Effects of slope gradient on runoff from bare-fallow purple soil in China under natural rainfall conditions

Purple soil is highly susceptible for overland flow and surface erosion, therefore understanding surface runoff and soil erosion processes in the purple soil region are important to mitigate flooding and erosion hazards. Slope angle is an important parameter that affects the magnitude of runoff and thus surface erosion in hilly landscapes or bare land area. However, the effect of slope on runoff generation remains unclear in many different soils including Chinese purple soil. The aim of this study was to investigate the relationship between different slope gradients and surface runoff for bare-fallow purple soil, using 5 m × 1.5 m experimental plots under natural rainfall conditions. Four experimental plots(10°, 16°, 20° and 26°) were established in theYanting Agro-ecological Experimental Station of Chinese Academy of Science in central Sichuan Basin. The plot was equipped with water storage tank to monitor water level change. Field monitoring from July 1 to October 31, 2012 observed 42 rainfall events which produced surface runoff from the experimental plots. These water level changes were converted to runoff. The representative eight rainfall events were selected for further analysis, the relationship between slope and runoff coefficient were determined using ANOVA, F-test, and z-score analysis. The results indicated a strong correlation between rainfall and runoff in cumulative amount basis. The mean value of the measured runoff coefficient for four experimental plots was around 0.1. However, no statistically significant relationship was found between slope and runoff coefficient. We reviewed the relationship between slope and runoff in many previous studiesand calculated z-score to compare with our experimental results. The results of z-score analysis indicated that both positive and negative effects of slope on runoff coefficient were obtained, however a moderate gradient(16°-20° in this study) could be a threshold of runoff generation for many different soils including the Chinese purple soil.     

Enzyme-Induced Carbonate Precipitation for the Protection of Earthen Dikes and Embankments Under Surface Runoff: Laboratory Investigations

Earthen structures such as shore protection dikes and river embankments easily suffer from erosion under surface water runoff.This study made experimental efforts to explore the enzyme-induced carbonate precipitation(EICP)method for slope erosion control under surface runoff for earthen structures.The sandy soils were treated by the EICP method for various rounds.Surface characteristics were evaluated by the surface penetration resistance,calcium carbonate content,and surface hard crust thickness of EICP-treated soils.Slope runoff erosion experiments were carried out to evaluate the erosion control performances of the EICP treatment.The surface penetration resistance,calcium carbonate content,and surface hard crust thickness were found to significantly increase with the treatment rounds.In the erosion experiments,it was observed that the level of damages decreased and the water flow volume required to trigger the damage increased with more treatments.The increase in the soil slope angle led to more serious surface damages.The amount and rate that the soil particles were eroded from the slope surfaces declined with more EICP treatments,which was consistent with those of visual observations.The preliminary investigations presented in this study have shown the potential of the EICP method for slope erosion control under surface runoff for earthen structures.     

Temporal stability of apparent soil electrical conductivity measured by electromagnetic induction techniques

Assessing and managing the spatial variability of hydropedological properties are important in environmental,agricultural,and geological sciences.The spatial variability of soil apparent electrical conductivity（ECa） measured by electromagnetic induction（EMI） techniques has been widely used to infer the spatial variability of hydrological and pedological properties.In this study,temporal stability analysis was conducted for measuring repeatedly soil ECa in an agricultural landscape in 2008.Such temporal stability was statistically compared with the soil moisture,terrain indices（slope,topographic wetness index（TWI）,and profile curvature）,and soil properties（particle size distribution,depth to bedrock,Mn mottle content,and soil type）.Locations with great and temporally unstable soil ECa were also associated with great and unstable soil moisture,respectively.Soil ECa were greater and more unstable in the areas with great TWI（TWI 〉 8）,gentle and concave slope（slope 〈 3%; profile curvature 〉 0.2）.Soil ECa exponentially increased with depth to bedrock,and soil profile silt and Mn mottle contents（R2= 0.57）,quadratically（R2 = 0.47）,and linearly（R 2 = 0.47）,respectively.Soil ECa was greater and more unstable in Gleysol and Nitosol soils,which were distributed in areas with low elevation（〈 380 m）,thick soil solum（〉 3 m）,and fluctuated water table（shallow in winter and spring but deep in summer and fall）.In contrast,Acrisol,Luvisol,and Cambisol soils,which are distributed in the upper slope areas,had lower and more stable soil ECa.Through these observations,we concluded that the temporal stability of soil ECa can be used to interpret the spatial and temporal variability of these hydropedological properties.     

Influences of soil moisture and salt content on loess shear strength in the Xining Basin,northeastern Qinghai-Tibet Plateau

Moisture and salt content of soil are the two predominant factors influencing its shear strength. This study aims to investigate the effects of these two factors on shear strength behavior of loess in the Xining Basin of Northeast Qinghai-Tibet Plateau, where such geological hazards as soil erosion, landslides collapse and debris flows are widespread due to the highly erodible loess. Salinized loess soil collected from the test site was desalinized through salt-leaching in the laboratory. The desalinized and oven-dried loess samples were also artificially moisturized and salinized in order to examine how soil salinity affects its shear strength at different moisture levels. Soil samples prepared in different ways(moisturizing, salt-leaching, and salinized) were measured to determine soil cohesion and internal friction angle. The results show that salt-leaching up to 18 rounds almost completely removed the salt content and considerably changed the physical components of loess, but the soil type remained unchanged. As salt content increases from 0.00% to 12.00%, both the cohesion and internal friction angle exhibit an initial decrease and then increase with salt content. As moisture content is 12.00%, the salt content threshold value for both cohesion and internal friction angle is identified as 3.00%. As the moisture content rises to 16.0% and 20.00%, the salt content threshold value for cohesion is still 6.00%, but 3.00% for internal friction angle. At these thresholds soil shear strength is the lowest, below which it is inversely related to soil salinity. Beyond the thresholds, however, the relationship is positive. Dissimilar to salinity, soil moisture content exerts an adverse effect on shear strength of loess. The findings of this study can provide a valuable guidance on stabilizing the engineering properties of salinized loess to prevent slope failures during heavy rainfall events.     

L波段对不同盐类土壤的微波介电特性分析

 土壤盐碱化是世界面临的一大难题。微波遥感探测土壤具有优势,L波段对土壤含水量和含盐量较为敏感。为了分析不同盐类对土壤介电特性的影响,本文利用L波段(1.43 GHz)微波谐振腔测量了我国盐碱土中普遍存在的3种盐类(NaCl,Na₂SO₄,NaHCO₃)土壤样品的介电常数,研究了土壤介电常数与含水量、含盐量和盐种类的关系。得出结论:实部主要由土壤的含水量决定,含盐量对实部的影响无明显规律;虚部值随含水量和含盐量的增加而增大;3种盐类土壤介电常数虚部随含盐量变化呈现不同的递增趋势,在含盐浓度一定的条件下,虚部值是ε″ _NaCI>ε″ _NaHCO3>ε″ _Na2SO4;在某一含盐量点3种盐类土壤虚部随含水量变化的斜率不同,以此能将3种盐类区分。该研究为建立含不同盐类土壤介电常数模型和微波遥感监测土壤盐碱化提供了实验的依据。     

Assessment of agri-spillways as a soil erosion protection measure in Mediterranean sloping vineyards

Suitable vineyard soils enhance soil stability and biodiversity which in turn protects roots against erosion and nutrient losses. There is a lack of information related to inexpensive and suitable methods and tools to protect the soil in Mediterranean sloping vineyards(25° of slope inclination). In the vineyards of the Montes de Málaga(southern Spain), a sustainable land management practice that controls soil erosion is actually achieved by tilling rills in the down-slope direction to canalize water and sediments. Because of their design and use, we call them agri-spillways. In this research, we assessed two agri-spillways(between 10 m and 15 m length, and slopes between 25.8° and 35°) by performing runoff experiments under extreme conditions(a motor driven pump that discharged water flows up to 1.33 l s~(-1) for 12 to 15 minutes: ≈1000 l). The final results showed: i) a great capacity by these rills to canalize large amounts of water and sediments; and, ii) higher water flow speeds(between 0.16 m s-1 and 0.28 m s~(-1)) and sediment concentrationrates(up to 1538.6 g l~(-1)) than typically found in other Mediterranean areas and land uses(such as badlands, rangelands or extensive crops of olives and almonds). The speed of water flow and the sediment concentration were much higher in the shorter and steeper rill. We concluded that agri-spillways, given correct planning and maintenance, can be a potential solution as an inexpensive method to protect the soil in sloping Mediterranean vineyards.     

Mechanism of slope failure in loess terrains during spring thawing

Slope failure in loess terrains of Northern China during spring thawing period is closely related to the freeze-thaw cycling that surface soils inevitably experienced. Field surveys were carried out on natural and artificial slopes in thirteen surveying sites located in the Northern Shaanxi, the center of Loess Plateau, covering five characteristic topographic features including tablelands, ridges, hills, gullies and valleys. Based on the scale that is involved in freeze-thaw cycling, the induced failures can be classified into three main modes, i.e., erosion, peeling and thaw collapse, depending on both high porosity and loose cementation of loess that is easily affected. Model tests on loess slopes with gradients of 53.1°, 45.0° and 33.7° were carried out to reveal the heat transfer, water migration and deformation during slope failure. The surface morphology of slopes was photographed, with flake shaped erosion and cracks noted. For three slope models, time histories for the thermal regime exhibit three obvious cycles of freeze and thaw andthe maximum frost depth develops downwards as freeze-thaw cycling proceeds. Soil water in the unfrozen domain beneath was migrated towards the slope surface, as can be noticed from the considerable change in the unfrozen water content, almost synchronous with the variation of temperature. The displacement in both vertical and horizontal directions varies over time and three obvious cycles can be traced. The residual displacement for each cycle tends to grow and the slopes with higher gradients are more sensitive to potentially sliding during freeze-thaw cycling.     

The characteristics of rill development and their effects on runoff and sediment yield under different slope gradients

Rill formation is the predominant erosion process in slope land in the Loess Plateau, China. This study was conducted to investigate rill erosion characteristics and their effects on runoff and sediment yielding processes under different slope gradients at a rate of 10°, 15°, 20° and 25° with rainfall intensity of 1.5 mm min-1 in a laboratory setting. Results revealed that mean rill depth and rill density has a positive interrelation to the slope gradient. To the contrary, width-depth ratio and distance of the longest rill to the top of the slope negatively related to slope gradient. All these suggested that increasing slope steepness could enhance rill headward erosion, vertical erosion and the fragmentation of the slope surface. Furthermore,total erosion tended to approach a stable maximum value with increasing slope, which implied that there is probably a threshold slope gradient where soil erosion begins to weaken. At the same time, the correlation analysis showed that there was a close connection between slope gradient and the variousindices of soil erosion: the correlation coefficients of slope gradient with maximal rill depth, number of rills and the distance of the longest rill from the top of the slope were 0.98, 0.97 and-0.98, respectively,indicating that slope gradient is the major factor of affecting the development of rills. Furthermore,runoff was not sensitive to slope gradient and rill formation in this study. Sediment concentration,however, is positively related to slope gradient and rill formation, the sediment concentrations increased rapidly after rill initiation, especially. These results may be essential for soil loss prediction.     

Responses of soil moisture to vegetation restoration type and slope length on the loess hillslope

Soil moisture, a critical variable in the hydrologic cycle, is highly influenced by vegetation restoration type. However, the relationship between spatial variation of soil moisture, vegetation restoration type and slope length is controversial. Therefore, soil moisture across soil layers (0-400 cm depth) was measured before and after the rainy season in severe drought (2015) and normal hydrological year (2016) in three vegetation restoration areas (artificial forestland, natural forestland and grassland), on the hillslopes of the Caijiachuan Catchment in the Loess area, China. The results showed that artificial forestland had the lowest soil moisture and most severe water deficit in 100-200 cm soil layers. Water depletion was higher in artificial and natural forestlands than in natural grassland. Moreover, soil moisture in the shallow soil layers (0-100 cm) under the three vegetation restoration types did not significantly vary with slope length, but a significant increase with slope length was observed in deep soil layers (below 100 cm). In 2015, a severe drought hydrological year, higher water depletion was observed at lower slope positions under three vegetation restoration types due to higher transpiration and evapotranspiration and unlikely recharge from upslope runoff. However, in 2016, a normal hydrological year, there was lower water depletion, even infiltration recharge at lower slope positions, indicating receiving a large amount of water from upslope. Vegetation restoration type, precipitation, slope length and soil depth during a rainy season, in descending order of influence, had significant effects on soil moisture. Generally, natural grassland is more beneficial for vegetation restoration than natural and artificial forestlands, and the results can provide useful information for understanding hydrological processes and improving vegetation restoration practices on the Loess Plateau     

Rainfall and inflow effects on soil erosion for hillslopes dominated by sheet erosion or rill erosion in the Chinese Mollisol region

Erosion agents and patterns profoundly affect hillslope soil loss characteristics. However, few attempts have been made to analyze the effects of rainfall and inflow on soil erosion for hillslopes dominated by sheet erosion or rill erosion in the Chinese Mollisol region. The objective of this study was to discuss the erosive agent(rainfall or inflow), hillslope erosion pattern(sheet erosion or rill erosion) and slope gradient effects on runoff and soil losses. Two soil pans(2.0 m long, 0.5 m wide and 0.5 m deep) with 5° and 10° slopes were subjected to rainfall(0 and 70 mm h–1) and inflow(0 and 70 mm h–1) experiments. Three experimental combinations of rainfall intensity(RI) and inflow rate(IR) were tested using the same water supply of 70 mm by controllingthe run time. A flat soil surface and a soil bed with a straight initial rill were prepared manually, and represented hillslopes dominated by sheet erosion and rill erosion, respectively. The results showed that soil losses had greater differences among treatments than total runoff. Soil losses decreased in the order of RI70+IR70 RI70+IR0 RI0+IR70. Additionally, soil losses for hillslopes dominated by rill erosion were 1.7-2.2 times greater at 5° and 2.5-6.9 times greater at 10° than those for hillslopes dominated by sheet erosion. The loss of 0.25 mm soil particles and aggregates varying from 47.72%-99.60% of the total soil loss played a dominant role in the sediment. Compared with sheet erosion hillslopes, rill erosion hillslopes selectively transported more microaggregates under a relatively stable rill development stage, but rills transported increasinglymore macroaggregates under an active rill development stage. In conclusion, eliminating raindrop impact on relatively gentle hillslopes and preventing rill development on relatively steep hillslopes would be useful measures to decrease soil erosion and soil degradation in the Mollisol region of northeastern China.     

Estimating purple-soil moisture content using Vis-NIR spectroscopy

Soil moisture is essential for plant growth in terrestrial ecosystems. This study investigated the visible-near infrared(Vis-NIR) spectra of three subgroups of purple soils(calcareous, neutral, and acidic) from western Chongqing, China, containing different water contents. The relationship between soil moisture and spectral reflectivity(R) was analyzed using four spectral transformations, and estimation models were established for estimating the soil moisture content(SMC) of purple soil based on stepwise multiple linear regression(SMLR) and partial least squares regression(PLSR). We found that soil spectra were similar for different moisture contents, with reflectivity decreasing with increasing moisture content and following the order neutral calcareous acidic purple soil(at constant moisture content). Three of the four spectral transformations can highlight spectral sensitivity to SMC and significantly improve the correlation between the reflectance spectra and SMC. SMLR and PLSRmethods provide similar prediction accuracy. The PLSR-based model using a first-order reflectivity differential(R ?) is more effective for estimating the SMC, and gave coefficient of determination(v2), root mean square errors of validation(RMSEV), and ratio of performance to inter-quartile distance(RPIQ)values of 0.946, 1.347, and 6.328, respectively, for the calcareous purple soil, and 0.944, 1.818, and 6.569,respectively, for the acidic purple soil. For neutral purple soil, the best prediction was obtained using the SMLR method with R ? transformation, yieldingv2,RMSEV and RPIQ values of 0.973, 0.888 and 8.791,respectively. In general, PLSR is more suitable than SMLR for estimating the SMC of purple soil.     

Spatial variation and soil nitrogen potential hotspots in a mixed land cover catchment on the Chinese Loess Plateau

Soil nitrogen(N) is critical to ecosystem services and environmental quality. Hotspots of soil N in areas with high soil moisture have been widely studied, however, their spatial distribution and their linkage with soil N variation have seldom been examined at a catchment scale in areas with low soil water content. We investigated the spatial variation of soil N and its hotspots in a mixed land cover catchment on the Chinese Loess Plateau and used multiple statistical methods to evaluate the effects of the critical environmental factors on soil N variation and potential hotspots. The results demonstrated that land cover, soil moisture, elevation, plan curvature and flow accumulation were the dominant factors affecting the spatial variation of soil nitrate(NN), while land cover and slope aspect were the most important factors impacting the spatial distribution of soil ammonium(AN) and total nitrogen(TN). In the studied catchment, the forestland, gully land and grassland were found to be the potential hotspots of soil NN, AN and TN accumulation, respectively. We concluded that land cover and slope aspect could be proxies to determine the potential hotspots of soil N at the catchment scale. Overall, land cover was the most important factor that resulted in the spatial variations of soil N. The findings may help us to better understand the environmental factors affecting soil N hotspots and their spatial variation at the catchment scale in terrestrial ecosystems.     

Changes in SOC and nutrients under intensive tillage in two types of slope landscapes

The net effect of tillage erosion on soil properties would be associated with the spatial variation in soil constituents,and therefore plays an important role in ecological agriculture.We conducted a consecutive tillage by hoeing 15 times during a period with no rainfall in the two slope landscapes(a linear slope and complex slope) of the Yangtze Three Gorges reservoir areas,to examine the relationship between soil erosion rates and the variations in soil chemical properties and compare the effects of soil redistribution on SOC and nutrients between the linear and complex slopes.After the simulated tillage,notable changes in 137 Cs inventories of the soil occurred in the summit and toeslope positions on the linear slope,while there were significant changes in 137 Cs inventories at convex and concave positions on the complex slope.Soil profile disappeared at the summit slope boundary,with the exposure area of 16.0% and 7.6% of the experimental plot,respectively,for the linear and complex slopes due to no soil replacement.Soil organic C and nutrients were completely depleted with the disappearance of soil profiles at soil eroding zones,whereas a remarkable increase in SOC,total N and available nutrient concentrations of the post-tillage surface soil and a decrease in total nutrient concentrations(P and K) were found at depositional zones on the linear slope.For the complex slope,however,changes in SOC and nutrient concentrations of the post-tillage surface soil exhibited a patterndifferent from that on the linear slope,which showed a remarkable decrease in SOC and total nutrient concentrations but a slight increase in available nutrient concentrations after tillage in the toeslope position.Due to the gradual increase in soil depth from top to bottom of the slope,SOC and nutrient inventories in the soil profiles were significantly correlated with soil redistribution rates on both the linear and complex slopes.Tillage causes remarkable changes of soil chemical properties in the surface soil layer and soil profile,and increases SOC and nutrient inventories for the soil profile downslope in steeply sloping landscapes.     

Stability analysis of an unsaturated soil slope considering rainfall infiltration based on the Green-Ampt model

Based on the principle of saturated infiltration and the Green-Ampt model, an unsaturated infiltration model for a soil slope surface was established for either constant moisture content, or depth-varying moisture content and the slope. Infiltration parameters in the partially saturated slope were revealed under sustained rainfall. Through analysis of the variation of initial moisture content in the slope, the ponding time, infiltration depth, and infiltration rate were deduced for an unsaturated soil slope subject to rainfall infiltration. There is no ponded water on the surface of the slope under sustained low-intensity rainfall. The results show that the infiltration parameters of an unsaturated slope are influenced by the initial moisture content and the wetting front saturation, the soil cohesion and rainfall intensity under sustained rainfall. More short-term slope failures can occur with the decrease of cohesion of the soil of the slope. The ponding time and infiltration depth differ considering constant or different initial moisture content respectively in the soil slope. Then, best-fit curves of the infiltration rate, ponding time, and infiltration depth to the wetting front saturation were obtained with constant or different initial moisture contents. And the slope failure time is roughly uniform when subject to a rainfall intensity I5 mm/h.     

Effects of soil shrinkage in permanent gullies formation: The case of Benggang erosion in the granite area of southern China

Soil shrinkage is an important factor in slope destabilization in granitic areas, which is also one of the most important conditions for the formation of permanent gullies. This study explored the effect of soil shrinkage on permanent gullies, and Benggang erosion in granitic areas in southeastern China was used as an example. Three types of Benggang in granitic area were selected to examine the soil shrinkage of three soil layers(the lateritic, transitional and sandy layers) and their effect on the development of Benggang erosion was studied. The results show that the maximum values of COLEH and COLEV(coefficient of linear extensibility in horizontal and vertical directions, respectively) are 3.09% and 1.60% in the laterite layers, 2.71% and 2.13% in transition layers, and 1.10% and 1.82% in sandy layers, indicating that the shrinkage potential of the soil layers exhibits the following order, from highest to lowest: the laterite layer, transition layer, and sandy layer. With a decreasing volumetric water content, the linear shrinkage ratio increases gradually and eventually stabilizes, and in the laterite, transition and sandy layers, the average values of the maximum linear shrinkage are 1.50%, 2.09%, and 1.74%, respectively. Axial shrinkage is most obvious in the transition layers, in which the volume change in the form of subsidence is greater than that in other layers. The soil shrinkage curves fit the trilinear model(R20.9), and the soil shrinkage characteristic curves were divided into structural, basic, and residual sections. The correlation analysis shows that the soil shrinkage rate is positively correlated with clay and Fe_2 O_3 content and negatively correlated with sand content. Clay and sand contents are the most important factors influencing soil shrinkage. Soil oxides can influence soil shrinkage by affecting the particle composition of the soil, so soil shrinkage is closely related to soil clay minerals. Our findings can provide a theoretical basis for revealing the mechanism of Benggang erosion and its control.     

Effects of gully erosion and gully filling on soil degradation in the black soil region of Northeast China

Gully erosion has caused soil degradation and even reduced soil productivity.However,only few studies on the effects of gully erosion and artificial controlling measures on soil degradation in the Black Soil Region of Northeast China are available.Thus,this study explores the relationships between gully erosion,gully filling and soil parameters.Two sets of soil samples were collected in the field at:(1) 72 sample points in the gully erosion study area,60 sample points in the ephemeral and classical gully erosion area(3,518 m2),12 sample points in the deposition zone(443 m2),(2)10 reference points along a slope unaffected by gully erosion representing the original situation before the gully was formed.All soil samples were analyzed for gravel content(GC),soil organic matter(SOM),total nitrogen(TN),available nitrogen(AN),available phosphorus(AP),and available potassium(AK).The soil property values on unaffected slope were fitted by the polynomial curves as the reference values in no gully erosion area.The interpolated soil property values in gully eroded study area were compared with these polynomial curves,respectively,and then,changes of soil property values were analyzed.Gully erosion caused an increase in GC and a decrease in SOM,TN,AN,AP and AK.The change of GC,SOM,TN,AN,AP,AK was 8.8%,-9.04 g kg-1,-0.92 g kg-1,-62.28 mg kg-1,-29.61 mg kg-1,-79.68 mg kg-1.The soil property values in the study area were below optimal values.Thus,we concluded that gully erosion and gully filling caused both on-site and off-site soil degradation.Soil degradation area was 0.65 % of the cultivated land.In addition,it was proved that gully filling were an improper soil and water conservation measure,which seems to exacerbate the problem.Thus,it is suggested that soil where soil is deep is moved to fill the gully,and then the area around the filled gullies should be covered by grass for preventing the formation and development of the gully.     

A quantification of the effects of erosion on the productivity of purple soils

Research on the effects of soil erosion on soil productivity has attracted increasing attention.Purple soil is one of the main soil types in China and plays an important role in the national economy.However,the relationship between erosion and the productivity of purple soils has not been well studied.The purpose of this research was to determine if soil depth,which is dependent on the rate of erosion,has an influence on crop yield and growth.Plot and pot experiments at different soil depths were performed.Results indicate that soils from different parental materials had different growth features and crop yields due to the differential fertility of the derived soils.The yield reduction rate increases exponentially with the depth of eroded soil(level of erosion).The yield reduction rate per unit eroded soil horizon(10 cm) is approximately 10.5% for maize and wheat.     

Slope wavenumber spectrum models of capillary and capillary-gravity waves

Capillary and capillary-gravity waves possess a random character, and the slope wavenumber spectra of them can be used to represent mean distributions of wave energy with respect to spatial scale of variability. But simple and practical models of the slope wavenumber spectra have not been put forward so far. In this article, we address the accurate definition of the slope wavenumber spectra of water surface capillary and capillary-gravity waves. By combining the existing slope wavenumber models and using the dispersion relation of water surface waves, we derive the slope wavenumber spectrum models of capillary and capillary-gravity waves. Simultaneously, by using the slope wavenumber models, the dependence of the slope wavenumber spectrum on wind speed is analyzed using data obtained in an experiment which was performed in a laboratory wind wave tank. Generally speaking, the slope wavenumber spectra are influenced profoundly by the wind speed above water surface. The slope wavenumber spectrum increases with wind speed obviously and do not cross each other for different wind speeds. But, for the same wind speed, the slope wavenumber spectra are essentially identical, even though the capillary and capillary-gravity waves are excited at different times and locations. Furthermore, the slope wavenumber spectra obtained from the models agree quite well with experimental results as regards both the values and the shape of the curve.     

Analyzing and forecasting climate change in Harbin City,Northeast China

Based on sounding data from 1975 to 2005 and TM/ETM+ remote sensing images in 1989, 2001 and 2007, the climate changes in Harbin City, Northeast China in recent 30 years were analyzed and forecasted. Results show that in the lower troposphere the meridional wind speed and mean annual wind speed decrease, and in the lower stratosphere the temperature decreases while the meridional wind speed increases significantly. In the study area, the climate is becoming warmer and wetter in the middle lower troposphere. The expansion of urban area has great effects on the surface air temperature and the wind speed, leading to the increase of the surface air temperature, the decrease of the surface wind speed, and the increase of the area of urban high temperature zone. The quantitative equations have been established among the surface air temperature, the carbon dioxide (CO₂) concentration and the specific humidity (the water vapor content). It is predicted that the future increasing rate of the surface air temperature is 0.85°C/10yr if emission concentration of CO₂ remains unchanged; if emission concentration of CO₂ decreases to 75%, 50% and 25%, respectively, the surface air temperature will increase 0.65°C/10yr, 0.46°C/10yr and 0.27°C/10yr, respectively. The rise of the surface air temperature in the study area is higher than that of the global mean temperature forecasted by IPCC.     

Road lateral disconnection and crossing impacts in river landscape of Lancang River Valley in Yunnan Province, China

Roads are conspicuous components in a river landscape;however,their impacts on river landscape patterns and ecological processes have not been systematically studied at the watershed scale.In this paper,the Lancang River Valley in Yunnan Province,China was selected as a case to study road lateral disconnection and crossing impacts and identify river-road network interaction.This study was primarily focused on the road impacts on soil erosion intensity and patch density by using GIS analysis at different scales and explored their distribution with terrain factors.The results showed that river density revealed spatial autocorrelation although both of the roads and rivers were distributed unevenly in the valley.The lateral road(road curvature≥1.1)proportion correlated with soil erosion intensity(p 0.01)at the small sub-basin scale.Soil erosion intensity decreased with increasing lateral road buffer width.Light erosion generally accounted for a large proportion of the erosion in the lateral road buffer zones(1.0–4.0 km),while higher class lateral roads imposed greater impacts on soil erosion than lower class roads,which primarily had a moderate erosion level.In addition,the results of road-river intersection density indicated that road crossing impacts were significantly correlated with patch density at the small sub-basin scale.Topography factor(percent of slope25°in each sub-basin had a close relationship with the ratio of total length of road line with curvature value≥1.1 to the total number of intersections.The correlation(p 0.01)between road impacts and terrain factor revealed that topography affected the road impact distribution in the Lancang River Valley.