Historical development in soil micromorphological imaging

The book ＂micropedolog＂ by Kubieana and a large number of publications has induced many people to practice soil micromorphology. Quantification of the soil fabric and its components was a major challenge. The use of the image analyses in soil science was a breakthrough. Attempts to make soil thin sections go back to the beginning of the 2oth century. Microscopic techniques and recently high resolution electron microscope and use of computer assisted imaging techniques enabled the in vitro study of soils in three dimensional levels. It is now possible to store and process massive amounts of data. Micro- morphological concepts and techniques are applied in paleopedological, ecological, and archaeological studies. The aim of this work was to examine soil micromorphological imaging in historical perspective.     

Micromorphological aspects of two forest soils development derived from igneous rocks in Lahijan, Iran

In order to characterize various micromorphologic properties of two forest soils derived from different parent rocks in Lahijan, and use the data collected from micromorphological analysis to interpret dominant pedogenic processes. Two representative soil pedons, granite (P1) and andesitic basalt (P2) were selected in a mountain landform with northwest aspect. Samples for thin section preparation were taken from each horizon by Kubiena boxes or clods. Micromorphological analysis of soils derived from these two soil pedons in eastern part of Lahijan (northern Iran) were conducted based on the physicochemical and mineralogical data. Micromorphological properties were characterized using a polarized light microscope under plain and cross light. Thin section study indicated that the nature of the parent material clearly affected the content of clay formation. It also showed that clay accumulation in the Bt horizons was not only due to clay illuviation (argillan), but that strong in situ weathering of primary minerals also contributed to the enrichment of clay in soils derived from andesitic basalt. Comparing the results of clay mineralogy obtained from X-ray diffraction (XRD) with microscopic studies revealed that birefringence fabric (b-fabric) of the groundmass was partly striated due to smectitic minerals in soil of andesitic basalt (Hapludalf), whereas speckled birefringence fabric was dominant in soil of granite (Udorthent) because of the absence of these minerals. We speculate that pores of skeletal fragments or microcracks in P1 were a place for illuvial clay protection. However, the main factor for illuvial clay film disruption (striation and deformation) was biological activity (faunal turbation and root pressure) in P1 and expandable minerals and faunal turbation in P2.     

Micromorphological-investigation on the Earth's Critical Zone

Soils, the Earth＇s Critical Zone, play a vital and fundamental role in the Earth＇s terrain eco- environment system and human life. Although the concepts of soil/quality and sustainable development have been introduced for decades, we are still failing to understand how well soils function and they need tobe cared and protected. We have been increasingly witnessing and becoming the victim of shrinking forests,     

Regional variation in carbon sequestration potential of forest ecosystems in China

Enhancing forest carbon(C) storage is recognized as one of the most economic and green approaches to offsetting anthropogenic CO_2 emissions. However, experimental evidence for C sequestration potential(C_(sp)) in China's forest ecosystems and its spatial patterns remain unclear, although a deep understanding is essential for policy-makers making decisions on reforestation. Here, we surveyed the literature from 2004 to 2014 to obtain C density data on forest ecosystems in China and used mature forests as a reference to explore C_(sp). The results showed that the C densities of vegetation and soil(0–100 cm) in China's forest ecosystems were about 69.23 Mg C/ha and 116.52 Mg C/ha, respectively. In mature forests, the C_(sp) of vegetation and soil are expected to increase to 129.26 Mg C/ha(87.1%) and 154.39 Mg C/ha(32.4%) in the coming decades, respectively. Moreover, the potential increase of C storage in vegetation(10.81 Pg C) is estimated at approximately twice that of soil(5.01 Pg C). Higher C_(sp) may occur in the subtropical humid regions and policy-makers should pay particular attention to the development of new reforestation strategies for these areas. In addition to soil nutrients and environment, climate was an important factor influencing the spatial patterns of C density in forest ecosystems in China. Interestingly, climate influenced the spatial patterns of vegetation and soil C density via different routes, having a positive effect on vegetation C density and a negative effect on soil C density. This estimation of the potential for increasing forest C storage provided new insights into the vital roles of China's forest ecosystems in future C sequestration. More importantly, our findings emphasize that climate constraints on forest C sequestration should be considered in reforestation strategies in China because the effects of climate were the opposite for spatial patterns of C density in vegetation and soil.Enhancing forest carbon(C) storage is recognized as one of the most economic and green approaches to offsetting anthropogenic CO2 emissions. However, experimental evidence for C sequestration potential(Csp) in China's forest ecosystems and its spatial patterns remain unclear, although a deep understanding is essential for policy-makers making decisions on reforestation. Here, we surveyed the literature from 2004 to 2014 to obtain C density data on forest ecosystems in China and used mature forests as a reference to explore Csp. The results showed that the C densities of vegetation and soil(0–100 cm) in China's forest ecosystems were about 69.23 Mg C/ha and 116.52 Mg C/ha, respectively. In mature forests, the Csp of vegetation and soil are expected to increase to 129.26 Mg C/ha(87.1%) and 154.39 Mg C/ha(32.4%) in the coming decades, respectively. Moreover, the potential increase of C storage in vegetation(10.81 Pg C) is estimated at approximately twice that of soil(5.01 Pg C). Higher Csp may occur in the subtropical humid regions and policy-makers should pay particular attention to the development of new reforestation strategies for these areas. In addition to soil nutrients and environment, climate was an important factor influencing the spatial patterns of C density in forest ecosystems in China. Interestingly, climate influenced the spatial patterns of vegetation and soil C density via different routes, having a positive effect on vegetation C density and a negative effect on soil C density. This estimation of the potential for increasing forest C storage provided new insights into the vital roles of China's forest ecosystems in future C sequestration. More importantly, our findings emphasize that climate constraints on forest C sequestration should be considered in reforestation strategies in China because the effects of climate were the opposite for spatial patterns of C density in vegetation and soil.     

Physico-chemical properties and enzyme activities of the arable soils in Lhasa, Tibet, China

An understanding of the physical,chemical,and biological properties of a soil provides a basis for soil use and management.This paper reports the major physico-chemical properties and enzyme activities of the soils of Lhasa’s main arable lands and the factors that influence these soil properties.Composite and core samples were taken from the three main arable soil types(alluvial soil,subalpine arable steppe soil,and subalpine arable meadow soil) and were analysed using standard methods.The bulk density and the ventilation porosity ratio of the soils were close to the recommended values for arable lands,and the dominant soil texture was sandy.The soil moisture release rates were arable steppe soil > alluvial soil > arable meadow soil.Soil organic matter content,Cation-Exchange Capacity(CEC),total and available nitrogen content,and catalase activity of the arable meadow soil were higher than those of the alluvial and the arable steppe soils,while soil pH in the arable meadow was lower.Most of the measured properties did not show a significant variance among these three soils.However,the measured indices(apart from the total potassium) indicate that there are notable differences among the three types of soil.The results implied that the utilisation patterns of the arable soil or human activities,such as tillage practices and fertiliser applications,have a substantialeffect on the soil properties in this region.Our results suggest that the cultivation practices in the region have apparently positive impact on the soil organic matter,nutrient contents and bulk density probably due to the sound fertiliser management such as the applications of farmyard manure and chemical fertilisers.However,intense cultivation practices lowered the activity of most soil enzymes.The results demonstrate that the choice of soil management strategy had a significant impact on the soil physicochemical and biological properties in the region studied.     

Methodology for the diagnostics of soil polygenesis on the basis of macro- and micromorphological studies

A methodology for studying soil polygenesis and lithological homogeneity of soil profiles is suggested. This methodology is particularly important for mountain soils, where the lithological heterogeneity of the soil profiles created by denudation and accumulation processes is often observed. The methodology includes several stages： （a） the study of the lithological homogeneity/ heterogeneity of soil profiles by field and laboratory methods, （b） the stage-by-stage macro-, meso-, micro-, and submicromorphological analyses of soil profiles with additional use of the methods of neighboring sciences, and （e） the subdivision of soil features into the groups of recent and inherited （relict） features. In the latter group, the subgroups of lithorelict features inherited from the parent material and pedorelict features inherited from the previous stages of soil formation can be distinguished. Two major models of soil polygenesis are suggested. Simple models describe the soils, in which new features appear due to the changes in the environmental conditions in the course of soil evolution. Complex models describe the soils, in which such changes are combined with deposition of new portions of sediments onto the soil surface with the development of buried soil horizons （the synlithogenie pedogenesis）. The models of continuous and discontinuous synlithogenic pedogenesis can be further distinguished. It is argued that the micromorphological method applied to the studies on soil mierofabrics, microforms of soil humus, soil porosity, coatings, and various pedo- and lithorelict features yields valuable information on polygenetic soils.     

Assessment of soil organic carbon stock in the upper Yangtze River basin

Soil organic carbon is of great importance to terrestrial ecosystems.Studies on the amount and spatial distribution of soil organic carbon stock in various types of soil can help to better understand the role of soil in the global carbon cycle and provide a scientific basis for the assessment of the magnitude of carbon stored in a given area.Here we present estimates of soil organic carbon stock in soils in the upper reaches of the Yangtze River based on soil types as defined by Chinese Soil Taxonomy and recently compiled into a digital soil database.The results showed that the total soil organic carbon stock of the upper Yangtze River to a depth of 100 cm was 1.452×1013kg.The highest soil organic carbon stock was found in felty soils(2.419×1012kg),followed by dark brown soils(1.269×1012kg),and dark felty soils(1.139×1012kg).Chernozems and irrigation silting soils showed the lowest soil organic carbon stock,mainly due to the small total area of such soils.The soil organic carbon density of these major soil types ranged from 5.6 to 26.1 kg m-2.The average soil organic carbon density of the upper reaches of the Yangtze River was 16.4 kg m-2,which was higher than that of the national average.Soil organic carbon density indicated a distinct decreasing trend from west to east,which corresponds to the pattern of increasing temperature from cold to subtropical.     

Numerical modeling of shallow water table behavior with Lisse effect

Air entrapment is an important consideration in environments with shallow water tables and sandy soil, like the condition of highly conductive sandy soils and flat topography in Florida, USA. It causes water table rises in soils, which are significantly faster and higher than those in soils without air entrapment. Two numerical models, Integrated Hydrologic Model (IHM) and HYDRUS-1D (a single-phase, one-dimensional Richards′ equation model) were tested at an area of west central Florida to help further understanding the shallow water table behavior during a long term air entrapment. This investigation employed field data with two modeling approaches to quantify the variation of air pressurization values. It was found that the air pressurization effect was responsible at time up to 40 cm of water table rise being recorded by the observation well for these two models. The values of air pressurization calculated from IHM and HYDRUS-1D match the previously published values. Results also indicated that the two numerical models did not consider air entrapment effect (as the predictive parameters remain uncertain) and thus results of depth to water table from these models did not compare to the observations for these selected periods. Incorporating air entrapment in prediction models is critical to reproduce shallow water table observations.     

Empirical Research on Carrying Capacity of Human Settlement System in Dalian City,Liaoning Province,China

Using the theories of population carrying capacity and ecological elasticity in other fields for reference, the connotation of regional human settlement system was defined from the viewpoint of the complex relationship among the factors such as regional population, resources, environment and economic and social development in the context of China′s rapid urbanization. Then the concept and characterization methods of the regional human settlement carrying capacity were proposed by means of population scale. Furthermore, a model of carrying capacity-pressure-state-response(CPSR) on regional human settlement system was established by referencing pressure-state-response(PSR) model, and the Catastrophe Theory was introduced to determine the corresponding standards of multi-criteria programming and evaluation. Taking Dalian City, Liaoning Province, China as an example, an empirical analysis on evaluation of human settlement system from 2000 to 2012 was carried out. The results showed that the carrying capacity of human settlement system in Dalian was fluctuating between 9.6 × 106 to 10 × 106 persons with a quantitative stage of the dynamic regulation. During the research period the load index of human settlement system in Dalian dropped from 0.96 to 0.84 with a lower pressure of human settlement system than the national average level. And the emergency response grades of human settlement system in Dalian were kept in grade Ⅱ(orange warning) or grade Ⅲ(yellow warning). Human settlement system of Dalian was in slight security state as a whole, but the load had a tendency of increase in recent years. The related departments should pay close attention to regional human settlement system and take active measures to improve human settlement by both intensity control and total quantity control. By comparison, analysis and discussion, it was considered that the results were basically accordded with the current situations of human settlement in Dalian, and the evaluation results were more reliable, visualized and easily applied in practice. Therefore, the above-mentioned concepts, characterization and evaluation methods of the regional human settlement system and carrying capacity could provide a new thought and method for quantitative evaluation of human settlement.     

Tillage pedogenesis of purple soils in southwestern China

Land cultivation and tillage process, and their consequent impacts on soil erosion, have been criticized as the main cause of degradation of land or soil quality. However, purple soils, classified as Regosols in FAO Taxonomy or Entisols in USDA Taxonomy, are formed from purple rocks of the Trias- Cretaceous system, have been developed or at least accelerated the development due to continual tillage operation, especially digging and ridging. The present study took micromorphological investigation on the sedimentary rocks and the soils under different operations of tillage. Results show that the purple rock of Feixiangguan Formation of the Trias system （Tlf） is the easiest to physical weathering and the most fertile soil material enriched in nutrients, and it has been, therefore, mostly cultivated and intensively tilled around the year. It has the fastest soil formation rate. Soil formation rate in the cropland with conventional tillage is higher than that in the forestiand and the grassland. It implies that the artificial brokenness and tillage disturbance play a great role in physical weathering and initiating soil formation processes.     

Mapping Soil Salinity Using a Similarity-based Prediction Approach:A Case Study in Huanghe River Delta,China

Spatial distribution of soil salinity can be estimated based on its environmental factors because soil salinity is strongly affected and indicated by environmental factors. Different with other properties such as soil texture, soil salinity varies with short-term time. Thus, how to choose powerful environmental predictors is especially important for soil salinity. This paper presents a similarity-based prediction approach to map soil salinity and detects powerful environmental predictors for the Huanghe(Yellow) River Delta area in China. The similarity-based approach predicts the soil salinities of unsampled locations based on the environmental similarity between unsampled and sampled locations. A dataset of 92 points with salt data at depth of 30–40 cm was divided into two subsets for prediction and validation. Topographical parameters, soil textures, distances to irrigation channels and to the coastline, land surface temperature from Moderate Resolution Imaging Spectroradiometer(MODIS), Normalized Difference Vegetation Indices(NDVIs) and land surface reflectance data from Landsat Thematic Mapper(TM) imagery were generated. The similarity-based prediction approach was applied on several combinations of different environmental factors. Based on three evaluation indices including the correlation coefficient(CC) between observed and predicted values, the mean absolute error and the root mean squared error we found that elevation, distance to irrigation channels, soil texture, night land surface temperature, NDVI, and land surface reflectance Band 5 are the optimal combination for mapping soil salinity at the 30–40 cm depth in the study area(with a CC value of 0.69 and a root mean squared error value of 0.38). Our results indicated that the similarity-based prediction approach could be a vital alternative to other methods for mapping soil salinity, especially for area with limited observation data and could be used to monitor soil salinity distributions in the future.     

An evaluation on using soil aggregate stability as the indicator of interrill erodibility

Aggregate stability is a very important predictor of soil structure and strength,which influences soil erodibility.Several aggregate stability indices were selected for estimating interrill erodibility of four soil types with contrasting properties from temperate and subtropical regions of China.This study was conducted to investigate how closely the soil interrill erodibility factor in the Water Erosion Prediction Project(WEPP) model relates to soil aggregate stability.The mass fractal dimension(FD),geometric mean diameter(GMD),mean weight diameter(MWD),and aggregate stability index(ASI) of soil aggregates were calculated.A rainfall simulator with a drainable flume(3.0 m long × 1.0 m wide × 0.5 m deep) was used at four slope gradients(5°,10°,15° and 20°),and four rainfall intensities(0.6,1.1,1.7 and 2.5 mm/min).Results indicated that the interrill erodibility(Ki) values were significantly correlated to the indices of ASI,MWD,GMD,and FD computed from the aggregate wet-sieve data.The Ki had a strong positive correlation with FD,as well as a strong negative correlation with ASI,GMD,and MWD.Soils with a higher aggregate stability and lower fractal dimension have smaller Ki values.Stable soils were characterized by a high percentage of large aggregates and the erodible soils by a high percentage of smaller aggregates.The correlation coefficients of Ki with ASI and GMD were greater than those with FDand MWD,implying that both the ASI and GMD may be better alternative parameters for empirically predicting the soil Ki factor.ASI and GMD are more reasonable in interrill soil erodibility estimation,compared with Ki calculation in original WEPP model equation.Results demonstrate the validation of soil aggregation characterization as an appropriate indicator of soil susceptibility to erosion in contrasting soil types in China.     

Key variables explaining soil organic carbon content variations in croplands and non-croplands in Chinese provinces

Soil organic carbon (SOC) plays an important role in global carbon cycles.Large spatial variations in SOC contents result in uncertain estimates of the SOC pool and its changes.In the present study,the key variables explaining the SOC contents of croplands (CPs) and non-croplands (NCPs) in Chinese provinces were investigated.Data on SOC and other soil properties (obtained from the Second National Soil Survey conducted in the late 1970s to the early 1990s),climate parameters,as well as the proportion of the CP to the total land area (Pcp) were used.SOC content variations within a province were larger than those among provinces.Soil clay and total phosphorus content,ratio of annual precipitation to mean temperature,as well as Pcp were able to explain 75% of the SOC content variations in whole soil samples.Soil pH,mean temperature during the growing season from May to October,and mean annual wind velocity were able to explain 63% of the SOC content variations in NCP soils.Compared with NCP soils,CP soils had lower SOC contents,with smaller variations within and among provinces and lower C/N ratios.Stepwise regression showed that the soil clay content was a unique factor significantly correlated with the SOC content of CP soils.However,this factor only explained 24% of the variations.This result suggested that variables related to human activities had greater effects on SOC content variations in CP soils than soil properties and climate parameters.Based on SOC contents directly averaged from soil samples and estimated by regression equations,the total SOC pool in the topsoil (0-20 cm) of China was estimated at 60.02 Pg and 57.6 Pg.Thousands of years of intensive cultivation in China resulted in CP topsoil SOC loss of 4.34-4.98 Pg.     

Development and application of an instrument for simulating wetting-drying cycles of expansive soils under loads

Alternating rainfall and evaporation in nature severely impact the shear strength of expansive soils. This study presents an instrument for simulating the effect of wetting–drying cycles on the strength of expansive soils under different loads, and its testing error is verified. With this instrument,direct shear tests were performed on samples experiencing 0-6 cycles under vertical loads of 0 kPa,5 kPa, 15 kPa, and 30 k Pa. The results found that this instrument provides a new method for evaluating the effects of wetting–drying cycles on soils, and this method represents actual engineering conditions more accurately than do preexisting methods. It accurately controls the water content within 1% while simulating the specified loads at different soil depths.Cohesion is significantly affected by wetting–drying cycles, while the friction angle is not as sensitive to these cycles. Decrease in shear strength can be attributed to the fissures in soils caused by wetting–drying cycles. The existence of vertical loads effectively restricts shrinkage fissuring and cohesion attenuation, consequently inhibiting the attenuation of shear strength.     

Litter decay in rangeland sites with varying history of human disturbance: a study with Hazargangi Chiltan mountain

Hazarganji Chiltan National Park in Balochistan, Pakistan was established in 1980 and the protected area was further extended in 1998. Large area of this mountain is still open for unmanaged human disturbances such as collection of wood for fuel purpose and livestock grazing. Removal of vegetation of rangelands has a significant negative impact on soil organic matter(SOM). This research evaluates litter decomposition in three sites of Hazarganji Chiltan mountain with varying history of human disturbances(unprotected site, young protected site and old protected site). Twigs of Pistacia khinjuk with approximately equal weight and length were placed in litter bags of mesh size 2 mm and were buried in 0-5 cm depth in three sites in January. Half of the twigs of each site received rain simulation in April, August, October, November and January while the other half of the twigs were subjected under natural conditions for 15 months. Twigs from each plot of each treatment of each site were collected from soil after every rain simulation in the previous month of experiment and were processed for weight loss assessment. Results showed that weight loss of twigs by decomposition was significantly higher in the soil of unprotected site as compared to other two sites and there was no difference between rain simulation and control treatments except that loss of weight of twigs of unprotected site was higher under control than rain simulation condition. To confirm that SOM was the major controlling factor for the decomposition of litter decay, soils of each site were collected and burned to remove SOM;thereafter, burned soil samples were mixed with homogenous powder of oven-dried native plants, incubated for 6 months and were provided with dissolved organic matter of the soils of each site. Results showed that there was no difference in the decomposition of litter between soils under controlled laboratory condition, which confirmed that SOM was a major controlling factor for the litter decay in soil under field conditions. The pyrosequencing analysis of the DNA of soils collected from three sites revealed the presence of bacterial species Thermovum composti.     

Effects of Anthropogenic Disturbance on Sediment Organic Carbon Mineralization Under Different Water Conditions in Coastal Wetland of a Subtropical Estuary

The changes in soil organic carbon(C) mineralization as affected by anthropogenic disturbance directly determine the role of soils as C source or sink in the global C budget. The objectives of this study were to investigate the effects of anthropogenic disturbance(aquaculture pond, pollutant discharge and agricultural activity) on soil organic C mineralization under different water conditions in the Minjiang River estuary wetland, Southeast China. The results showed that the organic C mineralization in the wetland soils was significantly affected by human disturbance and water conditions(P 0.001), and the interaction between human disturbance activities and water conditions was also significant(P 0.01). The C mineralization rate and the cumulative mineralized carbon dioxide-carbon(CO_2-C)(at the 49th day) ranked from highest to lowest as follows: Phragmites australis wetland soil aquaculture pond sediment soil near the discharge outlet rice paddy soil. This indicated that human disturbance inhibited the mineralization of C in soils of the Minjiang River estuary wetland, and the inhibition increased with the intensity of human disturbance. The data for cumulative mineralized CO_2-C showed a good fit(R~2 0.91) to the first-order kinetic model C_t = C_0(1 – exp(–kt)). The kinetic parameters C_0, k and C_0 k were significantly affected by human disturbance and water conditions. In addition, the total amount of mineralized C(in 49 d) was positively related to C_0, C_0 k and electrical conductivity of soils. These findings indicated that anthropogenic disturbance suppressed the organic C mineralization potential in subtropical coastal wetland soils, and changes of water pattern as affected by human activities in the future would have a strong influence on C cycling in the subtropical estuarine wetlands.     

Lithological indicators of discontinuities in mountain soils rich in calcium carbonate in the Polish Carpathians

Six soils located within the Polish Carpathians,developed on calcium carbonate–rich sedimentary parent materials and representing various reference groups,were investigated in order to detect the lithic discontinuity.We propose using a multidirectional approach to assess the lithic discontinuity in these soils,one that includes grain size distribution,geochemical composition,heavy mineral content and micromorphology,supported by a traditional soil survey.A further aim of this process was to identify the possible admixture of allochthonous material of aeolian origin.The studied soils presented lithic discontinuities mostly at the contact of underlying calcium carbonate–rich coarsegrained slope deposits with the overlaying colluvium layer having a lower content of rock fragments.The significant changes in grain size distribution,especially in the silt and sand content,as well as high Uniformity Values and partially,high Lithological Discontinuity Index values,confirmed the occurrence of a lithic discontinuity in all studied soils.High heterogeneity in the soil profiles was also confirmed by the distribution of the major oxides;however,their distribution did not clearly indicate the lithic discontinuity.The most visible distinctions were noted from CaO content,which resulted from the deposition of carbonate-free materials(aeolian silts)and their mixing with the calcium carbonate–rich parent material.Furthermore,the analysis of heavy mineral content confirmed the allochthonous origin of the upper(and in some cases also the middle)parts of all profiles,which was manifested by the presence of highly weathering-resistant minerals such as zircon,epidote and various types of garnets.The micromorphological features of some of the studied soils showed distinctiveness within the soil profile,manifested by changes in b-fabric pattern,the occurrence and distribution of secondary carbonate and the coarse and fine coarse and fine ratio.Based on the high content of silt within the upper and middle parts of the soils,the content of Hf and Zr,as well as the higher content of weathering-resistant minerals,admixture of aeolian silt could be considered in some of the studied soils,yet with weak character.However,the dominance of minerals typical for metamorphic and igneous rocks suggested that the supply of aeolian silt was associated with loess covers rather than local sedimentary material.     

System Reliability Analysis of an Offshore Jacket Platform

This study investigates strategies for solving the system reliability of large three-dimensional jacket structures.These structural systems normally fail as a result of a series of different components failures.The failure characteristics are investigated under various environmental conditions and direction combinations.Theβ-unzipping technique is adopted to determine critical failure components,and the entire system is simplified as a series-parallel system to approximately evaluate the structural system reliability.However,this approach needs excessive computational effort for searching failure components and failure paths.Based on a trained artificial neural network(ANN),which can be used to approximate the implicit limit-state function of a complicated structure,a new alternative procedure is proposed to improve the efficiency of the system reliability analysis method.The failure probability is calculated through Monte Carlo simulation(MCS)with Latin hypercube sampling(LHS).The features and applicability of the above procedure are discussed and compared using an example jacket platform located in Chengdao Oilfield,Bohai Sea,China.This study provides a reference for the evaluation of the system reliability of jacket structures.     

Dynamic monitoring of soil erosion for upper stream of Miyun Reservoir in the last 30 years

The Revised Universal Soil Loss Equation(RUSLE) was applied to assess the spatial distribution and dynamic properties of soil loss with geographic information system(GIS) and remote sensing(RS) technologies.To improve the accuracy of soil-erosion estimates,a new C-factor estimation model was developed based on land cover and time series normalized difference vegetation index(NDVI) datasets.The new C-factor was then applied in the RUSLE to integrate rainfall,soil,vegetation,and topography data of different periods,and thus monitor the distribution of soil erosion patterns and their dynamics during a 30-year period of the upstream watershed of Miyun Reservoir(UWMR),China.The results showed that the new C-factor estimation method,which considers land cover status and dynamics,and explicitly incorporates within-land cover variability,was more rational,quantitative,and reliable.An average annual soil loss in UWMR of 25.68,21.04,and 16.80 t ha-1a-1was estimated for 1990,2000 and 2010,respectively,corroborated by comparing spatial and temporal variation in sediment yield.Between 2000 and 2010,a 1.38% average annual increase was observed in the area of lands that lost less than 5 t ha-1a-1,while during 1990-2000 such lands only increased on average by 0.46%.Areas that classified as severe,very severe and extremely severe accounted for 5.68% of the total UWMR in 2010,and primarily occurred in dry areas or grasslands of sloping fields.The reason for the change in rate of soil loss is explained by an increased appreciation of soil conservation by developers and planners.Moreover,we recommend that UWMR watershed adopt further conservation measures such as terraced plowing of dry land,afforestation,or grassland enclosures as part of a concerted effort to reduce on-going soil erosion.