Characteristics of Wind Erosion and Deposition in Oasis-desert Ecotone in Southern Margin of Tarim Basin,China

The oasis-desert ecotone is a fragile ecological zone that is affected both by oasis and desert conditions. To understand the impact of the differences in wind power, and the influence of wind erosion and deposition on the ecotone, meteorological data and contemporaneous wind erosion and deposition data were collected on the southern margin of Tarim Basin with serious sand-blown hazards. The wind velocity, average wind velocity, sand drift potential(DP), resultant sand drift potential(RDP), and sand transportation rate decrease significantly and successively across four landscape types with increasing vegetation coverage(VC). Flat surfaces and areas of shifting sandy ground experience intense wind erosion with fast movement of mobile sand dunes; semi-fixed sand areas experience extensive wind deposition but only slight wind erosion; and fixed sand areas experience only slight wind erosion and deposition. Volume of wind erosion on bare newly reclaimed farmland is up to 6.96 times that of bare shifting sandy ground. Wind erosion volume per unit area and VC follow an exponential function relationship in natural conditions, while wind deposition volume per unit area does not conform to any functions which has close relationship with vary topography and arrangement patterns of vegetation besides for VC. The results indicate that the volume of wind erosion has a close correlation with VC, and different types and distribution patterns of topography and vegetation also profoundly influence the wind deposition volume in the field, and underground water tables in different landscape types control the plant community distribution.

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.

Quantification of driving factors on NDVI in oasis-desert ecotone using geographical detector method

Within oasis-desert ecotone regions,the normalized difference vegetation index(NDVI)is an important parameter for evaluating the growth of vegetation.An accurate quantitative study between NDVI and environmental and anthropogenic factors is critical for understand the driving factors of vegetation growth in oasis-desert ecotone.In 2016,four periods Landsat 8 OLI_TIRS images,relevant climatological parameters data(air temperature,air relative humidity,wind velocity and accumulated temperature),land cover type data and soil data were selected as proxies.In order to quantify the explanatory power for NDVI spatial and temporal distribution in the southern edge of Dunhuang City and northern side of the Mingsha Mountain,the geographical detector model was used to explain the potential influences of factors versus the spatial distribution of NDVI,and each explanatory variable's relative importance can be calculated.The factor detector results disclose that the spatial distribution of NDVI is primarily dominated by land cover type.The risk detector results show that,high NDVI region is located within woodland.The mean value of NDVI displays an increase and then decrease trend with air temperature increase.With the increase of wind velocity and decrease of air relative humidity,the NDVI value shows a decrease trend.The interactive q values between the two factors are higher than any q value of separated factors.Results also indicate that the strongest interactive effects of NDVI are different in distinct seasons.Consequently,anthropogenic activity is more important than environmental factors on NDVI in oasis-desert ecotone.We also demonstrate that air relative humidity rather than air temperature have played a greater role in NDVI spatial distribution.

Desert vegetation distribution and species-environment relationships in an oasis-desert ecotone of northwestern China

Environmental heterogeneity significantly affects the structure of ecological communities.Exploring vegetation distribution and its relationship with environmental factors is essential to understanding the abiotic mechanism(s)driving vegetation succession,especially in the ecologically fragile areas.In this study,based on the quantitative analysis of plant community and environmental factors in 68 plots at 10 different transects in the Minqin oasis-desert ecotone(ODE)of northwestern China,we investigated desert vegetation distribution and species-environment relationships using multivariate analysis.Two-way indicator species analysis(TWINSPAN),detrended correspondence analysis(DCA),and canonical correspondence analysis(CCA)methods were used.A total of 28 species,belonging to 27 genera in 8 families,were identified.Chenopodiaceae,Zygophyllaceae,Gramineae,and Leguminosae were the largest families.Annual and perennial herbs accounted for 28.60%of the total number of plants,while shrubs(42.90%)were the most dominant.Nitraria tangutorum was the constructive species of the desert plant community.We divided the 68 plots surveyed in this study into 7 community types,according to the results of TWINSPAN.The distribution of these 7 communities in the DCA ordination graph showed that species with a similar ecotype were clustered together.Results of CCA indicated that groundwater was the dominant factor influencing vegetation distribution,while distance between plot and oasis(Dis)and soil electrical conductivity(EC)were the local second-order factors.Our study suggests that optimizing the utilization of groundwater in oases is key to controlling the degradation of desert vegetation.The favorable topographic conditions of sand dunes should be fully utilized for vegetal dune stabilization,and the influence of soil salinity on the selection of afforestation tree species should be considered.

Species diversity and its relation with soil factors under different site conditions in a desert-oasis ecotone

Vegetation and soil surveys were conducted under different site conditions in 2007-2011 to study species diversity using richness, evenness and diversity indices, in the middle portion of the Heihe River Basin. The relationship between species distribution and soil environmental factors was also studied by Canonical Correspondence Analysis （CCA）. Results show that vegetation coverage and species diversity were the highest in the interdune lowland, and the lowest in the mobile dime. Results of the Hill＇s index （di- versity ordering） shows that species diversity is reduced along decreasing soil water content, and the order of species diversity was interdune lowland, flat slope, fixed dune, semifixed dune and mobile dune. The influence degree of soil factors on vegetation dis- tribution was soil water content 〉 pH 〉 total K 〉 organic matter 〉 available N 〉 total N 〉 available K 〉 total P 〉 saline content 〉 available P. Soil water content and pH were important factors significantly affecting spatial distribution difference of vegetation, the environmental explanation was 98%.

Effects of an oasis protective system on aeolian sediment deposition:a case study from Gelintan oasis,southeastern edge of the Tengger Desert,China

Desert-oasis ecotones are boundary areas between oases and desert ecosystems.Large efforts to control sediment and stabilize these boundaries depend on understanding sedimentary processes,especially aeolian transport and deposition.Previous studies on aeolian sediment deposition have focused primarily on a single land surface type or a single engineering approach.Few studies have considered deposition in a multi-layer oasis protective system.A complete oasis protective system consists of an outer bare sand area,a sand barrier zone,a shrub and herbaceous plant zone,and a farmland shelter zone.This study used sedimentary analysis to quantify grain-size characteristics in samples from the four land surfaces under different types of weather conditions in the Gelintan oasis of the Tengger Desert,the fourth largest desert in China.The results showed that aeolian sediment deposition decreased from the outer bare sand area through the oasis protective system and into the interior.The four land surface types showed significant differences in deposition volume(P<0.05).Deposited sediment showed gradual decrease in dominant grain-size from sand to silt,but sediment deposited during dust weather contained a larger coarse-grained fraction.From the outer desert to the inner oasis,transport mechanisms shifted from saltation(sand)to suspension(silt and smaller)in non-dust weather.During dust weather,deposition primarily occurs from near-surface aeolian sand transport with saltation.Sediment sorting decreased from exterior to interior zones of the protective system while skewness and kurtosis showed no significant change(P<0.05).These results can help inform strategies for stabilizing and protecting desert-oasis ecotones in this region and other localities.

Carbon assimilation characteristics of plants in oasis-desert ecotone and their response to CO_2 enrichment

Six species of more than 20-year-old desert woody plants in the oasis-desert ecotone were selected for study. The results showed that: (1) in different growing seasons δ13 C values of assimilating organ varied between -14‰ and -16‰ for Haloxylon ammodendron (HA),-14‰ - -15‰ for Calligonum mongolicum (CM) and -25‰ - -28‰ for Caragana korshinskii (CK), Nitraria sphaerocarpa (NS) and Hedysarum scoparium (HS). (2) The net photosynthetic rate (Pn) of HA and CM was significantly higher than those of the other species. With the decrease in Pn for the six species, their intercellular CO2 concentration increased, but stomatal limitation value decreased under the intensive light. At the same time, the photochemical efficiency of PS Ⅱ dropped to different degrees. (3) The CO2 enrichment experiment demonstrated that, Pn of HA and CM increased to different extent under 450 μmol/mol, but their Pn reduced or approximated to the current condition under 650 μmol/mol. Under 450 μmol/mol the efficiency for solar energy utilization of CK and HS significantly reduced and under 650 μmol/mol their respiration rate exceeded photosynthesis rate. It can be concluded that HA and CM have some function of pathway for C4, but the other three species have the function for C3. The decline in their Pn is mainly caused by non-stomatal factors. HA, CM, CK and HS exhibited photoinhibition, which disappeared in a short time. This is a kind of positive readjustment to adapting to the desert environment. HA and CM can adapt to the high CO2 environment, but CKand HS cannot. With the rise in atmospheric CO2 concentration and climate warming, the latter two species in the oasis-desert ecotone may be gradually degraded or even disappear.

The effect of hydrologic process changes on NDVI in the desert-oasis ecotone of the Hexi Corridor

In the arid inland river basins of northwestern China,human activities control almost all the surface hydrologic processes.The potential effects of these altered hydrologic processes are gradually becoming clear,especially since the 2000 implementation of the integrated water resources management projects in the Shiyang River,the Heihe River,the Tarim River,and the Shuler River.While the appearance of these eco-hydrology changes and consequent environmental effects in the oasis has attracted broad attention,related research is still lacking.Eco-hydrological process changes in the desert-oasis ecotone were investigated in the Pingchuan irrigation district in the middle reaches of the Heihe River.The results showed that the annual average amount of surface water irrigation during the past 20 years has decreased by 1.498×107 m3,while the annual average amount of well irrigation has increased by 1.457×107 m3,since 2000,when the State Council of China approved the water diversion scheme for the Heihe River Basin.The groundwater depth before the water diversion scheme generally varied between2.44–3.19 m(average 2.73±0.24 m),while that after the water diversion scheme has varied between 3.08–4.01 m(average3.79±0.62 m).The distribution area of<3 m groundwater depth decreased from 3612 to 394 hm2;while the distribution area of>3 m groundwater depth increased from 853 to 3843 hm2.However,although the hydrologic processes changed dramatically,no significant effects on vegetation productivity in the desert-oasis ecotone were detected during the study period.

策勒绿洲-沙漠过渡带不同沙丘的沉积物粒度特征及沉积环境

[目的]通过对策勒绿洲-沙漠过渡带不同沙丘类型下风沙沉积物粒度、磁化率分布特征及环境敏感粒级组分进行分析,探讨不同沙丘类型下风沙沉积物相关参数及分布规律。[方法]基于绿洲-沙漠过渡带4种沙丘各部位粒度数据及磁化率数据,采用数理统计方法进行相关性分析。[结果]4种沙丘在不同地貌部位表层的沙物质粒级含量有所差别,回涡、灌丛、新月形及风影沙丘表面沙物质主要由极粗粉砂、极细砂、细砂组成,百分含量总和由小到大依次为96.71%,97.54%,98.48%,98.65%。4种不同沙丘表面沙物质分选性均为分选中度好。不同沙丘的峰态平均值介于0.93~1.02,属于中等峰态,从总体上分析4种沙丘的峰态值从迎风坡底到顶部逐渐增大,顶部到背风坡底部逐渐减小。新月形沙丘偏度值最小,偏度值介于-0.03~0.01,主要表现为对称,风影、回涡及灌丛沙丘偏度值介于-0.04~0.44,为对称和正偏。风影、灌丛及新月形沙丘表面沙物质平均粒径与偏度值呈极显著正相关(p<0.01),表明沙粒平均粒径愈粗愈趋向正偏。风影、回涡及新月形沙丘表面沙物质偏度与峰态呈极显著正相关(p<0.01),沙物质分选性愈差,就愈趋于窄峰态。通过沉积环境判别得出沉积物为风成沙,主体为风成沉积环境,4种不同的沙丘环境敏感粒级组分集中于100~570μm,表明研究区域风沙活动强烈。由于地理要素所组成的差异化构造及人为原因,导致每个不同地貌部位表面沉积物的粒级-标准偏差值相对变化差异较大。[结论]绿洲-沙漠过渡带4种风积地貌沙物质粒径差异主要是由地形、风况及沙源沉积物结构所导致。

2015-2020年准噶尔盆地南缘荒漠绿洲交错带土地沙化敏感性时空变化

为探讨准噶尔盆地南缘荒漠绿洲交错带土地沙化的变化规律,选取干燥度指数、起沙风天数、土壤质地、植被覆盖度4个因子作为评价指标,基于多源数据开展准噶尔盆地南缘荒漠绿洲交错带2015—2020年土地沙化敏感性空间分布格局及其动态变化研究。结果表明:2015、2020年准噶尔盆地南缘荒漠绿洲交错带67%~70%的评估区域土地沙化敏感性处于敏感等级,一般敏感占评价区总面积的28%~31%,极敏感等级面积不足3%,主要发生在研究区东部戈壁区域。总体上,2015—2020年准噶尔盆地南缘荒漠绿洲交错带土地沙化敏感性除巴里坤山南部戈壁区域、奇台县、吉木萨尔县、克拉玛依局部区域、乌苏市西北角外,其余变化区域均由敏感性高等级向低等级转化,土地沙化敏感性呈改善趋势。

绿洲-荒漠交错带土壤水分变化特征初步研究

以甘肃省的民勤绿洲为例 ,选择土壤水分最为亏缺的 7月 ,对白刺 (Nitrariatangutorum)沙包不同迎风面 ,以及绿洲和荒漠交错地带的土壤水分进行了取样分析。结果表明 ,对于白刺沙包而言 ,其上层和深层土壤水分是迎风坡大于背风坡 ,中间层次 (4 0～ 80cm)则刚好相反。在绿洲与荒漠的交错带上 ,灌丛沙包与沙丘间低地水分变化有很大的不同 ,总体而言 ,丘间地水分含量大于灌丛沙包 ,但在距离绿洲 40 6m处 ,二者均出现一个土壤水分的最低值。在丘间地表层 ,水分变化是距离绿洲愈近 ,土壤含水量愈高 ;而深层土壤水分的变化趋势则刚好相反。在灌丛沙包上 ,其土壤水分大多在 1.5 %左右 ,远低于植物的萎蔫系数 ,故不能够满足植物生命活动之需 ;在绿洲至流动沙丘这一环境梯度带 ,其水分变化可以明显划分为 3个区间。基本规律是 ,愈靠近绿洲 ,土壤含水量也愈高 ;而随着与绿洲距离的逐渐拉大 ,其深层含水量增加、各土层之间的含水量差值也在逐步增大。在丘间地与灌丛沙包底部接触处的丘间地上层 ,存在一个 2 0cm厚度的高含水层 ,这一层次为灌丛植物在年内气候干旱期的生命维持提供着重要水源保证。

绿洲-荒漠过渡带景观的植被与土壤特征要素的空间异质性分析

采用变异函数的理论和方法 ,通过空间异质性特征比较 ,研究了阜康绿洲 荒漠过渡带景观中的植被盖度和土壤环境因子的空间异质性、空间格局及其关系 .在此基础上 ,应用Kriging局部块段插值法 ,以三维图形显示出各个要素的空间分布格局 .结果表明 ,除土壤全盐量空间相关性较弱外 ,其他各要素具有中等程度以上的空间相关性 ,且空间变异主要发生在较小尺度上 .其中 ,植被盖度的空间异质性程度较高 ,在 3km的尺度内具有明显的空间格局 .从空间分布格局看 ,植被盖度、土壤表层含水量和土壤 pH值沿样带相邻点差异对比明显 ,高值区和低值区交错 .草本盖度与土壤表层含水量、土壤 pH间有相关关系 ,灌木平均盖度主要依靠深层次地下水维系 .灌木和草本盖度的块金值具有明显差异 ,可能因为二者要求不同的生态条件 。

绿洲-荒漠过渡带四种植物光合及生理特征的研究

绿洲-荒漠过渡带植被的恢复和更新在过渡带生态环境建设中具有重要意义。通过对多枝柽柳,梭梭,头状沙拐枣和沙枣的光合特性、水势(ψ)以及生理指标的研究,结果表明,1)4种植物光响应曲线变化趋势基本一致,均表现为净光合速率(A)随着光合有效辐射(PAR)的增大迅速增大,当PAR达到了植物的光饱和点之后,A出现下降的趋势;作为C4植物的头状沙拐枣和梭梭都具有较高的光饱和点(LSP)和光补偿点(LCP),体现出了C4植物特有的高光合的优势,而其他一些光合参数K,Amax,Rday的变化规律并不完全一致;2)4种植物中,梭梭具有较低的清晨和正午水势,说明梭梭主要依靠夜间水分恢复能力来应对干旱环境;清晨水势除头状沙拐枣和沙枣之间差异不显著外,其他植物种之间的差异均达到了极显著水平(P<0.01),正午水势除多枝柽柳和沙枣之间差异不显著,其他植物种之间的差异也都达到了极显著水平(P<0.01);3)4种植物中脯氨酸和可溶性糖的变化较为一致,头状沙拐枣均显著高于其他3种植物(P<0.05);而丙二醛含量最高的是沙枣,最低的为头状沙拐枣和梭梭,除头状沙拐枣和梭梭之间差异不显著之外,其他植物种之间的差异均达到显著水平(P<0.05);4)在相关分析的基础上运用平均隶属函数法对这4种植物进行抗旱性排序,结果表明,4种植物的抗旱性强弱顺序依次是梭梭>多枝柽柳>沙枣>头状沙拐枣。

绿洲-荒漠交错带环境特征初步研究

以甘肃省石羊河下游的民勤绿洲为例 ,对其绿洲外围与荒漠交错地带的植被和与植被关系密切的灌丛沙包特征进行了系统研究 .结果表明 ,由于生态交错带边缘效应的存在 ,植被盖度的变化呈现绿洲附近与交错带外围靠近流沙的地方较低 ,而位于流沙和绿洲之间的部分相应较高 .植被盖度较高的部位主要集中于自流动沙丘至绿洲外 6 0 0m处 ,而非紧靠近绿洲 .这与地下水自沙漠向绿洲方向运移有关 .在绿洲外缘 30 0～ 6 0 0m的范围内植被盖度出现下降 ,原因可能与绿洲荒漠交错带界外区的形成有关 ,说明研究区绿洲外 0～ 6 0 0m范围即是该区域绿洲界外区的存在区域 .灌丛沙包上的裸沙率以绿洲界外区为最大 ,大量沙包裸露 ,可致沙子的活动性增强 ,因此该地带是对绿洲土地造成沙质荒漠化的最大流沙来源 .

克里雅河流域荒漠-绿洲交错带3种不同生活型植物的光合特性

利用LI-6400光合仪测定新疆克里雅河流域荒漠-绿洲交错带自然生长的芦苇、柽柳、胡杨叶片的气体交换参数及环境影响因子,通过对比3种植物光合特性的差异及其与环境因子间的关系,探讨3种植物对荒漠环境的适应特性和机制。结果表明:(1)3种植物叶片Pn日变化均呈不对称的双峰曲线,"午休"现象明显,Pn日均值的大小依次为胡杨>芦苇>柽柳,种间差异不显著。(2)Tr、PAR和Gs与3种植物Pn的日变化存在极显著或显著的相关关系,其中影响芦苇Pn的主要因子是Tr、PAR和Gs,作用效应为Tr>Gs>PAR;影响柽柳Pn的主要因子是Tr、Gs,作用效应为Tr>Gs;影响胡杨Pn的主要因子是Tr。(3)3种植物的光合作用对光强和CO2的响应特征可用二次方程描述;光补偿点和饱和点均为柽柳>胡杨>芦苇;CO2补偿点为胡杨>柽柳>芦苇,饱和点为胡杨>芦苇>柽柳。(4)3种植物的表观量子效率在0.0341—0.0411 mol/mol之间,羧化效率在0.0480—0.0546 mol m-2s-1之间。综合比较表明,3种干旱区植物在自然条件下日均净光合速率、光能利用率和CO2同化能力差异不显著,气孔限制是光合"午休"现象产生的主要原因;影响3种植物光合作用的主导因子各不相同,但Tr与Pn间的关系较其它因子更为密切。

阜康绿洲-荒漠交错带荒漠植被群落稳定性

以阜康绿洲-荒漠交错带的荒漠植被为研究对象,利用样区内植被常规调查资料,改进了法国生态学家M.Godron从工业生产中发现并引入生态学研究中的稳定性测定方法,并将研究方法推广到植被群落的空间稳定性研究。根据这种方法,累积种类百分数与累积相对盖度比值越趋近于20/80群落就越稳定,在20/80这一点上是群落的稳定点。研究结果证实:从空间上看,绿洲-荒漠交错带不同植物群落稳定性不同;绿洲-荒漠交错带的荒漠植被群落稳定性受种间竞争、环境压力和干扰活动三个因素的影响,即使建群种相同的群落稳定性也会出现较大差异。

绿洲-沙漠过渡带引种植物光合生理特征研究

为了研究引种植物在绿洲-沙漠过渡带极端干旱条件下的适应性,在自然条件下对3种引种植物文冠果、酸枣、紫叶小檗的光合、水分等生理指标进行了研究。结果表明,1)3种植物的光响应曲线变化趋势基本一致,均表现为随着光合有效辐射(PAR)的增大净光合速率(Pn)先增大后减小;文冠果和紫叶小檗的光饱和点明显高于酸枣(P<0.01),说明文冠果和紫叶小檗利用强光的能力较大,对光环境的适应性较强;紫叶小檗的最大净光合速率(Pnmax)和暗呼吸速率(Rd)也明显高于文冠果和酸枣,表明紫叶小檗具有高光合耐胁迫的优势。2)3种植物的叶绿素含量和丙二醛含量的变化一致,文冠果均显著高于其他2种植物(P<0.05);3种植物的可溶性糖含量差异不显著(P>0.05),而紫叶小檗的脯氨酸含量显著高于其他2种植物(P<0.01),说明在该生境下紫叶小檗能够较好的保持体内水分含量,较好的适应该生境。3)3种植物的清晨水势和正午水势都有相同的大小关系,都是文冠果较大,酸枣最小,而且植物种之间差异极显著(P<0.01),说明紫叶小檗和酸枣的吸水能力较强,它们主要依靠夜间水分恢复能力来应对干旱环境。总的来说,3种植物的光合参数及生理指标的变化趋势不是完全一致,这可能是由于植物种之间的个体差异,以及不同植物对同一生境的差异所致,因此,要想选取适合在策勒绿洲-沙漠过渡带大面积种植的引种植物,还需做进一步的研究。

新疆策勒沙漠-荒漠-绿洲典型下垫面小气候空间变化分析

利用从2010年8月1日至2011年6月30日新疆策勒绿洲-荒漠过渡带及绿洲内部4个观测点的风速、大气相对湿度(RH)、温度、太阳辐射能、光合有效辐射(PAR)同步观测资料,分析了小气候差异并初步探讨产生差异的原因。结果表明:不同空间的下垫面性质对小气候影响明显不同。在8月,半固定沙地、固定沙地和绿洲内部与流沙地前沿相比,日平均风速在2 m高处分别依次降低了42.69%、50.71%和94.32%,日平均风速在10 m高处分别依次降低了7.94%、13.66%和59.59%,这表明植被覆盖度越大,防风阻沙效果越好。夏季植被能够降温增湿,冬季12月份,绿洲内部在0.5 m高处日平均温度依次高于流沙地、半固定沙地、固定沙地1.47℃、1.20℃、2.74℃。4个下垫面的PAR与太阳辐射能变化趋势基本一致,绿洲内部的PAR值相对最小,太阳辐射能在6月达到最高值。夏季晴天在20:00~09:00左右近地表层会出现逆温现象。冬季晴天白天午后易出现大于起沙风的阵风,从流沙前沿到绿洲内部气温逐渐升高,大气相对湿度先逐渐降低后增大。

绿洲-荒漠过渡带芨芨草地SPAC系统蒸散与①多环境因子关系分析

利用波文比能量平衡法对天山北麓绿洲荒漠过渡带芨芨草地的夏季蒸散量进行测定,采用通径分析与相关分析相结合的方法探讨了蒸散与主要环境因子之间的关系,建立了适合该地区的蒸散预测模型。结果表明:(1)各种环境因子对蒸散影响的大小排序为:净辐射(R n)>土壤热通量(G)>空气温度(T气)>空气相对湿度(RH)>5 cm土壤温度(T土-5 cm)>实际水汽压(e a)>风速(Vwind)>5 cm土壤含水率(S土-5 cm);(2)各因子通过R n对蒸散产生的间接作用都大于其自身直接作用,反映出净辐射是制约蒸散大小的主导因子,是决定干旱区蒸散量的关键;(3)土壤热通量对蒸散的直接负效应远小于通过其他因子的间接正效应,出现其直接负效应与综合效应相反的结果;(4)建立并经过检验的蒸散预测模型表明:与温暖湿润区蒸散依靠水、热并重情况不同的是,极端干旱区主要依靠热量因子强度的增加,才能有较大的蒸散量。

绿洲-沙漠过渡带骆驼刺群落的防风阻沙作用

以塔克拉玛干沙漠南缘的策勒绿洲——沙漠过渡带为研究区,从防风阻沙的角度研究该区域主要植物群落-骆驼刺群落的生态学特性,并分别对骆驼刺样地和裸沙样地进行梯度风速和多向输沙的同步对比观测,结合输沙势的季节和方向分布,确定骆驼刺群落的防风阻沙作用。结果表明,多年生木质化草本植物骆驼刺在4月上旬萌发,5～7月为生长旺季,8月以后生长缓慢,以木质化过程为主。4～6月为该区域的强风盛行期,活体骆驼刺植被的盖度并不能有效防止风蚀,但头年生长的骆驼刺地上部分干枯死亡后仍处于直立状态,在翌年风季来临时有效发挥防风阻沙作用。与裸沙地相比,覆盖度在30%左右的骆驼刺样地风速可降低26%～67%,对应的地表输沙通量也仅为裸沙地表的15%。根据实测输沙量与风能的关系推断,如果没有骆驼刺植物的保护,每年从策勒绿洲西部风沙前沿进入绿洲内的单宽输沙量可达到170.24 t.km-1.a-1,而骆驼刺地表单宽输沙量仅为26.43 t.km-1.a-1,可见骆驼刺群落具有极好的阻沙效果。