A biodiversity evaluation framework for restoration of aquatic macrophyte communities in shallow lakes driven by hydrological process management

Macrophyte community diversity and composition respond to ecosystem conservation and local environmental factors. In this study, we developed a multidimensional diversity framework for macrophyte communities, including the taxonomic and functional alpha and beta diversity. We used the framework to explore the relationships among water level regimes and these diversity parameters in a case study of China's Baiyangdian Lake. Analysis of indicators of hydrologic alteration divided the water level from 1959 to 2019 into four regimes (dry, <6.42 m; low, 6.42–7.23 m; medium, 7.23–8.19 m; high, >8.19 m). Alpha and beta diversity were significantly higher in the medium regime than in the low and high regimes. Redundancy analysis indicated that the maximum water depth significantly affected taxonomic alpha diversity, and total nitrogen (TN) and chemical oxygen demand (COD) concentration significantly affected functional alpha diversity, respectively. Mantel tests showed that TN, Secchi depth (SD), and water depth in the high water level regime significantly increased the total beta diversity and turnover components. TN was the main factor that increased total taxonomic beta diversity. Water level regime mainly influenced interspecific relationships by changing the TN and COD concentration. The water level should be maintained between the medium and high water level regimes to promote restoration of the macrophyte community and improve ecosystem stability. The biodiversity evaluation framework would provide a deeper insight into the hydrological process management for restoration of aquatic macrophyte communities in shallow lakes.     

Rainfall intensity affects runoff responses in a semi-arid catchment

The source and hydrochemical makeup of a stream reflects the connectivity between rainfall, groundwater, the stream, and is reflected to water quantity and quality of the catchment. However, in a semi-arid, thick, loess covered catchment, temporal variation of stream source and event associated behaviours are lesser known. Thus, the isotopic and chemical hydrographs in a widely distributed, deep loess, semi-arid catchment of the northern Chinese Loess Plateau were characterized to determine the source and hydrochemical behaviours of the stream during intra-rainfall events. Rainfall and streamflow were sampled during six hydrologic events coupled with measurements of stream baseflow and groundwater. The deuterium isotope (²H), major ions (Cl⁻, SO₄²⁻, NO₃⁻, Ca²⁺, K⁺, Mg²⁺, and Na⁺) were evaluated in water samples obtained during rainfall events. Temporal variation of ²H and Cl⁻ measured in the groundwater and stream baseflow prior to rainfall was similar; however, the isotope compositions of the streamflow fluctuated significantly and responded quickly to rainfall events, likely due to an infiltration excess, overland dominated surface runoff during torrential rainfall events. Time source separation using ²H demonstrated greater than 72% on average, the stream composition was event water during torrential rainfall events, with the proportion increasing with rainfall intensity. Solutes concentrations in the stream had loglinear relationships with stream discharge, with an outling anomaly with an example of an intra-rainfall event on Oct. 24, 2015. Stream Cl⁻ behaved nonconservative during rainfall events, temporal variation of Cl⁻ indicated a flush and washout at the onset of small rainfall events, a dilution but still high concentration pattern in high discharge and old water dominated in regression flow period. This study indicates rainfall intensity affects runoff responses in a semi-arid catchment, and the stored water in the thick, loess covered areas was less connected with stream runoff. Solute transport may threaten water quality in the area, requiring further analysis of the performance of the eco-restoration project.     

末次冰消期（1.9万年）以来冲绳海槽中部黏土矿物来源及其环境响应

基于采自冲绳海槽中部的CS2站柱状沉积物黏土矿物和AMS¹⁴C年代分析，探讨了末次冰消期以来冲绳海槽中部黏土矿物的物质来源及其环境指示意义。结果显示，CS2站黏土矿物以伊利石为主，其次为绿泥石，高岭石和蒙脱石含量较少。根据黏土矿物分布趋势变化，CS2站柱状沉积物可划分为3个阶段：阶段（I 19~12 ka BP）和阶段Ⅱ （12~8 ka BP）期间沉积物主要来源于长江，台湾和黄河物质也有一定影响，其物质来源主要受海平面升降的控制；阶段Ⅲ（8~0 ka BP）主要来源于长江和台湾，黄河贡献有限，主要受黑潮演化的影响。CS2站（蒙脱石+高岭石） （/伊利石+绿泥石）比值可以作为东亚季风演化的矿物学指标，指标变化显示出东亚冬季风强度相对夏季风的强度在16.4~14.8 ka BP和12.8~11.6 ka BP期间有两次显著的加强，指示当时气候相对寒冷干燥，结果可以与格陵兰冰心δ¹⁸O和三宝洞δ¹⁸O记录等很好对比。     

黑龙江省地震科学台阵背景噪声特征分析

2019年黑龙江省完成"一带一路"地震科学台阵项目中台址勘选工作，基于科学台阵中136个台址的地面运动噪声数据，通过计算不同频段范围内背景噪声记录的加速度功率谱密度，研究不同环境噪声下科学台阵记录数据的地噪声特征及其台基响应。结果表明：黑龙江西北和东南部地区地面运动噪声水平低，观测环境较好；中部和东北部地区噪声水平较高，大庆地区尤为严重。勘选结果真实反映了黑龙江区域内的背景噪声分布，使我们对本区域地噪声水平和干扰因素有了新的认识。     

马尔科夫链分析在东海陆架盆地花港组沉积微相分析中的应用

通过对东海陆架盆地某凹陷取心井岩心仔细观察和描述，采用双属性划分标准，在研究区花港组岩心中识别出了28种岩石相类型.其中砾岩相5种，砂岩相15种，细粒岩相8种.针对22口取心井岩心详细划分沉积微相和岩石相，共取得2227个岩石相数据.针对研究区发育的湖泊、三角洲、河流3种沉积体系，运用马尔科夫链分析不同沉积微相类型中岩石相沉积序列模式，建立了不同沉积微相类型可能的岩石相组合规律及岩石相定量组合概率，为后期研究相同或相似类型的沉积相提供地质知识库，并为沉积相的识别提供定量的基础.     

CG-6型重力仪零漂特性研究

对中国地震局地震研究所最新引进的4台CG-6型相对重力仪的零漂特性进行测试研究，结果表明，4台重力仪的静态零漂率、混合零漂率和动态零漂率均小于8 μGal/h，满足厂家给出的技术指标。在较长观测时间内，各台仪器的零漂均存在不同程度的非线性特征，因此在进行较长时间的野外观测以及后续数据处理中，不宜将零漂率作为常数进行解算和零漂改正。     

土质滑坡格构锚杆抗滑机制及受力试验研究

通过滑坡防治格构锚固大型物理模型试验，分析了土质滑坡格构锚杆体系在坡顶荷载下的变形和位移，揭示了格构锚杆的抗滑机制，探讨了锚固力与坡体位移及锚杆变形的关系，提出了极限锚固力的计算方法。结果表明：滑坡滑动时，格构梁与坡体整体发生旋转滑移，锚杆在滑面处发生了弯曲变形，处于弯曲和轴向拉伸组合变形状态；格构锚杆的抗滑作用表现为锚杆在滑面处的抗剪抗滑和锚杆格构梁的挡土阻滑；格构锚杆的极限锚固力由初始预应力、锚杆弯曲变形引起锚拉力、坡体位移引起锚拉力三部分组成，可通过公式 计算。该研究结果可为格构锚固体系的优化设计提供一定的参考。     

湘黔桂新元古代拉伸纪晚期地层年代格架对比及关键地质事件初探

湘黔桂地区发育一套完整的新元古代拉伸纪晚期地层(下江群及其相当地层),是研究扬子克拉通与华夏板块碰撞拼接后华南大陆裂谷盆地演化的重要载体。本文报道了贵州省铜仁市万山区清水江组上部、平略组底部及中部变质凝灰岩和沉凝灰岩的年龄,分别为(763.8±5.5) Ma(N=24,MSWD=0.29)、(760.2±4.1) Ma(N=25,MSWD=0.39)、(759.1±3.9) Ma(N=26,MSWD=0.38)。通过对湘黔桂地区下江群及其相当地层中已有火山岩、火山碎屑沉积岩、含凝灰质岩石年龄的系统梳理与分析研究,进一步确定下江群其及相当地层的沉积时限在822~715 Ma,桂北丹洲群三门街组玄武岩是在武陵造山后伸展背景下湘黔桂地区裂谷最大裂陷时期的产物,清水江组与平略组内大量的火山物质可能来源于江南造山带东段800~760 Ma的中酸性喷出岩。结合地层、岩性、年代特征,本文恢复了湘黔桂盆地新元古代拉伸纪晚期的演化历史,并认为该套地层符合建立下江系条件。     

微量硫化物、硫酸盐硫同位素EA-IRMS在线测试分析

常规EA-IRMS硫同位素测试中, 硫化银(Ag2S)的需样量为0.2~1.0 mg, 硫酸钡(BaSO4)的需样量为0.35~1.5 mg, 较大的需样量已难以满足珍贵样品及微区样品的分析要求, 因此如何减少测试样品量已成为EA-IRMS测试分析工作中急需解决的问题。通过对EA-IRMS测试系统的研究发现, 在采用常规方法测试样品时, 由于初始He载气流速(100 mL/min)、进入分流接口时的流速(10 mL/min)与进入离子源时流速 (0.3 mL/min)的差异导致样品燃烧产生的目标气体中99.7%的气体被浪费, 样品的总体利用率仅有0.3%。因此如何减少样品在测试过程中的损耗, 提高样品的利用率, 从而减少需样量的关键在于缩小载气流速的差距。本实验在常规EA-IRMS测试技术基础上进行了关键改进,在元素分析仪和分流接口之间设计增加一个由六通阀和自动加热冷阱构成的装置, 自动加热冷阱可在Load模式时收集SO2气体, 六通阀在Load-Inject模式之间切换时可改变He载气流速, 通过与分流接口匹配的反吹He载气(10 mL/min)将冷阱中富集的SO2气体送入分流接口, 从而保证进入分流接口前样品燃烧产生的SO2气体全部收集。这一改进, 理论上可以将样品的利用率提高10倍, 该系统需硫量降至3~13 μg, 并且可以提高反应管的寿命, 降低清灰的频率, 提高工作效率。同时有效避免了拖尾的产生, 提高分析结果的精密度。本次微量样品实验获得的硫同位素数据与常规方法一致, 分析精度优于0.15‰(1SD), 测量值与真值的差异在0.4‰以内, 达到国际同类实验室先进水平。此外, 该方法可为微量有机碳、氮同位素EA-IRMS测试分析工作的开展提供参考经验。     

A simplified mathematical model for the dam-breach hydrograph for three reservoir geometries following a sudden full dam break

Natural Hazards - The prediction of dam-break water flow at dam site is essential to reduce the potential for loss of damage in the downstream floodplain. In this study, the influence of reservoir...