Showing papers in "Solid Earth in 2015"

Identifying areas susceptible to desertification in the Brazilian northeast

Abstract: . Approximately 57% of the Brazilian northeast region is recognized as semi-arid land and has been undergoing intense land use processes in the last decades, which have resulted in severe degradation of its natural assets. Therefore, the objective of this study is to identify the areas that are susceptible to desertification in this region based on the 11 influencing factors of desertification (pedology, geology, geomorphology, topography data, land use and land cover change, aridity index, livestock density, rural population density, fire hot spot density, human development index, conservation units) which were simulated for two different periods: 2000 and 2010. Each indicator were assigned weights ranging from 1 to 2 (representing the best and the worst conditions), representing classes indicating low, moderate and high susceptibility to desertification. The results indicate that 94% of the Brazilian northeast region is under moderate to high susceptibility to desertification. The areas that were susceptible to soil desertification increased by approximately 4.6% (83.4 km2) from 2000 to 2010. The implementation of the methodology provides the technical basis for decision-making that involves mitigating actions and the first comprehensive national assessment within the United Nations Convention to Combat Desertification framework.

Instaseis: instant global seismograms based on a broadband waveform database

Abstract: . We present a new method and implementation (Instaseis) to store global Green's functions in a database which allows for near-instantaneous (on the order of milliseconds) extraction of arbitrary seismograms. Using the axisymmetric spectral element method (AxiSEM), the generation of these databases, based on reciprocity of the Green's functions, is very efficient and is approximately half as expensive as a single AxiSEM forward run. Thus, this enables the computation of full databases at half the cost of the computation of seismograms for a single source in the previous scheme and allows to compute databases at the highest frequencies globally observed. By storing the basis coefficients of the numerical scheme (Lagrange polynomials), the Green's functions are 4th order accurate in space and the spatial discretization respects discontinuities in the velocity model exactly. High-order temporal interpolation using Lanczos resampling allows to retrieve seismograms at any sampling rate. AxiSEM is easily adaptable to arbitrary spherically symmetric models of Earth as well as other planets. In this paper, we present the basic rationale and details of the method as well as benchmarks and illustrate a variety of applications. The code is open source and available with extensive documentation at www.instaseis.net .

Impact of the addition of different plant residues on nitrogen mineralization-immobilization turnover and carbon content of a soil incubated under laboratory conditions

Abstract: . Application of plant residues as soil amendment may represent a valuable recycling strategy that affects carbon (C) and nitrogen (N) cycling in soil–plant systems. The amount and rate of nutrient release from plant residues depend on their quality characteristics and biochemical composition. A laboratory incubation experiment was conducted for 120 days under controlled conditions (25 °C and 58% water-filled pore space) to quantify initial biochemical composition and N mineralization of leguminous and non-leguminous plant residues, i.e., the roots, shoots and leaves of Glycine max, Trifolium repens, Zea mays, Populus euramericana, Robinia pseudoacacia and Elaeagnus umbellata, incorporated into the soil at the rate of 200 mg residue N kg−1 soil. The diverse plant residues showed a wide variation in total N, C, lignin, polyphenols and C / N ratio with higher polyphenol content in the leaves and higher lignin content in the roots. The shoot of Glycine max and the shoot and root of Trifolium repens displayed continuous mineralization by releasing a maximum of 109.8, 74.8 and 72.5 mg N kg−1 and representing a 55, 37 and 36% recovery of N that had been released from these added resources. The roots of Glycine max and Zea mays and the shoot of Zea mays showed continuous negative values throughout the incubation. After an initial immobilization, leaves of Populus euramericana, Robinia pseudoacacia and Elaeagnus umbellata exhibited net mineralization by releasing a maximum of 31.8, 63.1 and 65.1 mg N kg−1, respectively, and representing a 16, 32 and 33% N recovery, respectively. Nitrogen mineralization from all the treatments was positively correlated with the initial residue N contents (r = 0.89; p l 0.01) and negatively correlated with lignin content (r = −0.84; p ≤ 0.01), C / N ratio (r = −0.69; p ≤ 0.05), lignin / N ratio (r = −0.68; p ≤ 0.05), polyphenol / N ratio (r = −0.73; p ≤ 0.05) and (lignin + polyphenol) : N ratio (r = −0.70; p ≤ 0.05) indicating a significant role of residue chemical composition and quality in regulating N transformations and cycling in soil. The present study indicates that incorporation of plant residues strongly modifies the mineralization–immobilization turnover (MIT) of soil that can be taken into account to develop synchronization between net N mineralization and crop demand in order to maximize N delivery and minimize N losses.

High-temperature metamorphism during extreme thinning of the continental crust: a reappraisal of the North Pyrenean passive paleomargin

Abstract: An increasing number of field examples in mountain belts show that the formation of passive margins during extreme continent thinning may occur under conditions of high to very high thermal gradient beneath a thin cover of syn-rift sediments. Orogenic belts resulting from the tectonic inversion of distal margins and regions of exhumed continental mantle may exhibit high-temperature, low-pressure (HT-LP) metamorphism and coeval syn-extensional, ductile deformation. Recent studies have shown that the northern flank of the Pyrenean belt, especially the North Pyrenean Zone, is one of the best examples of such inverted hot, passive margin. In this study, we provide a map of HT-LP metamorphism based on a data set of more than 100 peak-temperature estimates obtained using Raman spectroscopy of the carbona-ceous material (RSCM). This data set is completed by previous PT (pressure and temperature) estimates based on mineral assemblages, and new 40 Ar– 39 Ar (amphibole, micas) and U–Pb (titanite) ages from metamorphic and magmatic rocks of the North Pyrenean Zone. The implications on the geological evolution of the Cretaceous Pyrenean paleomar-gins are discussed. Ages range mainly from 110 to 90 Ma, and no westward or eastward propagation of the metamor-phism and magmatism can be clearly identified. In contrast, the new data reveal a progressive propagation of the thermal anomaly from the base to the surface of the continental crust. Focusing on the key localities of the Mauleon basin, Arguenos–Moncaup, Lherz, Boucheville and the Bas-Agly, we analyze the thermal conditions prevailing during the Cre-taceous crustal thinning. The results are synthetized into a series of three regional thematic maps and into two detailed maps of the Arguenos–Moncaup and Lherz areas. The results indicate a first-order control of the thermal gradient by the intensity of crustal thinning. The highest grades of metamor-phism are intimately associated with the areas where subcon-tinental mantle rocks have been unroofed or exhumed.

Short-term grazing exclusion has no impact on soil properties and nutrients of degraded alpine grassland in Tibet, China

Abstract: . Since the 1980s, alpine grasslands have been seriously degraded on the Tibetan Plateau. Grazing exclusion by fencing has been widely adopted to restore degraded grasslands. To clarify the effect of grazing exclusion on soil quality, we investigated soil properties and nutrients by comparing free-grazing (FG) and grazing exclusion (GE) grasslands in Tibet. Soil properties – including soil bulk density, pH, particle size distributions, and proportion of aggregates – showed no significant difference between FG and GE plots. Soil organic carbon, soil available nitrogen, and available phosphorus contents did not differ with grazing exclusion treatments in both the 0–15 and 15–30 cm layer. However, soil total nitrogen and total phosphorus contents were remarkably reduced due to grazing exclusion at 0–15 cm depth. Furthermore, growing season temperature and/or growing season precipitation had significant effects on almost all soil property and nutrient indicators. This study demonstrates that grazing exclusion had no impact on most soil properties and nutrients in Tibet. Additionally, the potential shift of climate conditions should be considered when recommending any policy designed for restoration of degraded soil in alpine grasslands in the future. Nevertheless, because the results of the present study come from a short-term (6–8 years) grazing exclusion, the assessments of the ecological effects of the grazing exclusion management strategy on soil quality of degraded alpine grasslands in Tibet still need long-term continued research.

Scale effect on runoff and soil loss control using rice straw mulch under laboratory conditions

Abstract: . Amendments can control the runoff and soil loss by protecting the soil surface. However, scale effects on runoff and soil loss control have not been considered yet. The present study has been formulated to determine the efficiency of two plot sizes of 6 and 0.25 m2 covered by 0.5 kg m−2 of straw mulch with regard to changing the time to runoff, runoff coefficient, sediment concentration and soil loss under laboratory conditions. The study used a sandy-loam soil taken from summer rangeland, Alborz Mountains, northern Iran, and was conducted under simulated rainfall intensities of 50 and 90 mm h−1 and in three replicates. The results of the study showed that the straw mulch had a more significant effect on reducing the runoff coefficient, sediment concentration and soil loss on a 0.25 m2 plot scale. The maximum effectiveness in time to runoff for both the scales was observed at a rainfall intensity of 90 mm h−1. The maximum increasing and decreasing rates in time to runoff and runoff coefficient were observed at a rainfall intensity of 90 mm h−1, with 367.92 and 96.71% for the 0.25 m2 plot and 110.10 and 15.08% for the 6 m2 plot. The maximum reduction in the runoff coefficient was in the 0.25 m2 plot for the two rainfall intensities of 50 and 90 mm h−1, with rates of −89.34 and −96.71%. The maximum change in soil loss at the intensities of both 50 and 90 mm h−1 occurred in the 0.25 m2 plot, with 100%, whereas in the 6 m2 plot, decreasing rates of soil loss for the intensities of both 50 and 90 mm h−1 were 46.74 and 63.24%, respectively.

Linking soil erosion to on-site financial cost: lessons from watersheds in the Blue Nile basin

Abstract: . The study was conducted in three watersheds (Dapo, Meja and Mizewa) in the Ethiopian part of the Blue Nile Basin to estimate the on-site cost of soil erosion using the productivity change approach, in which crop yield reduction due to plant nutrients lost with the sediment and runoff has been analysed. For this purpose, runoff measurement and sampling was conducted during the main rainy season of 2011 at the outlet of two to three sub-watersheds in each watershed. The sediment concentration of the runoff, and N and P contents in runoff and sediment were determined. Crop response functions were developed for the two plant nutrients based on data obtained from the nearest Agricultural Research Centres. The response functions were used to estimate crop yield reduction as a result of the lost N and P assuming there is no compensation through fertilization. The results show a significant yield reduction and resultant financial loss to the farmers. Considering only grain yield of maize (Zea mays), farmers at Dapo annually lose about USD 220 ha−1 and 150 ha−1 due to the loss of N and P, respectively. In view of the importance of the crop residues, including as feed, the loss can be even greater. The study demonstrated that in addition to the long-term deterioration of land quality, the annual financial loss suffered by farmers is substantial. Therefore, on farm soil and water conservation measures that are suitable in biophysical and socio-economic terms in the landscapes and beyond need to be encouraged.

Evaluation of soil fertility in the succession of karst rocky desertification using principal component analysis

Abstract: . Expanding of karst rocky desertification (RD) area in southwestern China is strangling the sustainable development of local agricultural economy. It is important to evaluate the soil fertility at RD regions for the sustainable management of karst lands. The changes in 19 different soil fertility-related variables along a gradient of karst rocky desertification were investigated in five different counties belonging to the central Hunan province in China. We used principal component analysis method to calculate the soil data matrix and obtained a standardized integrate soil fertility (ISF) indicator to reflect RD grades. The results showed that the succession of RD had different impacts on soil fertility indicators. The changing trend of total organic carbon (TOC), total nitrogen (TN), available phosphorus, microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) was potential RD (PRD) > light RD (LRD) > moderate RD (MRD) > intensive RD (IRD), whereas the changing trend of other indicators was not entirely consistent with the succession of RD. The degradation trend of ISF was basically parallel to the aggravation of RD, and the strength of ISF mean values were in the order of PRD > LRD > MRD > IRD. The TOC, MBC, and MBN could be regarded as the key indicators to evaluate the soil fertility.

Soil microbiological properties and enzymatic activities of long-term post-fire recovery in dry and semiarid Aleppo pine ( Pinus halepensis M.) forest stands

Abstract: . Wildfires affecting forest ecosystems and post-fire silvicultural treatments may cause considerable changes in soil properties. The capacity of different microbial groups to recolonise soil after disturbances is crucial for proper soil functioning. The aim of this work was to investigate some microbial soil properties and enzyme activities in semiarid and dry Aleppo pine (Pinus halepensis M.) forest stands. Different plots affected by a wildfire event 17 years ago without or with post-fire silvicultural treatments 5 years after the fire event were selected. A mature Aleppo pine stand, unaffected by wildfire and not thinned was used as a control. Physicochemical soil properties (soil texture, pH, carbonates, organic matter, electrical conductivity, total N and P), soil enzymes (urease, phosphatase, β-glucosidase and dehydrogenase activities), soil respiration and soil microbial biomass carbon were analysed in the selected forests areas and plots. The main finding was that long time after this fire event produces no differences in the microbiological soil properties and enzyme activities of soil after comparing burned and thinned, burned and not thinned, and mature plots. Moreover, significant site variation was generally seen in soil enzyme activities and microbiological parameters. We conclude that total vegetation recovery normalises post-fire soil microbial parameters, and that wildfire and post-fire silvicultural treatments are not significant factors affecting soil properties after 17 years.

MODIS normalized difference vegetation index (NDVI) and vegetation phenology dynamics in the Inner Mongolia grassland

Abstract: . The Inner Mongolia grassland, one of the most important grazing regions in China, has long been threatened by land degradation and desertification, mainly due to overgrazing. To understand vegetation responses over the last decade, this study evaluated trends in vegetation cover and phenology dynamics in the Inner Mongolia grassland by applying a normalized difference vegetation index (NDVI) time series obtained by the Terra Moderate Resolution Imaging Spectroradiometer (MODIS) during 2002–2014. The results showed that the cumulative annual NDVI increased to over 77.10 % in the permanent grassland region (2002–2014). The mean value of the total change showed that the start of season (SOS) date and the peak vegetation productivity date of the season (POS) had advanced by 5.79 and 2.43 days, respectively. The end of season (EOS) was delayed by 5.07 days. These changes lengthened the season by 10.86 days. Our results also confirmed that grassland changes are closely related to spring precipitation and increasing temperature at the early growing period because of global warming. Overall, productivity in the Inner Mongolia Autonomous Region tends to increase, but in some grassland areas with grazing, land degradation is ongoing.

Rainfall and human activity impacts on soil losses and rill erosion in vineyards (Ruwer Valley, Germany)

Abstract: . Vineyards are one of the eco-geomorphological systems most conditioned by human activity in Germany. The vineyards of the Ruwer Valley (Germany) are characterized by high soil erosion rates and rill problems on steep slopes (between 23 and 26°) caused by the increasingly frequent heavy rainfall events as well as deterioration due to incorrect land use managements. The objective of this paper is to determine and to quantify the hydrological and erosive phenomena in one vineyard in Germany during different seasons and under different management conditions (before, during and after vintage). For this purpose, a combined methodology was applied. Climatic (rainfall depth distributions and return periods), pedological (soil analysis and classification), geomorphological (sediment movements and rills evolution) and biological (botanic marks on the vines) variables were used on the two experimental plots in the village of Waldrach (Trier, region of Rhineland-Palatinate). The results showed high infiltration rates (near 100 %) and subsurface flow which were detected by rainfall simulations performed at different times of the year (between September and December). The highest variations of the monitored rills (lateral and frontal movements) were noted before and during vintage, when footsteps occurred concentrated during a short period of time (between September and October). Finally, two maps of soil loss were generated, indicated by botanic marks on the graft union of the vines. 62.5 t ha−1 yr−1 soil loss was registered in the experimental plots of the new vineyards (2 years), while 3.4 t ha−1 yr−1 was recorded in the old one (35 years).

Litter contribution to soil organic carbon in the processes of agriculture abandon

Abstract: . The mechanisms of litter decomposition, translocation and stabilization into soil layers are fundamental processes in the functioning of the ecosystem, as they regulate the cycle of soil organic matter (SOM) and CO2 emission into the atmosphere. In this study the contribution of litters of different stages of Mediterranean secondary succession on carbon sequestration was investigated, analyzing the role of earthworms in the translocation of SOM into the soil profile. For this purpose the δ13C difference between meadow C4-C soil and C3-C litter was used in a field experiment. Four undisturbed litters of different stages of succession (45, 70, 100 and 120 since agriculture abandon) were collected and placed on the top of isolated C4 soil cores. The litter contribution to C stock was affected by plant species and it increased with the age of the stage of secondary succession. One year after the litter position, the soil organic carbon increased up to 40% in comparison to soils not treated with litter after 120 years of abandon. The new carbon derived from C3 litter was decomposed and transferred into soil profile thanks to earthworms and the leaching of dissolved organic carbon. After 1 year the carbon increase attributed to earthworm activity was 6 and 13% in the soils under litter of fields abandoned for 120 and 45 years, respectively.

Thickness of the lithosphere beneath Turkey and surroundings from S-receiver functions

Abstract: . We analyze S-receiver functions to investigate variations of lithospheric thickness below the entire region of Turkey and surrounding areas. The teleseismic data used here have been compiled combining all permanent seismic stations which are open to public access. We obtained almost 12 000 S-receiver function traces characterizing the seismic discontinuities between the Moho and the discontinuity at 410 km depth. Common-conversion-point stacks yield well-constrained images of the Moho and of the lithosphere–asthenosphere boundary (LAB). Results from previous studies suggesting shallow LAB depths between 80 and 100 km are confirmed in the entire region outside the subduction zones. We did not observe changes in LAB depths across the North and East Anatolian faults. To the east of Cyprus, we see indications of the Arabian LAB. The African plate is observed down to about 150 km depth subducting to the north and east between the Aegean and Cyprus with a tear at Cyprus. We also observed the discontinuity at 410 km depth and a negative discontinuity above the 410, which might indicate a zone of partial melt above this discontinuity.

Reducing sediment concentration and soil loss using organic and inorganic amendments at plot scale

Abstract: . Various organic and inorganic mulches are used for soil conservation purposes, the effectiveness of which on soil characteristics has not been comprehensively considered from different aspects. The present study surveys the efficiency of straw mulch, manure and TA-200 polyacrylamide with respective rates of 500, 300 and 50 g m−2 in changing sediment concentration and soil loss. The experiments were conducted for sandy-loam soil taken from a summer rangeland, the Alborz Mountains, northern Iran. The experiments were performed under laboratory conditions with simulated rainfall intensities of 30, 50, 70 and 90 mm h−1 and a slope of 30%. The results showed that the straw mulch decreased soil erosion at rate of 45.60% compared to the control plots and performed better than manure (8.98% reduction) and PAM (4.74% reduction). The results showed that the maximum reduction in sediment concentration and soil loss for all soil amendments occurred at the rainfall intensity of 90 mm h−1 with the rates of 58.69 and 63.24% for straw mulch, 14.65 and 13.14% for manure and 20.15 and 23.44% for TA-200.

Soil organic carbon along an altitudinal gradient in the Despeñaperros Natural Park, southern Spain

Abstract: . Soil organic carbon (SOC) is extremely important in the global carbon (C) cycle as C sequestration in non-disturbed soil ecosystems can be a C sink and mitigate greenhouse-gas-driven climate change. Soil organic carbon changes in space and time are relevant to understand the soil system and its role in the C cycle. This is why the influence of topographic position on SOC should be studied. Seven topographic positions from a toposequence between 607 and 1168 m were analyzed in the Despenaperros Natural Park (Jaen, SW Spain). Depending on soil depth, one to three control sections (0–25, 25–50 and 75 cm) were sampled at each site. The SOC content in studied soils was below 30 g kg−1 and strongly decreases with depth. These results were related to the gravel content and to the bulk density. The SOC content from the topsoil (0–25 cm) varied largely through the altitudinal gradient ranging between 27.3 and 39.9 g kg−1. The SOC stock (SOCS) varied between 53.8 and 158.0 Mg ha−1 in the studied area, which had been clearly conditioned by the topographic position. Therefore, results suggest that elevation should be included in SOCS models and estimations at local and regional scales.

Understanding the factors influencing rill erosion on roadcuts in the south eastern region of South Africa

Abstract: . Erosion on roadcuts is a concern due to the potential of causing environmental degradation, which has significant economic costs. It is therefore critical to understand the relationship between roadcut characteristics and soil erosion for designing roadcuts that are less vulnerable to erosion and to help road rehabilitation works. This study investigated the characteristics (i.e. gradient, length, percentage of vegetation cover and soil texture) of degraded (i.e. with rills) and non-degraded roadcuts (i.e. without rills) and explored the relationship of the roadcut characteristics with the dimensions (widths and depths) of the rills. Degraded roadcuts were steep (52.21°), long (10.70 m) and had a low percentage of vegetation cover (24.12) when compared to non-degraded roadcuts which had a gradient of 28.24°, length of 6.38 m and 91.7% of vegetation cover. Moreover, the gradient and percentage of vegetation cover of the roadcut significantly determine the rill dimensions. The widths and depths of the rills increase with the increase in slope gradient and decrease with an increase in percentage of vegetation cover. Moreover, the widths and depths of the rills decreased downslope of the roadcuts. Based on these results, re-vegetation of roadcuts as well as construction of gentle gradients could minimise rill erosion and hence the negative on-site and off-site effects.

Assessment of environmental soil quality around Sonepur Bazari mine of Raniganj coalfield, India

Abstract: . Assessment of soil quality is one of the key parameters for evaluation of environmental contamination in the mining ecosystem. To investigate the effect of coal mining on soil quality, opencast and underground mining sites were selected in the Raniganj coalfield area, India. The physical, chemical, and biological parameters of the soils, and trace metals and PAHs (polycyclic aromatic hydrocarbons) in the soils were evaluated. Soil dehydrogenase (+79 %) and fluorescein (+32 %) activities were significantly higher in underground mine (UGM) soil, whereas peroxidase activity (+57 %) was higher in opencast mine (OCM) soil. Content of As, Be, Co, Cr, Cu, Mn, Ni, and Pb was significantly higher in OCM soil, whereas Cd was higher in UGM. In general, the PAHs contents were higher in UGM soils, probably due to the natural coal burning at these sites. The observed values for the above properties were converted into a unitless score (0–1.00) and the scores were integrated into an environmental soil quality index (ESQI). In the unscreened index (ESQI-1) all the soil parameters were included and the results showed that the quality of the soil was better for UGM (0.539) than the OCM (0.511) soils. Principal component analysis was employed to derive ESQI-2 and accordingly, total PAHs, loss on ignition, bulk density, Be, Co, Cr, Ni, Pb, and microbial quotient (respiration: microbial biomass ratio) were found to be the most critical properties. The ESQI-2 was also higher for soils near UGM (+10.1 %). The observed indicators and the ESQI results revealed that soil quality assessment for these coal mining soils is largely depended on soil PAHs and potentially toxic trace metals. The proposed ESQI may be further refined by incorporating specific parameters related to human exposure risks and exposure pathways.

Aggregate breakdown and surface seal development influenced by rain intensity, slope gradient and soil particle size

Abstract: . Aggregate breakdown is an important process which controls infiltration rate (IR) and the availability of fine materials necessary for structural sealing under rainfall. The purpose of this study was to investigate the effects of different slope gradients, rain intensities and particle size distributions on aggregate breakdown and IR to describe the formation of surface seal. To address this issue, 60 experiments were carried out in a 35 × 30 × 10 cm detachment tray using a rainfall simulator. By sieving a sandy loam soil, two sub-samples with different maximum aggregate sizes of 2 mm (Dmax2 mm) and 4.75 mm (Dmax4.75 mm) were prepared. The soils were exposed to two different rain intensities (57 and 80 mm h−1) on several slopes (0.5, 2.5, 5, 10 and 20%) each at three replicates. The result showed that for all slope gradients and rain intensities, the most fraction percentages in soils Dmax2 and Dmax4.75 mm were in the finest size classes of 0.02 and 0.043 mm, respectively. The soil containing finer aggregates exhibited higher transportability of pre-detached material than the soil containing larger aggregates. Also, IR increased with increasing slope gradient, rain intensity and aggregate size under unsteady state conditions because of less development of surface seal. However, under steady state conditions, no significant relationship was found between slope and IR. The findings of this study revealed the importance of rain intensity, slope steepness and soil aggregate size on aggregate breakdown and seal formation, which can control infiltration rate and the consequent runoff and erosion rates.

Soil aggregation, erodibility, and erosion rates in mountain soils (NW Alps, Italy)

Abstract: . Erosion is a relevant soil degradation factor in mountain agrosilvopastoral ecosystems that can be enhanced by the abandonment of agricultural land and pastures left to natural evolution. The on-site and off-site consequences of soil erosion at the catchment and landscape scale are particularly relevant and may affect settlements at the interface with mountain ecosystems. RUSLE (Revised Universal Soil Loss Equation) estimates of soil erosion consider, among others, the soil erodibility factor (K), which depends on properties involved in structure and aggregation. A relationship between soil erodibility and aggregation should therefore be expected. However, erosion may limit the development of soil structure; hence aggregates should not only be related to erodibility but also partially mirror soil erosion rates. The aim of the research was to evaluate the agreement between aggregate stability and erosion-related variables and to discuss the possible reasons for discrepancies in the two kinds of land use considered (forest and pasture). Topsoil horizons were sampled in a mountain catchment under two vegetation covers (pasture vs. forest) and analyzed for total organic carbon, total extractable carbon, pH, and texture. Soil erodibility was computed, RUSLE erosion rate was estimated, and aggregate stability was determined by wet sieving. Aggregation and RUSLE-related parameters for the two vegetation covers were investigated through statistical tests such as ANOVA, correlation, and regression. Soil erodibility was in agreement with the aggregate stability parameters; i.e., the most erodible soils in terms of K values also displayed weaker aggregation. Despite this general observation, when estimating K from aggregate losses the ANOVA conducted on the regression residuals showed land-use-dependent trends (negative average residuals for forest soils, positive for pastures). Therefore, soil aggregation seemed to mirror the actual topsoil conditions better than soil erodibility. Several hypotheses for this behavior were discussed. A relevant effect of the physical protection of the organic matter by the aggregates that cannot be considered in $K$ computation was finally hypothesized in the case of pastures, while in forests soil erodibility seemed to keep trace of past erosion and depletion of finer particles. A good relationship between RUSLE soil erosion rates and aggregate stability occurred in pastures, while no relationship was visible in forests. Therefore, soil aggregation seemed to capture aspects of actual vulnerability that are not visible through the erodibility estimate. Considering the relevance and extension of agrosilvopastoral ecosystems partly left to natural colonization, further studies on litter and humus protective action might improve the understanding of the relationship among erosion, erodibility, and structure.

Vegetation in karst terrain of southwestern China allocates more biomass to roots

Abstract: . In mountainous areas of southwestern China, especially Guizhou province, continuous, broadly distributed karst landscapes with harsh and fragile habitats often lead to land degradation. Research indicates that vegetation located in karst terrains has low aboveground biomass and land degradation that reduces vegetation biomass, but belowground biomass measurements are rarely reported. Using the soil pit method, we investigated the root biomass of karst vegetation in five land cover types: grassland, grass–scrub tussock, thorn–scrub shrubland, scrub–tree forest, and mixed evergreen and deciduous forest in Maolan, southern Guizhou province, growing in two different soil-rich and rock-dominated habitats. The results show that roots in karst vegetation, especially the coarse roots, and roots in rocky habitats are mostly distributed in the topsoil layers (89 % on the surface up to 20 cm depth). The total root biomass in all habitats of all vegetation degradation periods is 18.77 Mg ha−1, in which roots in rocky habitat have higher biomass than in earthy habitat, and coarse root biomass is larger than medium and fine root biomass. The root biomass of mixed evergreen and deciduous forest in karst habitat (35.83 Mg ha−1) is not greater than that of most typical, non-karst evergreen broad-leaved forests in subtropical regions of China, but the ratio of root to aboveground biomass in karst forest (0.37) is significantly greater than the mean ratio (0.26 ± 0.07) of subtropical evergreen forests. Vegetation restoration in degraded karst terrain will significantly increase the belowground carbon stock, forming a potential regional carbon sink.

Spatial variability of soil properties and soil erodibility in the Alqueva reservoir watershed

Abstract: . The aim of this work is to investigate how the spatial variability of soil properties and soil erodibility ($K$ factor) were affected by the changes in land use allowed by irrigation with water from a reservoir in a semiarid area. To this end, three areas representative of different land uses (agroforestry grassland, lucerne crop and olive orchard) were studied within a 900 ha farm. The interrelationships between variables were analyzed by multivariate techniques and extrapolated using geostatistics. The results confirmed differences between land uses for all properties analyzed, which was explained mainly by the existence of diverse management practices (tillage, fertilization and irrigation), vegetation cover and local soil characteristics. Soil organic matter, clay and nitrogen content decreased significantly, while the K factor increased with intensive cultivation. The HJ-Biplot methodology was used to represent the variation of soil erodibility properties grouped in land uses. Native grassland was the least correlated with the other land uses. The K factor demonstrated high correlation mainly with very fine sand and silt. The maps produced with geostatistics were crucial to understand the current spatial variability in the Alqueva region. Facing the intensification of land-use conversion, a sustainable management is needed to introduce protective measures to control soil erosion.

Responses of vertical soil moisture to rainfall pulses and land uses in a typical loess hilly area, China

Abstract: . Soil moisture plays a key role in vegetation restoration and ecosystem stability in arid and semiarid regions. The response of soil moisture to rainfall pulses is an important hydrological process, which is strongly influenced by land use during the implementation of vegetation restoration. In this study, vertical soil moisture variations of woodland (Pinus tabulaeformis), native grassland (Stipa bungeana), shrubland (Hippophea rhamnoides), cropland (Triticum aestivum) and artificial grassland (Onobrychis viciaefolia) in five soil profiles were monitored in a typical loess hilly area during the 2010 growing season. The results demonstrated that rainfall pulses directly affected soil moisture variation. A multi-peak pattern of soil moisture appeared during the growing season, notably in the surface soil layer. Meanwhile, the response of each vegetation type to rainfall was inconsistent, and a time-lag effect before reaching the peak value was detected, following each heavy rainfall event. The response duration of soil moisture, however, varied markedly with the size of rainfall events. Furthermore, higher soil water content was detected in grassland and shrubland. Woodland was characterized by relatively lower soil moisture values throughout the investigation period. Our research suggests that vegetation restoration efforts should give priority to grassland and shrubland at the research site. We suggest that more studies should be focused on the characteristics of community structure and spatial vegetation distribution on soil moisture dynamics, particularly within the grass and shrub ecosystems.

Changes in soil quality after converting Pinus to Eucalyptus plantations in southern China

Abstract: . Vegetation plays a key role in maintaining soil quality, but long-term changes in soil quality due to plant species change and successive planting are rarely reported. Using the space-for-time substitution method, adjacent plantations of Pinus and first, second, third and fourth generations of Eucalyptus in Guangxi, China were used to study changes in soil quality caused by converting Pinus to Eucalyptus and successive Eucalyptus planting. Soil chemical and biological properties were measured and a soil quality index was calculated using principal component analysis. Soil organic carbon, total nitrogen, alkaline hydrolytic nitrogen, microbial biomass carbon, microbial biomass nitrogen, cellobiosidase, phenol oxidase, peroxidase and acid phosphatase activities were significantly lower in the first and second generations of Eucalyptus plantations compared with Pinus plantation, but they were significantly higher in the third and fourth generations than in the first and second generations and significantly lower than in Pinus plantation. Soil total and available potassium were significantly lower in Eucalyptus plantations (1.8–2.5 g kg−1 and 26–66 mg kg−1) compared to the Pinus plantation (14.3 g kg−1 and 92 mg kg−1), but total phosphorus was significantly higher in Eucalyptus plantations (0.9–1.1 g kg−1) compared to the Pinus plantation (0.4 g kg−1). As an integrated indicator, soil quality index was highest in the Pinus plantation (0.92) and lowest in the first and second generations of Eucalyptus plantations (0.24 and 0.13). Soil quality index in the third and fourth generations (0.36 and 0.38) was between that in Pinus plantation and in first and second generations of Eucalyptus plantations. Changing tree species, reclamation and fertilization may have contributed to the change observed in soil quality during conversion of Pinus to Eucalyptus and successive Eucalyptus planting. Litter retention, keeping understorey coverage, and reducing soil disturbance during logging and subsequent establishment of the next rotation should be considered to help improving soil quality.

Karst bare slope soil erosion and soil quality: a simulation case study

Abstract: . The influence on soil erosion by different bedrock bareness ratios, different rainfall intensities, different underground pore fissure degrees and rainfall duration are researched through manual simulation of microrelief characteristics of karst bare slopes and underground karst crack construction in combination with artificial simulation of rainfall experiment. The results show that firstly, when the rainfall intensity is small (30 and 50 mm h−1), no bottom load loss is produced on the surface, and surface runoff, underground runoff and sediment production are increased with the increasing of rainfall intensity. Secondly, surface runoff and sediment production reduced with increased underground pore fissure degree, while underground runoff and sediment production increased. Thirdly, raindrops hit the surface, forming a crust with rainfall duration. The formation of crusts increases surface runoff erosion and reduces soil infiltration rate. This formation also increases surface-runoff-erosion-damaged crust and increased soil seepage rate. Raindrops continued to hit the surface, leading the formation of crust. Soil permeability showed volatility which was from reduction to increases, reduction, and so on. Surface and subsurface runoff were volatile with rainfall duration. Fourthly, when rock bareness ratio is 50 % and rainfall intensities are 30 and 50 mm h−1, runoff is not produced on the surface, and the slope runoff and sediment production present a fluctuating change with increased rock bareness ratio. Fifthly, the correlation degree between the slope runoff and sediment production and all factors are as follows: rainfall intensity-rainfall duration-underground pore fissure degree–bedrock bareness ratio.

Effects of rodent-induced land degradation on ecosystem carbon fluxes in an alpine meadow in the Qinghai–Tibet Plateau, China

Abstract: . The widespread land degradation in an alpine meadow ecosystem would affect ecosystem carbon (C) balance. Biomass, soil chemical properties and carbon dioxide (CO2) of six levels of degraded lands (D1–D6, according to the number of rodent holes and coverage) were investigated to examine the effects of rodent-induced land degradation on an alpine meadow ecosystem. Soil organic carbon (SOC), labile soil carbon (LC), total nitrogen (TN) and inorganic nitrogen (N) were obtained by chemical analysis. Soil respiration (Rs), net ecosystem exchange (NEE) and ecosystem respiration (ER) were measured by a Li-Cor 6400XT. Gross ecosystem production (GEP) was the sum of NEE and ER. Aboveground biomass (AGB) was based on a linear regression with coverage and plant height as independent variables. Root biomass (RB) was obtained by using a core method. Soil respiration, ER, GEP and AGB were significantly higher in slightly degraded (D3 and D6, group I) than in severely degraded land (D1, D2, D4 and D5, group II). Positive values of NEE average indicate that the alpine meadow ecosystem is a weak C sink during the growing season. The only significant difference was in ER among different degradation levels. Rs, ER and GEP were 38.2, 44.3 and 46.5% higher in group I than in group II, respectively. Similar difference of ER and GEP between the two groups resulted in an insignificant difference of NEE. Positive correlations of AGB with ER, NEE and GEP, and relatively small AGB and lower CO2 fluxes in group II, suggest the control of AGB on ecosystem CO2 fluxes. Correlations of RB with SOC, LC, TN and inorganic N indicate the regulation of RB on soil C and N with increasing number of rodent holes in an alpine meadow ecosystem in the permafrost region of the Qinghai–Tibet Plateau (QTP).

A lithosphere-scale structural model of the Barents Sea and Kara Sea region

Abstract: . We introduce a regional 3-D structural model of the Barents Sea and Kara Sea region which is the first to combine information on the sediments and the crystalline crust as well as the configuration of the lithospheric mantle. Therefore, we have integrated all available geological and geophysical data, including interpreted seismic refraction and reflection data, seismological data, geological maps and previously published 3-D models into one consistent model. This model resolves four major megasequence boundaries (earliest Eocene, mid-Cretaceous, mid-Jurassic and mid-Permian) the top crystalline crust, the Moho and a newly calculated lithosphere–asthenosphere boundary (LAB). The thickness distributions of the corresponding main megasequences delineate five major subdomains (the northern Kara Sea, the southern Kara Sea, the eastern Barents Sea, the western Barents Sea and the oceanic domain comprising the Norwegian–Greenland Sea and the Eurasia Basin). Relating the subsidence histories of these subdomains to the structure of the deeper crust and lithosphere sheds new light on possible causative basin forming mechanisms that we discuss. The depth configuration of the newly calculated LAB and the seismic velocity configuration of the upper mantle correlate with the younger history of this region. The western Barents Sea is underlain by a thinned lithosphere (80 km) resulting from multiple Phanerozoic rifting phases and/or the opening of the NE Atlantic from Paleocene/Eocene times on. Notably, the northwestern Barents Sea and Svalbard are underlain by thinnest continental lithosphere (60 km) and a low-velocity/hot upper mantle that correlates spatially with a region where late Cenozoic uplift was strongest. As opposed to this, the eastern Barents Sea is underlain by a thicker lithosphere (~ 110–150 km) and a high-velocity/density anomaly in the lithospheric mantle. This anomaly, in turn, correlates with an area where only little late Cenozoic uplift/erosion was observed.

Soil physical quality changes under different management systems after 10 years in the Argentine humid pampa

Abstract: . South American countries with the highest surface of land under no-tillage (NT) management are Brazil, Argentina and Chile. In Argentina, 78.5% of the agricultural land is cropped under NT management. Several experiments have confirmed the improvements in soil aggregation and infiltration achieved by NT management in dry-land farming areas associated with increases of bulk density (δb) under NT management. An increase in bulk density implies a reduction of the macro and mesoporosity that is in contradiction with the increased infiltration that occurs at macro and mesopores. We hypothesize that the increase of bulk density in NT management mainly affects the mesopores. We evaluated the evolution of the soil physical parameters in three management systems in four farmers' fields. We found that the reduction in total porosity under NT management is mainly a product of a reduction in the percentage of mesopores in the soil. In this work, the results indicate a modification of some soil physical parameters (porosity, near-saturated hydraulic conductivity, soil structure) due to uninterrupted agricultural production, but the management system did not affect the yields of crop.

Land use effects on soil organic carbon sequestration in calcareous leptosols in former pastureland - a case study from the Tatra Mountains (Poland)

Abstract: . The purpose of the paper is to describe soil organic carbon (SOC) sequestration rates in calcareous shallow soils in reforested areas in the Tatra Mountains with a particular focus on different forms of organic matter (OM) storage. Three plant communities creating a mosaic on the slopes of the studied valley were taken into account. Fifty years since the conversion of pastureland to unused grassland, dwarf pine shrub and larch forest have emerged in the study area, along with the development of genetic soil horizons as well as SOC sequestration in the soil despite the steepness of slopes. SOC stock was measured to be the highest in soils under larch forest (63.5 Mg ha−1), while in soil under grassland and under dwarf pine shrub, this value was found to be smaller (47.5 and 42.9 Mg ha−1, respectively). The highest amount of mineral-associated OM inside stable microaggregates (MOM FF3) was found in grassland soil (21.9–27.1 % of SOC) and less under dwarf pine shrub (16.3–19.3 % of SOC) and larch forest (15.3–17.7 % of SOC). A pool of mineral-associated OM inside transitional macroaggregates (MOM FF2) was found in soil under dwarf pine shrub (39.2–59.2 % of SOC), with less under larch forest (43.8–44.7 % of SOC) and the least in grassland soil (37.9–41.6 % of SOC). The highest amount of the free light particulate fraction (POM LF1) was found in soil under dwarf pine shrub (6.6–10.3 % of SOC), with less under larch forest (2.6–6.2 % of SOC) and the least in grassland soil (1.7–4.8 % of SOC).

Predicting parameters of degradation succession processes of Tibetan Kobresia grasslands

Abstract: . In the past two decades, increasing human activity (i.e., overgrazing) in the Tibetan Plateau has strongly influenced plant succession processes, resulting in the degradation of alpine grasslands. Therefore, it is necessary to diagnose the degree of degradation to enable implementation of appropriate management for sustainable exploitation and protection of alpine grasslands. Here, we investigated environmental factors and plant functional group (PFG) quantity factors during the alpine grassland succession processes. Principal component analysis (PCA) was used to identify the parameters indicative of degradation. We divided the entire degradation process into six stages. PFG types shifted from rhizome bunchgrasses to rhizome plexus and dense-plexus grasses during the degradation process. Leguminosae and Gramineae plants were replaced by sedges during the advanced stages of degradation. The PFGs were classified into two reaction groups: the grazing-sensitive group, containing Kobresia humilis Mey, and Gramineae and Leguminosae plants, and the grazing-insensitive group, containing Kobresia pygmaea Clarke. The first group was correlated with live root biomass in the surface soil (0–10 cm), whereas the second group was strongly correlated with mattic epipedon thickness and K. pygmaea characteristics. The degree of degradation of alpine meadows may be delineated by development of mattic epipedon and PFG composition. Thus, meadows could be easily graded and their use adjusted based on our scaling system, which would help prevent irreversible degradation of important grasslands. Because relatively few environmental factors are investigated, this approach can save time and labor to formulate a conservation management plan for degraded alpine meadows.

A Web-based spatial decision supporting system for land management and soil conservation

Abstract: . Today it is evident that there are many contrasting demands on our landscape (e.g. food security, more sustainable agriculture, higher income in rural areas, etc.) as well as many land degradation problems. It has been proved that providing operational answers to these demands and problems is extremely difficult. Here we aim to demonstrate that a spatial decision support system based on geospatial cyberinfrastructure (GCI) can address all of the above, so producing a smart system for supporting decision making for agriculture, forestry, and urban planning with respect to the landscape. In this paper, we discuss methods and results of a special kind of GCI architecture, one that is highly focused on land management and soil conservation. The system allows us to obtain dynamic, multidisciplinary, multiscale, and multifunctional answers to agriculture, forestry, and urban planning issues through the Web. The system has been applied to and tested in an area of about 20 000 ha in the south of Italy, within the framework of a European LIFE+ project (SOILCONSWEB). The paper reports – as a case study – results from two different applications dealing with agriculture (olive growth tool) and environmental protection (soil capability to protect groundwater). Developed with the help of end users, the system is starting to be adopted by local communities. The system indirectly explores a change of paradigm for soil and landscape scientists. Indeed, the potential benefit is shown of overcoming current disciplinary fragmentation over landscape issues by offering – through a smart Web-based system – truly integrated geospatial knowledge that may be directly and freely used by any end user ( www.landconsultingweb.eu ). This may help bridge the last very important divide between scientists working on the landscape and end users.