Yanlong Kong

Processes affecting isotopes in precipitation of an arid region

The isotopic composition of precipitation has been measured in samples simultaneously collected during individual precipitation events at two neighbouring high-altitude stations (Houxia at 2100 m a.s.l. and Gaoshan at 3545 m a.s.l.) in the Tianshan Mts., northwest China. The observed changes of δ18O (δ2H) and deuterium excess with surface air temperature, altitude and season have been evaluated to derive information on the effects of subcloud evaporation and moisture recycling on the formation of precipitation and its isotopic composition under arid climatic conditions. Consulting the long-term monthly averages of ‘d’ excess and temperature of the nearest GNIP station Wulumuqi, a striking similarity was found with the results of the two high-altitude stations concerning the relation between ‘d’ excess and temperature. The ‘d’ excess-temperature plot of the Wulumuqi data shows an hysteresis effect which appears to signify seasonal changes in the interplay between subcloud evaporation and moisture recycling. Finally, for the first time a negative altitude gradient of the d excess has been found for all stations including two more GNIP stations in northwest China but far away from the study area. This ‘inverse altitude effect’ may manifest a decrease of the recycled fraction in air moisture with altitude.

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

ABSTRACT 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–World Meteorological Organization (IAEA–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‰ 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±0.6% for the Tianshan mountain stations and reach values up to 15.0±0.7% in the Urumqi region. The article includes a discussion of these findings in the context of water cycling in the studied region.

Impacts of human activities on the occurrence of groundwater nitrate in an alluvial plain: A multiple isotopic tracers approach

Nitrate pollution is a severe problem in areas with intensive agricultural activities. This study focuses on nitrate occurrence and its constraints in a selected alluvial fan using chemical data combined with environmental isotopic tracers (18O, 3H, and 15N). Results show that groundwater nitrate in the study area is as high as 258.0 mg/L (hereafter NO3−) with an average of 86.8 mg/L against national drinking water limit of 45 mg/L and a regional baseline value of 14.4 mg/L. Outside of the riparian zone, nitrate occurrence is closely related to groundwater circulation and application of chemical fertilizer. High groundwater nitrate is found in the recharge area, where nitrate enters into groundwater through vertical infiltration, corresponding to high 3H and enriched 18O in the water. In the riparian zone, on the contrary, the fate of groundwater nitrate is strongly affected by groundwater level. Based on two sampling transects perpendicular to the riverbank, we found that the high level of nitrate corresponds to the deeper water table (25 m) near the urban center, where groundwater is heavily extracted. Groundwater nitrate is much lower (<12.4 mg/L) at localities with a shallow water table (5 m), which is likely caused by denitrification in the aquifer.

Identification of Different Moisture Sources through Isotopic Monitoring during a Storm Event

AbstractRain samples were collected for isotopic analyses during the entirety of an extreme rainfall event in Beijing, China, on 21 July 2012, the city’s heaviest rainfall event in the past six decades. Four stages of the storm event have been identified with corresponding isotopic characteristics: 1) isotopes deplete as rain increases, 2) isotopes enrich as rain decreases, 3) isotopes quickly deplete as rain increases, and 4) isotopes remain constant as rain reduces to a small amount. The rainout effect dominates the depletion of isotopic composition in stages 1 and 3. The incursion of a new air mass with enriched heavy isotopes was the main cause for the enriched isotopic composition during stage 2. A Rayleigh distillation model was used to describe the isotopic trends during stages 1 and 3. The Rayleigh distillation model and a binary mixing model were used to estimate the initial isotopic composition of different air masses, which were found to be similar to δ18O of precipitation at nearby Global Netw...

Recent studies on hydrothermal systems in China: a review

This paper reviews the state-of-the-art in hydrothermal systems in China with emphasis on current studies of potential and reservoir engineering. Three hydrothermal systems, namely, Yangbajing, Xianyang, and Xiongxian, are used as case studies to represent high temperature granite reservoirs, medium-to-low temperature sandstone reservoirs, and medium-to-low temperature carbonate reservoirs, respectively. There is a huge potential of hydrothermal resources in China that have not been fully studied for possible exploitation. The study reveals that the potential of developing hydrothermal resources is preferable to exploitation of hot-dry-rock (HDR) systems in the near future. In order to enhance the utilization efficiency and prolong the economic lifetime of a geothermal field, reinjection needs to be increased, including treated wastewater as an option. In this regard, deep karstic aquifers containing hot water are the most ideal targets for development due to their favorable characteristics including high single-well yield, low salinity, easy reinjection, and fewer environmental impacts when exploited. The next challenge lies in the geothermal reservoir management for sustainable production. Numerical models describing the full complexity of coupled physicochemical thermodynamic processes such as the open source OpenGeoSys modeling platform are powerful tools for production planning as well as for assessing the possible environmental impacts. Comprehensive reservoir simulation should be employed to provide an optimal fluid production scheme and to maximize the sustainability in the development of a hydrothermal field.

Isotopic spatial variations and isotopic effects of two heavy summer precipitation events across Beijing

Stable isotopes of precipitation samples collected during two heavy rainfall events on July 29 and September 1, 2014 at 11 stations from Beijing Network of Isotopes in Precipitation, are analyzed to discuss eventful isotopic effects. No significant correlations between precipitation δ18O and temperature/elevation are found. After correction with the Rayleigh distillation model for the rainfall on July 29, a significant correlation between isotopes and latitude was obtained for both rainfall events. This implies both rainfalls are formed by southern moisture sources, which were also confirmed by water vapor budget and HYSPLIT model.

Progress and perspectives of geothermal energy studies in China: from shallow to deep systems

In October 2015, the first Sino-German International Symposium on “Sustainable Utilization of Geothermal Energy” was held at the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS), Beijing, China. Around 120 researchers attended the meeting. It was agreed by the participants that a special issue of the papers presented at the symposium on Chinese geothermal systems be organized and published in the international journal “Environment Earth Sciences”. Up to today, when we close the special issue, 30 papers have been accepted and published in this issue. From these papers one can find out the major progress made in geothermal energy studies in China in the past 5 years or so and, therefore, the papers provide a comprehensive overview of recent geothermal research in China. According to the statistics published by the International Geothermal Association (IGA) in 2015, China had continued to lead the world in terms of total amount of geothermal used yearly for space heating and other direct use purposes. The present Thematic Issue covers studies on shallow geothermal energy (0–200 m), medium-deep hydrothermal energy (200–3000 m) as well as deep “hot dry rock” petrothermal energy (> 3000 m) in China. A prior introduction to studies on hydrothermal systems can be found in Kong et al. (2014). In the following we will highlight each of the papers in this Thematic Issue, and locations of study areas can be found in Fig. 1.