Impact of climate change and human activities on the spatiotemporal dynamics of surface water area in Gansu Province, China

Understanding the dynamics of surface water area and their drivers is crucial for human survival and ecosystem stability in inland arid and semi-arid areas.This study took Gansu Province,China,a typical area with complex terrain and variable climate,as the research subject.Based on Google Earth Engine,we used Landsat data and the Open-surface Water Detection Method with Enhanced Impurity Control method to monitor the spatiotemporal dynamics of surface water area in Gansu Province from 1985 to 2022,and quantitatively analyzed the main causes of regional differences in surface water area.The findings revealed that surface water area in Gansu Province expanded by 406.88 km2 from 1985 to 2022.Seasonal surface water area exhibited significant fluctuations,while permanent surface water area showed a steady increase.Notably,terrestrial water storage exhibited a trend of first decreasing and then increasing,correlated with the dynamics of surface water area.Climate change and human activities jointly affected surface hydrological processes,with the impact of climate change being slightly higher than that of human activities.Spatially,climate change affected the'source'of surface water to a greater extent,while human activities tended to affect the'destination'of surface water.Challenges of surface water resources faced by inland arid and semi-arid areas like Gansu Province are multifaceted.Therefore,we summarized the surface hydrology patterns typical in inland arid and semi-arid areas and tailored surface water'supply-demand'balance strategies.The study not only sheds light on the dynamics of surface water area in Gansu Province,but also offers valuable insights for ecological protection and surface water resource management in inland arid and semi-arid areas facing water scarcity.

Land-Air Interaction over Arid/Semi-arid Areas in China and Its Impact on the East Asian Summer Monsoon. Part I:Calibration of the Land Surface Model (BATS)Using Multicriteria Methods

To improve the land surface simulation in the arid and semi-arid areas of northern China, the observational data from two field experiments in Dunhuang and Tongyu are used to optimize the parameters in the land surface model, BATS, through calibration with the multicriteria method. Sensitivity analysis to the parameters in Dunhuang and Tongyu indicates that different parameters need to be calibrated in two sites with different environmental and climate regimes. Comparison of observed sensible heat flux, latent heat flux, and ground surface temperature with the simulated ones shows the simulations with the optimized parameters have been substantially improved. Especially, the holistic simulations with the calibration of the parameter values are much closer to the observations in the arid region （Dunhuang）, and the energy partition with the calibrated parameters can also be simulated well in the semi-arid region （Tongyu）. Whole results demonstrate that the parameter calibration of the land surface model is important when the model is to be used to investigate the land-air interaction.

Three-year Variations of Water, Energy and CO_2 Fluxes of Cropland and Degraded Grassland Surfaces in a Semi-arid Area of Northeastern China

Based on 3 years （2003-05） of the eddy covariance （EC） observations on degraded grassland and cropland surfaces in a semi-arid area of Tongyu （44°25′N, 122°52′E, 184 m a.s.1.）, Northeast China, seasonal and annual variations of water, energy and CO2 fluxes have been investigated. The soil moisture in the thin soil layer （at 0.05, 0.10 and 0.20 m） clearly indicates the pronounced annual wet-dry cycle; the annual cycle is divided into the wet （growing season） and dry seasons （non-growing season）. During the growing season （from May to September）, the sensible and latent heat fluxes showed a linear dependence on the global solar radiation. However, in the non-growing season, the latent heat flux was always less than 50 W m^-2, while the available energy was dissipated as sensible, rather than latent heat flux. During the growing season in 2003-05, the daily average sensible and latent heat fluxes were larger on the cropland surface than on the degraded grassland surface. The cropland ecosystem absorbed more CO2 than the degraded grassland ecosystem in the growing season in 2003-05. The total evapotranspiration on the cropland was more than the total precipitation, while the total evapotranspiration on the degraded grassland was almost the same as the total annual precipitation in the growing season. The soil moisture had a good correlation with the rainfall in the growing season. Precipitation in the growing season is an important factor on the water and carbon budget in the semi-arid area.

The causes of land landscape changes in semi-arid area of Northwest China: a case study of Yulin city

Rapid land landscape change has taken place in many arid and semi-arid regions such as the vulnerable ecological area over the last decade. In this paper, we quantified land landscape change of Yulin in this area between 1985 and 2000 using remote sensing and GIS. It was found that fallow landscape decreased by 125,148 hm^2 while grassland and woodland increased by 107,975 hm^2 and 17,157 hm^2, respectively. The major factors responsible for these changes are identified as the change in the government policy on preserving the environment, continued growth in mining, and urbanization. The efforts in restoring the deteriorated ecosystem have reaped certain benefits in reducing the spatial extent of sandy land through replacement by non-irrigated farmland, woodland and grassland. On the other hand, continued expansion of mining industry and urbanization has exerted adverse impacts on the land landscape. At present regional economic development conflicts directly with the protection of the natural environment. Such a conflict has caused the destruction to the land resources and fragmentation of the landscape accompanied by land desertification, the case is even serious in some localities.

Foliar δ^13C Values and Water Use Efficiency ofSemi-arid Plants in Horqin Sandy Land, China

Water was a key factor restricting the plantation in sandy areas. Foliar δ^(13)C value regarded as an indicator of longterm water use efficiency(WUE) of plants was generally used to evaluate the adaptability of plants to arid and semi-arid environment. In Horqin sandy land of China, the foliar δ^(13)C values of 114 species in 35 families naturally growing in the area, and 15 species of sand-fixing trees and shrubs were measured and analyzed in 2012. The results showed that 97 species in all 114 species were C_3 plants and only 17 species were C_4 plants. Most C_4 plants belonged to Gramineae family. The foliar δ^(13)C value of C_3 plants was between -25.000 and -31.075‰ with an average of-28.226‰, while those of C_4 plants between -12.578 and -16.334‰, with an average of -13.678‰. The δ^(13)C values of mature leaves collected in August were averagely 0.85‰ less than that of juvenile leaves collected in June. The foliar δ^(13)C values and WUE of 15 sand-fixing tree species in Horqin sandy land ranked in the order as: S.vulgaris >H.rhamnoides >C.ovata >P.mongolica >T.chinensis >R.typhina >S.matsudana >E.angustifolia >U.pumila >S.gordejevii >X.sorbifolia >C.microphylla >H.fruticosum >C.korshinskii >E.bungeanus.

Impact of Coal Mining Subsidence on Sandy Geomorphology and Vegetation Habitat in Sandy Area

[Objectives]To explore the problem of"secondary desertification"caused by coal mining subsidence in sandy area and its control countermeasures.[Methods]The collapse fissure changes,vegetation displacement and tilt,dry sand layer and wind erosion/aeolian deposit rate of the edge,middle and basin of subsidence area were studied in detail.[Results]The width and density of fissures at the edge of subsidence area were the smallest,followed by those in the center,and the width and density of fissures in the basin of the subsidence area were the greatest,while the staggering and surface damage showed the opposite trend.The average displacement length of vegetation in the subsidence area reached 60 cm,the slope was 5.67-28.63,and the maximum wind erosion/aeolian deposit at the trunk roots was-30.52 cm/+25.41 cm,most serious at the edge of subsidence.The changes in displacement length and slope of vegetation were positively linearly correlated with the height and surface damage of collapse fissures.The thickness of dry land layer at the edge of the subsidence area reached 14 cm,4-6 cm greater than that of the control,and the thickness of dry land layer in the middle and basin of the subsidence area was both about 11 cm,1-4 cm greater than that of non-subsidence area.The wind erosion rate at the edge of the subsidence area was up to 83.34%,followed by that(52.06%)in the middle.The aeolian deposit rate in the subsidence basin was 51.84%.[Conclusions]The subsidence edge has the strongest impact on the sandy geomorphology and vegetation habitat,and is a key area for ecological restoration.It is recommended that the coal mining subsidence should be treated in a timely manner to avoid the occurrence of"secondary desertification".

断缝体识别及储层发育模式——以准噶尔盆地玛湖凹陷玛东地区百口泉组为例

断缝体是一种新的储集体类型。它是由断层、褶皱所伴生的裂缝与基质孔共同构成,具有立体不规则孔缝特征的构造地质体。断缝体包括断层滑动面、破碎带及诱导缝,既是致密砂砾岩油气藏富集的主要因素,又是钻井风险防控及储层精准改造的关键因素。准噶尔盆地玛湖凹陷玛东地区百口泉组致密砂砾岩储层具有埋深较大、岩性致密、非均质性强、异常压力高、压裂改造难度大等特征,其断缝体刻画成为制约油气效益开发的技术难点。文中以准噶尔盆地玛湖凹陷玛东地区三叠系百口泉组致密砂砾岩储层裂缝为研究对象,在地震、岩心、成像测井等资料分析的基础上,从不同尺度精细描述了裂缝响应特征及断缝体储层发育模式。通过钻井资料及压裂资料分析,断缝体识别方法得到了验证,同时也为油田地质工程一体化效益开发提供了重要的技术支撑。

鄱阳湖地区级配不良偏细砂砾石料力学特性

基于大型三轴试验数据,研究了级配和相对密度D_(r)对鄱阳湖地区级配不良偏细砂砾石料强度和变形特性的影响。结果表明:随着小于5 mm粒径颗粒质量分数的增加,砂砾石料压实性能降低;随着大于5 mm粒径颗粒质量分数P_(5)和D_(r)的增大,强度指标、初始切线弹性模量与体积模量增大;本文研究范围内,随P_(5)和D_(r)的增大,强度指标c、φ、φ_(0)、Δφ线性增大,且P^(5)和D_(r)对强度指标的作用效应几乎不存在相互影响;随P 5和D_(r)的增大,邓肯E-B模型参数K、K_(b)增大,且P_(5)越高D_(r)对K、K_(b)的影响越显著,D_(r)越大时P_(5)对K、K_(b)的影响越强烈,存在相互影响效应;提出了考虑级配与D_(r)双重影响的强度指标和变形参数经验计算公式,该公式能高精度预测鄱阳湖地区级配不良偏细砂砾石覆盖层料的力学指标。

风沙区不同配置农田防护林防护效应及其对农田土壤水分的影响

[目的]明确风沙区不同配置农田防护林产生的防护效果差异以及影响田间土壤含水率的作用因子,为该地区水分管理和土地利用提供理论依据。[方法]选择南疆阿拉尔市十团3种典型配置的农田防护林,研究不同配置防护林内土壤含水率、风速、光照强度、空气温湿度等因素,综合分析土壤含水率变异性决定因子。[结果]疏透度为41%的5行新疆杨对田间小气候改善作用在0~1 H范围最显著,疏透度为47%的1行胡杨+2行新疆杨的林内有效防护距离最长,且田间土壤含水率显著大于5行新疆杨且大于4行新疆杨。5行新疆杨林内土壤含水率主要受空气温度、湿度、光照强度的影响,4行新疆杨和1行胡杨+2行新疆杨土壤含水率与防护林距离和土层深度有关。总体来看,林带疏透度对土壤含水率有直接负向作用,同时土壤容重随土层深度变化间接对含水率产生负向影响。[结论]合理调整农田防护林配置结构,能够提高防护林防护效益,为风沙区作物生长提供有利条件,同时促进当地水资源合理利用和可持续发展。

高寒半干旱区沙地植被土壤水分变化特征及其影响因素

为揭示高寒半干旱区不同降雨强度对植被差异下沙化土地土壤含水量变化过程的影响。以青海共和盆地东缘黄沙头乔木、灌木和裸地为研究对象,基于2020、2021和2022年5月—9月植物生长季土壤含水量、降雨量和细根分布监测数据,分析2020年、2021年、2022年各生境0—200 cm深度土壤水分对小雨、中雨、大雨的响应。连续动态监测结果表明,大雨、中雨条件下,随土层深度的增加土壤水分对降雨的响应时间延长。乔木林和灌木林土壤水分对中雨、大雨最大响应深度为70 cm、100 cm,裸地对中雨、大雨最大响应深度为50 cm、100 cm。随土层深度的增加,小雨对乔木、灌木、裸地土壤水分的补充作用逐渐降低;中雨对灌木林土壤水分的补充作用逐渐降低,乔木林与之相反;大雨时乔木林、灌木林变异系数呈现S型变化,因此大雨对其土壤水分的补充存在明显的分层利用现象。不同植被类型土壤水分空间变化差异以及对降雨的响应受植被冠层截留对降水再分配的影响,土壤含水量与环境因子间的主成分分析表明,郁闭度、叶面积指数、150—200 cm土壤容重、细根生物量密度、根表面积密度、根长密度、比根长是反映研究区土壤水分的显著因子(P<0.05)。研究表明不同降雨强度植被土壤含水量存在明显差异,高寒半干旱区沙化土地乔、灌植被的建植可提升深层土壤储水能力;结果可为沙化土地恢复和水土流失防控提供科学依据。

平原沙土区河岸带不同植被类型对土壤团聚体稳定性的影响

[目的]明晰不同植被类型对土壤团聚体稳定性及团聚体有机碳含量的影响,为平原沙土区河岸带土壤团聚体稳定性和抗蚀能力提升提供基础数据。[方法]以江苏省平原沙土区丰县复新河河岸带15年生杨树纯林、柳树纯林、杨柳混交林3种植被类型及对照为对象,用湿筛法对0—20 cm, 20—40 cm, 40—60 cm^(3)个层次土壤颗粒进行物理分级,测定了>0.25 mm团聚体含量(R0.25)、平均重量直径(MWD)、几何平均直径(GMD)、分形维数(D)及有机碳等主要指标,并利用线性回归对各指标相关性进行分析。[结果](1)试验地各土层团聚体以<0.25 mm微团聚体为主,占总团聚体含量的50.33%~80.00%。3种植被类型>2 mm和0.25~2 mm粒径团聚体含量高于对照,各土层中杨树纯林>2 mm大团聚体含量最高。(2)与对照相比,3种植被类型R0.25,MWD和GMD分别提高了41.77%~91.28%,29.89%~79.08%和37.60%~94.32%,其中杨树纯林效果最好。杨树纯林和柳树纯林D显著低于对照(p<0.05)。(3)试验地土壤团聚体有机碳含量范围为1.51~6.48 g/kg。与对照相比,3种植被类型下土壤团聚体有机碳含量提高了31.67%~71.68%,杨树纯林团聚体有机碳含量显著高于柳树纯林和杨柳混交林(p<0.05)。杨树纯林在0—20 cm土层各粒径团聚体有机碳含量最高。(4)线性回归分析表明土壤团聚体稳定性与有机碳显著相关,尤其是与大团聚体有机碳含量显著相关。此外,细根生物量、全氮含量、碳氮比和含水率也是影响团聚体稳定性的重要因素。[结论]平原沙土区河岸带杨树纯林更有利于提高土壤团聚体稳定性,增加土壤抗蚀能力。

合水地区长6_(3)深水重力流沉积特征研究

合水地区是鄂尔多斯盆地近年来原油勘探的重点区块,在系统分析沉积构造、岩石学特征、结构粒度特征等沉积相识别标志的基础上,结合区域沉积背景,开展了合水地区长6_(3)重力流沉积类型及展布特征研究。结果表明,合水地区长6_(3)油层亚组为湖泊-重力流沉积体系,发育半深湖-深湖沉积亚相,可进一步划分为浊流沉积、砂质碎屑流、滑塌沉积三种重力流沉积类型;其中砂质碎屑流及浊流为主要控砂微相,主要分布在研究区的中部、南部区域,为区内有利储集相带。

沉积模式约束的蚀源区砂砾岩分布预测研究

古潜山油气藏表面普遍发育一套准原地沉积成因的砂砾岩储层,物性好、产能高但展布规律复杂,亟需开展储层分布预测,支持潜山油气藏开发。该文以渤海A油田太古界潜山为例,采用“将今论古”思路,建立蚀源区砂砾岩沉积原型模式。基于微古地貌恢复,充分利用三维地震资料的低频响应特征,实现了古潜山蚀源区砂砾岩储层分布预测,取得以下认识:(1)蚀源区砂砾岩沉积受局部地形地貌控制,在山地区、山间洼地、山间沟谷形成不同沉积组合模式;(2)在印模法基础上,采用层面斜率属性差异放大技术实现了微古地貌精细刻画,基于低频地震数据开展地震属性分析,利用属性分布与微地貌单元的对应关系,进一步判断储层分布预测结果的合理性。A油田研究结果显示,其蚀源区砂砾岩分布符合山地区发育的“山间侵蚀河道-山前冲积扇”组合模式,山间沟谷内砂砾岩呈连续条带状,山峰山脊区砂砾岩发育程度低、呈不连续斑块状分布,山前斜坡地貌单元砂砾岩呈连片分布。

晋北风沙区3个种源山桃生长及抗逆性比较分析

以晋北风沙区3个种源山桃为试验材料,分别研究其生长及抗逆性状.结果表明,怀仁市金沙滩山桃种源在生长状况、耐寒性、耐旱性方面优于其余2个种源.怀仁市金沙滩山桃种源较适宜于在晋北风沙区推广.

Origin and depositional model of deep-water lacustrine sandstone deposits in the 7th and 6th members of the Yanchang Formation(Late Triassic),Binchang area,Ordos Basin,China

Sandstones attributed to different lacustrine sediment gravity flows are present in the 7th and 6th members of the Yanchang Formation in the Ordos Basin, China. These differences in their origins led to different sandstone distributions which control the scale and connectivity of oil and gas reservoirs. Numerous cores and outcrops were analysed to understand the origins of these sandstones. The main origin of these sandstones was analysed by statistical methods, and well logging data were used to study their vertical and horizontal distributions. Results show that the sandstones in the study area accu- mulated via sandy debris flows, turbidity currents and slumping, and sandy debris flows predominate. The sand- stone associated with a single event is characteristically small in scale and exhibits poor lateral continuity. How- ever, as a result of multiple events that stacked gravity flow-related sandstones atop one another, sandstones are extensive overall, as illustrated in the cross section and isopach maps. Finally, a depositional model was developed in which sandy debris flows predominated and various other types of small-scale gravity flows occurred frequently, resulting in extensive deposition of sand bodies across a large area.

Species composition and diversity,and carbon stock in a dune ecosystem in the Horqin Sandy Land of northern China

In this study, we determined carbon allocation and carbon stocks in the plant-soil system of different dune ecosystems in northeastern China. We quantified the species composition, above and below-ground bio masses, and carbon stocks of three dune types （i.e. active dunes, semi-stabilized dunes and stabilized dunes） and their corresponding inter-dune lowlands （i.e. interdune lowlands of active dunes, interdune lowlands of semi-stabilized dunes and interdune lowlands of stabilized dunes） in the Horqin Sandy Land. The results showed that the succession series on interdune lowlands of the Horqin Sandy Land confirmed differences in species composition of the various dune types. Aboveground carbon （AGC） on the interdune lowlands of semi-stabilized dunes （33.04 g C/m2） was greater （P〈0.05） than that on the interdune lowlands of active dunes （10.73 g C/m2）. At the same time, the different dune types did not show any significant differences （/：〉〉0.05） in belowground plant carbon （BGC）. However, the percentage of plant BGC in interdune lowlands of active dunes （81.5%） was significantly higher （P〈0.05） than that in the interdune lowlands of semi-stabilized dunes （58.9%）. The predominant carbon pool in the study dune ecosystem was in the soil. It accounted for 95% to 99% of total carbon storage. Soil organic carbon （SOC） was at least 55% greater （P〈0.05） in the interdunes than in the dunes. Stabilized dunes showed at least a 37% greater （P〈0.05） SOC content than active dunes up to a 1-m soil depth. Meanwhile, SOC content of interdune lowlands of semi-stabilized dunes was greater （P〈0.05） than that of interdune lowlands of active dunes only up to a 20-cm soil depth. The dune ecosystem showed a great potential to store carbon when interdune lowlands of active dunes were conversed to interdune lowlands of semi-stabilized dunes, which stored up to twice as much carbon per unit volume as interdune lowlands of active dunes.

Revisit of event-based rainfall characteristics at Shapotou area in northern China

Distribution of rainfall event sizes and interval lengths between events are important characteristics of arid and semi-arid climates. Understanding their importance will contribute to our ability to understand ecosystem dynamics in these regions. Rainfall event timing and magnitude are important drivers of ecosystem processes and are instrumental in creating land-scape heterogeneity in arid and semi-arid regions. Rainfall event characteristics were analyzed using an automatic tip-ping-bucket rain-gauge record across the entire summer monsoon season from 2008 to 2015 at the arid desert area of Shapotou in the Tengger Desert, China. Changing the minimum inter-event time （MIT） from 30 min to 24 h alters the number of rainfall events from 64 to 25 for the event depth larger than 0.1 mm. The mean rainfall intensity declined from 0.95 mm/h to 0.53 mm/h, and the geometric mean event duration rose from 0.55 h to 4.4 h. The number of rainfall events, mean rainfall intensity, and geometric mean event duration differed under different criteria of individual rainfall depths, except that for an individual rainfall depth of 0.5, 1.0, and 5.0 mm. The aforementioned features differed only at the lowest range of the mean rainfall intensity and depth for MIT=3 and 6 h. These findings suggest that identification of event-based rainfall in this specific arid region can be better achieved by setting the MIT at six hours. The wide variation in rainfall event properties indicate the need for paying more attention to the proper selection and reporting of event criteria in studies that adopt event-based data analysis. This is especially true in quantifying effective rainfall for soil water replenishment in terms of rainfall depth and intensity with infrequent rainfall events.

Estimation of Small Reservoir Sedimentation in Semi-Arid Southern Zimbabwe

Small surface reservoirs play an important role of providing ready and convenient source of water for various uses in semi-arid areas which are characterized by erratic and low rainfall. Lack of current data on reservoir capacity loss due to sedimentation is one of the challenges to the sustainable management of surface reservoirs. The study investigated the capacity loss due to sedimentation from 2000-2012, and estimated the trap efficiency of the Mutangi reservoir which is located in semi-arid Chivi, Southern of Zimbabwe. Hydrographic surveys, grab sampling and water depth-capacity methods were used to determine the capacity of the dam as of 2012. To compute capacity loss from 2000 to 2012, the 2000 and 2012 dam capacities were compared whilst the trap efficiency of the reservoir was determined using a set of empirical models that relates trap efficiency to the capacity-watershed area ratio and capacity-inflow ratio. The results show that Mutangi reservoir has a trap efficiency of 95% - 98% (av = 96.4%) and has lost 37% of its capacity due to sedimentation in 12 years (2000 and 2012). Rates of sedimentation were 8539 t·yr-1, 9110?t·yr-1 and 8265 t·yr-1 for the hydrographic survey, grab sampling and water depth-capacity method respectively, and the little difference in these figures demonstrates that any method can be used to determine sedimentation rates. The area specific sediment yield (ASY) ranged from 14 - 15.5 t·ha-1·yr-1 (av = 14.956 t·ha-1·yr-1). At the current rate of sedimentation the projected dead level of the reservoir will be lost to sedimentation in 8 years while the useful life of the reservoir is estimated to be 30 years. Capacity loss due to sedimentation is further complicating the already strained water scarcity situation in semi-arid areas and management decisions should be made based on the current sedimentation rates estimated by different methods. These results imply that management practices that reduce erosion, hence sedimentation in these small reservoirs should be practiced in order to prolong their lifespan.