中国防沙治沙实践与沙漠科学发展的70年——Ⅰ.初创篇

防沙治沙工作自新中国成立之初就是国家层面上的重要任务.随着国家大规模社会经济活动的展开,干旱半干旱区的绿洲、农田、牧场、公路、铁路、渠道、乡镇村落和一些重要基础设施都面临着风沙危害,需要积极应对,开展防沙治沙工作.而面对沙漠科学基本空白的科研工作者们,则需要在形成防沙治沙关键科技支撑的同时,发展中国沙漠科学,这就是20...     

Modulus and damping from shaking table tests of reinforced soil walls

The paper presents rational procedures to estimate normalised shear modulus and damping ratio from measured responses of reinforced soil model walls tested in a 1-g shaking table. Displacement measured at the top of the model walls and input base acceleration time histories are used to produce equivalent hysteretic responses of the model walls. Equivalent hysteretic loops at different strain amplitudes are developed and used to calculate normalised modulus degradation curves and damping ratio for the tested model walls. Model wall responses are also analysed using the single degree of freedom (SDOF) model to determine damping ratio and phase difference, and to verify the validity of SDOF model for application with reinforced soil walls.

Results indicate that the normalised shear modulus significantly decreased at the early stage of the base shaking (i.e. γ_s < 0.03%). For example, about 68% and 80% reductions in shear modulus occurred at γ_s = 0.005% and 0.01% respectively. In addition, a 90% reduction in the normalised shear modulus realised at relatively strong input base acceleration (i.e. for γ_s > 0.03%). Minimum damping ratio of 5% to 10% for both model walls was obtained, increased to 15% to 20% at strain amplitude γ_s = 0.3%, and reached higher values thereafter. Finally, dynamic properties determined from the proposed method are compared with experimental and empirical relationships proposed in literature as well as resonant column test results.     

基于沙地指数模型的沙地监测方法

沙漠化是干旱、半干旱地区的重要生态环境问题,我国西北地区沙漠化土地分布广泛,加剧的沙漠化问题影响着区域经济和社会的发展,遥感技术的进步为沙漠化评估与制图提供了重要手段。本文以内蒙古自治区浑善达克沙地为研究区,基于面向对象方法,对研究区Landsat8 OLI影像进行沙地最优尺度分割。以分割对象为基础,实验在冬夏季影像上分层分阶段提取沙地。在冬季影像上,本文提出新比值型指数RSBI（Ratio Soil Brightness Index）对沙地进行提取,精度较SBI指数提高4.11%。后基于改进型植被覆盖度指数（FMSAVI）与反照率（Albedo）构建二维特征空间,建立沙地分类指数模型（DCI）,对夏季影像沙区分类。该方法总体精度为83.24%,较NDVI-Albedo二维特征空间模型精度提高5.59%,较FMSAVI模型提高16.20%。本文结合RSBI指数与FMSAVI-Albedo特征空间反演的DCI指数模型来提取沙地信息并对沙地分类,减少了沙地提取误差,提高了分类精度,为沙地信息的研究提供了新思路。     

2000—2020年中国荒漠化潜在发生范围区林草覆被时空变化特征

干旱地区林草植被生长动态变化是研究荒漠化形成发展和演变过程的重要依据。本文基于改进方向性像元二分模型构建的2000—2020年中国荒漠化潜在发生范围区（PEDC）年植被覆盖度数据集,采用Sen+Mann-Kendall时间序列趋势变化检测方法,分析了2000—2020年PEDC,特别是林草覆盖区的植被生长状况时空变化特征。研究结果表明：① 2000—2020年,PEDC平均植被覆盖度为0.284,改进的植被覆盖度估算结果能够较好地反映研究区植被覆盖状况,估算精度为86.98%。PEDC植被生长状况不断趋好,其中干旱区表现最为突出,显著增加区域达到了48%,而亚湿润干旱区平均增长量最大为0.1。② 林草生态恢复工程措施效果显著,但植被恢复是个长期缓慢的过程,特别是林草面积的恢复。2000—2010年林草面积增加较少（0.002%）;2010—2020年增加较多（0.371%）。③ 2000—2020年PEDC林地植被改善最明显,草地则较为稳定,植被覆盖度显著性增加区域分别为76.4%和71.8%。其中林地植被覆盖度在亚湿润干旱区增长量最大为0.15,而整个研究区草地增长了0.06。本文更深入地掌握PEDC林草覆盖区长时间序列植被生长状况,为进一步制定和实施各项生态工程提供重要信息参考。     

蒙古国中部草原地区风蚀沙漠化的风沙活动特征——以乔伊尔市为例

蒙古国是中蒙俄经济走廊的重要区段,但面临严重的荒漠化问题,区域经济社会发展受到严重威胁,而蒙古国中部草原地区是主要的荒漠化新扩展区,正经历强烈的草原风蚀沙漠化过程。以戈壁苏木贝尔省首府乔伊尔市为研究区,利用自建自动气象观测站（2019年5月—2020年7月）、集沙仪观测站（2019年8月—2020年8月）及当地气象站（1990—2018年）数据,对当地风蚀沙漠化的风动力条件、风沙流输沙及其他影响因素等基本特征进行了研究。结果表明：（1） 乔伊尔市具有强劲的风动力条件,年输沙势可达735.96 VU,合成输沙势为428.76 VU,合成输沙方向为SSW（195.06°）,风向变率指数为0.58,属高风能环境、中等变率双峰风况。（2） 临界起沙风速因受土壤水分和植被盖度的共同影响而随季节变化,夏季最高,冬季最低,春季与秋季居中,且相差较小。（3） 地表具有强烈的风沙活动,年风沙流输沙通量可达2.135 t·m^-1·a^-1,Owen最大输沙量模型适于该区风沙流模拟。研究结果对于蒙古国中部草原区防沙治沙和生态恢复具有重要参考价值。     

科尔沁沙地沙丘植被对丘间低地水体的影响北大核心CSCD

在流动沙丘以建立固沙植被的方式向固定沙丘转化的过程中,植被将改变沙丘水分再分配过程,影响沙丘的水文调节功能,甚至可能引起沙丘生态系统水资源失衡。为探明植被对沙丘水文调解功能的影响,以科尔沁沙地不同植被盖度的沙丘-丘间地水体组合体为研究对象,于2021年生长季开展了沙丘植被盖度、丘间低地水体变化特征、气象因素的动态观测,以期明确沙丘植被变化对丘间低地水体的影响。结果表明:(1)沙丘植被盖度影响沙丘水分对外补给能力,随着沙丘表面固沙植被盖度增加,单位面积沙丘对外水分补给能力降低,表现为流动沙丘(58.25 mm)>半固定沙丘(24.75 mm)>固定沙丘(14.87 mm),占同期降水量的比例分别为21.39%、9.09%、5.46%。(2)生长季流域降水补给量、植被盖度、气温显著影响沙丘对丘间低地水体的水分补给量,丘间低地水体获补量与流域降水补给量显著正相关,与植被盖度、气温极显著负相关。(3)依据水量平衡原理推导出沙丘水分对外补给量(Y)与影响因素(降水补给量X_(1),植被盖度X_(2),平均气温X_(3))的关系模型,Y=1052.737+0.1X_(1)-11.459X_(2)-37.585X_(3),R2=0.641。可根据模型预测沙丘水分对外补给量,为流动沙丘生物治理模式的合理选择提供支持。     

Spatio-temporal Variation of Vegetation Ecological Quality and Its Response to Climate Change in Rocky Desertification Areas in Southwest China during 2000-2020

Vegetation restoration is the primary task of ecological reconstruction and rocky desertification control in Karst areas. With vegetation net primary productivity and coverage as two key indicators, a vegetation ecological quality evaluation model was built based on meteorological and remote sensing data. Spatiotemporal variation of vegetation ecological quality index and its response to climate change in rocky desertification areas in Southwest China during 2000-2020 were also analyzed by using the difference method and linear trend method. The results showed that: (1) Vegetation ecological quality in rocky desertification areas in Southwest China showed a fluctuating upward trend during 2000-2020. In 2020, the vegetation ecological quality index reached 69.7, which was 19.9% and 9.3% higher than the averaged values for 2000 and 2000-2019, respectively, ranking the fourth highest since 2000. (2) Vegetation ecological quality of the rocky desertification areas in Yunnan, Guangxi and Guizhou provinces have been improved by 89.2%, 99.2% and 98.5%, respectively, from 2000 to 2020, with their vegetation ecological quality index values increasing by 0.5-0.75 per year in southeast Yunnan, most areas in Guizhou and northwest Guangxi. (3) Precipitation was an important meteorological factor affecting the vegetation ecological quality in rocky desertification areas. The vegetation ecological quality index in the northwest and central Yunnan rocky desertification areas has been rising slowly, but with localized declines at a yearly rate of nearly 0.25 caused by climatic warming and drying.     

青岛灵山岛晚中生代重力流沉积特征及环境分析

青岛灵山岛晚中生代发育一套重力流沉积,国内学者对其成因机制存在争议。笔者通过对造船厂、灯塔、千层崖、羊礁洞、老虎嘴、背来石等剖面的重点观察发现:灵山岛晚中生代地层出露以厚度不等的细粒砂泥岩与火山熔岩、火山碎屑岩为主,夹沉火山碎屑岩和侵入体,地层从老到新组合为一个水体变浅的水退序列。地层中发育不同类型、不同尺度、不同期次的软沉积变形构造,如软沉积变形褶皱、布丁构造、负载构造和火焰构造、软双重构造等。灵山岛晚中生代重力流沉积碎屑岩主要是块体搬运沉积(砂质滑塌和砂质碎屑流)和浊流沉积,向上过渡为陆相三角洲前缘沉积,其成因机制是物源供应充足的湖盆三角洲前缘在构造坡度或沉积坡度控制下,受地震和火山活动影响发生的块体搬运沉积和浊流沉积。初步研究认为沉积时的古斜坡方向为南东—北西方向。     

基于全球土地退化零增长监测体系构建的中国沙化土地监测体系及效果评估

土地荒漠化是非常重要的生态环境问题,而科学评价荒漠化治理和零增长目标是否实现的必要前提是具有完善统一的评价体系。为此,联合国防治荒漠化公约（UNCCD）提出了土地退化零增长（LDN）的概念和监测指标。防治土地退化是中国的重要生态目标,中国已开展了多次全国土地荒漠化和沙化监测工作。但是,如何将这些监测结果用于土地退化的评估实践,尚未见报道。因此,本研究针对中国四大沙地,利用3期全国荒漠化和沙化监测数据,与基于UNCCD框架体系下的土地退化零增长（LDN）指标进行对比分析,并基于土地沙化程度变化趋势提出了中国沙化土地退化指标体系（CSLDN）。结果表明：UNCCD所提出的LDN监测指标与中国的荒漠化监测数据总体精度为0.51,中国沙化土地监测指标与LDN指标具有宏观一致性。此外,经本地优化后的CSLDN指标克服了低植被盖度区域LDN对土地退化和恢复的评价不准确的问题,更准确刻画了精细尺度空间内的土地动态变化状况,对土地退化防治意义重大。     

Mapping the dynamic degree of aeolian desertification in the Shiyang River Basin from 1975 to 2010

The Shiyang River Basin is an area of China that is severly affected by aeolian desertification. Thus, we established an aeolian desertified land classification system for visual interpretation, which classified the Aeolian Desertified Land(ADL)into Slight(SL), Moderate(M), Severe(S) and Extremely Severe(ES) according to the severity. Imagery of Landsat series(acquired in 1975, 1990, 2000 and 2010) were employed to monitor the status, trend and spatial pattern of aeolian desertification, especially to map the overall spatial pattern of ADL dynamics by proposing a new Dynamic Index(DI) in the Shiyang River Basin from 1975 to 2010. The results show a generally decreasing trend from 1975 to 2010. However, the ES ADL kept increasing throughout the whole study period. Moreover, the area of ADLs with different severity increased with increasing severity, this S and ES ADLs dominated characteristics of aeolian desertification was contrary to those sandy lands in eastern China where was dominated by SL and M ADLs. Among the three sub-periods of 1975-1990, 1990-2000 and 2000-2010, the first two were the restoration stage, while the last one was the expansion stage of aeolian desertification. Moreover, all these new ADLs occurred in Minqin County during 2000-2010, indicating a detrimental increase of aeolian desertification in Minqin, and the concentration of ADLs toward the lower reaches of the Shiyang River Basin.The DI works well to identify areas with desertification changes no matter the sub-periods. Moreover, DI results disclosed a stable status of aeolian desertification, and the DI decreased with increasing ADL severity. These results indicate that it will be difficult to control the expansion of aeolian desertification in Minqin County over an extended period of time.Thus, we suggest effective and long-lasting aeolian desertification control programs in the Shiyang River Basin, especially in Minqin, and SL and M ADLs should have priority in facilitating a quick reversal of aeolian desertification.