Desert-oasis Ecotone Research Articles

The trade-off in the establishment of artificial plantations by evaluating soil properties at the margins of oases

The establishment of forest plantations in oasis–desert ecotones is crucial for reducing wind erosion, sand fixation, and for maintaining the stability of oases. In such oasis–desert ecotones in the arid regions of northwestern China, the dominant forest plantations are Haloxylon ammodendron, Populus simonii Carr. and Pinus sylvestris var. mongolica Litv. However, the effects of these plantations on soil properties remain unknown. We undertook soil properties surveys on soils under native desert land, 21-year-old Haloxylon ammodendron, 27-years-old Populus simonii Carr. and 33-years-old Pinus sylvestris var. mongolica Litv. plantations. We found that the Populus simonii Carr. and Pinus sylvestris var. mongolica Litv. plantations significantly improved the porosity, physical stability index, water-holding capacity, and macroaggregates of the soil as well as soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), microbial biomass carbon (MBC), and nitrogen (MBN) contents, and urease, β-glucosidase and alkaline phosphatase activities. The 21-year-old Haloxylon ammodendron plantation (no irrigation) significantly increased urease and β-glucosidase activities and MBC content—but not soil porosity, bulk density, water-holding capacity,or SOC, TN and TP contents—when compared with the desert land. Based on these results, it was concluded that establishment of Populus simonii Carr. and Pinus sylvestris var. Mongolica Litv. plantations could significantly ameliorate soil properties with the necessary irrigation input. While establishment of a Haloxylon ammodendron plantation does not require irrigation, it did not have the desired effect on the physical and chemical properties of the soil. An artificial Haloxylon ammodendron plantation degenerates after about 30years, and will not withstand wind erosion due to its low soil physical stability index and scarce carbon and nitrogen sequestration capacities. Water resources are extremely scarce in this region so a balance between ecological benefits and irrigation inputs should be considered in the design and establishment of artificial plantations in the oasis–desert ecotones. A single, large Haloxylon ammodendron, Populus simonii Carr. or Pinus sylvestris var. mongolica Litv. plantation is not recommended—the complex forest systems of these plantations should be properly designed and established in the desert–oasis areas.

Spatial change of the grain-size of aeolian sediments in Qira oasis-desert ecotone, Northwest China

In order to understand the environmental influence of oasis-desert ecotone to oasis ecological system, we comparatively analyzed the grain size characteristics of various aeolian sediments, including the sediments in oasis-desert ecotone, shelterbelt and the inside oasis and in Qira River valley. The results showed that the grain size characteristics (including grain-size distribution curve, grain size parameters, and content of different size classes) of sediments in the oasis-desert ecotone were consistent along the prevailing wind direction with a grain-size range of 0.3-200 μm and modal size of 67 μm. All of the sediments were good sorting and mainly composed of suspension components and saltation components, but not denatured saltation and creeping components (>200 μm). They were typically aeolian deposits being short-range transported. The grain sizes of sediments in oasis-desert ecotone were smaller than that in the material sources of Qira River valley and desert (0.3-800 μm), but very similar to those of the modern aeolian deposits in oasis-desert ecotone, shelterbelt and the inside oasis. The denatured saltation and creep components (>200 μm) were suppressed to transport into oasis-desert ecotone because of the high vegetation cover in oasis-desert ecotone. Therefore, like the shelterbelts, the oasis-desert ecotone could also block the invasion of desert. They safeguarded the oasis ecological environment together.

Evaluation of two empirical wind erosion models in arid and semi-arid regions of China and the USA

Wind erosion models are important tools for assessing soil erodibility and identifying management practices to control erosion. The Agricultural Policy/Environmental eXtender (APEX) model and Revised Wind Erosion Equation (RWEQ) were tested using data collected from the Tarim Basin of China and Columbia Plateau of the United States of America. Adequate performance in simulating soil loss was achieved using the original APEX model and RWEQ in respectively a cotton field and desert-oasis ecotone in the Tarim Basin and winter wheat - summer fallow (WW-SF) field in the Columbia Plateau. We calibrated the APEX model and RWEQ to improve performance because both models have many empirical parameters. After calibration, both models adequately simulated soil loss from all land use types except the RWEQ from the red date orchard in the Tarim Basin. Inadequate performance of the calibrated RWEQ in the red date orchard was likely due to underestimating maximum mass transport.

Soil macropore characteristics following conversion of native desert soils to irrigated croplands in a desert-oasis ecotone, Northwest China

Sustainable use of cultivated desert soils is important for agricultural productivity in desert-oasis ecosystems. However, how soil macropore characteristics may change as a result of agricultural exploitation remains unclear. The objective of this study was to quantify and compare soil properties and macropore characteristics in an old oasis field (>50years of cultivation, OOF), young oasis field (20 years, YOF), and adjacent uncultivated sandy land (0year, USL) in Northwest China. Three replicated soil samples were collected from each site to investigate soil properties. Meanwhile, twelve (four replicates by three sites) intact soil core columns, 15cm in diameter and 30cm in height, were taken to analyze soil structure. Each soil column was scanned with a helical medical X-ray computed tomography (CT) at a voxel resolution of 0.469mm×0.469mm×0.600mm. The results indicated that soil properties and macropore features improved after cultivation. Silt and clay content and dry mean weight diameter (DMWD) of aggregates increased with cultivation time, whereas bulk density decreased. Soil organic carbon and total nitrogen were 7.3 times and 6.7 times greater in soils at the OOF site than USL site, respectively. The increase in silt and clay content and aggregates formation likely resulted from irrigation with silt-laden river water, which in turn impacted soil nutrient accumulation. Soils at the OOF and YOF sites had greater macroporosity compared with soil at USL, and macroporosity also increased with cultivation time. X-ray CT revealed that soil macroporosity was 8.7–18.9 times greater in irrigated croplands than native desert. Soil macropores were mainly distributed at soil depths of 0–200mm at the OOF and YOF sites, while smaller and less continuous macropores were randomly distributed across soil depths at the USL site. The larger number of macropores at the cultivated sites can be attributed to greater soil organic carbon, tillage-induced soil horizons, and alternate wetting and drying processes. Few soil macropores at the USL site may be associated with wind erosion and soil fauna burrows. Conversion of native desert soils to irrigated croplands had a positive effect on soil pore development in the desert-oasis ecotone.

民勤绿洲荒漠过渡带人工梭梭群落与水土因子的关系

PDF HTML阅读 XML下载 导出引用 引用提醒 民勤绿洲荒漠过渡带人工梭梭群落与水土因子的关系 DOI: 10.5846/stxb201509041825 作者: 作者单位: 甘肃省治沙研究所 作者简介: 通讯作者: 中图分类号: Q944.53 基金项目: 国家科技支撑计划资助项目（2012BAD16B0203）；兰新高铁特大风区风沙灾害防治技术资助项目（HHS-TSS-STS-1504）；国家自然科学基金资助项目（41361004）；国家重点基础研究发展计划资助项目（2012CB723203）；甘肃省沙生植物保护利用科技创新团队资助项目（1207TTCA002） Relationships between artificial Haloxylon ammodendron communities and soil-water factors in Minqin oasis-desert ecotone Author: Affiliation: State Key Laboratory Breeding Base of Desertification and Aeolian Sand Disaster Combating,Gansu Desert Control Research Institute,Lanzhou,Gansu Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:作为绿洲可持续发展的重要生态屏障，人工梭梭群落的演替关系着民勤绿洲的生态安全。以民勤绿洲边缘人工梭梭群落为研究对象，在野外调查的基础上，采用双向指示种分类（TWINSPAN）和典范对应分析（CCA）数量生态学方法分析了人工梭梭群落与水土环境因子的关系。结果表明：（1）TWINSPAN方法将人工梭梭群落划分为4个群丛类型：群丛I梭梭+白刺-沙蒿-盐生草（Haloxylon ammodendron+Nitraria tangutorum-Artemisia frigida-Halogeton glomeratus）、群丛Ⅱ梭梭+沙拐枣-沙米（Haloxylon ammodendron+Calligonum mongolicum-Agriophyllum squarrosum）、群丛Ⅲ梭梭+白刺-芦苇（Haloxylon ammodendron+Nitraria tangutorum-Phragmites australis）、群丛Ⅳ梭梭+柽柳+盐爪爪（Haloxylon ammodendron+ Tamarix ramosissima+Kalidium foliatum）；（2）CCA排序第1轴代表生境水分及有机质梯度的变化，第2轴代表生境土壤盐分的环境梯度。Monte Carlo检验和前项选择结果表明，人工梭梭群落演替的环境调控因子排序为土壤水分（10%） > 有机质（9.7%） > pH（8.8%） > 速效磷（8.4%） > 土壤沙粒（7.8%） > 地下水埋深（7.8%） > 样方距离绿洲之间的距离（7.2%） > 全氮（6.9%） > 电导率（6.7%）。TWINSPAN分类结果在CCA样方-环境因子排序图中有较好的反映，分类和排序结果较为吻合。（3）土壤含水量、酸碱度、沙粒体积百分比、速效磷、有机质、全氮、电导率与空间因子样方与绿洲的距离解释了物种格局变化的19.8%，其中土壤因子占15.6%，地下水因子占1.1%，土壤与地下水因子交互作用解释部分占3.1%。对于50%以上未能被解释的变异部分，可能归咎于未被选取的环境因子如降水、风蚀沙埋、封禁或者随机过程。 Abstract:The ecological safety of Minqin oasis depends on the evolution of artificial Halxylon ammodendron communities that acts as important barriers and promotes the continual development of the oasis. The relationship between artificial H.ammodendron communities and environmental factors was evaluated and analyzed using the quantitative ecology methods, two-way indicator species analysis (TWINSPAN) and canonical correspondence analysis (CCA) in this research. The results showed that (1) there were 4 types of associations in artificial H.ammodendron communities using TWINAPAN:AssociationⅠH. ammodendron+Nitraria tangutorum-Artemisia arenaria-Halogeton glomeratus; AssociationⅡH.ammodendron+Calligonum mongolicum-Agriophyllum squarrosum; Association Ⅲ H. ammodendron+Nitraria tangutorum+Phragmites australis; Association Ⅳ H. ammodendron+Tamarix ramosissima +Kalidium foliatum. (2) The first axis of CCA ordination represented the environmental gradient of water and soil organic matter, meanwhile soil electrical conductivity was reflected by second axis of CCA ordination. Forward selection and Monte Carlo test suggested that the ordination of environmental factors determining species distribution of artificial H. ammodendron communites was soil water content(10%) > soil organic matter(9.7%) > pH(8.8%) > available phosphorus(8.4%) > sand(7.8%) > groundwater depth(7.8%) > distance between oasis and desert(7.2%) > total nitrogen(6.9%) > electrical conductivity(6.7%).The classification results of TWINSPAN were exactly reflected in the CCA two-dimensional ordination diagram for samples and environmental variables. (3) PCCA revealed that soil factors such as soil water content, organic matter, sand, electrical conductivity, available phosphorus, total nitrogen, pH, and groundwater factors together explained 19.8% of the variance in species distribution of artificial H. ammodendron communities. Soil factors alone explained 15.6% of the variance, groundwater factors accounted for 1.1% of the variance, and the interaction between soil and groundwater factors explained 3.1% of the variance. The partitioning of variance using the PCCA helped identify the important habitat factors regulating species distribution of artificial H. ammodendron communities at the study site. However, the fact that more than half of the variance was unaccounted for by the factors studied suggested that other influences that were not examined could also play a role in determining the occurrence and distribution of artificial H. ammodendron communities, such as rain events, wind erosion, and sand burying, as well as banned and random events. 参考文献 相似文献 引证文献

Groundwater facilitated water-use efficiency along a gradient of groundwater depth in arid northwestern China

Groundwater strongly impacts ecosystem performance in arid regions by driving vegetation structure and species distribution. It is unknown how water use efficiency varies along a gradient of depth to groundwater (DWT). In this study, we developed a framework to estimate water use efficiency (WUE), groundwater use efficiency (GUE), and rain use efficiency (RUE), and to examine the contribution of rainfall to transpiration in groundwater-dependent ecosystems (GDEs). The method was applied to an arid region in northwest China with a gradient of groundwater depth from 0.5 to 12m. The results indicate that the above-ground primary production, evapotranspiration, plant transpiration, WUE, and GUE decreased significantly from riparian forest, wetland, oasis edge, desert-oasis ecotone, and to sandy desert along a gradient of increasing DWT. RUE is found to be 0.26gm−2mm−1 at the sandy desert without groundwater contribution where 21% of rainfall is used for transpiration. Water use efficiency increases to 0.85gm−2mm−1 at the riparian site where groundwater is about 0.5m depth. The fraction of rainfall consumed by plants increases with a decreasing DWT from a threshold of 6.3m, suggesting groundwater enhances rain use efficiency in GDEs.

Varying water utilization of Haloxylon ammodendron plantations in a desert-oasis ecotone

Haloxylon ammodendron is a desert shrub used extensively in China for restoring degraded dry lands. An understanding of the water source used by H. ammodendron plantations is critical achieving sustainable vegetation restoration. We measured mortality, shoot size, and rooting depth in 5-, 10-, 20-, and 40-year-old H. ammodendron plantations. We examined stable isotopic ratios of oxygen (δ18O) in precipitation, groundwater, and soil water in different soil layers and seasons, and in plant stem water to determine water sources at different shrub ages. We found that water acquisition patterns in H. ammodendron plantations differed with plantation age and season. Thus, the main water source for 5-year-old shrubs was shallow soil water. Water sources of 10-year-old shrubs shifted depending on the soil water conditions during the season. Although their tap roots could absorb deep soil water, the plantation main water sources were from soil water, and about 50% of water originated from shallow and mid soil. This pattern might occur because main water sources in these plantations were changeable over time. The 20- and 40-year-old shrubs acquired water mainly from permanent groundwater. We conclude that the main water source of a young H. ammodendron plantation was soil water recharged by precipitation. However, when roots reached sufficient depth, water originated mainly from the deep soil water, especially in the dry season. The deeply rooted 20- and 40-year-old shrubs have the ability to exploit a deep and reliable water source. To achieve sustainability in these plantations, we recommend a reduction in the initial density of H. ammodendron in the desert-oasis ecotone to decelerate the consumption of shallow soil water during plantation establishment.

Effects of farmland shelterbelts on accumulation of soil nitrate in agro-ecosystems of an oasis in the Heihe River Basin, China

Using tree shelterbelts to protect adjacent crops from the destructive effects of wind, wind-driven particles, direct sunlight, and extreme climatic conditions is a common agricultural practice. Trees and crops, however, will inevitably compete for the same water and nutrient resources, especially along their common border. This study evaluated the effects of shelterbelts on the amounts of nitrate and water in the adjacent cropland soils under field conditions in an oasis-desert ecotone in the Heihe River Basin, China. Nitrate contents were measured in an experimental plot during the cropping season to a depth of 300cm in a poplar/wheat system at distances of 2, 14, 29, and 42m from the shelterbelt with three replicates in the soil profiles. Both soil-water content and crop yield increased with distance from the shelterbelt. Nitrate concentrations in the soil, however, generally decreased with distance from the trees and with depth. Nitrate concentrations in the 200–300cm layer were much higher at distances from the shelterbelt of 2 and 14m than at 29 and 42m, indicating that more nitrate accumulated in deeper layers closer to the shelterbelt. A survey of nitrate accumulation in nearby fields supported these findings. The higher amount of residual nitrogen (N) closer to the shelterbelt was due to the shading of the crop by the trees that reduced N uptake, mineralization of soil organic matter, and accumulation of litter and increased the lateral movement of nitrate. The accumulated N compensated for the N lost due to the interception and uptake by nearby trees. Nitrates likely leached into and polluted the groundwater. Decreasing N fertilization near the trees and partial replanting of the shelterbelt should be considered for managing nitrate levels in the region.

Two energy balance closure approaches: applications and comparisons over an oasis-desert ecotone

Studies of energy balance that rely on eddy covariance (EC) are always challenged by energy balance closure, which is mainly caused by the underestimations of latent heat flux (LE) and sensible heat flux (Hs). The Bowen ratio (BR) and energy balance residual (ER) approaches are two widely-used methods to correct the LE. A comprehensive comparison of those two approaches in different land-use types is essential to accurately correcting the LE and thus improving the EC experiments. In this study, two energy balance approaches (i.e., BR and ER) were compared to correct the LE measured at six EC sites (i.e., three vegetated, one mixed and two non-vegetated sites) in an oasis-desert ecotone of the Heihe River Basin, China. The influences of meteorological factors on those two approaches were also quantitatively assessed. Our results demonstrated that the average energy closure ratio ((LE+Hs)/(Rn–Gs); where Rn is the surface net radiation and Gs is the surface soil heat flux) was approximately close to 1.0 at wetland, maize and village sites, but far from 1.0 at orchard, Gobi and desert sites, indicating a significant energy imbalance at those three latter sites. After the corrections of BR and ER approaches that took into account of soil heat storage, the corrected LE was considerably larger than the EC-measured LE at five of six EC sites with an exception at Gobi site. The BR and ER approaches yielded approximately similar corrected LE at vegetated and mixed sites, but they generated dissimilar results at non-vegetated sites, especially at non-vegetated sites with low relative humidity, strong wind, and large surface-air temperature difference. Our findings provide insight into the applicability of BR and ER approaches to correcting EC-based LE measurements in different land-use types. We recommend that the BR-corrected and ER-corrected LE could be seriously reconsidered as validation references in dry and windy areas.

Soil properties and herbaceous characteristics in an age sequence of Haloxylon ammodendron plantations in an oasis-desert ecotone of northwestern China

Haloxylon ammodendron, a typical desert shrub with C4 pathway of photosynthesis, possessing a strong ability to adapt to an extreme drought environment, has a rapid growth rate in sandy lands and is widely used in sand-fixing shelter-forest systems in oasis-desert ecotones. To assess the effects of H. ammodendron plantation on the soil, we measured soil properties and herbaceous characteristics along a nearly 40-year chronosequence after H. ammodendron was planted in shifting sand dunes in an oasis-desert ecotone. Results showed that silt and clay fractions increased significantly in the topsoil. The accumulation rates of soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) were faster in the early stages (0–9 years) and slower in the late stages (9–39 years). The soil pH and electrical conductivity (EC) were higher than those in the non-vegetation dunes. Moreover, the soil properties in the topsoil (0–5 cm) showed larger variation scope than those in the deeper soil layers (5–20 cm). The significant relationships of the soil silt+clay content with the chemical properties mainly appeared in the topsoil. The wind erosion susceptibility of the soil, evaluated by erodible fraction (EF), decreased significantly with increasing H. ammodendron plantation age. Additionally, the annual pioneer herb, Agriophyllum squarrosum, was gradually substituted by the annual salt-tolerant herb, Bassia dasyphylla, with increasing plantation age. These results showed beneficial effects of H. ammodendron plantation on improving soil conditions. However, the dynamics of the herbaceous species also reminded us that the long-term effects of H. ammodendron plantation, especially on changes in vegetation composition, still need further evaluation.

Spatial-temporal variability of soil water content in a cropland-shelterbelt-desert site in an arid inland river basin of Northwest China

Knowledge of the spatial-temporal variability of soil water content (SWC) is critical for understanding a range of hydrological processes. In this study, the spatial variance and temporal stability of SWC were investigated in a cropland-shelterbelt-desert site at the oasis-desert ecotone in the middle of the Heihe River Basin, China. The SWC was measured on 65 occasions to a depth of 2.8m at 45 locations during two growing seasons from 2012 to 2013. The standard deviation of the SWC versus the mean SWC exhibited a convex upward relationship in the shelterbelt with the greatest spatial variation at the SWC of around 22.0%, whereas a linearly increasing relationship was observed for the cropland, desert, and land use pattern. The standard deviation of the relative difference was positively linearly correlated with the SWC (p<0.05) for the land use pattern, whereas such a relationship was not found in the three land use types. The spatial pattern of the SWC was more time stable for the land use pattern, followed by desert, shelterbelt, and cropland. The spatial pattern of SWC changed dramatically among different soil layers. The locations representing the mean SWC varied with the depth, and no location could represent the whole soil profile due to different soil texture, root distribution and irrigation management. The representative locations of each soil layer could be used to estimate the mean SWC well. The statistics of temporal stability of the SWC could be presented equally well with a low frequency of observation (30-day interval) as with a high frequency (5-day interval). Sampling frequency had little effect on the selection of the representative locations of the field mean SWC. This study provides useful information for designing the optimal strategy for sampling SWC at the oasis-desert ecotone in the arid inland river basin.

Leaf C:N:P stoichiometrical and morphological traits of Haloxylon ammodendron over plantation age sequences in an oasis‐desert ecotone in North China

AbstractHaloxylon ammodendron, a typical C4 desert shrub, is widely used in vegetation reestablishment programs to stabilize shifting sand dunes and to control shifting sands encroaching into oases in the oasis‐desert ecotones in northwestern China. In this study, we investigated the morphological traits and analyzed leaf carbon (C), nitrogen (N), and phosphorus (P) stoichiometrical characteristics in an age sequence of 2‐, 5‐, 9‐, 13‐, 16‐, 31‐, and 39‐year old H. ammodendron plantations, to assess their growth development and degeneration processes. Results showed that the height, stem diameter, and canopy increased rapidly in the early establishment stage (2–9 years), and thereafter, showed a slower increase from 13 to 39 years. The leaf C and N concentrations and N:P ratio showed a rapid increase from ages 2–5, but C:N exhibited a significant decline. After 5 years, plantation leaf C, N, C:N, and N:P were stable, and leaf P and C:P showed no significant difference among all plantation ages. Leaf C and N concentrations were mainly affected by soil properties. Limiting nutrient factors in soil changed from nitrogen before 2 years to phosphorus after 5 years. The findings suggested that leaf stoichiometrical characteristics combined with morphological traits can be used to reflect the degeneration trend of H. ammodendron. Further research is needed to reveal the processes and mechanisms of H. ammodendron growth development and degeneration, and its adaption to the soil environment.

Uncertainty in Ecohydrological Modeling in an Arid Region Determined with Bayesian Methods.

In arid regions, water resources are a key forcing factor in ecosystem circulation, and soil moisture is the critical link that constrains plant and animal life on the soil surface and underground. Simulation of soil moisture in arid ecosystems is inherently difficult due to high variability. We assessed the applicability of the process-oriented CoupModel for forecasting of soil water relations in arid regions. We used vertical soil moisture profiling for model calibration. We determined that model-structural uncertainty constituted the largest error; the model did not capture the extremes of low soil moisture in the desert-oasis ecotone (DOE), particularly below 40 cm soil depth. Our results showed that total uncertainty in soil moisture prediction was improved when input and output data, parameter value array, and structure errors were characterized explicitly. Bayesian analysis was applied with prior information to reduce uncertainty. The need to provide independent descriptions of uncertainty analysis (UA) in the input and output data was demonstrated. Application of soil moisture simulation in arid regions will be useful for dune-stabilization and revegetation efforts in the DOE.

Validation of SWEEP for creep, saltation, and suspension in a desert–oasis ecotone

Abstract Wind erosion in the desert–oasis ecotone can accelerate desertification, but little is known about the susceptibility of the ecotone to wind erosion in the Tarim Basin despite being a major source of windblown dust in China. The objective of this study was to test the performance of the Single-event Wind Erosion Evaluation Program (SWEEP) in simulating soil loss as creep, saltation, and suspension in a desert–oasis ecotone. Creep, saltation, and suspension were measured and simulated in a desert–oasis ecotone of the Tarim Basin during discrete periods of high winds in spring 2012 and 2013. The model appeared to adequately simulate total soil loss (ranged from 23 to 2272 g m−2 across sample periods) according to the high index of agreement (d = 0.76). The adequate agreement of the SWEEP in simulating total soil loss was due to the good performance of the model (d = 0.71) in simulating creep plus saltation. The SWEEP model, however, inadequately simulated suspension based upon a low d (⩽0.43). The slope estimates of the regression between simulated and measured suspension and difference of mean suggested that the SWEEP underestimated suspension. The adequate simulation of creep plus saltation thus provides reasonable estimates of total soil loss using SWEEP in a desert–oasis environment.

Effects of variability in landscape types on the microclimate across a desert–oasis region on the southern margins of the Tarim Basin, China

ABSTRACTMicroclimates play important roles in controlling water budgets and water vapor transportation, as well as vegetation growth characteristics. In order to understand the differences in meteorological parameters under different vegetation cover (VC) and terrain conditions, wind velocity, air temperature, relative humidity (RH), photosynthetically active radiation (PAR), and solar radiation were simultaneously monitored on shifting, semi-fixed and fixed sandy lands, and an oasis. The air temperature and RH differences among the four landscape types were obvious in the period from May to October. It was found that the higher elevations of semi-fixed sandy land can influence PAR and solar radiation during sand-blowing weather. The differences of air temperature and RH among the four sites during the dust-storm and rainy days were not obvious, but their differences during sand-blowing weather were greater than during rainy weather and less than during floating-dust and sunny weather. The differences of PAR and solar radiation among the four landscape types were most obvious during the dust-storm event. During most of the weather types studied, significant positive correlations were found between wind velocity and temperature, PAR, and solar radiation, as well as between temperature and PAR, and solar radiation. Meanwhile, significant negative correlations were found between RH and wind velocity, temperature, PAR, and solar radiation. VC and topography were found to be the main factors influencing the changes in meteorological parameters between desert–oasis ecotone and oasis.

绿洲荒漠过渡带风况对波文比和蒸散发的影响研究

PDF HTML阅读 XML下载 导出引用 引用提醒 绿洲荒漠过渡带风况对波文比和蒸散发的影响 DOI: 10.5846/stxb201404250822 作者: 作者单位: 北京大学,北京大学环境与能源学院,北京大学环境与能源学院,北京大学环境与能源学院,北京大学 作者简介: 通讯作者: 中图分类号: 基金项目: 林业公益性行业科研专项(201304305); 国家自然科学基金项目(30972421); 国家自然科学基金项目(91025008) Effects of wind conditions on the bowen ratio and evapotranspiration in an oasis-desert ecotone Author: Affiliation: Energy and environment school, Peking University,,,,Peking University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:波文比-能量平衡法是目前蒸散发研究常用的方法之一。在利用波文比-能量平衡法对荒漠地区,尤其对绿洲荒漠过渡带的蒸散发进行研究时,发现有波文比波动大、蒸散发结果准确性不高等问题。如何提高波文比-能量平衡法在绿洲荒漠过渡带的准确性成为荒漠干旱区精确研究水分收支急需解决的问题。在以前的研究基础上,发现绿洲荒漠过渡带的不同风况对波文比有不同影响,这可能是造成波文比-能量平衡法在绿洲荒漠过渡带精度不高的主要原因。为了证明这个假设,于2010-2012年在西北民勤绿洲荒漠过渡带进行了野外连续观测,观测了不同风况条件下波文比、不同高度的温度差、湿度差以及蒸散发的变化规律,分析了它们的特征及其影响因素。结果表明,研究区观测期内波文比值在-17.3-16.2范围内变化,波动较大,呈"U"型变化,生长季中期波文比值低于初期和末期;在无风天气,绿洲荒漠过渡带温度、湿度梯度不受水平气流的影响,波文比波动小,异常值少,波文比方法测算出的蒸散量较为准确,能够代表实际蒸散量,所测得民勤绿洲荒漠过渡带波文比日均值为0.07,日蒸散量为1.6mm/d;在绿洲风和荒漠风天气,绿洲荒漠过渡带空气温度、湿度结构发生明显改变,波文比波动大,不同风况使得大气处于逆温或逆湿的状态,波文比-能量平衡法所测得的蒸散量负值增多,适用性降低。因而在应用波文比-能量平衡法估算绿洲荒漠过渡带的蒸散发时应该选择合适的天气和观测点,避开风况对观测结果的影响。 Abstract:The Bowen ratio-energy balance method is one of the most commonly used methods for estimating evapotranspiration. However, the Bowen ratio can fluctuate greatly and reduce the accuracy of estimates when it is applied to the study of evapotranspiration in desert areas, especially at an oasis-desert ecotone. Improving the precision of the Bowen ratio-energy balance method has become a major focus of studies aiming to accurately estimate water budgets in arid areas. In this study, we found that wind conditions had obvious effects on the Bowen ratio at an oasis-desert ecotone. This may be the main cause of low precision estimates from the Bowen ratio-energy balance method when used at oasis-desert ecotones. In order to test this hypothesis, we recorded meteorological data from May 2010 to June 2012 through the Bowen ratio system at an oasis-desert ecotone in Minqin, China. We analyzed variation in the Bowen ratio, temperature gradient, humidity gradient, and evapotranspiration between two different heights on windy days. The Bowen ratio was lower in the middle of the growing season than at the beginning or end of the season and fluctuated wildly between -17.3 and 16.2. On windless days, horizontal airflow had little effect, causing small fluctuations in the Bowen ratio, and few abnormal values. Thus, the accuracy of evapotranspiration estimates using the Bowen ratio-energy balance method was high. The daily Bowen ratio calculated by the method was 0.07, and the daily evapotranspiration estimate was 1.6 mm/d on windless days. However, the temperature gradient and humidity gradient changed significantly on windy days. Temperature and humidity inversion led to large fluctuations in the Bowen ratio, and more negative evapotranspiration estimates. In these conditions, the accuracy evapotranspiration estimates using the Bowen ratio-energy balance method was reduced. Therefore, when using the Bowen ratio-energy balance method to estimate evapotranspiration at oasis-desert ecotones, it is important to choose the right measurement points and weather to avoid adverse impacts of wind. 参考文献 相似文献 引证文献

Responses of shelterbelt stand transpiration to drought and groundwater variations in an arid inland river basin of Northwest China

Plant water use characteristics and transpiration responses under dry conditions are considered essential for effective and sustainable ecosystem management in arid areas. This study was conducted to evaluate the response of shelterbelt stand transpiration to precipitation, soil drought and groundwater variations in an oasis-desert ecotone in the middle of the Heihe River Basin, China. Sap flow was measured in eight Gansu Poplar trees (Populus Gansuensis) with different diameter at breast height over three consecutive growing seasons (2012-2014). The groundwater evapotranspiration via plant use was estimated by the White method with diurnal water table fluctuations. The results showed that precipitation increased the stand transpiration but not statistically significant (paired t-test, p > 0.05). The recharge of soil water by irrigation caused stand transpiration acceleration significantly (t-test, p < 0.05). Stand transpiration and canopy conductance increased by 27% and 31%, respectively, when soil water conditions changed from dry to wet. Canopy conductance decreased logarithmically with vapor pressure deficit, while there was no apparent relationship between canopy conductance and solar radiation. The sensitivity of canopy conductance to vapor pressure deficit decreased under dry soil conditions. Groundwater evapotranspiration (0.6-7.1 mm day(-1)) was linearly correlated with stand transpiration (1.1-6.5 mm day(-1)) (R-2 = 0.71), and these two variables had similar variability. During the drought period, approximately 80% of total stand transpiration came from groundwater evapotranspiration. This study highlighted the critical role of irrigation and groundwater for shelterbelt, and might provide the basis for the development of water requirement schemes for shelterbelt growth in arid inland river basins. (C) 2015 Elsevier B.V. All rights reserved.

Quantification of Environmental Flow Requirements to Support Ecosystem Services of Oasis Areas: A Case Study in Tarim Basin, Northwest China

Recently, a wide range of quantitative research on the identification of environmental flow requirements (EFRs) has been conducted. However, little focus is given to EFRs to maintain multiple ecosystem services in oasis areas. The present study quantifies the EFRs in oasis areas of Tarim Basin, Xinjiang, Northwest China on the basis of three ecosystem services: (1) maintenance of riverine ecosystem health, (2) assurance of the stability of oasis–desert ecotone and riparian (Tugai) forests, and (3) restoration of oasis–desert ecotone groundwater. The identified consumptive and non-consumptive water requirements are used to quantify and determine the EFRs in Qira oasis by employing the summation and compatibility rules (maximum principle). Results indicate that the annual maximum, medium, and minimum EFRs are 0.752 × 108, 0.619 × 108, and 0.516 × 108 m3, respectively, which account for 58.75%, 48.36%, and 40.29% of the natural river runoff. The months between April and October are identified as the most important periods to maintain the EFRs. Moreover, the water requirement for groundwater restoration of the oasis–desert ecotone accounts for a large proportion, representing 48.27%, 42.32%, and 37.03% of the total EFRs at maximum, medium, and minimum levels, respectively. Therefore, to allocate the integrated EFRs, focus should be placed on the water demand of the desert vegetation’s groundwater restoration, which is crucial for maintaining desert vegetation to prevent sandstorms and soil erosion. This work provides a reference to quantify the EFRs of oasis areas in arid regions.

The spatio-temporal variability of groundwater depth in a typical desert-oasis ecotone

Eight groundwater observation wells were installed along the river plain, where the landscapes varied from floodplain, to oasis farmland, to desert-oasis ecotone to desert, in a typical desert-oasis ecotone in northwestern China. Ten years of data were used to analyze temporal and spatial changes in the groundwater depth. The results indicated that in the last decade: (1) the groundwater depths in the floodplain (GW1) and the desert (GW8) were basically stable; (2) the groundwater depths in the oasis farmland (GW2, GW3, GW4) increased dramatically: the annual fluctuations were 1.43, 1.01 and 0.79 m respectively, with the groundwater depths increasing by 0.13–0.18 m every year; (3) the groundwater depths in the desert-oasis ecotone (GW5, GW6, GW7) also increased dramatically: the annual fluctuations were 1.10, 1.06 and 1.05 m respectively, and the depths increased by 0.10–0.15 m every year; (4) the influence distance between the river and both the farmland and the desert-oasis ecotone was about 1000–2000 m in the study area. These results show that the natural seasonal fluctuation influence on groundwater depths was not significant, but the human-induced fluctuations such as intensive irrigation caused a significant increase in groundwater depth in both the farmland and the desert-oasis ecotone, seriously affecting sustainable agriculture development and the environment, in the oasis.

Changes in soil and vegetation with stabilization of dunes in a desert–oasis ecotone

AbstractRevegetation of indigenous plants in a desert–oasis ecotone is an effective way of maintaining the stability of oases. Understanding the changes in vegetation and soil is crucial for restoration management. The properties of soil and vegetation at stabilized sites of different ages were investigated in a typical desert–oasis ecotone, located in the Hexi Corridor region in arid northwestern China, over a period of 40 years. The results indicated that after 40 years the organic matter, total‐N and available‐P at 0–2 cm soil depth increased from 0.1, 0.1 g kg−1, 7 mg kg−1 to 2.0, 0.9 g kg−1, and 75 mg kg−1, respectively. At 2–5 cm the organic matter, total‐N and available‐P increased from 0.4, 0.1 g kg−1, and 7 mg kg−1 to 2.3, 0.4 g kg−1, and 38 mg kg−1, respectively. The number of herbaceous species increased from 4 to 9 and the herbaceous cover increased from 6 to 28 % after 40 years. The height and cover of the sand‐binding vegetation Haloxylon ammodendron (H. ammodendron) reached the highest levels of 446 cm and 68 % after 25 years. After 35 years H. ammodendron dwindled and its belowground and aboveground biomass both decreased significantly. With effective natural regeneration, after 40 years the population of H. ammodendron remained stable and its cover and density remained at 38 % and 1870 ha−1 respectively. The positive mutual feedback between vegetation and soil permitted the sand‐binding vegetation community to become stable over time.