Search Results (6)

Given the high proportion of global fossil energy consumption, the Ordovician karst water in the North China-type coalfield, as a green energy source that harnesses both water and heat, holds significant potential for mitigating environmental issues associated with fossil fuels. In this work, we collected geothermal water samples and conducted borehole temperature measurements at the Xinhu Coal Mine in the Huaibei Coalfield, analyzed the chemical composition of regional geothermal water, elucidated the characteristics of thermal storage, and explored the influence of regional structure on the karst geothermal system in the northern region. The results indicate that the geothermal water chemistry at the Xinhu Coal Mine is of the Na-K-Cl-SO₄ type, with its chemical composition primarily controlled by evaporation and concentration processes. The average temperature of the Ordovician limestone thermal reservoir is 48.2 °C, and the average water circulation depth is 1153 m, suggesting karst geothermal water undergoing deep circulation. The geothermal gradient at the Xinhu Coal Mine ranges from 22 to 33 °C/km, which falls within the normal range for ground-temperature gradients. A notable jump in the geothermal gradient at well G1 suggests a strong hydraulic connection between deep strata within the mine. The heat-accumulation model of the hydrothermal mine geothermal system is influenced by strata, lithology, and fault structures. The distribution of high ground-temperature gradients in the northern region is a result of the combined effects of heat conduction from deep strata and convection of geothermal water. The Ordovician limestone and extensional faults provide a geological foundation for the abundant water and efficient heat conduction of the thermal reservoirs. Full article

A two-dimensional longitudinal profile model was used to evaluate groundwater flow along a 48 km flowline in the Southeastern Hueco Aquifer, extending from the Diablo Plateau in Texas to the Sierra de San Ignacio in Chihuahua, Mexico. The model, incorporating geologically distributed permeability values, closely matched the predevelopment potentiometric surface. Predicted recharge rates and travel times aligned with published estimates and environmental isotopes, suggesting potential transboundary groundwater movement. The model estimated recharge rates needed to reach flow capacity, or the maximum volume a system can transmit, typically saturating the water table. Current moisture levels are insufficient, but flow capacity may have been reached during late Pleistocene pluvial periods. Required recharge rates were 297% higher than initial calibration in the U.S. and 1080% higher in Mexico, with only U.S. estimates appearing plausible for the Pleistocene–Holocene transition. These findings are relevant to regional waste disposal considerations because water tables near land surface present a risk to groundwater resources. A transient simulation modeled hydraulic head decay due to recharge abatement linked to climate change over 14,000 years. It simulated a decrease from a “flow capacity” recharge rate of 10.4 mm/year to 3.5 mm/year today. The modeling simulations ended with the hydraulic head remaining only 20 m above current levels, suggesting a minimal-to-negligible fossil hydraulic gradient in the low-permeability flow system. Full article

The beginning of 2022 was a time of major changes in the perception of energy availability and security in European countries. The aggression of Russia against Ukraine destabilizing the European energy economy, combined with the withdrawal from fossil fuels which has been going on for a dozen years, has strengthened activities to introduce new energy technologies based on renewable energy sources. One of the most promising and stable sources of renewable energy is geothermal energy, in particular enhanced geothermal systems (EGS) in hot dry rocks (HDR). These deposits occur at a great depth in almost every place on Earth, but due to their low permeability, they require hydraulic fracturing, which results in high investment costs. This technology has been developed for several decades. The current situation in Europe seems to confirm that its rapid development to a level that guarantees stable and profitable operation is crucial. This is of particular importance in the case of former member states of the economic zone of the Council for Mutual Economic Assistance, which until recently were heavily dependent on Russian energy. This review, based on the latest available data, covers potential HDR prospective areas in the countries of the south-eastern Baltic basin, including Lithuania, Latvia, Estonia and Poland. It is specific to this region that the original heat flux density is lower as a result of the paleoclimatic effect associated with the youngest ice age; however, thermal conditions do not deviate too much compared to western Europe, especially Rhine Graben, and significantly exceed the conditions of Finland, where an EGS project is currently being operated. In Lithuania, the most prospective area is the ZNI intrusion (south of Klaipeda), characterized by a geothermal gradient of up to 40 °C/1000 m. In addition, the Precambrian batholith south of Liepāja (Latvia) and the Rapakivi granites in the north and center of Estonia are promising EGS sites. Poland has relatively the most explored EGS potential, in both volcanic, crystalline and sedimentary rocks, especially in the area of the Szczecin Trough, Gorzów Block, Moglino-Łódź Trough and Karkonosze Mountains. Unfortunately, local tectonic conditions, in particular the development of faults and natural fracture zones that affect the directions of fracture propagation during hydraulic fracturing, have not been sufficiently recognized, which is one of the main barriers to the expansion of EGS pilot projects in these countries. These issues present challenges for the researchers, especially in terms of petrophysical analyses of rocks in target zones and local stress conditions, which have a key impact on fracturing operations and profitability of the systems. Despite high investment costs on the one hand and a significant slowdown in the global economy in 2022 on the other, it remains hopeful that the authorities of individual countries will decide to accelerate research work, leading to the implementation of pilot projects of EGS installations, and that this technology will be further improved to ensure a stable clean energy supply. Full article

Environmental problems may develop in groundwater basins when water levels change due to long-term wetter or drier climate or land development. A term related to water-level elevation is flow capacity, which develops in aquifers when the water table is at or very close to land surface. Non-capacity develops in systems where the water table is too deep for capillary water to reach the land surface. Flow capacity is the maximum amount of water that an aquifer can transmit. Sufficient moisture is not available for flow capacity to be established in most aquifers in arid zones and these aquifers are at non-capacity, but many aquifers in today’s deserts were at flow capacity when paleoclimates were cooler and moister during the late Pleistocene. Climate change and anthropogenic activities can cause aquifers to move toward flow capacity but in the last 15,000 years, almost always toward non-capacity. This paper reviews environmental and geotechnical problems associated with the transition of groundwater basins from flow capacity to non-capacity, and vice versa. Five relevant topics are discussed and evaluated: (1) The effects of flow capacity and non-capacity on groundwater basins targeted for waste repositories; (2) The salt contamination of groundwater where flow capacity was present in the Late Pleistocene and is no longer present; (3) Trace element enrichment in salt crusts in playa sediments and environmental risks to groundwater when the flow systems transition from flow capacity to non-capacity; (4) The development and retention of environmental tracers in arid groundwater flow systems at flow capacity that cannot be explained under conditions of non-capacity; and (5) The relationship of flow capacity to fossil hydraulic gradients and non-equilibrium conditions where there is little groundwater extraction. A case example is provided with each of these topics to demonstrate relevance and to provide an understanding of topics as they relate to land management. Full article

To gain an insight into the origin of groundwater in the Hunshandake Desert (HSDK), stable and radioactive isotopes and the major ion hydrochemistry of groundwater, as well as other natural waters, were investigated in this desert. The results showed that the groundwaters in the HSDK are freshwater (total dissolved solid (TDS) < 700 mg/L) and are depleted in δ²H and δ¹⁸O when compared with the modern precipitation. The major water types are the Ca–HCO₃ and Ca/Mg–SO₄ waters. No Cl-type and Na-type waters occurred in the study area. The ionic and depleted stable isotopic signals in groundwater, as well as the high values of tritium contents (5–25 TU), indicate that the groundwaters studied here are young but not of fossil and meteoric water origin, i.e., out of control by the modern and palaeo-direct recharge. A clear difference in the isotopic signals are observed between the groundwaters in the north and south parts of the study area, but the signals are similar between the groundwaters in the north HSDK catchment and its neighboring catchment, the Dali Basin. The topographical elevation decreases from the south (1396 m a.s.l.) to the north (1317 m a.s.l.) and the Dali (1226 m a.s.l.). Groundwaters in the north are characterized by lower chloride and TDS concentrations, higher tritium contents, higher deuterium excess, and more depleted values of δ²H and δ¹⁸O than those in the south. The spatial distribution pattern of these environmental parameters indicates a discrepancy between the hydraulic gradient of groundwater and the isotopic and hydrochemical gradients of groundwater in the HSDK, suggesting different recharge sources between the two parts in the desert. A combined analysis using the isotopic and physiochemical data of natural waters collected from the Dali Basin and the surrounding mountains was performed to investigate this problem. It indicates that groundwaters in the HSDK Desert are recharged from remote mountain areas (about 150–200 km to the east and southeast) but not from the north neighboring catchment. Full article

Coral reefs globally are impacted by natural and anthropogenic stressors that are compounded by climate change. Understanding past reef responses to natural stressors (cyclones, sea-level change, freshwater inputs, and sedimentation) can provide important insights to further understand recent (within the past century) trends in coral cover and diversity. Here we use a compilation of recently published data to investigate the Holocene development of five fringing reefs that are located on a cross-shelf transect on the central Great Barrier Reef, and that are exposed to varying degrees of natural and anthropogenic sedimentation, storm exposure, and Holocene sea-level change. Forty-two reef cores collected using a combination of manual percussion coring and hydraulic drilling techniques, were analysed and dated using uranium-thorium methods. The chronostratigraphic records of reef development established using 105 recently published radiometric ages and seven new uranium-thorium ages from the reef cores and fossil microatolls preserved across the reef flats were compared to investigate cross-shelf variations in reef development. This is the first study to conduct an internal investigation of reef framework across an inshore–offshore gradient to examine the varying levels of influence of sedimentation, sea level and cyclones. Our observations from the central Great Barrier Reef show that reefs furthest offshore from the mainland coast were typically initiated earliest after the post-glacial marine transgression. Reef flat size, morphology, and growth style varied according to constraints placed on reef development by the composition, depth, shape, and relief of the underlying substrate. We establish that terrigenous sedimentation had a marked effect on the development of inshore reefs closest to the mainland (within 10 km of the mainland coast). Periods of relatively high terrigenous sedimentation correspond with enhanced reef accretion rates, and also resulted in a superior record of palaeo-ecological coral composition (i.e., better preservation) at inshore sites. In contrast, mid-Holocene cyclones played a seemingly more important role in the development of reefs >10 km from the mainland; although cyclones clearly affect reefs closer inshore, their geomorphology is affected by a range of controlling factors. Insights provided by these five Holocene reef chronostratigraphies provide useful baseline understanding of reef condition and growth along a cross-shelf transect where the reefs are exposed to variable stressors. Full article