Morphology and controlling factors of the longitudinal profile of gullies in the Yuanmou dry-hot valley

The morphology of the gully longitudinal profile (GLP) is an important topographic index of the gully bottom associated with the evolution of the gullies. This index can be used to predict the development trend and evaluate the eroded volumes and soil losses by gullying. To depict the morphology of GLP and understand its controlling factors, the Global Positioning System Real-time Kinematic (GPS RTK) and the total station were used to measure the detail points along the gully bottom of 122 gullies at six sites of the Yuanmou dry-hot Valley. Then, nine parameters including length (Lt), horizontal distance (Dh), height (H), vertical erosional area (A), vertical curvature (Cv), concavity (Ca), average gradient (Ga), gully length-gradient index (GL), normalized gully length-gradient index (Ngl), were calculated and mapped using CASS, Excel and SPSS. The results showed that this study area is dominated by slightly concave and medium gradient GLPs, and the lithology of most gullies is sandstone and siltstone. Although different types of GLPs appear at different sites, all parameters present a positively skewed distribution. There are relatively strong correlations between several parameters: namely Lt and H, Dh and H, Lt and A, Dh and A, H and GL. Most GLPs, except three, have a best fit of exponential functions with quasistraight shapes. Soil properties, vegetation coverage, piping erosion and topography are important factors to affect the GLP morphology. This study provides useful insight into the knowledge of GLP morphology and its influential factors that are of critical importance to prevent and control gully erosion.     

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.     

Reasonable selection of yield criteria for quantitative analysis of unsaturated soil slope stability

The yield criterion parameters of the soil material change with different values of the cohesion and the angle of friction because of sustained rainfall infiltration. Based on the Mohr-Coulomb(M-C) and Drucker-Prager(D-P) yield criteria, some reasonable yield criteria selections were discussed for quantitative analysis of unsaturated soil slope stability. Moreover, a critical point was found at the effective angle of friction equaling to 16.5° by transformation of parameters related to unsaturated soil under sustained rainfall. When the effective angle of friction more than 16.5° through parameter transformation of different yield criteria under natural condition, the calculation result of the safety factor was such that: f(DP1) f(M-C) f(equivalent M-C) f(DP2) f(DP3). While the effective angle of friction less than 16.5°, through parameter transformation, the safety factors were in the following order: f(DP1) f(M-C) f(DP2) f(equivalent M-C) f(DP3). The calculated results from a case study showed that the equivalent M-C yield criterion should be the best at evaluating soil slope stability before rainfall; the DP2 yield criterion should be selected to calculate the soil slope stability at the effective angle of friction less than 16.5° under sustained rainfall. The yield criterion should be selected or adjusted reasonably to calculate the safety factor of unsaturated soil slopes before and during sustained rainfall.     

Spatio-temporal Variation of Soil Respiration and Its Driving Factors in Semi-arid Regions of North China

Soil respiration (SR) is the second-largest flux in ecosystem carbon cycling. Due to the large spatio-temporal variability of environmental factors, SR varied among different vegetation types, thereby impeding accurate estimation of CO₂ emissions via SR. However, studies on spatio-temporal variation of SR are still scarce for semi-arid regions of North China. In this study, we conducted 12-month SR measurements in six land-use types, including two secondary forests (Populus tomentosa (PT) and Robinia pseudoacacia (RP)), three artificial plantations (Armeniaca sibirica (AS), Punica granatum (PG) and Ziziphus jujuba (ZJ)) and one natural grassland (GR), to quantify spatio-temporal variation of SR and distinguish its controlling factors. Results indicated that SR exhibited distinct seasonal patterns for the six sites. Soil respiration peaked in August 2012 and bottomed in April 2013. The temporal coefficient of variation (CV) of SR for the six sites ranged from 76.98% to 94.08%, while the spatial CV of SR ranged from 20.28% to 72.97% across the 12-month measurement. Soil temperature and soil moisture were the major controlling factors of temporal variation of SR in the six sites, while spatial variation in SR was mainly caused by the differences in soil total nitrogen (STN), soil organic carbon (SOC), net photosynthesis rate, and fine root biomass. Our results show that the annual average SR and Q₁₀ (temperature sensitivity of soil respiration) values tended to decrease from secondary forests and grassland to plantations, indicating that the conversion of natural ecosystems to man-made ecosystems may reduce CO₂ emissions and SR temperature sensitivity. Due to the high spatio-temporal variation of SR in our study area, care should be taken when converting secondary forests and grassland to plantations from the point view of accurately quantifying CO₂ emissions via SR at regional scales.     

Inbreeding depression on growth and survival of full-sib family of Manila clam (<Emphasis Type="Italic">Ruditapes philippinarum</Emphasis>)

In present study, the inbreeding depression (ID) of growth and survival of Manila clam (Ruditapes philippinarum) was investigated at larval and juvenile stages. Nine inbred families (A ₂, B ₂, C ₂, D ₂, E ₂, F ₂, G ₂, H ₂ and I ₂) were established by mating within nine full-sib families with expected inbreeding coefficient of 0.25. Inbred families showed significant differences in shell length and hatching rate of D-larvae (straight-hinged larvae). The larvae of the nine inbred families grew slower than those of control group (CG), and their ID value ranged from 0.81% ± 6.09% to 16.10% ± 1.49%. The ID value of larval survival rate varied between 27.47% ± 9.36% and 70.50% ± 13.66%. The ID was also detected for juvenile growth in A ₂, B ₂, C ₂, and D ₂, which ranged from 4.60 ± 2.21 to 17.71 ± 7.73. The A ₂ family maintained the highest juvenile survival rate, whereas the other inbred families exhibited ID values varying between 62.79% ± 4.54% and 96.14% ± 0.87%. The linear relationship of estimated ID between growth and survival was negatively correlated (R = ?0.434, P < 0.05). The results of this study suggested that the ID of growth was common at the larval stage but was less prevalent at juvenile stage. In contrast, the ID of survival increased from larval to juvenile stage. A better understanding of the effect of inbreeding may aid to selective breeding of Manila clam.     

Distribution and quantitative zonation of unloading cracks at a proposed large hydropower station dam Site

Rock mass unloading is an important rock engineering problem because unloading may impact the stability of a rock mass slope. Based on hydroelectric engineering principles, this study focuses on the classification of unloading zones to reflect the rock mass structure characteristics. Geological background and slope structure of the study region were considered to investigate the distribution and deformation of the unloading process. Quantitative indices were classified according to the formation mechanisms and the geological exhibition of unloading zones. The P-wave velocity (V _P ), the ratio of the wave velocity (K _V , the ratio of the test P-wave velocity along the adit depth to the P-wave velocity of intact rock), the sum of joint openings every 2 meters (S _t ), and the density of open joints (D _t ) were calculated as quantitative indices for the rock mass unloading zone. The characteristics of the unloading zone of rock mass slopes at the dam site were successfully determined. The method of combining qualitative data with quantitative indices was found to be effective for the classification of slope unloading zones.     

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.     

Identifying the driving factors of sediment delivery ratio on individual flood events in a long-term monitoring headwater basin

The Sediment Delivery Ratio (SDR) has multi-fold environmental implications both in evaluating the soil and water losses and the effectiveness of conservation measures in watersheds. Various factors, including hydrological regime and watershed properties, may influence the SDR at interannual timescales. However, the effect of certain important dynamic factors, such as rainfall peak distribution, runoff erosion power and sediment bulk density, on the sediment delivery ratio of single flood events (SDRe) has received little attention. The Qiaogou headwater basin is in the hilly-gully region of the Chinese Loess Plateau, and it encompasses a 0.45 km2 catchment. Three large-scale field runoff plots at different geomorphological positions were chosen to obtain the observation data, and the 20-year period between 1986 and 2005 is presented. The results showed that the SDRe of the Qiaogou headwaters varied from 0.49 to 2.77. Among the numerous influential factors, rainfall and runoff were the driving factors causing slope erosion and sediment transport. The rainfall erosivity had a significant positive relationship with the sediment transport modulus (R²=0.85, P<0.01) but had no significant relationship with SDRe. The rainfall peak coefficient was significantly positively correlated with the SDRe (R²=0.64, P<0.05), indicating the influence of rainfall energy distribution on the SDRe. The runoff erosion power index was not only significantly related to the sediment transport modulus (R²=0.84, P<0.01) but also significantly related to the SDRe (R²=0.57, P<0.01). In addition, the relative bulk density was significantly related to the SDRe, indicating that hyper-concentrated flow characteristics contributed to more transported sediment in the catchment. Thus, the rainfall peak coefficient, runoff erosion power and sediment relative bulk density could be used as dynamic indexes to predict the SDRe in the hilly areas of the Chinese Loess Plateau.     

An exploratory analysis of vegetation strategies to reduce shallow landslide activity on loess hillslopes,Northeast Qinghai-Tibet Plateau,China

Heavy summer rainfall induces significant soil erosion and shallow landslide activity on the loess hillslopes of the Xining Basin at the northeast margin of the Qinghai-Tibet Plateau. This study examines the mechanical effects of five native shrubs that can be used to reduce shallow landslide activity. We measured single root tensile resistance and shear resistance, root anatomical structure and direct shear and triaxial shear for soil without roots and five root- soil composite systems. Results show that Atriplex canescens (Pursh) Nutt. possessed the strongest roots, followed by Caragana korshinskii Kom., Zygophyllum xanthoxylon (Bunge) Maxim., Nitraria tangutorum Bobr. and Lycium chinense Mill. Single root strength and shear resistance relationships with root diameter are characterized by power or exponential relations, consistent with the Mohr- Coulomb law. Root mechanical strength reflects their anatomical structure, especially the percentage of phloem and xylem cells, and the degree and speed of periderm lignifications. The cohesion force of root- soil composite systems is notably higher than that of soil without roots, with increasing amplitudes of cohesion force for A. canescens, C. korshinskii, Z. xanthoxylon, N. tangutorum and L. chinense of 75.9%, 75.1%, 36.2%, 24.6% and 17.0 % respectively. When subjected to shear forces, the soil without root samples show much greater lateral deformation thanthe root-soil composite systems, reflecting the restraining effects of roots. Findings from this paper indicate that efforts to reduce shallow landslides in this region by enhancing root reinforcement will be achieved most effectively using A. canescens and C. korshinskii.     

Unusual hydrocarbon waxes detected in <Emphasis Type="Italic">Salix oritrepha</Emphasis> leaf from Nianbaoyeze Mountains,eastern Qinghai-Tibetan Plateau

Plant biomarkers, such as hydrocarbon waxes, are frequently found in various sediments and could be adopted as paleovegetation and paleoclimate indicators. Nevertheless, scarce researches have focused on leaf waxes in higher plants of alpine region. Herein, hydrocarbon leaf wax components of Salix oritrepha, which flourish in Nianbaoyeze Mountains in eastern Tibetan Plateau were fully discussed. The n-alkane distribution in leaves ranges from n-C₂₁ to n-C₂₉ with maxima at n-C₂₅, which were entirely different with Salix taxa displayed in previous surveys in non-alpine regions. The unusual even carbon nalkenes from n-C_22:1 to n-C_30:1, which were thought to appear only in aquatic organisms, were firstly reported in an alpine plant. Additionally, iso-(2-methyl) alkanes, ranging from i-C₂₃ to i-C₂₉ with maxima at i-C₂₅, which have been commonly reported in microorganisms, were also identified in an alpine plant for the first time. Unusual hydrocarbon distribution detected in Salix oritrepha leaf from Nianbaoyeze Mountains is most likely due to the extreme environment in such alpine region.     

Effects of different phosphorus concentrations and N/P ratios on the growth and photosynthetic characteristics of <Emphasis Type="Italic">Skeletonema costatum</Emphasis> and <Emphasis Type="Italic">Prorocentrum donghaiense</Emphasis>

The effects of different phosphorus (P) concentrations (0.36, 3.6, and 36 μmol/L corresponding to low-, middle-, and high-P concentration groups, respectively) and nitrogen (N)/P ratios on the growth and photosynthetic characteristics of Skeletonema costatum and Prorocentrum donghaiense were studied. For both species, the high-P (HP) concentration group showed the greatest algal density and highest specific growth rate. Changes in the maximum efficiency of photosystem II (F _v /F _m ) were monitored under the various P and N/P conditions. The largest decrease in F _v /F _m was in the low-P (LP) group in S. costatum and in the HP group in P. donghaiense. There were high rapid light curves and photochemical quantum yields (Φ _PSII) for S. costatum in the HP group, while the actual photosynthetic capacity was higher in P. donghaiense than in S. costatum in the MP group. Under eutrophic but relatively P-restricted conditions, P. donghaiense had higher photosynthetic activity and potential, which could cause this dinoflagellate to increasingly dominate the phytoplankton community in these conditions. Under the same P concentration and N/P ratio, P. donghaiense had a larger relative maximum rate of electron transport and higher Φ _{PS II} values than those of S. costatum. These differences between P. donghaiense and S. costatum may explain the interaction and succession patterns of these two species in the Changjiang (Yangtze) River estuary from a photosynthesis perspective.     

Estimation of soil reinforcement by the roots of four post-dam prevailing grass species in the riparian zone of Three Gorges Reservoir,China

Soil erosion and bank degradation is a major post-dam concern regarding the riparian zone of the Three Gorges Reservoir. The development and succession of vegetation is a main countermeasure,especially to enhance bank stability and mitigate soil erosion by the root system. In this study, the roots of four prevailing grass species, namely, Cynodon dactylon, Hemarthria altissima, Hemarthria compressa, and Paspalum paspaloides, in the riparian zone were investigated in relation to additional soil cohesion. Roots were sampled using a single root auger. Root length density(RLD) and root area ratio(RAR) were measured by using the Win RHIZO image analysis system. Root tensile strength(TR) was performed using a manualdynamometer, and the soil reinforcement caused by the roots was estimated using the simple Wu's perpendicular model. Results showed that RLD values of the studied species ranged from 0.24 cm/cm3 to20.89 cm/cm3 at different soil layers, and RLD were significantly greater at 0–10 cm depth in comparison to the deeper soil layers(10 cm). RAR measurements revealed that on average 0.21% of the reference soil area was occupied by grass roots for all the investigated species. The measured root tensile strength was the highest for P. paspaloides(62.26MPa) followed by C. dactylon(51.49 MPa), H.compressa(50.66 MPa), and H. altissima(48.81MPa). Nevertheless, the estimated maximum root reinforcement in this investigation was 22.5 k Pa for H.altissima followed by H. compressa(21.1 k Pa), P.paspaloides(19.5 k Pa), and C. dactylon(15.4 k Pa) at0–5 cm depth soil layer. The root cohesion values estimated for all species were generally distributed at the 0–10 cm depth and decreased with the increment of soil depth. The higher root cohesion associated with H. altissima and H. compressa implies their suitability for revegetation purposes to strengthen the shallow soil in the riparian zone of the Three Gorges Reservoir. Although the soil reinforcement induced by roots is only assessed from indirect indicators, the present results still useful for species selection in the framework of implementing and future vegetation recovery actions in the riparian zone of the Three Gorges Reservoir and similar areas in the Yangtze River Basin.     

Carbon budget of bastard halibut<Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> in relation to body weight and temperature

The effects of body weight and temperature on the carbon budget of the juvenile bastard halibut ,Paralichthys olivaceus ,were studied at temperature 13.5,18,21.5 and 24℃,respectively.The carbon intake,faecal and growth carbon were measured ,and the carbon respiration was calculated using the carbon budget equation (Cc=Gc Fc Rc),The combined relationship between different components of the carbon budgent,body weight and temperature could be described by regression equations:Cc=1.0206 W^0.8126E^0.1483T;Gc=0.0042w^1.4096(-5.11 T^3 285.90T^2-5173.72T 30314.03);Fc=0.0485W^0.7711e^0.1624T;Uc=1.4333W^0.6715e^0.1487t,Body weight had no significant effect on the carbon absorption efficiency and the conversion efficiency.     

The influence of environmental variables on distribution patterns of Irano-Turanian forests in Alborz Mountains,Iran

Topographic and edaphic variables are the main ecological factor determining species spatial variability on mountainous forests. A field study was performed in central Alborz to investigate how the edaphic and topographic parameters can affect the tree and shrub communities. Initially, 27 forest stands were identified and the homogeneous units were separated regarding physiognomy. In each single homogeneous unit, one random sample plot (1000 m2) and totally 43 plots were established. In each plot, the presence and abundance of all trees and shrubs were recorded and four soil samples were taken from depths of 0-5 and 5-20 cm. Concerning classification results, eight different forest communities were identified. The lowest and highest soil pH values were observed in Malus orientalis and pistacia-Amygdalus communities, respectively. The water saturation percent of pure- and mixed Juniperus excelsa and Rhus coriaria was the highest amongst communities. The clay content was the highest in pure J. excelsa. The 0-5 organic matter and Nitrogen content in mixed J. excelsa were significantly higher than pure J. excelsa and other communities. The CCA (Canonical Correspondence Analysis) results indicated that the altitude, precipitation, pH, EC, SP, clay and CaCO₃ are the most important factors determine the distribution of trees and shrub in central Alborz     

The influence of plant root system architectural properties upon the stability of loess hillslopes,Northeast Qinghai,China

To investigate the influence of root system architectural properties of three indigenous (cold-adapted) shrubs on the hillslope stability of loess deposits in the Xining Basin, northeast part of Qinghai-Tibet Plateau (QTP), indoor direct shear tests have been conducted on the remolded rooted soil of three shrubs. Test results show that root system architectural indices (root area ratio (RAR), root length density (RLD) and root density (RD)) of the shrubs decline with depth and the relationship between RAR, RD and depth is exponential, while a power relationship describes the relationship between RLD and depth. The cohesion force of remolded rooted soil for the shrubs initially increases with depth, but it then demonstrates a slightly decreasing trend, which can be described with a power relationship. Power relationships also describe relationships between cohesion force and RAR, RLD and RD for the shrubs. As the growth period increases from 10 to 17 months, the incremental increase in RAR is 48.32% ~ 210.25% for Caragana korshinskii Kom and 0.56% ~ 166.85% for Zygophyllum xanthoxylon (Bunge) Maxim. This proportional increase is notably larger than that for RLD and RD. The increment in RAR is marginally greater for C. korshinskii than it is for Z. xanthoxylon. Correspondingly, the cohesion force incremental rates of remolded rooted soil for C. korshinskii and Z. xanthoxylon are 12.41% ~ 25.22% and 3.45% ~ 17.33% respectively. Meanwhile, as root content increases, the contribution by roots to cohesion force increases markedly until a threshold condition is reached.     

Variable hydrological effects of herbs and shrubs in the arid northeastern Qinghai-Tibet Plateau,China

This study aims to assess the hydrological effects of four herbs and four shrubs planted in a selfestablished test area in Xining Basin of northeastern Qinghai-Tibet Plateau, China. The RainfallIntercepting Capability(RIC) of the herbs and shrubs was evaluated in rainfall interception experiment at the end of the third, fourth and fifth month of the growth period in 2007. The leaf transpiration rate and the effects of roots on promoting soil moisture evaporation in these plants were also assessed in transpiration experiment and root-soil composite system evaporation experiment in the five month's growth period. It is found that the RIC of the fourstudied herbs follows the order of E. repens, E. dahuricus, A. trachycaulum and L. secalinus; the RIC of the four shrubs follows the order of A. canescens, Z. xanthoxylon, C. korshinskii and N. tangutorum. The RIC of all the herbs is related linearly to their mean height and canopy area(R~2 ≥ 0.9160). The RIC of all the shrubs bears a logarithmic relationship with their mean height(R~2 ≥ 0.9164), but a linear one with their canopy area(R~2 ≥ 0.9356). Moreover, different species show different transpiration rates. Of the four herbs, E. repens has the highest transpiration rate of 1.07 mg/(m~2·s), and of the four shrubs, A. canescens has the highest transpiration rate(0.74 mg/(m~2·s)). The roots of all the herbs and shrubs can promote soil moisture evaporation. Of the four herbs, the evaporation rate of E. repens root-soil composite system is the highest(2.14%), and of the four shrubs,the root-soil composite system of A. canescens has the highest evaporation rate(1.41%). The evaporation rate of the root-soil composite system of E. dahuricus and Z. xanthoxylon bears a second-power linear relationship with evaporation time(R~2 ≥ 0.9924). The moisture content of all the eight root-soil composite systems decreases exponentially with evaporation time(R~2 ≥ 0.8434). The evaporation rate and moisture content of all the plants' root-soil composite systems increases logarithmically(R~2 ≥ 0.9606) and linearly(R~2 ≥ 0.9777) with root volume density. The findings of this study indicate that among the four herbs and four shrubs, E. repens and A. canescens possess the most effective hydrological effects in reducing the soil erosion and shallow landslide in this region.     

Equality testing for soil grid unit resolutions to polygon unit scales with DNDC modeling of regional SOC pools

Matching soil grid unit resolutions with polygon unit map scales is important to minimize the uncertainty of regional soil organic carbon(SOC) pool simulation due to their strong influences on the modeling.A series of soil grid units at varying cell sizes was derived from soil polygon units at six map scales,namely,1:50 000(C5),1:200 000(D2),1:500 000(P5),1:1 000 000(N1),1:4 000 000(N4) and 1:14 000 000(N14),in the Taihu Region of China.Both soil unit formats were used for regional SOC pool simulation with a De Nitrification-DeC omposition(DNDC) process-based model,which spans the time period from 1982 to 2000 at the six map scales.Four indices,namely,soil type number(STN),area(AREA),average SOC density(ASOCD) and total SOC stocks(SOCS) of surface paddy soils that were simulated by the DNDC,were distinguished from all these soil polygon and grid units.Subjecting to the four index values(IV) from the parent polygon units,the variations in an index value(VIV,%) from the grid units were used to assess its dataset accuracy and redundancy,which reflects the uncertainty in the simulation of SOC pools.Optimal soil grid unit resolutions were generated and suggested for the DNDC simulation of regional SOC pools,matching their respective soil polygon unit map scales.With these optimal raster resolutions,the soil grid units datasets can have the same accuracy as their parent polygon units datasets without any redundancy,when VIV 1% was assumed to be a criterion for all four indices.A quadratic curve regression model,namely,y = – 0.80 × 10~(–6)x~2 + 0.0228 x + 0.0211(R~2 = 0.9994,P 0.05),and a power function model R? = 10.394?~(0.2153)(R~2 = 0.9759,P 0.05) were revealed,which describe the relationship between the optimal soil grid unit resolution(y,km) and soil polygon unit map scale(1:10 000x),the ratio(R?,%) of the optimal soil grid size to average polygon patch size(?,km~2) and the ?,with the highest R~2 among different mathematical regressions,respectively.This knowledge may facilitate the grid partitioning of regions during the investigation and simulation of SOC pool dynamics at a certain map scale,and be referenced to other landscape polygon patches' mesh partition.     

Temporal variations in internal tide multimodal structure on the continental shelf,South China Sea

Temporal variations in multimodal structures of diurnal (D ₁) and semidiurnal (D ₂) internal tides were investigated on the continental slope of the Dongsha Plateau, based on 2-month moored acoustic Doppler current profiler observations. Harmonic analysis indicated that the D ₁ components (K ₁ and O ₁) dominated the internal tide field. The vertical structure of the K ₁ constituent presented a first-mode structure while the M ₂ constituent seemed to exhibit a high-mode structure. Amplitude spectra analysis of the current data revealed differences in baroclinic current amplitudes between different water depths. Temporal variations in modal structures ware analyzed, based on the D ₁ and D ₂ baroclinic tides extracted from the baroclinic velocity field with band-pass filters. Analysis showed that the magnitude of the D ₁ internal tide current was much larger than the D ₂ current, and temporal variations in the modal structure of the D ₁ internal tide occurred on an approximately fortnightly cycle. The EOF analyses revealed temporal transformation of multimodal structures for D ₁ and D ₂ internal tides. The enhancement of the D 1 internal tide was mainly due to the superposition of K ₁ and O ₁, according to the temporal variation of coherent kinetic energy.     

Estimating the properties of weathered bedrock and pilerock interaction from the geological strength index

The effect of variable rock mass properties on pile-rock interaction poses a great challenge to the design of stabilizing piles and numerical analysis of pile-rock interaction. The paper presents a novel method to estimate the properties of weathered bedrock, which can be applied to routine design of landslide-stabilizing piles for collivial landslides. The Ercengyan landslide located in the Three Gorges Reservoir, China, is the area of interest for this study. A geological investigation and triaxial tests were conducted to estimate the basic parameters, including Geological Strength Index(GSI), uniaxial compressive strength σ_(ci) and Hoek-Brown constant m_i of intact bedrock in the study area. Hoek-Brown criterion was used to estimate mechanical properties of the weathered rock, including elastic modulus E_m, cohesion c, friction angle Φ, and normal ultimate lateral resistance p_(max). A parametric study was performed to evaluate the effect of parameterizations of GSI, σ_(ci) and m_i on the bedrock properties and p-y curves. The estimated rock mass properties were used with PLAXIS 2D software to simulate pile-rock interaction. Effect of GSI on stress at the pile-rock interface and in the rock, pile bending moment, pile shear force, and p-y curve were analysed.     

Effects of vegetation coverage and seasonal change on soil microbial biomass and community structure in the dry-hot valley region

Soil microorganisms are sensitive indicator of soil health and quality. Understanding the effects of vegetation biomass and seasonal change on soil microorganisms is vital to evaluate the soil quality and implement vegetation restoration. This study analyzed the soil phospholipid fatty acids (PLFAs) in fresh and withered Kudzu (Pueraria montana var. lobata) vegetation conditions in different seasons. The results showed that vegetation biomass and seasonal change significantly affected microbial biomass and its community structure. Both fresh and withered Kudzu cover significantly increased soil microbial biomass, and the growth effect of microbes in the soil with fresh Kudzu cover was more obvious than that with withered Kudzu cover. Compared with the dry season, the rainy season significantly increased the microbial biomass and the B/F (the ratio of bacterial to fungal PLFAs) ratio but dramatically reduced the G+/G- (the ratio of gram-positive to gram-negative bacteria PLFAs). Kudzu cover and seasonal change had a significant effect on microbial structure in soil covered by higher vegetation biomass. Furthermore, soil temperature and moisture had different correlations with specific microbial biomass in the two seasons. Our findings highlight the effect of Kudzu vine cover on the soil microenvironment and soil microhabitat, enhancing the soil quality in the Dry-hot Valley of Jinsha River, Southwest China.