Drip irrigation enhances shallow groundwater contribution to crop water consumption in an arid area

Shallow groundwater plays a key role in agro‐hydrological processes of arid areas. Groundwater often supplies a necessary part of the water requirement of crops and surrounding native vegetation, such as groundwater‐dependent ecosystems. However, the impact of water‐saving irrigation on cropland water balance, such as the contribution of shallow groundwater to field evapotranspiration, requires further investigation. Increased understanding of quantitative evaluation of field‐scale water productivity under different irrigation methods aids policy and decision‐making. In this study, high‐resolution water table depth and soil water content in field maize were monitored under conditions of flood irrigation (FI) and drip irrigation (DI), respectively. Groundwater evapotranspiration (ET_g) was estimated by the combination of the water table fluctuation method and an empirical groundwater–soil–atmosphere continuum model. The results indicate that daily ET_g at different growth stages varies under the two irrigation methods. Between two consecutive irrigation events of the FI site, daily ET_g rate increases from zero to greater than that of the DI site. Maize under DI steadily consumes more groundwater than FI, accounting for 16.4% and 14.5% of ET_a, respectively. Overall, FI recharges groundwater, whereas DI extracts water from shallow groundwater. The yield under DI increases compared with that under FI, with less ET_a (526 mm) compared with FI (578 mm), and irrigation water productivity improves from 3.51 kg m^?3 (FI) to 4.58 kg m^?3 (DI) through reducing deep drainage and soil evaporation by DI. These results highlight the critical role of irrigation method and groundwater on crop water consumption and productivity. This study provides important information to aid the development of agricultural irrigation schemes in arid areas with shallow groundwater.     

Mining spatiotemporal association patterns from complex geographic phenomena

ABSTRACT

Spatiotemporal association pattern mining can discover interesting interdependent relationships among various types of geospatial data. However, existing mining methods for spatiotemporal association patterns usually model geographic phenomena as simple spatiotemporal point events. Therefore, they cannot be applied to complex geographic phenomena, which continuously change their properties, shapes or locations, such as storms and air pollution. The most salient feature of such complex geographic phenomena is the geographic dynamic. To fully reveal dynamic characteristics of complex geographic phenomena and discover their associated factors, this research proposes a novel complex event-based spatiotemporal association pattern mining framework. First, a complex geographic event was hierarchically modeled and represented by a new data structure named directed spatiotemporal routes. Then, sequence mining technique was applied to discover the spatiotemporal spread pattern of the complex geographic events. An adaptive spatiotemporal episode pattern mining algorithm was proposed to discover the candidate driving factors for the occurrence of complex geographic events. Finally, the proposed approach was evaluated by analyzing the air pollution in the region of Beijing-Tianjin-Hebei. The experimental results showed that the proposed approach can well address the geographic dynamic of complex geographic phenomena, such as the spatial spreading pattern and spatiotemporal interaction with candidate driving factors.     

统一硬化模型与下加载面模型的理论关系

Hashiguchi下加载面本构模型是国际上具有较大影响力的超固结土本构模型之一。因此,选取该模型进行理论和构建方法分析,并与UH模型进行对比。对比结果表明,Hashiguchi下加载面模型通过定义单一的数学公式来拟合超固结土内变量的变化规律,从而得到了超固结土应力−应变关系的公式;而统一硬化（unified hardening,简称UH）模型掌握了超固结土体的强度特性,因而能够更准确、合理地描述超固结土的应力−应变关系。相较于Hashiguchi下加载面本构模型,UH模型在理论上更为先进。同时,两个模型的试验预测与试验数据的对比也验证了UH模型在数值计算上的正确性与优越性。     

北山构造带南部上地壳二维初至波层析成像

花海盆地—北山构造带南部位于青藏高原东北缘以北地区,是特提斯洋和古亚洲洋两大构造域的交接部位,自新元古代晚期以来经历了多期次、多阶段的板块裂解-俯冲-碰撞-拼合的演化历史,尤其是中生代以来的逆冲推覆和走滑作用,以及受新生代以来印度板块和欧亚板块碰撞的远程效应影响,导致青藏高原东北缘的向北扩展,形成了现今复杂的地质地貌结构。其地壳结构记录了多期构造作用的叠加,上地壳结构更是促进我们理解青藏高原东北缘向外的扩展机制及其对周缘块体的改造作用的天然记录本。本文利用2018年中国地质科学院在北山构造带南部完成的180 km深反射地震剖面的初至波(Pg震相)数据,通过层析成像反演方法,获得了花海盆地—北山构造带4 km深度范围内的上地壳P波速度结构。其主要特征为:花海盆地、总口子盆地和扎格高脑盆地均表现为较低的速度和较小的垂向速度梯度;研究区内的晚古生代花岗岩体具有明显的高速异常和较大的垂向速度梯度特征;左行走滑的阿尔金断裂带在花海盆地内表现为向北倾的高角度走滑性质,深度至少切穿花海盆地基底;北山南缘断裂带的推测隐伏区呈现速度等值线下凹的低速异常特征。同时,反演揭示的多处低速异常区指示了北山构造带南部的多处断层发育情况。     

二维初至波层析成像揭示的北祁连—阿拉善南缘浅层地壳结构

北祁连造山带—阿拉善南缘位于青藏高原东北缘及其以北地区, 其地壳结构记录了早古生代以来祁连山、河西走廊盆地、合黎山及相邻盆地之间的盆山演化历史及耦合关系, 对其地壳浅层速度结构的探测有助于揭示该区浅层地壳结构及构造变形的演化历史。本文利用北祁连—阿拉善南缘225 km长的深反射地震剖面的初至波(Pg震相)数据, 通过层析成像反演方法, 获得了沿线2 km以浅的上地壳P波速度结构。其主要特征为: 酒东盆地的沉积盖层厚度最大可达2 km, 盆地深度的南北差异可能与阿拉善地块与祁连造山带间的挤压作用相关; 民乐盆地的平均深度为1.5 km, 该盆地内的速度等值线弯曲形态反映了盆地在新生代之后不同的抬升和剥蚀速率; 银额盆地的沉积厚度至少在1.5 km左右, 且盆地内沉积地层产状较为平缓; 榆木山构造带南北两侧的酒东盆地与民乐盆地虽然地表高程相差近1 km, 但具有近乎相同的速度结构和沉积厚度, 推断榆木山构造带的隆升与其南北两侧的两个断层背冲作用有关; 此外, 反演得到的P波速度结构揭示了沿线发育的多条断裂和块体边界位置, 为讨论青藏高原东北缘向北扩展与阿拉善地块挤压作用提供了新的证据。     

方解石811N:一种可能的微区碳氧锶同位素分析标准

同位素标准物质是同位素分析的基准物质和数据比较的重要依据。方解石811作为碳酸盐碳氧同位素的实验室标准物质,具有良好的适用性,但由于制备时间久远,存量日益减少,且性状信息缺乏,影响了该标准在微区微量分析中的运用。本次研究选用未制备的811方解石(811N)作为研究对象,结合多种分析技术从不同尺度对其矿物组成、元素含量分布、碳氧同位素组成进行分析,揭示其相关信息及规律,并探讨了其Sr同位素组成,从而为下一步811N的制备和使用提供参考信息,有助于该样在不同碳酸盐分析和研究,特别是微区微量元素和同位素中的运用。实验结果表明,方解石811N较为纯净,主要为方解石,只含有微量的白云石、针铁矿、黏土矿物;除主要化学成分(CaCO₃)外,含有微量的Mg、Mn、Sr、Si、REE、U、Th等元素,Mg、Mn、Sr含量在整体分布上存在一定的变化,但在局部相对均匀。碳氧同位素组成整体差异程度相对较小,且其差异程度和元素均匀性呈对应关系,主要区域碳氧同位素组成均匀。Sr同位素组成在不同区域中无明显差异。本次研究认为811N是合适的碳酸盐碳氧同位素分析标准物质,该样制备后能够满足碳氧同位素分析和研究的需要,同时该样具备适用于微区微量C、O、Sr同位素分析和研究的潜力。     

南海东北部陆坡天然气水合物区的滑塌和泥火山活动

本文研究了南海东北部陆坡天然气水合物区滑塌和泥火山活动的特征及表现形式,探讨了滑塌和泥火山活动对天然气水合物成藏的影响,提出了滑塌主导和滑塌、泥火山共同作用两种控制模式。根据地震数据、浅层剖面和海底地形数据解释,将研究区划分为规则滑塌区和泥火山活动影响区,并识别出泥火山、泥火山脊、凹槽、凹坑等特征地形。滑塌和泥火山活动是陆坡天然气水合物发育区重要的地形控制因素,两种活动共同作用产生复杂的地形特征。综合多条地震测线中似海底反射层(BSR)形态、连续性和滑塌、泥火山活动的关系,认为滑塌控制的区域,BSR连续,天然气水合物储藏较完整,泥火山活动区天然气水合物储藏也仅受到局部破坏。同时指出滑塌和泥火山活动对研究区长期天然气渗漏活动具有重要作用。     

Exploring the Moon's surface for remnants of the lunar mantle 1. Dunite xenoliths in mare basalts. A crustal or mantle origin?

Remotely sensed observations from recent missions (e.g., GRAIL, Kaguya, Chandrayaan‐1) have been interpreted as indicating that the deep crust and upper mantle are close to or at the lunar surface in many large impact basins (e.g., Crisium, Apollo, Moscoviense). If this is correct, the capability of either impact or volcanic processes to transport mantle lithologies to the lunar surface should be enhanced in these regions. Somewhat problematic to these observations and interpretations is that examples of mantle lithologies in the lunar sample collection (Apollo Program, Luna Program, lunar meteorites) are at best ambiguous. Dunite xenoliths in high‐Ti mare basalt 74275 are one of these ambiguous examples. In this high‐Ti mare basalt, olivine occurs in three generations: olivine associated with dunite xenoliths, olivine megacrysts, and olivine microphenocrysts. The dunite xenoliths are anhedral in shape and are generally greater than 800 μm in diameter. The interior of the xenoliths are fairly homogeneous with regard to many divalent cations. For example, the Mg# (Mg/Mg + Fe × 100) ranges from 82 to 83 in their interiors and decreases from 82 to 68 over the 10–30 μm wide outer rim. Titanium and phosphorus X‐ray maps of the xenolith illustrate that these slow diffusing elements preserve primary cumulate zoning textures. These textures indicate that the xenoliths consist of many individual olivine grains approximately 150–200 μm in diameter with low Ti, Al, and P cores. These highly incompatible elements are enriched in the outer Fe‐rich rims of the xenoliths and slightly enriched in the rims of the individual olivine grains. Highly compatible elements in olivine such as Ni exhibit a decrease in the rim surrounding the xenolith, an increase in the incompatible element depleted cores of the individual olivine grains, and a slight decrease in the “interior rims” of the individual olivine grains. Inferred melt composition, liquid lines of descent, and zoning profiles enable the reconstruction of the petrogenesis of the dunite xenoliths. Preservation of primary magmatic zoning (Ti, P, Al) and lack of textures similar to high‐pressure mineral assemblages exhibited by the Mg‐suite (Shearer et al. 2015) indicate that these xenoliths do not represent deep crustal or shallow mantle lithologies. Further, they are chemically and mineralogically distinct from Mg‐suite dunites identified from the Apollo 17 site. More likely, they represent olivine cumulates that crystallized from a low‐Ti mare basalt at intermediate to shallow crustal levels. The parent basalt to the dunite xenolith lithology was more primitive than low‐Ti basalts thus far returned from the Moon. Furthermore, this parental magma and its more evolved daughter magmas are not represented in the basalt sample suite returned from the Taurus‐Littrow Valley by the Apollo 17 mission. The dunite xenolith records several episodes of crystallization and re‐equilibration. During the last episode of re‐equilibration, the dunite cumulate was sampled by the 74275 high‐Ti basalt and transported over a period of 30–70 days to the lunar surface.     

Research on China’s aquaculture efficiency evaluation and influencing factors with undesirable outputs

Taking the aquaculture area, the number of farming boats and that of aquaculturist as input variables, the aquaculture production as desirable output variable and polluted economic loss as undesirable ...     

Understanding Today's Online GIS User Through the Lens of a WorldMap Survey

WorldMap is an open source online mapping application which aims to lower barriers for scholars who wish to visualize, analyze, organize, present, and publish mapped information. In late 2013, 290 respondents among the 8,000 registered users participated in an online survey in which they described their activities, purposes, experiences, and preferences regarding the system. Participants also described their professional background, GIS skill level, age, gender, and country of work. This study analyzes the results of the survey, by summarizing the responses to each question independently and by examining the relationships and dependencies of these answers across the different questions to try to better understand why users responded the way they did. The study is based on the user‐centered design (UCD) approach. We aim to use the survey results to improve our understanding of user demographics and needs. Findings from this study will be used to guide WorldMap improvements, and we hope the findings will also shed light on the broader requirements of online GIS users.