Localizing and quantifying groundwater-surface water interactions at different scales: A tracer approach at the River Moselle,Germany

Groundwater-surface water interactions (GSI) connect rivers and streams with riparian areas and the adjacent aquifer. Although these interactions exert a substantial control of quantity and quality of both groundwater and surface water, knowledge on GSI along rivers at the regional scale, particularly for inland waterways, is still limited. We investigated GSI along the river Moselle, an important federal inland waterway in Germany, by using radon and tritium to identify gaining (water flux from the aquifer to the surface water) and losing (water flux from the surface water to the aquifer) stream conditions, respectively. Gaining stream conditions were identified by continuously measuring radon along the river during boat surveys with a high spatial resolution (every 2 km) during intermediate (October 2020) and near low flow conditions (August/September 2021). The tritium concentrations in surface water and groundwater and the resulting tritium inventories were used to characterize losing stream conditions Monthly tritium inventories from 2017 to 2022 revealed a mean loss for the whole period of 20.3 % and a mean gain of 21.8%. Both were probably triggered by a combination of losing stream conditions and flood-induced mass transfer of water from the aquifer back into the river as well as discharge fluctuations. At the investigated site Lehmen there were direct indications of an influence of surface water due to elevated tritium concentrations in the groundwater (up to 13.3 Bq L⁻¹). Using radon mass balance modelling, good agreements of simulated versus measured radon data with respect to two groundwater end-member scenarios were obtained during intermediate flow (Spearman's ρ: 0.97 and 0.99; MAE: 10.1 and 3.4 Bq L⁻¹) and near low flow (Spearman's ρ: 0.97 and 0.99; MAE: 11 and 6.5 Bq L⁻¹). Considerable groundwater inflow was limited to the meander of Detzem, where cumulated groundwater inflow of about 19 m³ s⁻¹ (9.5% of total discharge) and 4.2 m³ s⁻¹ (3.8% of total discharge) was simulated during intermediate and near low flow, respectively. However, the groundwater inflow was relatively low compared to alpine streams, for example. The study will help to better identify and quantify GSI at the regional scale and provide methodological guidance for future studies focusing on inland waterways.     

鲁西新太古代济宁群含铁岩系形成时代——SHRIMP U-Pb锆石定年

济宁群以隐伏的地质体分布于华北克拉通鲁西地区,以往被划归古元古代。近年来在济宁群的钻探和地球物理研究中,发现存在较大规模条带状硅铁建造,其形成时代引起地学界极大关注。本文对济宁群变质碎屑沉积岩和长英质火山岩进行了锆石SHRIMP年龄测定。含砾绿泥绢云千枚岩的碎屑锆石年龄主要集中在～2.7Ga,可靠的最年轻碎屑锆石年龄为2.61±0.01Ga。变质长英质火山岩岩浆锆石年龄为2.56±0.02Ga。研究表明,济宁群形成于新太古代晚期,而不是以往认为的古元古代。华北克拉通条带状铁建造主要形成于新太古代晚期。济宁群在岩石组合、变质作用方面与鞍山、冀东以及五台地区同时代含硅铁建造的表壳岩系有差别,但是与本溪南芬铁矿的岩石组合有相似之处。这些可能为我国的隐伏太古宙BIF铁矿的研究与勘探提供了重要依据。     

Evidence for methane and ammonia in the coma of comet P/Halley

Methane and ammonia abundances in the coma of Halley are derived from Giotto IMS data using an Eulerian model of chemical and physical processes inside the contact surface to simulate Giotto HIS ion mass spectral data for mass-to-charge ratios (m/q) from 15 to 19. The ratio m/q = 19/18 as a function of distance from the nucleus is not reproduced by a model for a pure water coma. It is necessary to include the presence of NH3, and uniquely NH3, in coma gases in order to explain the data. A ratio of production rates Q(NH3)/Q(H2O) = 0.01-0.02 results in model values approximating the Giotto data. Methane is identified as the most probable source of the distinct peak at m/q = 15. The observations are fit best with Q(CH4)/Q(H2O) = 0.02. The chemical composition of the comet nucleus implied by these production rate ratios is unlike that of the outer planets. On the other hand, there are also significant differences from observations of gas phase interstellar material.     

Constraining and enabling factors to using long-term climate information in decision-making

We carry out a structured review of the peer-reviewed literature to assess the factors that constrain and enable the uptake of long-term climate information in a wide range of sectoral investment and planning decisions. Common applications of long-term climate information are shown to relate to urban planning and infrastructure, as well as flood and coastal management. Analysis of the identified literature highlights five categories of constraints: disconnection between users and producers of climate information, limitations of climate information, financial and technical constraints, political economy and institutional constraints and finally psycho-social constraints. Five categories of enablers to the uptake of long-term climate information in decision-making are also identified: collaboration and bridge work, increased accessibility of climate information, improvement in the underlying science, institutional reform and windows of opportunity for building trust.

Policy relevance

Our review suggests that stand-alone interventions aimed at promoting the uptake of climate information into decision-making are unlikely to succeed without genuine and sustained relationships between producers and users. We also highlight that not every decision requires consideration of long-term climate information for successful outcomes to be achieved. This is particularly the case in the context of developing countries, where the immediacy of development challenges means that decision makers often prioritize short-term interventions. Care should therefore be taken to ensure that information is targeted towards investments and planning decisions that are relevant to longer-term timescales.     

Spatial distribution,variation and trend of five-day antecedent rainfall in Singapore

ABSTRACT

This paper presents the spatial distribution, variation and trend of 5-day antecedent rainfall in Singapore based on rainfall data from 22 meteorological stations. The effect of climate was analyzed by dividing the study period into three decades i.e. Decade 1: 1982–1991, Decade 2: 1992–2001 and Decade 3: 2002–2011. Kriging interpolation was used for rainfall mapping. The results show that spatial distribution of 5-day antecedent rainfall does not coincide with that of the annual rainfall. The maximum annual rainfall occurred in the northwestern side of Singapore. On the other hand, the maximum 5-day antecedent rainfall occurred in the north and northeastern sides. The results of this study suggest that the climate change has increased the amount of 5-day antecedent rainfall quite significantly, i.e. from 420.5 (1987) to 592.9 mm (2006), thus affecting the vulnerability of the area with respect to rainfall-induced slope failure. The analyses also showed that most of slope failures were located in the north and northeast of Singapore between December and earlier March. More slope failures were observed in Decade 3 as compared to Decades 1 and 2. In other words, the analysis confirmed that 5-day antecedent rainfall had affected the slope stability in Singapore.     

Impacts of saturation-dependent anisotropy on the shrinkage behavior of clay rocks

Geomaterials such as soils and rocks can exhibit inherent anisotropy due to the preferred orientation of mineral grains and/or cracks. They can also be partially saturated with multiple types of fluids occupying the pore space. The anisotropic and unsaturated behaviors of geomaterials can be highly interdependent. Experimental studies have shown that the elastic parameters of rocks evolve with saturation. The effect of saturation has also been shown to differ between directions in transversely isotropic clay rock. This gives rise to saturation-dependent stiffness anisotropy. Similarly, permeability anisotropy can also be saturation-dependent. In this study, constitutive equations accommodating saturation-dependent stiffness and hydraulic anisotropy are presented. A linear function is used to describe the relationship between the elastic parameters and saturation, while the relative permeability–saturation relationship is characterized with a log-linear function. These equations are implemented into a hydromechanical framework to investigate the effects of saturation-dependent properties on the shrinkage behavior of clay rocks. Numerical simulations are presented to demonstrate the role of saturation-dependent stiffness and hydraulic anisotropy in shrinkage behavior. The results highlight that strain anisotropy and time evolution of pore pressures are substantially influenced by saturation-dependent stiffness and hydraulic anisotropy.

     

Evolution of anisotropy with saturation and its implications for the elastoplastic responses of clay rocks

Many clay rocks have distinct bedding planes. Experimental studies have shown that their mechanical properties evolve with the degree of saturation (DOS), often with higher stiffness and strength after drying. For transversely isotropic rocks, the effects of saturation can differ between the bed-normal (BN) and bed-parallel (BP) directions, which gives rise to saturation-dependent stiffness and strength anisotropy. Accurate prediction of the mechanical behavior of clay rocks under partially saturated conditions requires numerical models that can capture the evolving elastic and plastic anisotropy with DOS. In this study, we present an anisotropy framework for coupled solid deformation-fluid flow in unsaturated elastoplastic media. We incorporate saturation-dependent strength anisotropy into an anisotropic modified Cam-Clay (MCC) model and consider the evolving anisotropy in both the elastic and plastic responses. The model was calibrated using experimental data from triaxial tests to demonstrate its capability in capturing strength anisotropy at various levels of saturation. Through numerical simulations, we demonstrate the role of evolving stiffness and strength anisotropy in the mechanical behavior of clay rocks. Plane strain simulations of triaxial compression tests were also conducted to demonstrate the impacts of material anisotropy and DOS on the mechanical and fluid flow responses.     

Multitemporal terrestrial laser scanning point clouds for thaw subsidence observation at Arctic permafrost monitoring sites

This paper investigates different methods for quantifying thaw subsidence using terrestrial laser scanning (TLS) point clouds. Thaw subsidence is a slow (millimetre to centimetre per year) vertical displacement of the ground surface common in ice-rich permafrost-underlain landscapes. It is difficult to quantify thaw subsidence in tundra areas as they often lack stable reference frames. Also, there is no solid ground surface to serve as a basis for elevation measurements, due to a continuous moss–lichen cover. We investigate how an expert-driven method improves the accuracy of benchmark measurements at discrete locations within two sites using multitemporal TLS data of a 1-year period. Our method aggregates multiple experts’ determination of the ground surface in 3D point clouds, collected in a web-based tool. We then compare this to the performance of a fully automated ground surface determination method. Lastly, we quantify ground surface displacement by directly computing multitemporal point cloud distances, thereby extending thaw subsidence observation to an area-based assessment. Using the expert-driven quantification as reference, we validate the other methods, including in-situ benchmark measurements from a conventional field survey. This study demonstrates that quantifying the ground surface using 3D point clouds is more accurate than the field survey method. The expert-driven method achieves an accuracy of 0.1 ± 0.1 cm. Compared to this, in-situ benchmark measurements by single surveyors yield an accuracy of 0.4 ± 1.5 cm. This difference between the two methods is important, considering an observed displacement of 1.4 cm at the sites. Thaw subsidence quantification with the fully automatic benchmark-based method achieves an accuracy of 0.2 ± 0.5 cm and direct point cloud distance computation an accuracy of 0.2 ± 0.9 cm. The range in accuracy is largely influenced by properties of vegetation structure at locations within the sites. The developed methods enable a link of automated quantification and expert judgement for transparent long-term monitoring of permafrost subsidence. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

华北地台南缘张士英岩体的锆石SHRIMP U-Pb测年、Hf同位素组成及其地质意义

张士英岩体位于华北地台南缘,岩石类型包括钾长花岗岩、似斑状花岗岩和石英斑岩脉,其中只在钾长花岗岩中发育有暗色岩石包体,在包体和寄主岩中发育反映岩浆混合作用的岩石结构。钾长花岗岩、似斑状花岗岩和石英斑岩脉的SHRIMP锆石U-Pb年龄分别为107.3±2.4Ma、106.7±2.5Ma和101±3Ma。锆石Hf同位素分析结果显示,钾长花岗岩的锆石εHf(t)为-15.96～-20.80,单阶段模式年龄(tDM1)为1396～1643Ma,两阶段模式年龄(tDM2)为1880～2018Ma;似斑状花岗岩的锆石εHf(t)为-18.97～-22.18,tDM1为1512～1640Ma,tDM2为1925～2080Ma;除了一粒年龄为2.6Ga的锆石具有εHf(t)为-0.71、tDM1为2943Ma和tDM2为3036Ma的组成,石英斑岩的锆石εHf(t)为-23.41～-27.95,tDM1为1678～1896Ma,tDM2为2144～2330Ma。这些数据暗示,除了存在少量太古宙地壳物质的贡献外,张士英岩体的物质来源可能主要为1.9～2.3Ga期间形成的新生地壳,但也不排除古老地壳与富集地幔源混合的可能。综合分析前人研究成果表明,在太平洋板块俯冲方向发生转变的过程中,先存断裂带发生拉张。张士英岩体与中国东部同期岩浆活动一起可能形成于这种受断裂带控制的伸展环境。