Aerial tracer particle distribution system for surface image velocimetry

A novel aerial tracer particle distribution system has been developed. This system is mounted on an Unmanned Aerial Vehicle (UAV) and flown upstream from where surface velocimetry measurements are conducted. This enables surface velocimetry techniques to be applied in rivers and channels lacking sufficient natural tracer particles or surface features. Lack of tracers is a common problem during low flows, in lowland rivers, or in artificial channels. This is particularly problematic for analysis conducted using Particle Image Velocimetry (PIV) techniques where dense tracer particles are required. Techniques for colouring tracer particles with biodegradable dye have also been developed, along with methods for extracting them from Red Green Blue (RGB) imagery in the Hue Saturation Value (HSV) colour space. The use of coloured tracer particles enables flow measurements in situations where sunglint, surface waves, moving shadows, or dappled lighting on riverbeds can interfere with and corrupt results using surface velocimetry techniques. These developments further expand the situations where surface velocimetry can be applied, as well as improving the accuracy of the results.

Estimation of subsurface flow from high-resolution temperature profiles

Subsurface flow rates are critical for hydrology and geothermal research, while field characterization remains a challenge. There are several analytical solutions for calculating the vertical water flux based on measured temperatures. Heat is a popular natural tracer to estimate subsurface flow rates. However, quantifying flow rates is impeded by insufficient sensors spacing during field investigations or simplifying assumptions for analysis such as sinusoidal temperature boundary. The objective of this study is to develop a convenient method to investigate subsurface flow on the sub-meter scale. Here, we present a program to estimate water fluxes based on temperature-depth profiles, so-called TempFlow. TempFlow is a numerical program written in MATLAB that calculates steady state flow in transient heat tracing based on the inversion of measured high-resolution temperature-depth series observed at a certain time. In this program, the Fiber Optic Distributed Temperature Sensing (FO-DTS) is recommended for temperature collection. FO-DTS techniques provide high-resolution temperature measurements with continuous temperature profiles that account for sub-meter scale and nonperiodic boundary conditions in saturated sediments. The estimated subsurface flow using TempFlow was validated in a medium-scale tank with a series of experiments, where the hydraulic and temperature boundary conditions were well-controlled. The results indicate that the estimation using TempFlow obtained similar results as the experiments. Thus, the method could potentially be used to determine the flow rate of the subsurface.

Southern Africa: The Missing Piece To The Dust Provenance Puzzle of East Antarctica?

Mineral dust is a natural tracer of atmospheric composition and climate variability. Yet, there is still much to be known about the Southern Hemisphere dust cycle during the last Pleistocene. Major efforts have attempted to solve the ‘puzzle’ of the origin of the potential source areas that contribute dust to the Southern Ocean and East Antarctica (EA). Here we present a comprehensive geochemical characterization of an important potential source area, which role as a dust supplier to different environments of the SH has significantly been underestimated, that is, the Southern Africa (SAF) region. On the basis of Sr-Nd-Pb isotope ratios and rare earth element concentrations analyzed in sediments collected along the major dust-producing areas in the Namibian coast (Kuiseb, Omaruru and Huab riverbeds and the Namibian sand sea region), this study demonstrates for the first time that SAF emerges as the second most important dust source to EA during interglacial times.

Investigation of runoff generation and Radon-222 activities in a forested catchment using HydroGeoSphere

<p>Radon (<sup>222</sup>Rn) is widely used as a natural tracer to investigate surface/groundwater interactions for hydrological systems. Because <sup>222</sup>Rn activities in groundwater are higher compared to surface water, it can be used to quantify groundwater inflow rates into rivers and streams. Here we present a process-based model to simulate <sup>222</sup>Rn emanation and transport in groundwater to investigate surface/groundwater interactions for the  Große Ohe catchment, located in the Bavarian Forest National Park (Germany). For representing surface and groundwater flow in the catchment as well as transport, decay, and emanation of <sup>222</sup>Rn, the processed based hydrological model HydroGeosphere (HGS) is used. HGS is an integrated surface sub-surface hydrological model (ISSHM) which can simulate reactive transport in surface and sub-surface flow. The model was calibrated using measured in-stream<sup> 222</sup>Rn activities and continuous discharge observations. Main objective of this study is to investigate runoff generation in the catchment and how hydrological processes are affecting the age and residence time composition of groundwater.  </p>

Characterization of Fluid Connectivity in Reservoirs using Strontium Isotopes

<p>Routine measurements of formation pressure while drilling reservoirs can indicate the presence of internal barriers to vertical fluid movement when there is a sudden shift in the pressure data. However, pinpointing the location of a barrier is often not possible since the density of pressure measurements is low and irregular. The aim of this contribution is to show how the Strontium isotopic system can help characterize the fluid connectivity and pinpoint the precise location of low permeability barriers in reservoir units and sedimentary sequences. As an example, we use a 25 m thick interval within the Middle Jurassic Hugin reservoir unit of the Langfjellet oil discovery on the Norwegian Continental Shelf. The location of the barrier is constrained by the upper and lower pressure measurements and could correspond to any of the several layers of silt, shale or coal layers in this interval. In this study, we collected every 2-4 m a total of 40 samples from a 110 m long cored section of a technical side-track well over the available. Each sample was prepared and analyzed using the SrRSA method (Strontium Residual Salt Analysis), which measures the <sup>87</sup>Sr/<sup>86</sup>Sr ratio in salt residue that precipitated in the pore space after the core dried out. The <sup>87</sup>Sr/<sup>86</sup>Sr is a natural tracer because the ratio is not affected by mass fractionation. The <sup>87</sup>Sr/<sup>86</sup>Sr in rocks is mostly acquired by water-rock interactions during diagenesis and evolves through mixing and equilibration of different water bodies, unless low-permeability barriers prevent equilibration. Therefore, the SrRSA patterns observed in the well represent a 1D snapshot of the fluid dynamics at the time of oil filling, which is a frozen image of competing equilibrium vs disequilibrium conditions. The SrRSA data follow a smooth trend of content values at 0.713 and display a sudden jump to lighter 0.709 values near the top of the 25 m thick interval that suggests the presence of a potential barrier. The lithological core log shows that the SrRSA step change corresponds to a coal-shale unit, which is interpreted to represent the barrier. The SrRSA data further demonstrate the reservoir unit at Langfjellet does not contain any other barriers to fluid flow, since pressure equilibration could have masked a possible compartmentalization. This study shows that the SrRSA method is a powerful tool that should be routinely applied for the characterization of fluid connectivity of storage units.</p>

Radon as a Natural Tracer for Monitoring NAPL Groundwater Contamination

In this research, the radioactive noble gas radon was used as a tracer for Non-Aqueous Phase Liquids (NAPLs) contamination, since it is much more soluble in these substances than in air or water. Soil radon remains trapped within the NAPLs, resulting in a local reduction in the radon concentration within close proximity to the contaminated area. This technique was applied to a contaminated site in Roma (Italy). The main residual NAPLs are total hydrocarbons and methyl-tertiary-butyl ether (MTBE), a water-soluble additive. The monitoring activities included two sampling campaigns of groundwater from 18 wells in February and May 2020. Concentration maps were produced using radon data. The results show that the radon deficit traces the location of NAPLs in the fuelling station very well, with a residual source zone extending in a NNW-SSE direction. A good correspondence between a low amount of radon and a higher concentration of NAPLs was found. A reduction in the average amount of radon in the May 2020 survey indicated a stronger remobilization of NAPLs compared to that of the February 2020 monitoring campaign. The peaks of Volatile Organic Compounds (VOCs) detected between 8–9 and 11–12 m depths indicate the presence of residual blobs of NAPLs in the vadose zone of the aquifer.

Isoscape of amount-weighted annual mean precipitation tritium (³H) activity from 1976 to 2017 for the Adriatic–Pannonian region – AP³H_v1 database

Tritium (3H) as a constituent of the water molecule is an important natural tracer in hydrological sciences. The anthropogenic tritium introduced into the atmosphere unintentionally became an excellent tracer of processes on a time scale of up to 100 years. A prerequisite for tritium applications is to know the distribution of tritium activity in precipitation. Here we present a database of isoscapes derived from 41 stations for amount-weighted annual mean tritium activity in precipitation for the period 1976 to 2017 on spatially continuous interpolated 1 km×1 km grids for the Adriatic–Pannonian region (called the AP3H_v1 database), with a special focus on post-2010 years, which are not represented by existing global models. Five stations were used for out-of-sample evaluation of the model performance, independently confirming its capability of reproducing the spatiotemporal tritium variability in the region. The AP3H database is capable of providing reliable spatiotemporal input for hydrogeological application at any place within Slovenia, Hungary, and their surroundings. Results also show a decrease in the average spatial representativity of the stations regarding tritium activity in precipitation from ∼440 km in 1970s, when bomb tritium still prevailed in precipitation, to ∼235 km in the 2010s. The post-2010 isoscapes can serve as benchmarks for background tritium activity for the region, helping to determine potential future local increases in technogenic tritium from these backgrounds. The gridded tritium isoscape is available in NetCDF-4 at https://doi.org/10.1594/PANGAEA.896938 (Kern et al., 2019).