate change. Specifically, will the accretion rates keep pace with sea-level rise, and what is the source and fate of OC in the system? Mass accumulation, accretion and OC burial rates were determined via 210Pb dating (i.e. 100 year time scale) on sediment cores collected from two mangrove forest sites within Everglades National Park, Florida (USA). Enhanced mass accumulation, accretion and OC burial rates were found in an upper layer that corresponded to a well-documented storm surge deposit. Accretion rates were 5.9 and 6.5 mm yr− 1 within the storm deposit compared to overall rates of 2.5 and 3.6 mm yr− 1. These rates were found to be matching or exceeding average sea-level rise reported for Key West, Florida. Organic carbon burial rates were 260 and 393 g m− 2 yr− 1 within the storm deposit compared to 151 and 168 g m− 2 yr− 1 overall burial rates. The overall rates are similar to global estimates for OC burial in marine wetlands. With tropical storms being a frequent occurrence in this region the resulting storm surge deposits are an important mechanism for maintaining both overall accretion and OC burial rates. Enhanced OC burial rates within the storm deposit could be due to an increase in productivity created from higher concentrations of phosphorus within storm-delivered sediments and/or from the deposition of allochthonous OC. Climate change-amplified storms and sea-level rise could damage mangrove forests, exposing previously buried OC to oxidation and contribute to increasing atmospheric CO2 concentrations. However, the processes described here provide a mechanism whereby oxidation of OC would be limited and the overall OC reservoir maintained within the mangrove forest sediments.

Soil erosion and hydrology of the western Mediterranean badlands throughout rainfall simulation experiments: A review

Abstract: Rainfall simulation experiments are widely used in geomorphological research in badland areas. This technique contributed significantly to our understanding of badland geomorphology in the Mediterranean belt. Due to the different types of simulated rainfall applied and the variable size of the plots a review of the State-of-the-Art is necessary. This study confirmed that rainfall simulations are well suited to (i) analyse runoff-infiltration processes and sediment detachment within badlands, and (ii) to establish the factors determining the hydrological and erosion response at interrill scale in badland areas. The hydrological response of badlands is characterized by rapid responses, low to moderate infiltration rates (ranging from close to 0 to 55 mm h − 1 ) and high runoff coefficients (i.e. > 60%). Positive relationships are observed between antecedent soil moisture content and rainfall intensity on the one hand, and runoff coefficients on the other. Sediment concentration and soil detachment rates are among the highest measured on the Mediterranean region (i.e. up to 84.8 g l − 1 and 4722.4 g m − 2 h − 1 ). Results show that rainfall intensity, runoff coefficient, and slope angle have a positive influence on sediment concentration and sediment detachment; in the case of rock fragment cover, its influence is variable according to the soil cover percentage. Rainfall simulations increase our understanding of the temporal and spatial variability of the soil erosion processes. However, rainfall simulation provides mostly qualitative rather than quantitative information because of the small plot size and the simulated rainfall characteristics due to facility for repeating experiments and recording a high quantity of data in short time. However, this method allows the comparison amongst different environments and soil conditions as the rainfall properties can be reproduced.

Soil organic carbon storage capacity positively related to forest succession on the Loess Plateau, China

Abstract: article i nfo Secondary forest succession Soil organic carbon Soil carbon storage Vegetation restoration Land use change Ziwuling forest region Land-use change resulting from natural restoration probably enhances the carbon sequestration capacity of terrestrial ecosystems. To explore those factors which foster changes in the soil carbon pool in forest restora- tion, a study comparing soil organic carbon at different vegetation succession stages along a 150-year chronosequence was conducted in the Ziwuling forest region located in the central part of the Loess Plateau, China. It showed that in long-term (~150 yr) secondary forest succession the soil organic carbon storage (Cs), soil organic carbon (SOC), total nitrogen (TN), and C/N ratio all increased rapidly and tended to be at their highest at roughly the 50-year restoration mark. From this point onward the values gradually stabilized indi- cating that the SOC and the TN accumulated mainly in the early restoration stages. The Cs was significantly and positively correlated with the SOC, the TN, and the C/N ratio (P b 0.01). The Cs in the soil was higher in the upper rather than the lower soil layers. However, the increments of the Cs mainly changed in the lower soil layers. Soil water storage was not the key factor influencing the Cs. The results suggested that changes to the Cs were the result of the accumulation of the SOC and the TN during forest succession and this capacity has shown to be positively related to forest succession on the Loess Plateau, China.

Adsorption characteristics of modified sand for the removal of hexavalent chromium ions from aqueous solutions: Kinetic, thermodynamic and equilibrium studies

Abstract: The objective of this study is to investigate the removal of Cr(VI) from aqueous solutions by using modified sand as adsorbent. The modified sand was characterized by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDX) and FTIR. pH zpc of the raw and modified sands was found to be 6.98 and 6.66, respectively. Removal efficiency of the modified sand was investigated by using batch adsorption experiments. The effect of important parameters such as initial concentration, contact time, adsorbent dosage, pH and temperature on removal of Cr(VI) was investigated. It was demonstrated that the removal efficiency increased from 67.24% to 80.40% by the decreasing initial metal concentration from 15 to 5 mg L − 1 . Effect of pH was investigated by varying the solution pH from 2.0 to 8.0. The optimum pH for adsorption of Cr(VI) on modified sand was found to be 2.5 with a maximum removal of ~ 80.40%. Extent of removal decreases by increasing the temperature from 25 °C to 35 °C confirming exothermic nature. Kinetics of removal process was studied by applying pseudo-first order and pseudo-second order models. Pseudo-first order rate constant was found to be 0.037 min − 1 while the rate constant for pseudo-second order reaction was found to be 0.0236 g mg − 1 min − 1 at 25 °C. Values of thermodynamic parameters viz. ∆G°, ∆H° and ∆S° were calculated and found to be − 3.67 kJ mol − 1 , − 68.74 kJ mol − 1 and − 0.243 kJ mol − 1 K − 1 , respectively at 25 °C. The values of ΔG° were found to be negative at all temperatures indicating the spontaneity of the removal process. A negative value of ∆H° further confirms the exothermic nature of removal process. The experimental data were fitted to Langmuir as well as Freundlich adsorption isotherm equations. The results obtained in the present study show the modified sand to be a better adsorbent for removal of Cr(VI).

Risk assessment of soil erosion in different rainfall scenarios by RUSLE model coupled with Information Diffusion Model: A case study of Bohai Rim, China

Abstract: Risk assessment of soil erosion addresses the likelihood of the occurrence of erosion as well as its consequences. This in turn can provide precautionary and relevant suggestions to assist with disaster reduction. In light of the great threat of soil erosion to global soil resources, it is necessary to implement this type of risk assessment. This study aims to appraise the risk of soil erosion caused by water along the Bohai Sea region during the rainy season. A new method, namely the RUSLE–IDM coupled model, which embeds the IDM (Information Diffusion Model) into the RUSLE(Revised Universal Soil Loss Equation)model, is applied to reveal soil erosion risk in different scenarios, with rainfall exceeding the probability of 0.1 and 0.02 respectively. From this case study, three conclusions can be drawn as follows: (i) This coupled method can effectively examine soil erosion risk and show comparable results of different scenarios, which cannot only calculate the erosion amount, but also identify the likelihood; (ii) Soil erosion caused by water is serious from July to September, but comparatively speaking, the greatest amount of attention should be paid to the prevention of soil erosion in July, as the erosion amount at this time is times larger than during September; (iii) Vegetation coverage and soil erosion control practices are controllable and important factors for the future soil conservation in this area.

Factors influencing storm-generated suspended-sediment concentrations and loads in four basins of contrasting land use, humid-tropical Puerto Rico

Abstract: The significant characteristics controlling the variability in storm-generated suspended-sediment loads and concentrations were analyzed for four basins of differing land use (forest, pasture, cropland, and urbanizing) in humid-tropical Puerto Rico. Statistical analysis involved stepwise regression on factor scores. The explanatory variables were attributes of flow, hydrograph peaks, and rainfall, categorized into 5 flow periods: (1) the current storm hydrograph, (2) the flow and rainfall since the previous storm event, (3) the previous storm event, (4) 2nd previous storm event, and (5) the 3rd previous storm event. The response variables (storm generated sediment loads and concentrations) were analyzed for three portions of the storm hydrograph: (1) the entire storm, (2) the rising limb, and (3) the recessional limb. Hysteresis differences in sediment concentration between the rising and falling limb were also analyzed using these explanatory variables. Sediment availability in the study basins is related to land use and underlying geology. The supply of sediment and its location in the watershed have a strong influence on how current and previous storm events, and flow and rainfall between storm events, affect sediment loads and concentrations. In basins with limited sediment availability (forest and pasture), previous storm events supply sediment to the channel. This in-channel sediment becomes the source of sediment on the rising limb of the next event and clockwise hysteresis occurs. In the cropland basin with high sediment availability, sediment delivered to the channel during events becomes the source of sediment on the rising limb of the next event and clockwise hysteresis occurs. In the urbanizing basin with high sediment availability, counterclockwise hysteresis is prevalent as stormwater runoff dilutes suspended-sediment concentrations on the rising limb and upland sediment arrives on the hydrograph recession. In the urbanized basin, previous storm events flush sediment from the system. The statistical approaches presented here can be used to generate hypotheses on the location and delivery of watershed sediment sources which can improve the design of appropriate field studies.

Application of data-driven evidential belief functions to landslide susceptibility mapping in Jinbu, Korea

Abstract: Evidential belief function (EBF) model was applied and validated for analysis of landslide susceptibility in the Pyungchang area of Korea using geographic information system. Areas of landslide occurrence in the study area were determined from the interpretation of aerial photographs and subsequent field surveys. Landslide locations were randomly allocated for landslide susceptibility map generation (70%) and validation (30%) purposes. Maps relevant to landslide occurrence (topography, geology, soil, and forest cover) were assembled in a spatial database, from which 17 landslide-related factors were extracted. The relationships between the observed landslide locations and these factors were identified and quantified using the EBF model. Three relationships were calculated: disbelief (Dis), uncertainty (Unc), and belief (Bel). The quantified relationships between each factor and landslide locations of each factor with known landslides were then used as factor ratings in an overlay analysis to create landslide susceptibility indices and maps. The most representative of the resulting susceptibility maps (the Bel map) was validated using the landslide data reserved for validation. The landslide susceptibility map demonstrates 85.96% accuracy. Thus, the EBF model was found to be effective in terms of prediction accuracy.

Field investigation of rill and ephemeral gully erosion in the Sparacia experimental area, South Italy

Abstract: This paper reports the results of a field investigation aiming at characterizing the morphology and hydraulics of both rills and ephemeral gullies (EGs) monitored at Sparacia experimental area, Sicily, Italy. The comparison between rill and interrill erosion measurements showed that sediment delivery processes occurred in some erosive events and that the rill erosion rate was dominant in many cases. The measurements were used for testing both the empirical relationships between the channel (rill, EGs and gully) length and its eroded volume and among the morphological variables (length, width, depth and volume) describing the channelized process. Finally, the rill and EGs hydraulic geometry was modelled by three well known power equations relating the discharge with the mean flow velocity, with the flow depth and with the width of each channel segment, respectively. The rill measurements also showed that the flow velocity was affected by the rill segment slope while the flow depth and width were controlled by the plot slope. Therefore, three equations, taking into account these slope effects, were proposed to estimate the hydraulic characteristics of the rills monitored at the Sparacia area.

Fractal features of soil particle-size distribution and total soil nitrogen distribution in a typical watershed in the source area of the middle Dan River, China

Abstract: Fractal scaling theory was employed to analyze the fractal dimension of soil particle-size distribution (PSD) for different plant communities with similar soil types in a watershed in the middle Dan River Valley, China. A total of 296 soil samples were collected from 78 sites. PSD and total soil nitrogen (TSN) were determined in soil from depths of 0–60 cm in four soil horizons for different plant communities. Soils in this area typically comprise silt and fine sand. The fractal dimensions of the six selected plant communities ranged from 2.73–2.89, with fractal dimension (Dm) values of grassland and forestland being lower (2.73–2.78) than those of cropland (2.81 and 2.89). There was an obvious decreasing trend in TSN content with increasing depth under the various plant communities. Spatial patterns of TSN changed significantly with land-use types. Organic nitrogen was the main component of soil nitrogen. There was a strong positive correlation between the fractal dimension and the silt and clay content (n = 78, R2 = 0.96, P

Post-fire mulching for runoff and erosion mitigation Part II: Effectiveness in reducing runoff and sediment yields from small catchments

Abstract: article Agricultural straw, hydromulch, and wood shred or wood strand mulches increasingly are being used as post-fire hillslope treatments, but the differences in effectiveness among these mulch treatments are not fully understood. Following the 2002 Hayman fire in central Colorado and the 2003 Cedar fire in southern California, matched catchments were monitored for five to seven post-fire years to determine the effective- ness of wheat straw mulch (Hayman fire only) and hydromulch in reducing post-fire runoff, peak flow rates, and sediment yields from natural rainfall. Measured runoff and sediment yields were caused by short dura- tion high intensity summer storms at the Hayman fire and long duration winter rains at the Cedar fire. The wheat straw mulch treatment significantly reduced peak flow rates and sediment yields at the Hayman fire. The annual peak flow rates in the first two post-fire years in the straw mulch catchment were 4.5 and 3.9 m 3 s −1 km −2 (respectively) as compared to 4.3 and 7.1 m 3 s −1 km −2 (respectively) in the control. In post-fire years one and two, the maximum event sediment yields in the straw mulch catchment were 7.2 and 10 Mg ha −1 , respectively, which were less than half of the maximum event sediment yields in the con- trol catchment (19 and 24 Mg ha −1 , respectively). The straw mulch catchment had no detectable runoff or sediment yield after the second post-fire year, but the control catchment continued to have measurable run- off and sediment yields through the seventh post-fire year. The straw mulch treatment effect in runoff reduc- tion was not significant in the statistical model. Total ground cover was 80% immediately after the application of straw mulch, and decreased to 10% by the end of first post-fire year, yet total ground cover values remained high as litter and vegetation, including invasive cheatgrass, increased. The hydromulch cover at both fires declined rapidly and provided less than 10% of the ground cover within 2.5 months after application at which point the catchment was presumed to be untreated. Due to differences in precipitation, the three catchments at the Cedar fire had significantly different hydrologic responses during the presumed untreated portion of the study, which precluded evaluation of treatment effectiveness during the short treated period. The peak flow responses from the hydromulch and control catchments at the Hayman fire were also different during the presumed untreated period and were not tested. Although the runoff and sediment yields did not differ during the presumed untreated period and were tested for treat- ment effects, the Hayman hydromulch treatment did not significantly affect either response during the first post-fire year—the presumed treated period. Unit-area sediment yields from the catchments were similar to those measured on hillslope plots at both the Hayman and Cedar fires in the first post-fire years, but in later years the sediment yields from the catchments were at least double the sediment yields measured on hillslope plots. The longer periods of greater erosion rates in the catchments likely reflect the addition of channel erosion processes and a difference in hydrologic connectivity at the catchment scale. Published by Elsevier B.V.

Fragility of Western Mediterranean landscapes during Holocene Rapid Climate Changes

Abstract: In this paper we explore the evidence for Holocene Rapid Climate Changes (RCCs) in Western Mediterranean records, examining similarities and differences in the timing and nature of impacts on different components of the natural environment (vegetation, fluvial and coastal sedimentation, fire activity, soil formation). Marine, lacustrine, and fluvial archives of the Western Mediterranean (Iberian Peninsula and Northwest Africa) provide evidence for both pervasive millennial-scale climatic variability and abrupt (decadal- to centennial-scale) transitions. We focus in particular on three RCCs characterised by high-latitude cooling, glacier advances and North-Atlantic ice-rafting events: the mid-Holocene RCC interval 6–5 cal ka BP, the late-Holocene RCC interval 3.5–2.5 cal ka BP, and the historical RCC interval known as the Little Ice Age (LIA, 1300–1950 AD). Evidence from multiple records indicates wide-ranging impacts of RCCs in the Western Mediterranean region. The three RCC intervals were characterised, however, by contrasting hydrological situations in the Western Mediterranean, with prevailing dry conditions including marked aridification events during the RCC intervals 6–5 and 3.5–2.5 cal ka BP, and prevailing or recurrent wet conditions during the LIA. We examine issues of proxy sensitivity in palaeoecological and geomorphological records and evaluate examples of contrasting geomorphological responses to regional climatic triggers between humid and semi-arid sectors of the Western Mediterranean. Finally, we consider the long-term sensitivity of the region to rapid climate change, the role of threshold changes, and the extent to which this region represents a “fragile” landscape.

GIS-based hydrological zones and soil geo-database of Ethiopia

Abstract: Land and water are vital resources to maintain the environment and livelihoods of mankind. Understanding the spatial variability of these resources has significant importance for planning, management, and utilization thereof. Despite their importance, there is no available, coherent, and systematically organized method for the characterization and mapping of the soil and hydrological systems in Ethiopia. A review-based research aimed at developing a geo-database of soils for hydrological studies and generation of the hydrological zones of the country based on the surface runoff potential is reported. In this analysis, data from 930 rainfall and 212 meteorological stations were used. Analysis based on a weighted overlay technique within ArcGIS using data from various sources and scales was conducted. A regression equation was used to develop the soil geo-database, scale factors of soil, land slope and climatic layers. An iterative analysis and expert knowledge was also used to determine the weights of the layers for the hydrological zoning. Results from this study provide valuable information about the hydrological zones of Ethiopia and an improved spatial soil database at 1:250,000 scale for the first time. Generated maps and zones will improve the hydrological understanding of the various regions of the country.

Soil erosion under the impacts of future climate change: assessing the statistical significance of future changes and the potential on-site and off-site problems

Abstract: Soil erosion by water is a major environmental threat to the sustainability and productive capacity of agriculture in many tropical and sub-tropical regions of the world. In temperate regions, meanwhile, the ‘off-site’ transport of sediment and pollutants into nearby water courses and the ‘muddy flooding’ of properties and infrastructure pose a much greater threat. These adverse impacts may become a more serious future environmental problem under the impacts of future climate change, ranging from direct changes in precipitation characteristics to the more indirect effects of temperature in governing plant biomass and shifts in land use to accommodate the new climatic regime. A number of modelling studies have been conducted in various locations to examine how climate change and its impacts will affect soil erosion, but few studies attempt to quantify how statistically significant those changes are, or whether the changes will pose agricultural and/or environmental problems. This study aims to address these issues, by developing simple methodologies to assess the statistical significance of future soil erosion rates based on comparing relative changes to natural variability around present-day rates, and determine whether these changes may be problematic by comparing absolute soil erosion rates to tolerable thresholds. A modelling study across six hillslopes in Northern Ireland is conducted to demonstrate these methodologies, using the Water Erosion Prediction Project (WEPP) model. The direct impacts of climate change are modelled using statistical downscaling methods and a simple sensitivity analysis in the case of sub-daily precipitation data, whilst a scenario approach is taken in order to model the indirect impacts of changing land use and management. Results indicate a mix of soil erosion increases and decreases, depending on which scenarios are considered. Downscaled climate change projections in isolation generally result in erosion decreases, whereas large increases are projected under many scenarios where changes in sub daily rainfall intensity and land use are accounted for. Only the most extreme scenarios reveal the potential for on-site problems of soil erosion, whilst the off-site impacts are likely to become a more considerable environmental issue with respect to water quality and muddy flooding under a wide range of future scenarios. A number of scenarios reveal statistically significant increases in soil erosion from the present day, but these are confined to only two out of the six sites. At the remaining four sites, high absolute rates are projected under many scenarios, despite not representing statistically significant increases, and there also exist a number of cases where statistically significant increases translate to low absolute erosion rates. This illustrates the importance of analysing both relative and absolute soil erosion rates, as the former allows us to isolate the impacts of climate change in contributing to erosion, whereas the latter allows us to determine whether those changes may be problematic by comparing them to tolerable thresholds. The methodologies outlined and demonstrated in this study provide a simple means of generating these additional pieces of information which could prove useful in decision-making contexts.

Using 137Cs and 210Pbex to assess soil redistribution on slopes at different temporal scales

Abstract: Increasing risk of soil loss as a result of climate change, has generated a need for reliable information on erosion rates at different temporal scales. Use of the fallout radionuclides 137Cs, 210Pbex and 7Be as tracers of sediment mobilization and redistribution makes it possible to obtain estimates of soil redistribution rates within both undisturbed and cultivated landscapes over a range of timescales. Mediterranean landscapes are characterized by a great diversity of physiography and land use, and as a consequence erosion and deposition patterns are highly variable spatially. To document such spatial variability, a slope transect located in the subhumid Pre-Pyrenean mountains (NE Spain) was selected to use 137Cs and 210Pbex to assess medium- and longer-term soil redistribution rates. A total of 23 sectioned soil cores spaced 50 m apart were collected along the slope transect, where 7Be had been previously used to document soil redistribution resulting from an individual storm event. The inventories of both radionuclides varied markedly, between 409 and 6080 Bq m− 2 for 137Cs, and between 0 and 6734 Bq m− 2 for 210Pbex. Estimates of soil redistribution, derived from the 137Cs depth profiles, using appropriate conversion models, show that erosion rates along the transect vary between 2.6 and 31.9 Mg ha− 1 year− 1, and that sedimentation rates vary between 0.2 and 24.5 Mg ha− 1 year− 1. The highest soil losses occur in cultivated fields, within the midslope zone of the transect, while the highest deposition rates are found in tilled fields within the lower part of the transect. Erosion rates from 210Pbex varied widely between 0.1 and 83.7 Mg ha− 1 year− 1 on the lower slope, whereas sedimentation rates ranged between 0.8 and 110 Mg ha− 1 year− 1 also at the bottom slope. The spatial distribution of the radionuclides along the transect reflects the effects of different land use and slope gradient on water erosion. The results obtained confirm the potential for using 137Cs and 210Pbex measurements for assessing soil redistribution on slopes in the Mediterranean environment over different temporal scales.

Estimating wet soil aggregate stability from easily available properties in a highly mountainous watershed

Abstract: A comparison study was carried out with the purpose of verifying when the adaptive neuro-fuzzy inference system (ANFIS), artificial neural network (ANN), generalized linear model (GLM), and multiple linear regression (MLR) models are appropriate for prediction of soil wet aggregate stability (as quantified by the mean weight diameter, MWD) in a highly mountainous watershed (Bazoft watershed, southwestern Iran). Three different sets of easily available properties were used as inputs. The first set (denoted as SP) consisted of soil properties including clay content, calcium carbonate equivalent, and soil organic matter content. The second set (denoted as TVA) included topographic attributes (slope and aspect) and the normalized difference vegetation index (NDVI). The third set (denoted as STV) was a combination of soil properties, slope, and NDVI. The ANN and ANFIS models predicted MWD more accurately than the GLM and MLR models. Estimation of MWD using TVA data set resulted in the lowest model efficiency values. The observed model efficiency values for the developed MLR, GLM, ANN, and ANFIS models using the SP data set were 60.76, 62.98, 77.68 and 77.15, respectively. Adding slope and NDVI to soil data (i.e. STV data set) improved the predictions of all four methods. The obtained correlation coefficient values between the predicted and measured MWD for the developed MLR, GLM, ANN, and ANFIS models using STV data set were 0.24, 0.35, 0.84 and 0.73, respectively. In conclusion, the ANN and ANFIS models showed greater potential in predicting soil aggregate stability from soil and site characteristics, whereas linear regression methods did not perform well.

Spatially distributed modeling of soil organic matter across China: An application of artificial neural network approach

Abstract: Accurate prediction of spatial distribution of soil organic matter (SOM) at different scales is important for various applications related to land use and environmental problems. This study proposed a radial basis function neural networks model (RBFNN), combined with principal component analysis (PCA), to predict the spatial distribution of SOM content across China. To assess its feasibility, 6241 soil samples collected during the second national soil survey period were used. To predict the SOM at such scale, the entire study area was firstly divided into 22 different soil-landscape units according to soil types and vegetation types; then 11 quantitative environmental factors derived from climate, topography, and vegetation were converted into principal components (PC) and the first five PCs which explain 92.97% of the total data variance were selected as predictors for the purpose of eliminating the mulicollinearity of these actual variables and reducing the number of predictors; finally, a specific artificial neural network model was trained for each soil-landscape unit to capture the relationships between SOM and PCs and then used to predict the distribution of SOM content within the corresponding soil-landscape unit. The performance of this approach was evaluated by several validation indices and compared with multiple linear regression (MLR) and regression kriging (RK). The results have shown that RBFNN performs much better than both MLR and RK with much higher ratio of performance to deviation (RPD) and lower prediction errors (mean absolute error (MAE), mean relative error (MRE) and root mean squared error (RMSE)). The RPD obtained by RBFNN was 1.94, which resulted in relative improvement of 29.33% compared with RK and MLR. The three prediction errors of RBFNN were smaller than that of MLR and RK by 3.10 g.kg(-1), 17.25%, 6.25 g.kg(-1), and by 234 g.kg(-1), 5.93%, 6.24 g.kg(-1) respectively. Also, RBFNN presented a more realistic spatial pattern of SOM than RK and MLR. The good performance of this method can be attributed to the division of the study area and the capability of RBFNN to capture the nonlinear relationships between SOM and environmental factors within different soil-landscape units. The result suggests that the proposed method can play a vital role in improving prediction accuracy of SOM within a large area. (C) 2012 Elsevier B.V. All rights reserved.

Effect of forest floor characteristics on water repellency, infiltration, runoff and soil loss in Andisols of Tenerife (Canary Islands, Spain)

Abstract: Given its singular properties and location, forest floor (litter + duff) is a key factor in hydrological processes. Water infiltration research was carried out for the present study in Andisols at ten sites, six of which had coverings of pine forest and four of rainforest. Rainfall simulations were conducted on gentle, moderately-steep and steep slopes (10, 30 and 50%) to determine infiltration, runoff and soil loss as a function of the forest floor characteristics. The duff on the pine forest soils consists of moderately porous, extremely hydrophobic and consistent semi-decomposed organic material, which is rich in fungi hyphae. The duff on the rainforest soils is formed by highly porous, loose, semi-decomposed organic material. The study results highlight the influential role played by the forest floor in infiltration and runoff. Infiltration barely reaches 20 mm h − 1 in pine forest, compared to 50 mm h − 1 in rainforest. As a consequence, the pine forest runoff is twice that recorded in rainforest sites. The wetting front on gentle and moderately-steep slopes evidences the influence of the duff on infiltration. In pine forest, most of the rainwater remains in the duff and infiltration depends little therefore on the underlying mineral soil properties. In rainforest, the wetting front extends below the duff and the well-developed soil structure is a major factor in water infiltration. The differences noted in the two parameters are not found on the steep slopes. No soil loss differences are observed between the two vegetation covers and forest floors despite the greater runoff in pine forest. The results demonstrate the protective effect of the organic covering and how the stability of the Andisols helps combat water erosion processes.

Algae influence the hydrophysical parameters of a sandy soil

Abstract: Article history:Received 2 August 2011Received in revised form 31 January 2012Accepted 3 February 2012Available online xxxxKeywords:AlgaeBiological soil crustSoil water repellencySand duneSorptivityHydraulic conductivity Biological soil crusts have a major effect on water flow in soils. Two study sites, located at a pine-forest gladecovered with a biologicalsoil crust, formed the basis of our study. The sand soil atthe surface (Glade soil) wascompared to a control soil (Pure sand) with limited impact of vegetation or organic matter, occurring at50 cm depth beneath a glade area. To assess the influence ofalgae in the biological soil crust on the propertiesof pure sand, a coccal green alga (Choricystis minor), filamentous green alga (Klebsormidium subtile) and stra-menopile alga (Tribonema minus) were isolated from the top layer of glade soil and grown in the lab in Petridishes on sterile pure sand as monoalgal and bialgal (C. minor and K. subtile) crusts for 3, 5, 7, 9, 11, 13, 15, 17,19, and 21 days. Atthe end ofeach growth stage, the hydrophysicalparametersof crusted sand were estimat-ed after drying at 50 °C for 15 h (equivalent to a 3-day hot spell) and compared to the parameters of puresand. The hydrophysical parameters were substantially different between the two surfaces. The glade soilhad an index of water repellency about 18-times that of pure sand and the persistence of water repellencyalmost 54-times that of pure sand. Both sorptivity and hydraulic conductivity in the glade soil were about7% those of the pure sand, respectively. The growth of artificial algal crusts, characterized by an increase inorganic carbon content from 0.16% to 0.33%, resulted in an increase in water drop penetration time of thedried crusts up to 14-times that of the pure sand and a decrease in the water sorptivity of the dried crustsup to 10% that of the pure sand. Whereas K. subtile crusts (both monoalgal and bialgal with C. minor) hadup to a 9% decrease in hydraulic conductivity compared to pure sand, there was no impact of monoalgalC. minor and T. minus crusts on hydraulic conductivity. K. subtile was possibly limited to surface growth,whereas C. minor and T. minus penetrated to depth. Consequently, K. subtile may have clogged the toppores more effectively than the other two strains. The water repellency cessation time increased with anincrease in water drop penetration time for all the dried monoalgal and bialgal crusts used in this study. Agreater impact of K. subtile on the shifts in hydraulic behaviour could influence water capture and storage,potentially decreasing evaporation during dry periods, but enhancing overland flow diminishing leachingduring wet periods.© 2012 Elsevier B.V. All rights reserved.

Shrub encroachment with increasing anthropogenic disturbance in the semiarid Inner Mongolian grasslands of China

Abstract: Many arid grasslands around the world are affected by shrub encroachment. However, the transition states of shrub-encroached ecosystems are still poorly known, and the effects of human disturbances are difficult to quantify during the transition process. This study investigated plant biomass, community characteristics, and water capturing capability of the shrub and interspace grass patches during the different transition states of Caragana microphylla Lam-encroached grassland in response to the intensity of anthropogenic disturbances. The results indicate that the number of plant species increased with the disturbance intensity at the shrub patches and that the total aboveground biomass (AB) significantly decreased from the slightly disturbed site to the moderately disturbed site, then significantly increased from the moderately disturbed site to the seriously disturbed site. The total belowground biomass (BB) was much greater in the shrub patches than the interspace grass patches at the above three sites. The results also suggest that grass or shrub dominance were alternative stable states in the processes of shrub encroachment but that a threshold existed during state transition. Dye tracing experiments showed that shrubs had higher water capturing capability than grass. The shrubs could capture and transport water to the deeper soil layers in the shrub patches. We speculate that the competitive advantage for biomass and water by shrubs could be reversed for grass if the disturbance intensity does not exceed a threshold value. A continual increase of anthropogenic disturbance would further lower the water capturing capability of grasses, leading to an increase of biomass and the size of shrub patches and a shift in the landscape to a shrub-dominated state, which would be irreversible.