共查询到20条相似文献，搜索用时 15 毫秒
1.
The relative importance of soil crust and slope angle in runoff and soil loss: a case study in the hilly areas of the Loess Plateau, North China 总被引：2，自引：0，他引：2
Soil crust and slope angle are of important factors affecting runoff production and sediment yield. In the hilly areas of the Loess Plateau, North China, slope lands are distributed extensively and subjected to soil crusting; therefore, the research on the responses of runoff and soil loss to soil crust and slope angle is essential to soil and water conservation. In the study, five pairs of 1 m × 5 m plots with slope angles of 5°, 10°, 15°, 20° and 25° respectively, were established in Wangjiagou watershed, which was located at the Loess Plateau, China. Based on the two simulated rainfall events, uncrusted surface prior to the first simulated rainfall event, and crusted surface prior to the second rainfall event were distinguished. The runoff production and soil loss were measured at intervals of 5 min during the simulated events. It indicated that both soil crust and slope angle played an important role in runoff production and soil loss. With the reference slope angle of 5°, the relative importance of soil crust and slope angle in runoff production was calculated. It showed that soil crust effect on the total runoff volume decreased from 100 to ～40%, while slope angle effect increased from 0 to ～60% with increasing slope angle because soil crust less developed on the steeper slopes. Furthermore, soil crust effect was associated with rainfall duration. At the same slope angle, the relative importance of soil crust decreased with rainfall duration because new crust was formed on the uncrusted surface. The critical slope of erosion was also discussed. Soil loss increased with slope angle when the slope angle was less than 20°. Generally speaking, soil crust effect decreased with slope angle and/or rainfall duration. 相似文献
2.
Saïdati Bouhlassa Bouchaib Ammary Samuel Paré Naima Safsaf 《Hydrogeology Journal》2016,24(7):1699-1706
In arid regions, knowledge of the evaporation rate from the water table is essential for appropriate management of scarce resources and to prevent land degradation. Soil chloride profiles in the unsaturated zone of a bare soil in an arid area of south-eastern Morocco were used to assess the evaporation flux, using chloride inventories in conjunction with evaporative demand. Moisture fluxes were calculated from measured chloride concentrations on the basis of a steady-state flow model. The chloride profiles displayed large variations in concentrations and had (1) low chloride concentrations near the soil surface, (2) maximum chloride concentrations at depths of 11–14 cm beneath the soil surface, respectively in July and February, and (3) gradually decreasing chloride concentrations while depth increased below these peaks. Evaporative demands were found to be inversely proportional to the depth of evaporation fronts and proportional to evaporation fluxes. In addition, the evaporation along the profiles seems to be controlled by the soil composition and texture. The investigation of chloride profiles in February and July enabled the determination of a value for annual evaporation (～30 mm), which is in good agreement with the value estimated by the Allison-Barnes type model (～32 mm). 相似文献
3.
Inadequate moisture supply is one of the important factors limiting crop yields in the world. Increasing the efficiency of moisture available has an important role on the crop-producing capacity of the soil. This paper presents the results of the laboratory experiments conducted to assess the influence of two mulches of windy sand and light expanded clay aggregate (LECA) with three thicknesses (1, 3, and 4 cm) on soil surface in soil columns. Loamy soil was taken from the experimental site in Bayaz of Rafsanjan (a city in Kerman province in Iran). These experiments were done as completely randomized design with two treatments of mulches (windy sand and LECA) and tree replicates. The results show that the columns of treated soil with mulches had lower evaporation as compared to the control. The rate of evaporation from the soil surface of columns was decreased with increasing the thickness from 1 to 4 cm of each of the two mulches. The LECA mulch was more effective in reducing evaporation from the soil surface than the windy sand mulch with the same thicknesses. The most effective among the thicknesses for mulches was 3 cm. 相似文献
4.
http://dx.doi.org/10.1016/j.gsf.2016.08.003 总被引：1，自引：1，他引：0
The primordial crust on the Earth formed from the crystallization of the surface magma ocean during the Hadean. However, geological surveys have found no evidence of rocks dating back to more than 4 Ga on the Earth's surface, suggesting the Hadean crust was lost due to some processes. We investigated the subduction of one of the possible candidates for the primordial crust, anorthosite and KREEP crust similar to the Moon, which is also considered to have formed from the crystallization of the magma ocean. Similar to the present Earth, the subduction of primordial crust by subduction erosion is expected to be an effective way of eliminating primordial crust from the surface. In this study, the subduction rate of the primordial crust via subduction channels is evaluated by numerical simulations. The subduction channels are located between the subducting slab and the mantle wedge and are comprised of primordial crust materials supplied mainly by subduction erosion. We have found that primordial anorthosite and KREEP crust of up to ～50 km thick at the Earth's surface was able to be conveyed to the deep mantle within 0.1-2 Gy by that mechanism. 相似文献
5.
6.
Macropores resulting from soil pedogenesis and biological activity play important roles in soil water and chemical transport. Numerous studies have examined individual macropores and the effects of their size on solute transport, but few have assessed the effects of macropore continuity and of neighboring macropores. This paper describes a laboratory investigation of the effects of macropores, with varying degrees and types of continuity, on the transport and distribution of solutes in a sandy soil from the northern Loess Plateau, China. Breakthrough curves were obtained from 60 cm tall, 2-D columns containing standardized artificial macropores using an input solution of 1,190 mg/L KBr and 100 mg/L FD&C Blue #1 under a constant hydraulic head of 8 cm. The types of macropore were: open at both the surface and bottom of the soil column (O–O); open at the surface, closed at the bottom (O–C); and closed at the surface, open at the bottom (C–O). Columns with no macropores served as a control. In the O–O columns the solution reached the bottom 10–50 times faster than in any other treatment, bypassing most of the soil matrix. The presence of an O–C macropore resulted in weak retardation and much deeper penetration of the bromide and FD&C Blue #1 solution than in the control columns. However, the C–O macropore had little effect on either breakthrough curves or solute distributions. In further experiments that considered neighboring macropores effects, an inclined macropore strongly affected solute concentrations in the profile around a nearby vertical macropore. It was concluded that the length, type and position of single macropores, and the presence of neighboring macropores, all affect soil water flow and solute infiltration parameters in a sandy loam soil. 相似文献
7.
渤海湾西岸滨海盐渍土的盐渍化特征分析 总被引：4，自引：0，他引：4
渤海湾西岸滨海盐渍土的盐渍化特征与滨海平原的地面高程、气候条件、盐渍土的理化性状、地下水的矿化度及人类活动等密切相关。就土盐渍化的程度而言,地面高程较高处的土高于地面高程较低处的土,上层土高于下层土。受蒸发和降水影响,地下水位以上土的盐渍化敏感深度为1 m左右。随着气候的变化,滨海盐渍土显现出春季蒸发,上层土积盐;夏季淋洗,土中盐分向下移动的盐渍化特征。随着深度的增加,土的含盐量逐渐减少,至地下水位附近出现轻微增长。从剖面上地表至地下水位间可划分为3个不同聚盐形态和含盐量的土盐渍化程度分区带,即土蒸发浓缩聚盐带、土盐化变动带和土饱水溶盐带;平面上向海岸线方向延伸,土逐渐由非盐渍土变为弱盐渍土、中盐渍土和强盐渍土,含盐量和盐渍化程度也越来越高。地下水位浅和地下水矿化度高,则上层土的盐渍化程度就愈高。 相似文献
8.
在温度场、湿度场和人工水渠等多场耦合作用下,土体与外界环境的热交换条件和水热输运过程的改变极易引起土体成分和结构的变异,从而引发区域的生态失衡和次生盐渍化。本文选择吉林西部的农安、大安、乾安和镇赉4个典型盐渍化地区作为长期观测和研究评价的地点,对多场(水、热、盐)循环条件下不同盖层盐渍土进行现场调查取样,对室外内的工程地质性质、物理化学性质和物质组成进行了长期观测和测试分析。结果表明:吉林西部盐渍土属于碳酸型盐渍土,水分迁移量为3.5%4.6%;易溶盐质量分数总体随深度增加而降低,并且盐水在剖面上的分布明显受到季节影响,旱季蒸发作用和冬季土体冻结作用促使盐分随水分向上运移,浅表土体盐分大量集聚;随深度增加,阳离子交换量的变化趋势基本与易溶盐质量分数变化的趋势相同。 相似文献
9.
为研究土壤水分的蒸发机理,自主开发了大型环境箱试验装置,并以枫丹白露砂土为研究对象,室内模拟土壤水分的蒸发过程。该试验在控制大气参数和保持土壤底部水位稳定的条件下,对蒸发过程中大气参数（空气温度、相对湿度和流量）和土壤参数（土壤温度、基质吸力和体积含水量）的变化,特别是土壤表面基质吸力的变化进行了研究。同时根据试验结果对蒸发速率及累积蒸发量进行了计算分析。研究结果表明:蒸发主要限制在土壤浅层区域,浅层土壤的体积含水量和温度的变化均较大;空气温度和土壤蒸发过程对土壤温度的变化具有较大的影响;土壤表面空气相对湿度与蒸发过程具有相关性;土壤基质吸力随着蒸发的进行逐渐增大; 实际蒸发速率呈现3个阶段。 相似文献
10.
The concentrations of Hg, Cu, Pb, Cr, and Ni in soil samples collected from a specialized salt production site at Zhongba in the Three Gorges Reservoir region of the Yangtze River in China were analyzed to reconstruct the heavy metal contamination contexts of different historic periods over the last 4,500 years. The results show that the observed sequence for individual levels of heavy metal pollution was as follows: Hg > Cu > Ni > Pb ≈ Cr. Hg pollution was high during every time period except the Ming Dynasty, with peaks being observed from the Spring and Autumn period. The pollution of Cu and Ni peaked during the Xi Zhou and Xia Dynasties, respectively. The pollution level of Pb has gradually increased since the Qin Dynasty and has coincided with the use of leaded gasoline. Cr contamination was moderate in all soil strata with little indication of change. Comprehensive heavy metal contamination was high during all of these periods, except during the Ming Dynasty, with peaks being observed between the Spring and Autumn Period and throughout the Warring States Period. Enrichment factors (EFs) were used to obtain information on heavy metal sources. The EFs indicate that most of the Hg and Cu originated from human activities, whereas Pb, Cr, and Ni predominantly came from crust weathering. Several preliminary inferences regarding the development of heavy metal utilization in the area were generated. Cu usage had developed well during the Xi Zhou Dynasty and the Autumn Period. Hg usage emerged during the Xia Dynasty and matured between the Spring and Autumn Period and the Warring States Period. Ni usage conceivably started during the Xia Dynasty. Other factors, such as religious activities, technology, environmental awareness and the intensity of salt production, have also affected heavy metal pollution concentrations. 相似文献
11.
Wave–current interaction (WCI) is important in modulating hydrodynamics and water mixing in estuaries, and thereby the transport of water-borne materials. However, the effects of WCI on salt transport and salt intrusion in estuaries during storm events have been rarely examined. In the present study, we use a coupled atmosphere–ocean–wave–sediment transport (COAWST) modeling system to investigate the effects of WCI on salt intrusion in the highly stratified Modaomen Estuary during Typhoon Hagupit (2008). The model is validated by the measured wave, water elevation, and surface salinity data, and several diagnostic model experiments are conducted. WCI increases the storm surge by 0.8 m at the peak surge (25% of the total surge height). The wave-breaking-induced momentum flux and the Stokes drift increase the magnitude of the landward flow by 0.3 m s?1 (30% of the total landward flow). In addition, the waves increase water mixing by 2–4 times compared with that without waves. Hence, WCI significantly increases the landward advective salt transport and decreases the steady shear transport. The net effect of the WCI is a significant increase of salt import and salt intrusion during the typhoon event. However, in the aftermath of the storm, the imported salt water is rapidly flushed out by the increased river discharge, and the estuary regains its stratification within one day. 相似文献
12.
Contribution of shallow groundwater rapid fluctuation to soil salinization under arid and semiarid climate 总被引：4，自引：0，他引：4
Mohamed Khaled Ibrahimi Tsuyoshi Miyazaki Taku Nishimura Hiromi Imoto 《Arabian Journal of Geosciences》2014,7(9):3901-3911
Rising saline shallow groundwater and associated soil salinization problems are widespread especially in arid and semiarid areas. There have been numerous studies on groundwater-associated salinity, but more information is required on the effects of groundwater frequent and high fluctuations on soil salinization. In the present study, laboratory experiments and numerical simulations using HYDRUS-1D model were carried out for this purpose. The experimental and modeling results showed that groundwater fluctuation caused not only the accumulation of more salt in the soil profile compared to stable groundwater, but also an enhancement of the mechanism. Water table fluctuation induced a much greater spreading of the bromide (Br) tracer within the column than the constant water table. The Br content was on average five orders of magnitude greater under a fluctuating water table than under a constant one. Further, the numerical simulations showed that an increase in the groundwater fluctuation frequency brought about an increase in soil surface salinization under the same evaporation boundary conditions. Additional simulations with HYDRUS-1D were used to study the effects of various management strategies on soil salinization induced by shallow groundwater. Hence, by reducing the evaporation rate through the application of surface mulching, a significant reduction of salt concentration at the soil surface was observed. Moreover, frequent irrigations with small quantities were effective to reduce soil surface salt accumulation induced by saline shallow groundwater. 相似文献
13.
Effects of straw mulching on soil evaporation during the soil thawing period in a cold region in northeastern China 总被引：1，自引：0，他引：1
To study the effect of straw mulching on soil water evaporation, it is necessary to measure soil water evaporation under different conditions of straw mulching during the soil thawing period. A field experiment was conducted in winter, and soil evaporation was measured using a microlysimeter on bare land (LD) and 4500 (GF4500), 9000 (GF9000) and 13500 \(\hbox {kg/hm}^{2}\) (GF13500) straw mulch. The influence of different quantities of straw mulch on soil water evaporation during the thawing period was analyzed using the Mallat algorithm, statistical analysis and information cost function. The results showed that straw mulching could delay the thawing of the surface soil by 3–6 d, decrease the speed at which the surface soil thaws by 0.40–0.80 cm/d, delay the peak soil liquid water content, increase the soil liquid water content, reduce the cumulative evaporation by 2.70–7.40 mm in the thawing period, increase the range of soil evaporation by 0.04–0.10 mm in the early stage of the thawing period, and reduce the range of soil evaporation by 0.25–0.90 mm in the late stage of the thawing period. Straw mulching could reduce the range of and variation in soil evaporation and can reduce the effect of random factors on soil evaporation. When the amount of straw mulch exceeded 9000 \(\hbox {kg/hm}^{2}\), the effect of increasing the amount of straw mulch on daily soil water evaporation was small. 相似文献
14.
Chuanyong Ye Jianye Mao Yaqiong Ren Yingping Li Yongjie Lin Ian M. Power Yangbing Luo 《Aquatic Geochemistry》2018,24(3):209-229
The salt assemblages precipitated during evaporation of concentrated brine collected from Gasikule Salt Lake (GSL) were studied to better understand the formation of potassium deposits in the Qaidam Basin. The study included isothermal evaporation at 25 °C in the laboratory and solar evaporation in the ponds at GSL field. Brines increased in density and became moderately acidic (pH?≈?5.30) while major ion geochemistry and precipitate mineralogy all showed broad agreement between both systems. Four salt assemblages were identified in the isothermal evaporation experiment: halite?→?halite?+?hexahydrite?→?halite?+?bischofite?+?carnallite?→?bischofite. Alternately, three salt assemblages were recognized in the solar evaporation: halite?→?halite?+?epsomite?+?carnallite?→?halite?+?carnallite?+?bischofite. The key difference in salt assemblages between the two systems is attributed to differences in relative humidity and temperature conditions. Although the GSL has deep spring inflow recharge, the high abundance of MgSO4 salts demonstrates that the salt assemblages are similar to normal seawater evaporation. Thus, different proportions of deep spring inflow and river water could form both MgSO4-deficient potassium evaporite and normal seawater potassium evaporites. Therefore, nonmarine water may form diverse potassium evaporite deposits in continental basins when the geological structure as well as hydrogeological and climatic conditions is appropriate. 相似文献
15.
Along the mid- and north Atlantic coasts of the USA, over 90 % of salt marshes have been ditched. Ditching was largely abandoned by the mid-twentieth century; however, techniques that create permanent shallow water pools for mosquito control and bird habitat are increasingly being applied to marshes of the USA and elsewhere. Salt marshes in Plum Island Sound, Massachusetts, and Barnegat Bay, New Jersey, were used to examine differences between areas that have been ditched and those altered to increase the density of shallow pools in water table dynamics, salinity, soil and porewater chemistry, as well as short-term sedimentation, accretion, and elevation change rates. We found that the area with plugged ditches, berms, and pools in Plum Island had less drainage, higher salinity and porewater sulfide and ammonium concentrations, and higher soil organic matter than the adjacent ditched area. Despite averaging 8 cm lower in elevation, the Plum Island ditched area had less sediment deposition and was composed of higher elevation plant species than the area with plugged ditches, berms, and shallow pools. Elevation increased in the ditched area at a rate of 3.2 ± 0.5 mm/year, but elevation change was variable in the area with pools. In Barnegat Bay, the marsh area with pools and ditches had less sediment deposition and surface accretion than the ditch-only area, associated, in part, with the higher elevation. An average elevation difference of 4.5 cm was associated with a sixfold difference in mineral sediment deposition. Temporal sediment deposition and surface accretion was important in the ditch-only area but was absent or muted in the area with numerous pools. Elevation increased in both marsh areas at an average rate of 1.8 ± 0.8 mm/year, less than half the long-term average local rate of sea-level rise. Our results illustrate how physical manipulations including changes to tidal hydrology and surface topography interact with elevation to influence short-term biophysical feedbacks. 相似文献
16.
Interaction of metallic gold with (Na, K)Cl salt melts was investigated by the weight-loss method at 700–1000°C using silica glass ampoules. Interaction was not detected in hermetic evacuated ampoules over the whole temperature interval and even after the addition of 5 wt % Na2SO4 as a possible oxidizer to the salt. Gold solubility increased sharply in open ampoules, but this was accompanied by the evaporation of salt melt and, possibly, AuClx. The limiting gold solubility in the salt melt at 860°C was estimated as 1 wt % or 10000 ppm. The model of gold transport in a gas phase during magmatic degassing invokes shallow gold extraction by salt melt, melt evaporation, and removal of precipitated metallic particles by the gas phase. 相似文献
17.
The spatial distribution characteristics of soil salinity in coastal zone of the Yellow River Delta 总被引：6，自引：0，他引：6
Junbao Yu Yunzhao Li Guangxuan Han Di Zhou Yuqin Fu Bo Guan Guangmei Wang Kai Ning Huifeng Wu Jihong Wang 《Environmental Earth Sciences》2014,72(2):589-599
In coastal area, salinization is a common and serious problem for crop cultivation and ecological restoration of degraded wetlands. Therefore, the soil salinity has attracted increasing attention from farmers, government and environmental scientists. The factors controlling the soil salinity distribution have become a hot point in saline soil studies. In this study, statistics and geostatistics were used to explore the distribution of soil salinity in the Yellow River Delta (YRD) based on 150 soil samples that were collected in June 2010. Besides the experimental work, a geographical information system technique was adopted in this study. The results showed that the soil salinity ranged from 0.11 to 10.50 dS m?1 and the salinity in topsoil was higher than that in subsoil in the YRD, indicating that the salt in subsoil moved up and accumulated in topsoil as a function of evaporation. There was a significant difference among soil salinity spatial variances from different soil depths in the YRD. Generally, soil salinity of the topsoil was higher than that of the subsoil. Meanwhile, there were significant positive correlations in soil salinity between different soil depths. In addition, landforms, land uses, soil types and soil texture were important factors affecting soil salinity. The current distribution of soil salinity resulted from the comprehensive effects of anthropogenic activities and natural processes. The present study results suggest that the impacts of human activities were critical factors for salt redistribution in the coastal wetlands, which should be valuable for agricultural management and ecological restoration in the YRD. 相似文献
18.
The first oceanic crust in the central Atlantic is usually thought to have a Middle Jurassic age. The new interpretation of the two key parameters, the African homologue of the East Coast Magnetic Anomaly and the situation of the Triassic salt basin of Morocco and Novia Scotia, shows that this age was underestimated by about 20 Ma. In our kinematic reconstruction, the first oceanic crust begins at the Late Sinemurian. This difference in age is crucial for the evolution of those margins and we discuss here its consequences. To cite this article: M. Sahabi et al., C. R. Geoscience 336 (2004). 相似文献
19.
20.
基于膜下滴灌特有的"膜中"、"膜间"、"膜边"、"膜外"微区环境,利用2011—2013年田间对比试验方法获取的5 960个数据,运用柯布-道格拉斯模型,构建膜下滴灌环境土壤层次、灌水定额、土壤水分、气温、蒸发综合因素与土壤水盐关系及影响效应分析模型.结果表明,在气候干旱、蒸发强烈灌区,地膜覆盖与滴灌结合的地表介面灌溉形式下,土壤水盐具有水平方向由"膜中"向"膜边"地表裸露区定向迁移,垂直方向土壤水盐则由下向上层运移且趋于"膜外"边界积累的趋势,尤其是气温与蒸发因素交互作用,推进膜下滴灌土壤水盐在地膜覆盖与土壤裸露区域空间运移,研究结果进一步揭示了膜下滴灌"土壤水盐定向迁移"形成机理,为膜下滴灌土壤水盐地表排放模式应用提供了依据. 相似文献