EFFECT OF RAINFALL INTENSITY,SLOPE, LAND USE AND ANTECEDENT SOIL MOISTURE ON SOIL EROSION IN AN ARID ENVIRONMENT

Most climate change scenarios predict a significant increase in the frequency of high intensity rainfall events especially in the dry areas, which will increase runoff and soil erosion. Understanding the factors that control soil erosion is crucial to recommending appropriate measures to protect soils and reduce their vulnerability. The objective of this research was to investigate the effect of rainfall intensity, slope, land use and antecedent soil moisture on soil erosion and runoff. Twelve sites from Al‐Muwaqqar watershed, Jordan, were selected to represent six slope angles: 1, 2, 3, 5, 7 and 9%. Two sites, one cultivated with barley and one as rangeland, were selected within each slope. Erosion was measured under three rainfall intensities: 3, 5 and 10 mm h⁻¹; and three different antecedent soil moisture contents: dry, wet and very wet; using a rotating disk rainfall simulator. Regression equations indicated that rainfall intensity was the most important factor affecting soil erosion and that erosion could occur at a relatively small intensity on wet soils as a result of subsequent rainfall events. Soil erosion on cultivated land was primarily affected by moisture content, while on uncultivated land, it was mostly affected by slope steepness. Rainfall intensity, slope and antecedent moisture explained 84–89 and 59–66% of the variation in runoff and soil loss, respectively. The results indicated the significant influence of cultivating the land on soil erosion. Copyright © 2013 John Wiley & Sons, Ltd.     

Cracks in bread crust cause longer crispness retention

Crispness is among the most important factors that the consumer uses to assess the quality of crispy bread. However, this quality attribute is rapidly lost after baking. It is known that crispness retention can be increased more than eight times by enhancing the water vapor permeability of the crust. Current methods to achieve this, i.e., puncturing the bread before baking, require an extra process step. We hypothesize that cracks that appear spontaneously on the crust surface after baking can also enhance water vapor permeability and therefore improve crispness retention. We were able to confirm this hypothesis by preparing composite breads containing the same crumb but different crusts, with crust recipes of varying starch/protein ratios. Crusts systems that were generally high in gelatinized starch content and poor in evenly distributed gluten were more prone to crack after the whole process of part-baking, freezing, and baking off. These cracks led to an increased water vapor permeability of the crust and an eight times longer instrumental crispness retention compared to standard bread. In this paper we also discuss possible causes for crack formation in the crust. We hypothesize that effective cracks are caused by thermal shock in materials with a low ability to dissipate energy.     

干旱、半干旱地区土壤水分研究进展

土壤水分在干旱、半干旱地区生态系统中起着重要的作用。在简要总结土壤水分与植物关系、土壤水分与土壤呼吸关系、生物土壤结皮对降水再分配过程的影响、土壤水分时空动态、土壤水分监测技术五个方面研究进展的基础上,认为未来干旱、半干旱地区土壤水分研究在土壤水分平衡、土壤水分与土壤呼吸作用、土壤水分监测技术的改进等几个领域还有待于深入。     

最近10年来新疆风沙地貌研究进展

最新研究表明,塔克拉玛干沙漠风沙活动与气温变化呈现"风热同步"现象,虽然其风况类型多样,但整个沙漠处于低风能环境。不同沙丘部位上风沙流输沙量的对数与高度之间表现为线性关系。当气流与沙丘走向斜交时,两侧相同部位输沙率的差异不大,这是线形沙丘保持其动力形态平衡的主要原因之一。古尔班通古特沙漠也处于复合型低能风环境之中,冬季积雪和冻土对沙漠地表形成有利的保护,有效植被覆盖和生物结皮是沙面整体处于稳定状态的重要因素,风沙活动仅存在于沙垄顶部和两坡上部。沙漠中生物结皮发育、种类丰富,其类型和分布具有明显的景观异质性特征。天山北坡和昆仑山北坡的黄土研究揭示,新疆两大沙漠从中更新世以来出现明显的干旱化,沙漠逐步扩大至今天规模。此外,塔里木沙漠公路和古尔班通古特沙漠输水明渠沿线的风沙危害具有明显的时空分异特点。因此,根据工程设施所处地形与地貌部位,可定性判断风沙危害类型与强度,进而确定防治方案和措施。今后新疆风沙地貌学研究应注重研究领域的拓展、研究方法的突破和实验手段的创新3个方面。     

黄土结皮的发育机理与侵蚀效应研究

了解土壤结皮的发育特征及其对侵蚀的影响作用,是认识土壤侵蚀机理、建立精准侵蚀预报模型的重要理论支持之一。本文通过模拟降雨试验,探讨有无雨滴打击作用下黄土结皮的发育过程以及前期有无结皮时结皮侵蚀效应的动态特征。结果表明:(1)随降雨的进行,黄土结皮发生层容重、抗剪强度(含水率为20%)不断增加,30min内形成厚度约3～4mm稳定结皮层;(2)消除雨滴打击后,黄土结皮发育过程同有雨滴打击时类似,但程度减弱。雨滴打击同湿润作用对黄土结皮形成的贡献作用基本相当;(3)降雨初期有、无结皮处理抗剪强度差别大,随后急剧下降并趋同,因而黄土结皮影响抗蚀性的作用微弱,累积溅蚀量的差异主要由溅蚀起始时间的变化引起;(4)黄土结皮的存在明显的减少入渗、增加径流,但结皮效应随降雨进行逐渐消失。溅蚀效应的函数表达式为C=0.6670ln(t)-3.2459,结合溅蚀量的计算式,可较为准确地预测前期无结皮时某降雨历时的累积溅蚀量。     

老挝南部Antoun地区花岗闪长岩风化壳中常量和稀土元素分布

应用岩石薄片鉴定、X射线粉晶衍射、X射线荧光光谱和ICP-MS等分析方法,研究了热带季风型气候条件下老挝Attapeu省Antoun地区二叠纪花岗闪长岩上发育的砖红土型风化壳矿物组成、常量元素和稀土元素地球化学特征。结果表明,风化产物呈酸性,风化壳表土上形成薄层硅质壳层,表土中石英含量最高、铁氧化物含量低和高岭石含量低,符合典型的灰化土特征。随着风化作用加强,Fe2O3、TiO2和Al2O3出现富集,K2O、Na2O、CaO和MgO出现淋失。石英出现富集原因可能是雨季降水冲刷和酸性水淋溶掉高岭石等黏土矿物,而旱季SiO2含量上升至地表富集形成硅质薄壳缘故。剖面稀土元素分布型式为轻稀土富集型,∑REE在风化壳中部达到最高值318 mg kg-1,剖面上Ce和Eu均呈正异常-负异常-正异常变化趋势,∑REE最高值出现在Ce和Eu负异常和(Fe2+/Fe3+)较高层位,∑REE与Fe2O3显著正相关。REE富集与铁铝氧化物和黏土矿物吸附有关,也与相对还原的酸性环境有关。     

Influence of dew on biomass and photosystem II activity of cyanobacterial crusts in the Hopq Desert, northwest China

Dew is an important water source for desert organisms in semiarid and arid regions. Both field and laboratory experiments were conducted to investigate the possible roles of dew in growth of biomass and photosynthetic activity within cyanobacterial crust. The cyanobacteria, Microcoleus vaginatus Gom. and Scytonema javanicum (Kütz.) Born et Flah., were begun with stock cultures and sequential mass cultivations, and then the field experiment was performed by inoculating the inocula onto shifting sand for forming cyanobacterial crust during late summer and autumn of 2007 in Hopq Desert, northwest China. Measurements of dew amount and Chlorophyll a content were carried out in order to evaluate the changes in crust biomass following dew. Also, we determined the activity of photosystem II(PSII) within the crust in the laboratory by simulating the desiccation/rehydration process due to dew. Results showed that the average daily dew amount as measured by the cloth-plate method (CPM) was 0.154 mm during fifty-three days and that the crust biomass fluctuated from initial inoculation of 4.3 μg Chlorophyll a cm⁻² sand to 5.8-7.3 μg Chlorophyll a cm⁻² crust when dew acted as the sole water source, and reached a peak value of approximately 8.2 μg Chlorophyll a cm⁻² crust owing to rainfalls. It indicated that there was a highly significant correlation between dew amounts and crust moistures (r = 0.897 or r = 0.882, all P < 0.0001), but not a significant correlation between dew and the biomass (r = 0.246 or r = 0.257, all P > 0.05), and thus concluded that dew might only play a relatively limited role in regulating the crust biomass. Correspondingly, we found that rains significantly facilitated biomass increase of the cyanobacterial crust. Results from the simulative experiment upon rehydration showed that approximately 80% of PSII activity could be achieved within about 50 min after rehydration in the dark and at 5 °C, and only about 20% of the activity was light-temperature dependent. This might mean that dew was crucial for cyanobacterial crust to rapidly activate photosynthetic activity during desiccation and rehydration despite low temperatures and weak light before dawn. It also showed in this study that the cyanobacterial crusts could receive and retain more dew than sand, which depended on microclimatic characteristics and soil properties of the crusts. It may be necessary for us to fully understanding the influence of dew on regulating the growth and activity of cyanobacterial crust, and to soundly evaluate the crust's potential application in fighting desertification because of the available water due to dew.     

2种植被下生物结皮化学特征及其对下层土壤的影响

以毛乌素沙地的生物结皮层和结皮下层土壤为研究对象,对油蒿、羊柴2种植被条件下的土壤生物结皮层以及生物结皮下层土壤进行了化学性质的研究,探讨了不同植被下土壤生物结皮对土壤化学特征的影响。研究表明:生物结皮的土壤养分含量均高于流动沙地,油蒿灌丛下生物结皮的发育时间长,富集的养分含量也比羊柴灌丛的多,土壤生物结皮对下层土壤养分有明显影响,生物结皮下土壤的有机质、全效养分和速效养分的含量均高于对照流沙土壤土层,且呈随土层深度增加含量降低的趋势。     

黄土地表生物结皮对土壤贮水性能及水分入渗特征的影响

采用双环法对山西省偏关县3种结皮覆盖下(苔藓藻结皮、藻结皮和薄层藻结皮)土壤的贮水性能和渗透特征进行了对比研究.结果表明:不同结皮覆盖下土壤的贮水能力受结皮厚度和孔隙度状况的影响较大,0～10 cm土层饱和贮水量为502.69～525.80 t/hm2 ,滞留贮水量为169.71～198.29 t/hm2;初渗速率的变化范围为5. 19～11.10 mm/min,无结皮最高,苔藓藻结皮最低;稳渗速率变化范围为1.6 7～2.67 mm/min.采用的3种入渗模型(Kostiakov模型、Horton模型和Ph ilip模型)中Horton模型的拟合值更接近于实测值, 决定系数R2在0.98～0.99,更适用于描述本研究区具有生物结皮土壤的入渗特征.     

Factors affecting distribution of microbiotic crusts in the grain-for-green land of the loess region, northern Shaanxi, China

A field survey was conducted in the grain-forgreen land of the loess region, northern Shaanxi, China, from July to August of 2005 to provide a scientific evaluation of the grain-for-green project, including its soil and water conservation and other ecological benefits for the region. The distribution of microbiotic crusts were studied, while human disturbance, aspect, topography, vegetation structure and other factors affecting it were obtained from the analysis of survey data from 78 sample plots. Results show that crust coverage is larger on less-disturbed plots than on highly-disturbed ones, on north-facing plots than on south-facing ones and on gully-slopes than on ridge-slopes. Coverage increases with herbal coverage and trees can provide better conditions for distribution of crusts than shrubs. Therefore, crust coverage is larger in herb-dominated plots than in tree-dominated ones and crusts in shrub-dominated plots are smaller. However, we made no progress in our study on deciding how slope degrees and herb species affect the distribution of crusts. We believe that more studies are necessary for a further exploration of the relationship between them. __________ Translated from Journal of Beijing Forestry University, 2007, 29(1): 102–107 [译自: 北京林业大学学报]