Spatial variability of soil moisture content and its relation to environmental indices in a semi-arid gully catchment of the Loess Plateau, China

The degree of spatial variability of soil moisture and the ability of environmental attributes to predict that variability were studied at the Da Nangou catchment (3·5 km²) in the semi-arid loess area of China. Soil moisture measurements were performed biweekly at five depths in the soil profile (0–5 cm, 10–15 cm, 20–25 cm, 40–45 cm and 70–75 cm) from May to October 1998 and from May to September 1999 using Delta-T theta probe. Results indicated that with increasing soil depth, the mean soil moisture content increases significantly for five layers and the coefficients of variation (CV) also increases with depth from 10–15 cm. It was observed that heavier rains and higher mean moisture contents are often associated with lower spatial variability (CV). Environmental attributes such as land use and topography play controlling roles in the spatial distribution of soil moisture content. However, the relative roles of these environmental indices vary with soil depth. The dominant controls on spatial variability of the time-averaged soil moisture changes from land use, aspect, relative elevation and hillslope position in the surface soil (0–5 cm) to relative elevation, hillslope position and aspect in the subsurface soil (10–15 cm, 20–25 cm), and to land use, relative elevation and slope gradient at larger depths (40–45 cm, 70–75 cm). The dynamic behavior of influences of different environmental indices on the layer-averaged soil moisture depends on several factors. In general, the correlation of soil moisture with slope gradient shows a more significant increase following a greater amount of antecedent precipitation (except for the extremely heavy storms), and declines afterwards. The relation of soil moisture with relative elevation and hillslope position exhibits an opposite trend. It was observed that the influence of land use corresponds to the difference in vegetative characteristics, with a stronger influence in June and August with a greater difference in vegetation. A significant influence of cos(aspect) was found during early spring and autumn with a rapid transient in solar irradiation. Finally, it was found that the sample size is adequate to estimate the catchment mean soil moisture at all five depths and on all 10 observations in 1999 (81 sites), while it is only enough for the upper soil layers (0–5 cm and 10–15 cm) in 1998 (26 sites).     

Impacts of the local land-use system in a semi-arid region of northeastern China on soil properties, crop growth, and weed communities

We examined changes in soil properties, crop biomass, and weed communities in the Horqin Sandy Land of China to elucidate cropland degradation. We studied three local cropland types having periods of cultivation of up to 20 years: maize cropland on lowlands without irrigation (nonirrigated lowland), maize cropland on flat sandy lands with irrigation (irrigated flatland), and bean-centered cropland on sand dunes without irrigation (nonirrigated dunes). Soil properties and crop biomass were more degraded in nonirrigated lowland and nonirrigated dunes than in irrigated flatland. Weed communities in the nonirrigated croplands were the type that become established in drier conditions, whereas wetland weeds were more abundant on irrigated flatland. Trends of change in each indicator did not always occur in parallel and differed statistically among the cropland types. Monitoring these indicators within the context of local land-use systems can provide scientific evidence on which to base local management practices or recommendations for change.     

地下水埋深对半干旱区典型植物群落土壤酶活性的影响

土壤酶活性是反映土壤功能的关键指标,尤其在受到水分限制的半干旱区,土壤水分驱动的土壤酶活性生态功能的变化可以改变土壤养分周转并影响土壤碳质量.地下水埋深对半干旱区典型植物群落土壤酶活性的影响机制尚不明晰.以半干旱区科尔沁沙质草地两种典型植物群落(白草Pennisetum centrasiaticum和差巴嘎蒿Artem...     

内蒙古半干旱区蒸散估算和归因分析

蒸散(Evapotranspiration,ET)是生态系统水循环中的重要一环,决定了生态系统水分和热量传输。从区域尺度对蒸散及其蒸腾(Transpiration,T)和蒸发(Evaporation,E)组分进行量化,认识环境因素对其的影响机制,有助于合理利用、分配水资源,为研究气候变化对区域生态系统水文循环的影响提供参考。基于生态系统生产力模拟(Boreal ecosystem productivity simulator,BEPS)模型,验证模型在研究区域的适用性,量化1981—2018年内蒙古半干旱区的ET及其组分的变化情况,并对其进行归因分析。结果表明：经不同数据验证,BEPS模型计算结果能够精确反应研究区域ET及其组分的分布情况和变化趋势。1981—2018年研究区草地、农田和森林多年平均ET分别为278.22 mm、362.50 mm和308.81 mm。E、T和ET多年呈显著上升趋势,上升速率分别为0.42mm·a^-1、0.63 mm·a^-1和1.05 mm·a^-1。ET与T在全区域内空间分布格局相似,与E...     

半干旱黄土丘陵区人工植被深层土壤干化效应

科学评估不同植被恢复模式的土壤干化效应是目前黄土高原生态恢复一个亟需解决的关键问题。本文以半干旱黄土丘陵区14种典型人工植被为例,通过构建土壤水分相对亏缺指数CSWDI和样地土壤水分相对亏缺指数PCSWDI,定量评估了不同植被深层土壤干化效应。研究发现:除农地和撂荒草地外,各植被深层土壤水分均随土层深度的增加而升高,深层土壤水分含量同土层深度之间呈一元线性关系。不同人工植被深层土壤相对干化程度存在差异,以油松林地最高,杨树侧柏混交林地最低。不同植被类型受其自身蒸腾耗水、根系特征和耕作等影响,土壤干化的程度在剖面上存在差异,但总体趋势为随深度增加而降低。针阔叶植被配置模式土壤水分状况要稍好于阔叶纯林的配置模式。     

Spatial and environmental patterns of off-road vehicle recreation in a semi-arid woodland

Outdoor recreation is a widely recognized cultural ecosystem service. Ensuring that appropriate, high quality recreation opportunities are available requires, among other factors, knowledge of the environmental preferences of recreation users and spatial indicators of where those environmental features exist on the landscape and offer the potential to meet recreation goals. Diverse types of outdoor recreation exist, and different forms of recreation may be associated with different environmental features. The focus of this study is off-road vehicle (ORV) recreation. We demonstrate how readily available spatial environmental datasets, including high resolution image data provided within GoogleEarth, can be used to develop a cost-effective, objective indicator of ORV recreation across a landscape, which can inform management to provide desired recreation opportunities while protecting ecologically sensitive areas.ORV recreational tracks were delineated from GoogleEarth imagery throughout our study area in the Great Western Woodlands of Western Australia. In this region, ORV use is a popular recreation activity and a growing concern of conservation organizations, but is not yet actively managed. Most recreational ORV tracks in the study area are informal and user-created. Mapped ORV recreation tracks were used to model and map the environmental associations of ORV recreation. The pattern of existing tracks indicated associations between recreation and noteworthy environmental amenities in the study area such as the shores of salt lakes and rock outcrops with high ecological and cultural value. However, one of the most important determinants of ORV track presence was accessibility, especially proximity to a road. Access infrastructure, such as proximity to roads, is often used to proxy demand and use in expert-based spatial assessments of ecosystem services. The results of our empirical model underscore the importance of incorporating patterns of both supply (i.e., desired natural amenities) and demand (i.e., access) into ecosystem service assessments. In addition, when integrated with maps of environmental sensitivity and more detailed information about human use, the predictive map of areas providing potential recreation experiences can be used for comprehensive spatial planning of sustainable ORV recreation. One possibility suggested by our results is that careful planning and management of access routes may be an effective means to achieve sustainable ORV recreation.     

The CWSI variations of a cotton crop in a semi-arid region of Northeast Brazil

A field experiment was conducted with a cotton crop during the growing season of August 1993 to January 1994, in a semi-arid region of Northeast Brazil. The objective of this research is to evaluate the diurnal and seasonal variations of Crop Water Stress Index—CWSI, based on the canopy energy balance. Canopy temperature, air temperature, net radiation, wind speed and psychrometric measurements were made regularly at 10 and 14 h, and several diurnal cycles were also obtained. It was concluded that the irrigation should be initiated when the CWSI approaches 0.3. After a second stress event the crop took 3 days to resume transpiring at normal rate. The CWSI of NSP at 14 h presented more negative values than those obtained at 10 h. The response of CWSI with respect to T_c, r_c/r_a and R_n is evident and probably the most important source of error in CWSI determination.     

Effects of land cover and soil properties on denitrification potential in soils of two semi-arid grasslands in Inner Mongolia,China

High N₂O emissions have been observed in semi-arid grasslands, especially during freeze/thaw periods, when denitrification might be the main process of N₂O production. However, there have been few denitrification studies in semi-arid grassland. This study was designed to determine the denitrification potential of four representative land cover types (typical steppe, meadow steppe, marshland, arid steppe) in two grasslands in Inner Mongolia, China. We found that soils from different land cover types exhibited significantly different denitrification potentials, with highest rates in marshland and lowest rates in arid steppe. Denitrification potentials were maximal in the upper layer and generally decreased with depth for all soils. Soil water content, soil carbon and nitrogen availability, and C/N ratio were found to be significantly correlated with denitrification potentials in all soils. Addition of glucose or/and nitrate significantly increased denitrification activities throughout the profile for all soils, suggesting that both bioavailable carbon and nitrogen were limiting factors of denitrification in these grasslands soils. However, further field studies are needed to translate the denitrification potentials determined in laboratory measurements to denitrification rates under field conditions.     

近50年来西北半干旱区气候变化特征

选用西北半干旱区33个气象站1951-2004年温度、降水、相对湿度、风速、蒸发量等气象观测资料,分析主要气候要素变化规律,揭示了近50年来西北半干旱区气候变化的一些新特征.结果表明,西北半干旱区降水量近50年来年际变化趋势除个别地方外绝大多数地区呈下降趋势,降水量变化曲线线性拟合倾向率在-59.168～-1.143 mm/10 a之间,秋季降水量减少最多,春季次之,而夏季部分地区和冬季大部分地区降水量呈略增趋势.降水量存在3年、6～8年的周期振荡特征,3年周期振荡在1962-1966年为中心的局部时段内最强,之后逐渐减弱.6～8年振荡在1980-1985年为中心的局部时段内最强.气温距平呈上升趋势,气温距平变化曲线线性拟合倾向率在0.074～0.507 ℃/10 a之间,大部分地区呈先降后升型,转型时间为20世纪60年代后期至70年代前期.冬季气温增高最多,秋季、春季次之,夏季陕、甘、宁交界区及陇中地区气温增高而其余地区气温距平略呈下降趋势.相对湿度近50年来年呈波动变化.平均风速近50年来年际变化趋势除个别地方略增外,其余各地均呈下降趋势.蒸发量近50年来年际变化趋势除个别地方呈上升趋势外,其余各地蒸发量呈下降趋势.     

The role of drought among agro-pastoral communities in a semi-arid environment: The case of Botswana

Agro-pastoral livelihoods in semi-arid Botswana have evolved and adapted to recurrent droughts endemic to the region. Droughts, more than any other phenomena, have shaped and influenced rural communities' interaction with their environment on which they eke a living. The physical aspect of droughts and their effects are well known, but the often subtle and complex dynamics emanating from drought outbreaks are less understood among communities. A study was conducted during the 2009/2010 season to investigate how communities in Kgalagadi North and Bobonong Sub-districts perceive droughts, anticipate droughts and which sections of the respective communities were most vulnerable to drought shocks. An extensive agro-ecological knowledge base, in form of environmental indicators, was used by communities to predict imminent droughts. Preparations included storing excess crop harvests during good years, storing crop residues for livestock, buying commercial feed to supplement livestock and seeking alternative sources of income outside the agricultural sector. In spite of these efforts, drought still affected the communities negatively mainly through increased livestock mortalities and crop failure-especially among poorer households. Subsequently, it is recommended that any effective aid interventions ought to understand and appreciate these dynamics to enhance resilience to future droughts and ensure sustainable rural development.     

Effects of soil and vegetation on runoff along a catena in semi-arid Spain

Runoff and infiltration were investigated on abandoned fields of patchy vegetation in semi-arid Spain during 15 months of natural rainfall and by rainfall simulations. The aim was to ascertain sources and sinks of runoff and the effects of soils and plant cover. Soils of the catena developed from mica schists of the upper hillslopes, fan deposits of the lower hillslopes, and an alluvial terrace at the bottom. Runoff from natural events were from three sets of three pairs each of 10 × 2 m runoff plots. The pairs of each set had different densities of plant cover; the sets were vegetated with tussock grass, Stipa tenacissima, a shrub, Anthyllis cytisoides, and a bush, Retama sphaerocarpa. Nineteen natural rainfall events of intensities up to 18 mm/h produced 400 mm of rain during the study period. Because the rainfall threshold for runoff production was about 20 mm, only eight events produced runoff. The rainfall simulations used a sprinkler that produced 50 mm/h of rain for 30 minutes; runoff was recorded each minute in 0.24 m² bounded plots.The depth and structure of the soil mantle provide the main controls on runoff rates, which are lowest on the lower fan deposits and highest on the thin upslope soils. The river-bank terrace, with a surface covered by crusts and mosses, also yields relatively high runoff. In general, vegetation density varies inversely with runoff. Nevertheless, shrub and bush litter favor runoff, as does a particular spatial distribution of individual plants on the hillslope. Settling of the upper few centimeters of soils of the alluvial fan following cessation of cultivation 15 to 40 years ago has produced a near-surface compacted layer favoring shallow subsurface runoff. Apparently contradictory results between runoff plots and rainfall simulations are the result of differing processes.     

干旱区梨园不同覆盖条件下土壤环境因子综合性评价研究

在干旱沿黄灌区开展不同覆盖材料配合滴灌的灌溉保墒方式下,进一步研究了不同覆盖方式对梨园全生育期的土壤理化性状和养分含量变化影响,分析了土壤温度、水分、pH等和矿质营养元素间的相互关系,对覆盖后的土壤质量进行了综合性评价。试验处理分为无覆盖对照（T1）、园艺地布覆盖（T2）、玉米秸秆覆盖（T3）和黑地膜覆盖（T4）4个处理;试验设计为随机区组设计,每个处理小区均为167株梨树（约占地667 m²）,重复3次;各小区土样分0~20 cm、20~40 cm、40~60 cm土层取样。结果表明：（1） 园艺地布和黑地膜覆盖处理有一定的增温效应,而玉米秸秆覆盖有较好的降温和稳温效应,且增墒效应明显,土壤含水率比其他3种处理显著提高了1.0%~2.7%。（2） 相较无覆盖处理,黑地膜覆盖可提升表层土壤pH,并加速表层土壤有机质的分解,有机质含量较无覆盖处理下降33.1%;玉米秸秆覆盖可显著降低各土层的土壤pH,降低范围为1.8%~4.6%,并促进0~20 cm土层有机质的提升,土壤有机质含量增加12.2%;园艺地布覆盖下0~40 cm土层内土壤有机质含量和全盐量均有降低。（3） 黑地膜覆盖下0~20 cm和20~40 cm土层的碱解氮含量分别为73.00 mg·g^-1和64.53 mg·g^-1,均显著地高于无覆盖处理,无覆盖条件下土壤碱解氮在深层（40~60 cm土层）积累较多,显著地高于玉米秸秆和黑地膜覆盖;各处理0~20 cm和20~40 cm土层速效磷含量差异显著,大小顺序均为T4>T3>T2>T1,玉米秸秆覆盖可提升土壤速效钾和速效铁的含量。（4） 进行主成分分析表明不同覆盖方式对梨园浅层土壤环境因子的影响要明显大于深层土壤,在0~40 cm土层内各覆盖处理效果均好于无覆盖处理,其中玉米秸秆覆盖在0~20 cm和20~40 cm土层综合得分分别为1.189和0.326,覆盖效果最佳。     

Changes in soil nutrients, vegetation structure and herbaceous biomass in response to grazing in a semi-arid savanna of Ethiopia

The effect of grazing was studied on vegetation structure, herbaceous biomass, basal and bare ground covers, together with soil nutrient concentrations in two locations in an Ethiopian semi-arid savanna. The lightly grazed sites had significantly higher herbaceous diversity, total abundance, basal cover and aboveground biomass, and a lower percentage of bare ground compared with the heavy grazed sites. Grazing pressure had no effect on the density and number of woody species as well as on the proportion of encroaching woody species. The light grazing sites had higher organic carbon, phosphorus and exchangeable bases, and therefore a higher pH and higher electrical conductance, indicating an improved soil nutrient status compared with heavy grazing sites, mainly attributed to the higher basal cover and standing biomass at light grazed sites, and the export of nutrients through grazing and dung collection from the heavily grazed sites. There were significantly higher soil nutrients, species diversity, aboveground biomass and basal cover in the light grazing sites compared with heavy grazing sites. We concluded that changes in herbaceous vegetation, standing biomass and soil compositions are caused by interactions between grazing, soil and vegetation, and these interactions determine the transitions of semi-arid savannas.     

Variation and relationship between soil moisture and environmental factors in the source region of the Yangtze River from 2005 to 2016

This study analyzed soil moisture, soil erosion, and vegetation in the source region of the Yangtze River from 2005 to 2016. We found that soil moisture showed an increasing trend from 2005 to 2009 but decreased from 2009 to 2016. The surface soil moisture was severely affected by seasonal changes in the source region of the Yangtze River, especially in the soil from 0 to 40 cm. However, seasonal variation of soil moisture deeper than 40 cm was different from that in the upper layer. Soil moisture below 40 cm wasn't affected by the seasonal variation. Soil moisture from 0 to 50 cm and the average thickness of wind deposition showed a positive correlation in the study area from 2005 to 2016. For environmental protection in the source region of the Yangtze River, wind deposition played a role in water retention. Similarly, a positive correlation also existed between the average thickness of wind erosion and soil moisture. Deep-soil moisture was the key factor for vegetation structure on the Qinghai-Tibet Plateau. The results are also helpful for further understanding the variation of soil moisture on the Tibetan Plateau and providing a scientific basis for effectively protecting and controlling the ecological environment in the future.     

The significance of termites as decomposers in contrasting grassland communities of semi-arid eastern Australia

Decomposition of various litter forms including dead tussocks of two native perennial grasses, woollybutt (Eragrostis eriopoda) and mulga mitchell (Thyridolepis mitchelliana), as well as roots of woollybutt, dung of sheep and kangaroo, and bleached toilet rolls, was studied in contrasting grazing exclosures, half of which had termites excluded by biocide (termiticide) treatment. Dead mulga mitchell tussocks decayed more rapidly than woollybutt tussocks during the first 17 months post mortem. Thereafter, rate of decay differed little between species. After 3 years, only small amounts of tussock residues of either species remained and only then did the impact of biocide treatment become significant.Decomposition of kangaroo pellets was typically bimodal with significantly higher decomposition recorded in the controls (no biocide) up to 40 months after treatment, and many intact pellets remaining in the biocide-treated plots. While decomposition of sheep pellets showed similar bimodality, decomposition remained significantly lower in the biocide treatments for the entire duration of the experiment.Results suggest that abiotic processes, including those induced by UV radiation, may be dominant influences mediating decomposition of litter in these semi-arid ecosystems, especially following high-rainfall seasons when abundant grass biomass has been generated providing a surfeit of potential forage for harvester termites.     

Environmental variables related to wheat yields in the semiarid pampa region of Argentina

The current paper analyses various environmental parameters in relation to wheat yields in Bordenave, Province of Buenos Aires, Argentina. The variables used are: precipitation (ppt), maximum (Tx) and minimum temperature (Tmi) as well as those obtained by applying the Palmer model. Decadic and phenological scales are used for data corresponding to the period 1977–2000. The stepwise method is used to obtain a multi-variate equation to calculate yield taking into account environmental variables only. For a five variates model the coefficient of determination, R² equals 95.79% and the standard error of estimation is 129.0 kg ha⁻¹. In the sample yields, the incidence of total variability for thermal variables is 42.7% and for hydrological variables, 53%. The value and sign of the correlation coefficients were analysed throughout the cultivation cycle. The α coefficient is mainly responsible for yield variance during tillering and stem elongation. There is good correlation with the values of Palmer's Drought Severity Index (PDSI) for the flowering and grain filling stages.     

土壤制图中多目标属性的环境因子及其尺度选择——以黑龙江鹤山农场为例

研究影响不同土壤属性空间分布的协同环境因子及其作用尺度,对于理解不同土壤属性的成土发展、土壤推测制图及针对多种土壤属性的空间采样设计具有重要意义。针对多种土壤属性,探索不同土壤属性的重要相关环境因子及其作用尺度,并就不同环境因子及其尺度的不同对土壤属性推测制图的影响展开研究。以黑龙江省鹤山农场为研究区,以表层砂粒、粉粒、黏粒、有机质含量和土壤厚度5种土壤属性为研究对象,根据计算邻域窗口大小的不同,生成173个不同尺度的地形因子,对单尺度地形因子和多尺度地形因子进行重要性排序,并根据重要性排序构建单尺度环境因子集1和多尺度环境因子集2,和基于专家知识选出的基准环境因子集3进行制图精度的对比。结果表明：当单尺度地形因子进行重要性排序选择时,所选出的5种土壤属性的重要相关环境因子与基准环境因子集3明显不同。当多尺度环境因子参与时,尽管对各土壤属性的作用尺度不同,各土壤属性排名靠前的因子绝大多数是基准环境因子。砂粒和粉粒的重要相关因子及作用尺度相当,但与黏粒的重要相关因子和作用尺度差别很大,有机质和土壤厚度的重要相关因子十分相似。环境因子集2较基准环境因子集3的制图精度显著提高,RMSE均值提高百分比为7.8%~21.3%,较环境因子集1的制图RMSE均值提高百分比为8.7%~16.5%。因此,针对不同的土壤属性进行制图或采样设计时,需充分考虑其环境因子和作用尺度的不同,针对基准环境因子选择适宜的尺度较选择不同的相关环境因子更重要。     

阴山北部耕作土壤冻结过程温度变化的数值模拟

在建立土壤冻结模型的基础上,对内蒙古阴山北部农牧交错带耕作土壤冻结过程进行了数值模拟,计算方法采用三点中心差分格式,模拟出冻结缘变化情况下的土壤冻结过程中温度曲线.模拟结果与野外试验进行对比,结果可信.通过阴山北部耕作土壤的冻结模拟研究,揭示了该地区耕作土壤的冻结特性,对进一步研究该地区的土壤冻融变异下的风蚀提供帮助.     

Work division in family farm production units: Feminine responsibilities typology in a semi-arid region of Brazil

There has been evidence indicating that women in underdeveloped (or developing) countries carry a disproportionate burden of the costs of this economic dynamics while men enjoy its benefits. These criticisms on analysis moved gender from the periphery to the center of the development debate. Brazil and particularly the state of Ceará have not yet seen any of the repercussions of the analytical advances. This study on the role of women in the agriculture of the semi-arid aims to analyze the complexity of the factors that interact in order to recognize the nature of women's participation in semi-arid world areas comparatively to other disadvantaged environments. In the semi-arid area, rural women are able to cover a broader spectrum of tasks and fuller management activities when compared to other disadvantaged areas of the world. They cover all rural management activities. Besides, rural women's work is predominantly more complex when compared to mens work in semi-arid regions worldwide. Their greater ability to perform these activities is because these women combine different strategies in an efficient and dynamic way, adapting themselves to the demands of labor and the natural semi-arid environment.     

2000-2014年秦巴山区植被覆盖时空变化特征及其归因

利用MODIS-NDVI数据,辅以趋势分析、Hurst指数及偏相关分析等方法,本文探讨了2000-2014年秦巴山区植被覆盖时空变化特征及未来趋势,并对其驱动因素进行分析。研究发现:1近15年秦巴山区植被覆盖呈显著增加趋势,增速为2.8%/10a,其中2010年之前植被覆盖呈持续增加趋势,增速为4.32%/10a,而2010年之后呈连续下降态势,降速为-6.59%/10a;2空间上,植被覆盖格局呈现"中间高、四周低"的分布特征,高值区主要分布在陕西境内的秦岭山地和大巴山山地;3秦巴山区植被覆盖呈增加和减少趋势的面积分别占81.32%和18.68%;然而,分段结果表明,2010-2014年有71.61%的区域植被覆盖呈下降趋势;4秦巴山区植被覆盖变化的反向特征强于同向特征,其中46.89%的区域将由改善转为退化,而持续改善地区仅占34.44%;5植被覆盖变化主要归因于降水的减少,同时拉尼娜年的植被覆盖整体好于厄尔尼诺年;6人类活动对植被覆盖造成双重影响,是植被覆盖变化的另一重要影响因素。