Groundwaters circulating in Upper Mesozoic carbonates are of great interest for geothermal heat production and storage applications in the Geneva area. This study aims at providing new insights and proposing new interpretations about the mineral-water reactions and the fluid-flow paths mechanisms across the Geneva Basin (GB). Data from previous studies are combined and improved by new ones collected from cold and hot springs and geothermal exploration wells in 2018 and 2020 in the framework of the GEothermies program and HEATSTORE project. Major ions, trace elements, and the isotopes of Oxygen, Hydrogen, Sulfur, Strontium, and Carbo have been analysed and the results show that the sampled waters have a meteoric origin, the carbonate aquifers act as preferential host rocks for geothermal waters, and partial contribution from the Cenozoic sediments can be observed in some samples. The Jura Mountains and the Saleve Ridge are the main catchment areas and an evolution from a pure Ca-HCO3 footprint for the cold springs, to a Na > Ca-HCO3 and a Na-Cl composutions, is observed at the two geothermal wells. The residence time is in the order of a few years for the cold springs and reaches up to 15–20,000 years for the deep wells.
The Taihu (Tai lake) region is one of the most economically prospering areas of China. Due to its location within this district of high anthropogenic activities, Taihu represents a drastic example of water pollution with nutrients (nitrogen, phosphate), organic contaminants and heavy metals. High nutrient levels combined with very shallow water create large eutrophication problems, threatening the drinking water supply of the surrounding cities. Within the international research project SIGN (SinoGerman Water Supply Network, www.water-sign.de ), funded by the German Federal Ministry of Education and Research (BMBF), a powerful consortium of fifteen German partners is working on the overall aim of assuring good water quality from the source to the tap by taking the whole water cycle into account: The diverse research topics range from future proof strategies for urban catchment, innovative monitoring and early warning approaches for lake and drinking water, control and use of biological degradation processes, efficient water treatment technologies, adapted water distribution up to promoting sector policy by good governance. The implementation in China is warranted, since the leading Chinese research institutes as well as the most important local stakeholders, e.g. water suppliers, are involved.
Over the last decades, several methods have been developed for determining the porewater stable isotope composition (δ2H, δ18O) in low-permeability, argillaceous rocks and pertinent to the acquisition of spatially highly-resolved tracer profiles for investigating subsurface transport processes over large scales of time and space. One of these methods is the so-called isotope diffusive exchange technique (IDE) where the porewater of the rock equilibrates via the vapour phase with a test water of known isotope composition. In this study we aim for 1) identifying and assessing important parameters and artefacts these experiments are sensitive and prone to, respectively, 2) evaluating their impact on the porewater isotope composition derived from such experiments and 3) testing the reproducibility and accuracy of the method. For this, the experimental data and the calculated porewater isotope composition of 752 isotope diffusive exchange experiments, performed on drillcore samples from variable lithologies, were examined under these aspects. The investigations are complemented by comparison between porewater and groundwater isotope values in regions of water-conducting zones and an interlaboratory comparison. Ultimately, this allowed defining a stringent procedure for the evaluation of the experimental data and classifying experiments as 'reliable', less reliable' and 'failed'. For calculating the porewater isotope composition, a new approach was developed that accounts for sample-scale heterogeneity of the water content. This procedure of data evaluation and processing resulted in smooth isotope profiles with only little scatter across largely different lithologies. The interlaboratory comparison attests the method a very good reproducibility. The comparison with groundwater isotope data reveals slightly enriched δ18O and δ2H signatures by 0.3–0.6 and 1.7–2.7‰ VSMOW, respectively, for some samples investigated by the IDE method. No stringent explanation exists at this stage for these differences, but it must be emphasized that these deviations are small compared to the typical natural variations observed in profiles of these tracers. This demonstrates that porewater isotope data obtained by the IDE method represent the conditions in the in situ porewater reasonably well when strictly following the proposed procedures of the experimental setup, the evaluation of experimental data and the calculation of porewater isotope compositions.
Abstract. Dissolved organic matter (DOM) and microorganisms were characterized along the flow path of a geothermal facility that produces water from a deep (2800 m) carbonate rock reservoir for energy provision. A variety of analytical techniques were employed to distinguish between natural and synthetic organic matter, determine the composition of the microbial community, and evaluate the role of microorganisms in the operation of the geothermal site in Bad Blumau, Austria. Ion chromatography (IC), liquid chromatography with organic carbon detection (LC-OCD), and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) in negative electrospray ionization (ESI(−)) and positive atmospheric pressure photoionization (APPI(+)) mode were applied to the fluid samples for the purpose of characterizing the composition of DOM and distinguishing natural DOM from a chemical inhibitor used to prevent scaling. The concentrations of dissolved organic carbon (DOC) ranged from 8.5 to 10.4 mg C L−1. The chemical scaling inhibitor contributes approximately 1 mg C L−1 of DOC to the produced fluids. Depending on the applied ionization mode, the FT-ICR-MS results show that between 31 % and 65 % of the macromolecular formulas (150–1000 Da) detected in the fluid samples appear to originate from the inhibitor. However, the DOM is primarily composed of low-molecular-weight acids (LMWA), with acetate being the most prevalent, reaching up to 7.4 mg C L−1. To assess the diversity of the bacterial communities, targeted amplification of the 16S rRNA gene was conducted. The composition of the microbial community exhibited variation along the flow path, with Firmicutes, Proteobacteria, and Thermotogae representing the dominant bacterial phyla. Based on the community composition, metabolic pathways associated with the presence of acetate in the samples were predicted. Microorganisms may produce acetate through diverse fermentation processes, including those involving lysine, pyruvate, and hexitol. Assessing the presence and interaction of organic compounds and microorganisms in geothermal fluids can provide a broader understanding of processes within the geothermal facility. This understanding could be beneficial for efficient operation of a geothermal power plant.
The porosity and pore geometry of rock samples from a coherent granodioritic rock body at the Grimsel Test Site in Switzerland was characterised by different methods using injection techniques. Results from in situ and laboratory techniques are compared by applying innovative in situ resin impregnation techniques as well as rock impregnation and mercury injection under laboratory conditions. In situ resin impregnation of the rock matrix shows an interconnected pore network throughout the rock body, consisting mainly of grain-boundary pores and solution pores in magmatic feldspar, providing an important reservoir for pore water and solutes, accessible by diffusion. Porosity and pore connectivity do not vary as a function of distance to brittle shear zones. In situ porosity was found to be about 0.3 vol.%, which is about half the porosity value that was determined based on rock samples in the laboratory. Samples that were dried and impregnated in the laboratory were affected by artefacts created since core recovery, and thus showed higher porosity values than samples impregnated under in situ conditions. The extrapolation of laboratory measurements to in situ conditions requires great care and may not be feasible in all cases.
