Spatial and temporal patterns of stable water isotopes along the Yangtze River during two drought years

Changes in the level of the Yangtze River caused by anthropogenic water regulation have major effects on the hydrological processes and water cycle in surrounding lakes and rivers. In this study, we obtained isotopic evidence of changes in the water cycle of Yangtze River during the two drought years of 2006 and 2013. Isotopic evidence demonstrated that the δ¹⁸O and δD levels in Yangtze River exhibited high spatial heterogeneity from the upper to lower reaches, which were controlled by atmospheric precipitation, tributary/lake water mixing, damming regulation, and water temperature. Both the slope and intercept of Yangtze River evaporative line (δD = 7.88 δ¹⁸O + 7.96) were slightly higher than those of local meteoric water line of Yangtze River catchment (δD = 7.41 δ¹⁸O + 6.01). Most of the river isotopic values were located below the local meteoric water line, thereby implying that the Yangtze River water experienced a certain degree of evaporative enrichment on isotopic compositions of river water. The high fluctuations in the isotopic composition (e.g., deuterium excess [d‐excess]) in the middle to lower reaches during the initial stage of operation for the Three Gorges Dams (2003–2006) were due to heterogeneous isotopic signatures from the upstream water. In contrast to the normal stage (after 2010) characterized by the maximum water level and largest water storage, a relatively small variability in the deuterium excess was found along the middle to lower reaches because of the homogenization of reservoir water with a longer residence time and complete mixing. The effects of water from lakes and tributaries on the isotopic compositions in mainstream water were highlighted because of the high contributions of lakes water (e.g., Dongting Lake and Poyang Lake) efflux to the Yangtze River mainstream, which ranged from 21% to 85% during 2006 and 2013. These findings suggest that the retention and regulation of the Three Gorges Dams has greatly buffered the isotopic variability of the water cycle in the Yangtze catchment, thereby improving our understanding of the complex lake–river interactions along the middle to lower reaches in the future.     

九寨沟M_S7.0地震的前兆异常时空演化特征及其分析

以2017年8月8日九寨沟MS7.0地震震中为中心,对震前不同震中距前兆异常的时空演化过程进行分析。研究表明,震中距100km范围内无前兆异常,前兆异常主要分布在震中距100～500km范围内。震前2年新增前兆异常开始逐渐增多;不同震中距范围内的新增异常测项所占比例在震前1.5年左右达到最大,在震前又降低。在震中距300km范围内的异常测项所占比例相对较高。前兆异常时空演化过程存在3个不同的变化阶段,即α阶段(前兆异常的早期阶段,包括α_1和α_2,震前1000天以上)的异常主要分布在震中东北方向和西南方向,异常具有向外扩展的特征;β阶段(前兆异常的中期阶段,震前500～1000天)的异常表现为大范围出现异常;γ阶段(前兆异常的短期阶段,包括γ_1和γ_2,震前500天内)的异常分布在震中的东北方向,表现为远源区的异常向震中收缩过程(γ_1)和近源区的异常向外扩展的过程(γ_2)。通过与其他震例对比分析发现,前兆异常的3个阶段现象可能是大震前的共性特征,大震前前兆异常的显著增加对发震时间的预测具有一定的指示意义。     

Effect of thickness of planar nozzles on erosion depth of levee soils subjected to plunging water

In this study, the effect of the thickness of a planar jet on the erosion depth when the jet impinges on a surface composed of cohesive soil was analytically and numerically evaluated. The results showed that the erosion depth was practically independent of the nozzle thickness for erosion depths shallower than the potential core length (i.e. the region of the jet in which the central flow velocity is the same as the nozzle velocity). The relation between nozzle thickness and erosion depth was non-linear with continuously variable slope for erosion depths deeper than the potential core length. Finally, the relation was approximately linear when the erosion depth converged to the equilibrium erosion depth. The findings of this study indicate that direct and fast prediction of the erosion depth in the field is possible using the data from a small scale soil erosion test with similar flow velocities.     

2017年6月3日阿拉善左旗5.0级地震震源深度测定

2017年6月3日18时11分内蒙古阿拉善左旗（37.99° N,103.56° E）发生5.0级地震,利用近震深度震相sPL测定法、CAP波形反演法、sPn与Pn震相走时差法,进行震源深度精确测定。研究结果表明,3种方法测得的该地震震源深度基本一致,分布范围为8.5—11 km,表明该地震发生在上地壳。     

2016年射阳MS 4.4地震前后重力场变化

利用江苏重力测网2014-2017年重力场观测资料,采用绝对重力控制与相对重力联测相结合的平差方法,获取2016年射阳M_S 4.4地震前后重力场变化图。根据射阳M_S 4.4地震前后射阳地区各测线重力段差变化特点,绘制重力场等值线并进行对比分析,结合相关机理,探讨重力场变化与该地震的内在联系。同震观测数据显示：射阳M_S 4.4地震发生在重力异常值高梯度带附近,发震时震中地区位于NS挤压正异常、EW张拉负异常状态,震后区域重力梯度变化量开始减小,是一种典型的重力异常调整现象。     

Regeneration and utilization of nutrients during collapse of a <Emphasis Type="Italic">Mesodinium rubrum</Emphasis> red tide and its influence on phytoplankton species composition

High-biomass red tides occur frequently in some semi-enclosed bays of Hong Kong where ambient nutrients are not high enough to support such a high phytoplankton biomass. These high-biomass red tides release massive inorganic nutrients into local waters during their collapse. We hypothesized that the massive inorganic nutrients released from the collapse of red tides would fuel growth of other phytoplankton species. This could influence phytoplankton species composition. We tested the hypothesis using a red tide event caused by Mesodinium rubrum (M. rubrum) in a semi-enclosed bay, Port Shelter. The red tide patch had a cell density as high as 5.0×10⁵ cells L^?1, and high chlorophyll a (63.71 μg L^?1). Ambient inorganic nutrients (nitrate: \(\rm{NO}_3^-\), ammonium: \(\rm{NH}_4^+\), phosphate: \(\rm{PO}_4^{3-}\), silicate: \(\rm{SiO}_4^{3-}\)) were low both in the red tide patch and the non-red-tide patch (clear waters outside the red tide patch). Nutrient addition experiments were conducted by adding all the inorganic nutrients to water samples from the two patches followed by incubation for 9 days. The results showed that the addition of inorganic nutrients did not sustain high M. rubrum cell density, which collapsed after day 1, and did not drive M. rubrum in the non-red-tide patch sample to the same high-cell density in the red tide patch sample. This confirmed that nutrients were not the driving factor for the formation of this red tide event, or for its collapse. The death of M. rubrum after day 1 released high concentrations of \(\rm{NO}_3^-\), \(\rm{PO}_4^{3-}\), \(\rm{SiO}_4^{3-}\), \(\rm{NH}_4^+\), and urea. Bacterial abundance and heterotrophic activity increased, reaching the highest on day 3 or 4, and decreased as cell density of M. rubrum declined. The released nutrients stimulated growth of diatoms, such as Chaetoceros affinis var. circinalis, Thalassiothrix frauenfeldii, and Nitzschia sp., particularly with additions of \(\rm{SiO}_4^{3-}\) treatments, and other species. These results demonstrated that initiation of M. rubrum red tides in the bay was not directly driven by nutrients. However, the massive inorganic nutrients released from the collapse of the red tide could induce a second bloom in low-ambient nutrient water, influencing phytoplankton species composition.     

Water quality assessment of the Huaihe River segment of Bengbu (China) using multivariate statistical techniques

In the study, multivariate statistical methods including principal component analysis (PCA)/factor analysis (FA) and cluster analysis (CA) were applied to analyze surface water quality data sets obtained from the Huaihe River segment of Bengbu (HRSB) and generated during 2 years (2011–2012) monitoring of 19 parameters at 7 sampling sites. The results of PCA for 7 sampling sites revealed that the first four components of PCA showed 94.89% of the total variance in the data sets of HRSB. The Principal components (Factors) obtained from FA indicated that the parameters for water quality variations were mainly related to heavy metals (Pb, Mn, Zn and Fe) and organic related parameters (COD, PI and DO). The results revealed that the major causes of water quality deterioration were related to inflow of industrial, domestic and agricultural effluents into the Huaihe River. Three significant sampling locations—(sites 2, 3 and 4), (sites 1 and 5) and (sites 6 and 7)—were detected on the basis of similarity of their water quality. Thus, these methods were believed to be valuable to help water resources managers understand complex nature of water quality issues and determine the priorities to improve water quality.     

Discussion on research advances and hot issues in diagenesis of clastic-rock reservoirs

The research on diagenesis of clastic-rock reservoir is developing rapidly in recent ten years. Thus, it is of great significance in academic and scientific exploration to summarize the domestic and international research progress and the key issues of frontier research on diagenesis. The research progress, main achievement and recognition in diagenesis of clastic-rock reservoirs in recent years is discussed, and the hot issues or developing trend of diagenesis in the future is probed in this paper, on the basis of summarizing the previous research results and understanding, combined with the typical research examples at home and abroad. It is believed that great progress was obtained in provenance and parent rock constraints on sandstone types and their diagenetic evolution pathways, impact of fluid-rock interaction and its product on diagenesis, influence of thermodynamics and overpressure background on diagenesis and pore development, the timing sequence between hydrocarbon accumulation and filling process and the sandstone reservoir becoming low permeability-densification. At present, diagenetic research is developing in direction of the spatial and temporal dynamics and quantitative evolution mechanistic and diagenetic system controlled by the basin fluid dynamics, thermal dynamic processes, combining the micro-scale diagenesis research with the basin macroscopic background such as sedimentation from the source to the basin, burial history, hydrocarbon maturity and charge into reservoirs, tectonic evolution and fluid activity, and fluid and rock interaction.The aim of this paper is to induce the academic peers and experts in diagenesis and the related research fields to come forward with their valuable contributions, to cooperate and work together and joint efforts on the research exquisite, profundity and breadth of diagenesis, and application of the most advanced analytical measurement techniques and methods, as well as integration and infiltration of multidisciplinary, in order to promote the course of the clastic-rock reservoir diagenetic research in China.     

Color correction of texture images for true photorealistic visualization

Photorealistic visualization combines 3-D geometric models with their texture images to render the virtual world. This paper points out that the texture images should be radiometrically corrected to achieve a true realistic appearance. Such a correction should include not only the color adjustment among images of the same object, but also the shade variation caused by the illumination change. The objective of this study is to correct the input texture images such that their shade varies when being rendered under different illumination directions. To achieve this goal we first apply the specular-to-diffuse mechanism based on the dichromatic reflection model to remove the specular component from the texture image. The resultant diffusion-only image then undergoes a shade correction to produce a normalized shade-free texture image. In the final step, shades under any illumination are produced to achieve a true photorealistic effect. Presented in the paper are the principles and methods for such corrections, along with a performance evaluation based on the graphic and numerical results for roof texture images.     

渤海湾盆地歧口凹陷地层压力结构特征

深化含油气沉积盆地的压力结构研究,厘清异常压力的空间展布,对划分含油气系统、评价有利输导体系与明确勘探甜点区带具有重要的理论和实践意义。为深化渤海湾盆地富油凹陷的油气二次勘探,本文以歧口凹陷为研究对象,对其压力结构进行重点刻画。在实测地层压力的校正下,综合单井、连井和二维地震地层压力结构分析,厘清了歧口凹陷的压力结构特征,识别出4类纵向压力结构：①单超压带结构;②双超压带结构;③多超压带结构;④静水压力结构。纵向上,歧口地区存在3类纵向压力系统样式——单超压系统、双超压系统、静水常压系统。双超压系统是歧口凹陷的主要压力系统样式,广泛发育于主凹和各大次凹;从凹陷中心向盆地边缘,双超压系统逐渐向单超压系统、静水常压系统过渡。单超压系统主要分布于盆地边缘的斜坡和潜山区,如歧北高斜坡、羊三木-扣村潜山等。静水常压系统则主要分布在离深凹区更远的沈青庄潜山和埕北斜坡区域。上部超压系统和下部超压系统的顶板分别位于东营组和沙三段内部,侧向上受盆地边缘和深大断裂控制。上部超压系统的形成主要受欠压实作用控制,以歧口主凹为中心呈环带分布;而下部超压系统的形成主要受生烃作用控制,以主凹和几大次凹为中心分布。未来,下部超压系统中保存的天然气将成为歧口地区超深层天然气勘探的重点对象。