Identifying the source of atmospheric moisture over arid deserts using stable isotopes (2H and 18O) in precipitation

Precipitation is a major component of the hydrologic cycle in arid desert areas. To date, however, few studies have been conducted on investigating the isotope characteristics and moisture sources of precipitation in arid desert environments. The Alxa Desert Plateau is a critical arid desert area in North China. This study is the first to analyse the stable isotopic composition of precipitation to identify the sources of atmospheric moisture over this plateau. Our results show that the δD and δ¹⁸O values of precipitation across the plateau change greatly at both daily and monthly timescales, and exhibit seasonal variations. Among the main meteorological parameters, atmospheric temperature is the most predominant factor controlling the isotopic composition and the δD–δ¹⁸O relationship of local precipitation. Analyses of the precipitation isotopes with the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model reveal that (a) the westerly and polar moisture sources are the dominant controls on summer and winter precipitation and (b) the evaporation of local lake water significantly affects winter precipitation even though it only represents a small amount. Based on the isotope data of 2013–2016 precipitation, a local meteoric water line (LMWL) is derived: δD = (8.20 ± 0.22)·δ¹⁸O + (8.15 ± 2.16)‰ for the study site. Compared to the global meteoric water line, the LMWL has a greater slope and lower d‐excess. This can be explained by admixing of atmospheric moisture resulting from the evaporation of local lake water. Based on this LMWL, we are able to trace that groundwater of the Badain Jaran Desert originates from the surrounding mountains with altitudes of <4,000 m. The newly derived LMWL shows that the recharge altitudes of desert groundwater are overestimated on the basis of the previous LMWLs. This study not only provides insights into the hydrological cycle but also offers guidance for water resource management in arid desert areas of China. Additionally, this study provides techniques that can be applied to the analyses of precipitation isotopes in similar arid regions of the world.     

Resistivity and induced polarization response of a thin sheet

The relevant potential theory is given for a current point source in the presence of a conductive slab embedded in a homogeneous host region of infinite extent. The thin sheet representation is obtained from the exact integral formulation by a simple mathematical limit process. The same result is also deduced directly at the outset by applying a thin sheet boundary condition. The apparent resistivity for a two electrode array is then computed for the case where the bore hole intersects the thin sheet at right angles. The corresponding results for the dilution factor, relevant to the induced polarization response, are also obtained. It is shown that the apparent resistivity and the dilution factor are constant when the potential and the current electrode straddle the sheet but there is a characteristic decrease as the electrodes move away from the sheet.     

强震等震线、余震区形状与地震构造关系的研究

本文通过对川滇和华北地区不同地震构造环境中, 1966年以来强震的等震线长宽比、 余震区长度的对比研究, 认为强震等震线的长宽比、 余震区长度都与地震构造环境和震级相关。 对于强震等震线的长宽比和余震区长度, 地震构造环境和震级的影响相同的是, 都与发震断裂是否位于活动地块边界, 位于哪一级活动地块边界, 是与边界方向一致的大断裂, 还是配套小断裂等有关。 最重要的是与活动断层的规模, 尤其是与发震断裂的长度有关, 也与震级有关。 不同的是, 强震等震线的长宽比明显受地表覆盖层的影响, 而余震区长度与地表覆盖层关系不明显, 似乎与震源破裂面长度的关系更密切。     

Hyporheic exchange mechanism driven by flood wave

To study the hyporheic exchange driven by a single peak flood-induced water level fluctuation (i.e., flood wave), a method combining numerical simulation with theoretical derivation was proposed based on the Inbuk Stream, Korea, where flooding occurs frequently. The hyporheic exchanges induced by different flood waves were investigated by varying amplitude (A), duration (T), wave type parameter (r), and rising duration (t_p), which were adopted from the real-time stream stage fluctuations. Additionally, the idea of constant upstream flood volume (CUFV) condition for flood waves was put forward, and the effects of “Botan” (T/A) and peak number (N) on hyporheic exchange were studied. The results showed that the hyporheic exchange flux (q) was controlled by the water level h (sine-type) and its change rate v (cosine-type), and was proportional to the polynomial of them q ∝ (ω∙ h + v), where ω is the angular frequency of the flood wave. Based on this mechanism, the influence principles on hyporheic exchanges of the typical flood wave parameters (A, T, r and t_p) as well as T/A and N under CUFV condition were clarified. The main characteristic variables of hyporheic exchange, which were maximum aquifer storage and residence time, were positively correlated. They also had positive relations to the integral of the flood wave over time, which increased when the wave became higher, wider, rounder and less skewed. However, when CUFV condition was imposed, the residence time was positively correlated with T/A, whereas the maximum aquifer storage was negatively correlated with T/A. With the increase in N, water exchanged more frequently and some water returned to the stream early, leading to the slight decrease in maximum aquifer storage and residence time. These findings enriched the theory of hyporheic exchange driven by surface water fluctuation and be of great significance to enhance pollutant degradation in the hyporheic zone downstream of reservoirs.     

晋冀蒙交界地区地震危险性评估及地震活动性分析

本文利用晋冀蒙交界地区1500年以来记录较完整的M_S5.0及以上历史地震烈度资料和2000年以来的地震活动资料，分别进行地震灾害危险性和地震活动性分析。首先，利用ArcGIS将历史地震烈度资料数字化，没有等震线记录的地震用烈度衰减关系计算烈度圈半径。将研究区划分成0.1°×0.1°的网格，将烈度资料分配到与之相交的每个网格，并用烈度-频度关系计算每个网格的烈度a、b值。基于地震发生遵从泊松分布的假定，估算未来50年内晋冀蒙交界区遭受某一地震烈度的超越概率。同时，计算50年超越概率10%对应的地震烈度，计算结果表明张家口蔚县、阳原和山西广灵县周边地区的地震危险性较高。最后，采用中小地震能量密度值计算方法，对2000年以来的现今地震活动进行定量分析，与历史地震烈度资料分析结果进行对比，发现中小地震活动圈定的危险区与历史地震烈度资料评估计算的概率高值区相对应，因此，这两种方法可为晋冀蒙交界地区的地震活动性和危险性评价提供参考。     

安徽马头斑岩型钼铜矿床元素富集贫化规律及其找矿意义

本文在安徽马头斑岩型钼铜矿床中元素含量随主成矿元素Mo含量变化的基础上,对元素的富集贫化特征进行了系统研究,筛选出了富集和贫化元素,并对具有代表性的富集和贫化元素的矿化指示意义进行了探讨。结果发现,矿床中元素的富集和贫化在地表岩石中均有明显反映,综合利用富集元素的正异常和贫化元素的负异常能更有效指示出矿化带的产出位置,这无疑对此类隐伏矿床的地球化学勘查具有重要意义,也为其他类型矿床的地球化学勘查提供了思路。     

地表水水环境容量计算方法回顾与展望

为厘清中国地表水水环境容量计算方法演变历史,探讨计算方法发展趋势,在系统调研大量水环境容量研究文献基础上,详细梳理水环境容量从概念引入到研究至今的过程,归纳出中国地表水水环境容量研究过程中产生的五大类计算方法:公式法、模型试错法、系统最优化法（线性规划法和随机规划法）、概率稀释模型法和未确知数学法。解析了各类方法的基本思路、产生过程及应用进展,评述了各类方法的优缺点及适用范围。通过与国外水环境容量计算方法的比较,基于水环境系统复杂性及中国水资源管理特点与应用需求,认为中国应强化对概率稀释模型法、未确知数学法及随机规划法等3种方法的研究和改进。     

X射线荧光光谱法测试重晶石中的多元素

采用玻璃熔片法制样,建立了重晶石中多元素X射线荧光光谱分析方法.准确称取待测样品0.5000 g,X射线荧光专用熔剂5.000 g;二者混合后,通过高频熔样机在1150℃进行熔片处理8 min;将最终得到的样片放入干燥器中冷却至室温,然后准确称取玻璃片质量;上机测试,所得到的数据为该元素在玻璃片中的含量;通过换算最终得到实际样品中的该元素含量.使用理论α系数法和经验系数法相结合来回归校正共存元素间的吸收增强效应.本方法对于重晶石中各元素的测试相对标准偏差处于0.2%~4.7%之间,方法检出限在3.3×10-6~170.6×10-6之间.测试数据通过与国家标准物质比对,结果合理.     

一次中纬度飑线的阵风锋发展特征分析

2009年8月发生在辽宁省中部的一次飑线前部出现了两次特征不同的阵风锋发展过程,并伴随有灾害性大风和冰雹等强对流天气。应用多普勒雷达数据、常规探空、地面加密观测及飞机观测（AMDAR）数据对飑线系统进行了综合分析。结果显示环境场中强的风垂直切变促进飑线上对流单体发展并使飑线倾斜。西路冷空气进入飑线使对流加强,形成第一次阵风锋。而北路冷空气与飑线的暖心间温度梯度增大,造成地面风速增大是第二次阵风锋发展的直接诱因。最终飑线系统母体中的线状辐合带转移到第二次阵风锋上,该阵风锋形成新的飑线。     

广州“5.7”高空槽后和“5.14”槽前大暴雨过程对比分析

利用常规观测资料和雷达资料,对广州2010年5月7日槽后大暴雨和2010年5月14日槽前大暴雨过程进行对比分析。结果表明：＂5.7＂大暴雨主要受500hPa高空槽后西北气流和850hPa切变线的共同作用,与典型的华南前汛期暴雨形势不同的是槽后冷空气叠加在低层暖湿气流上,对层结不稳定起到增幅作用;＂5.14＂大暴雨过程主要受高空槽前的西南气流、切变线和地面弱冷空气共同影响。两次大暴雨过程都是由带有超级单体的飑线引发的,前者飑线长度更长,强回波范围更大,超级单体更多,降水强度和累积降水量更大;飑线维持和发展的机制不同,前者通过补充合并两广交界处不断新生对流单体,后者则是通过吸收合并其移动前方沿近地层辐合带新生单体,得以维持和发展。