Towards a New Classification Scheme of Geothermal Systems in China

ABSTRACT Classification of geothermal systems provides good basis for exploration and assessment of geothermal resources. China is rich in geothermal resources and genetic mechanisms are diverse with complicated geological backgounds. In this paper we propose a new classification which is based on the type of heat source, followed by mechanism of heat transfer. Four types of tectono-genic heat sources are identified and two types of heat transfer mechanisms have been used for the classification. The dominant factor in determining the uneven distribution or accumulation of heat energy in the crust is emphasized. Other influencing factors are used to further classify the resources into subcategories. Geothermal prospects or plays in the Himalayas are considered to be supplied with crustal magmatism/partial melting, caused by collision-induced conversion from mechanical to heat energy. Geothermal resources in some of the hot and warm basins in eastern and central China are fed by elevated heat flux from mantle upwelling in a rifting tectonic background. Typical examples are the Bohaibay,Songliao and Guanzhong Basins. Mantle heat also dominats those geothermal systems found in regions with recent volcanic activities. Good examples are Tengchong geothermal field in SW China and probably Changbaishan geothermal play in NE China. Deep faulting also induces heat accumulation in the crust that serves as an additional heat source, which is found in major fault zones. Tanlu fault zone in eastern China is a typical example of this kind, so are those in SE China, including Zhangzhou, Fuzhou geothermal fields. Geothermal systems with dominant radiogenic heat generation from radio nuclides have not been confirmed but maybe a new type to be discovered in China. This classification scheme is expected to be more effective in guiding exploration and assessment of geothermal resources. The search for deep geothermal resources (hot dry rock) should also benefit from this fundamental understanding and theoretical classification

Deep groundwater cycle in Xiongxian geothermal field

ABSTRACT The deep karstic aquifer containing hot water is ideal for space heating and maybe also for geothermal power generation. The hot water is characterized by high single-well yield, low salinity, gravity injection and less impact on environment when it is exploited. In order to run a karstic geothermal field sustainably, it is of high importance to identify the local groundwater circulation pattern in the field. Here we take Xiongxian geothermal field as an example to get insights into the characteristics of local groundwater circulation in karstic aquifers. Groundwater samples and surface water samples were collected, and analyzed for their hydrochemical and isotopic contents. Results show that the TDS of groundwater in karstic aquifers is between 1.9 and 2.6 g/L. According to the data of water table, the local groundwater flow direction is from Southwest to Northeast. This is confirmed by the TDS data, which increases gradually in this direction. However, this is orthogonal to the regional groundwater flow direction that is from Northwest to Southeast. This phenomenon highlights the control of aquifer lithology and geological structures on the groundwater flow field. Isotopic data illustrates some oxygen isotope shifts, although the reservoir temperature is less than 90 ℃. Finally, a conceptual model is proposed to depict the deep groundwater cycle in Xiongxian geothermal field, which will serve as a basis for the further simulated model for exploitation strategy and could be used as a reference in similar karstic aquifers

Response of riparian vegetation to water-table changes in the lower reaches of Tarim River, Xinjiang Uygur, China

The lower reaches of Tarim River in the Xinjiang Uygur region of western China had been dried out for more than 30 years before water began to be diverted from Konqi (Peacock) River via a 927-km-long channel in year 2000, aimed at improving the riparian ecological systems. Since then, eight intermittent water deliveries have been carried out. To evaluate the response of riparian vegetation to these operations, the groundwater regime and vegetation changes have been monitored along the 350-km-long stem of the river using a network of 40 dug wells at nine transects across the river and 30 vegetation plots at key sites. Results show that the water table rose remarkably, i.e. from a depth of 9.87m before the water delivery to 3.16m after the third water delivery. The lateral distance of affected water table extended to 1,050m from the riverbank after the fourth water delivery. The riparian vegetation has changed in composition, type, distribution, and growing behavior. This shows that the water deliveries have had significant effects on restoration of riparian ecosystems

Twenty-three unsolved problems in hydrology (UPH) – a community perspective

This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through on-line media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focussed on process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come

Design and baseline characteristics of the finerenone in reducing cardiovascular mortality and morbidity in diabetic kidney disease trial

Background: Among people with diabetes, those with kidney disease have exceptionally high rates of cardiovascular (CV) morbidity and mortality and progression of their underlying kidney disease. Finerenone is a novel, nonsteroidal, selective mineralocorticoid receptor antagonist that has shown to reduce albuminuria in type 2 diabetes (T2D) patients with chronic kidney disease (CKD) while revealing only a low risk of hyperkalemia. However, the effect of finerenone on CV and renal outcomes has not yet been investigated in long-term trials. Patients and Methods: The Finerenone in Reducing CV Mortality and Morbidity in Diabetic Kidney Disease (FIGARO-DKD) trial aims to assess the efficacy and safety of finerenone compared to placebo at reducing clinically important CV and renal outcomes in T2D patients with CKD. FIGARO-DKD is a randomized, double-blind, placebo-controlled, parallel-group, event-driven trial running in 47 countries with an expected duration of approximately 6 years. FIGARO-DKD randomized 7,437 patients with an estimated glomerular filtration rate >= 25 mL/min/1.73 m(2) and albuminuria (urinary albumin-to-creatinine ratio >= 30 to <= 5,000 mg/g). The study has at least 90% power to detect a 20% reduction in the risk of the primary outcome (overall two-sided significance level alpha = 0.05), the composite of time to first occurrence of CV death, nonfatal myocardial infarction, nonfatal stroke, or hospitalization for heart failure. Conclusions: FIGARO-DKD will determine whether an optimally treated cohort of T2D patients with CKD at high risk of CV and renal events will experience cardiorenal benefits with the addition of finerenone to their treatment regimen. Trial Registration: EudraCT number: 2015-000950-39; ClinicalTrials.gov identifier: NCT02545049

Noble gas geochemistry and chronology of groundwater in an active rift basin in central China

Stable noble gas isotopes are excellent groundwater tracers. Radioactive noble gases are emerging new tools in the study of groundwater circulation dynamics. Among these, the 85Kr and 81Kr, and 39Ar have advanced very fast in recent years and exhibit strong potential in the reconstruction of the history of groundwater recharge and evolution in sedimentary basins at different scales. Here, we report the findings in groundwater circulation dynamics as relative to intensive water-rock interactions, heat transfer and He gas flux in Guanzhong Basin located in Xi’an, the geographical centre of China, which is a rift basin created by collision between the Eurasia and Indian plates, with active neotectonic activities. The recent technological breakthrough in noble gas isotope measurements, i.e. the atomic trap trace analysis (ATTA) techniques on Kr and Ar gas radionuclei, has revolutionized groundwater dating. Noble gas samples from shallow and deep wells to 3000 m depth have been collected to study isotope variations to reconstruct the history of groundwater recharge and understand the water-rock interaction processes. Stable isotopes of water show strong water-rock interaction in the formation, creating a strong positive O-isotope shift up to 10 ‰, a phenomenon that is rarely seen in a fairly low temperature environment. Analysis of 85Kr and 81Kr show groundwater ages up to 1.3 million years old along both North-South and a West-East cross sections, which offers strong evidence about the slow moving flow, strong water-rock interaction, rich geothermal resources as well as He gas resources

Comparison of Geochemical characteristics of geothermal fluids from Eastern and Western Syntaxes, Himalayan belt, China

High temperature geothermal systems are widely present along the Himalayan belt in the NW China. Strong manifestations have been observed in the Eastern syntax, where geothermal fluids are alkaline with pH almost higher than 9.0 due to boiling and waters are mainly Cl·HCO3-Na and HCO3-Na types. Large amounts of CO2 from carbonate metamorphism are thought to be one of the reasons of calcite scaling and will be a problem for geothermal energy utilization. However, in the Western syntax, there are no obvious manifestations and geothermal fluid is Cl·SO4-Na type with pH about 7.0. High content of Mg, comparing with that of the Eastern syntax, is assumed to be sourced from dissolution of Mg containing minerals and longer water-rock interactions. Calcite is under-saturated indicating no scaling problem in the utilization. Both of the geothermal fluids are recharged by the local precipitation but with different water vapor sources based on water isotope analysis. Therefore, it’s concluded that geothermal fluids from these two syntaxes have gone through totally different geochemical processes and should be carefully monitored in utilization due to the calcite scaling problem

Quantifying recycled moisture fraction in precipitation of an arid region using deuterium excess

Terrestrial moisture recycling by evapotranspiration has recently been recognised as an important source of precipitation that can be characterised by its isotopic composition. Up to now, this isotope technique has mainly been applied to moisture recycling in some humid regions, including Brazil, Great Lakes in North America and the European Alps. In arid and semi-arid regions, the contribution of transpiration by plants to local moisture recycling can be small, so that evaporation by bare soil and surface water bodies dominates. Recognising that the deuterium excess (d-excess) of evaporated moisture is significantly different from that of the original water, we made an attempt to use this isotopic parameter for estimating moisture recycling in the semi-arid region of Eastern Tianshan, China. We measured the d-excess of samples taken from individual precipitation events during a hydrological year from 2003 to 2004 at two Tianshan mountain stations, and we used long-term monthly average values of the d-excess for the station Urumqi, which are available from the International Atomic Energy Agency&#x2013;World Meteorological Organization (IAEA&#x2013;WMO) Global Network of Isotopes in Precipitation (GNIP). Since apart from recycling of moisture from the ground, sub-cloud evaporation of falling raindrops also affects the d-excess of precipitation, the measured values had to be corrected for this evaporation effect. For the selected stations, the sub-cloud evaporation was found to change between 0.1 and 3.8%, and the d-excess decreased linearly with increasing sub-cloud evaporation at about 1.1&#x2030; per 1% change of sub-cloud evaporation. Assuming simple mixing between advected and recycled moisture, the recycled fraction in precipitation has been estimated to be less than 2.0&#x00B1;0.6% for the Tianshan mountain stations and reach values up to 15.0&#x00B1;0.7% in the Urumqi region. The article includes a discussion of these findings in the context of water cycling in the studied region