Zhonghe Pang

Panta Rhei-Everything Flows: Change in hydrology and society-The IAHS Scientific Decade 2013-2022

Abstract The new Scientific Decade 2013–2022 of IAHS, entitled “Panta Rhei—Everything Flows”, is dedicated to research activities on change in hydrology and society. The purpose of Panta Rhei is to reach an improved interpretation of the processes governing the water cycle by focusing on their changing dynamics in connection with rapidly changing human systems. The practical aim is to improve our capability to make predictions of water resources dynamics to support sustainable societal development in a changing environment. The concept implies a focus on hydrological systems as a changing interface between environment and society, whose dynamics are essential to determine water security, human safety and development, and to set priorities for environmental management. The Scientific Decade 2013–2022 will devise innovative theoretical blueprints for the representation of processes including change and will focus on advanced monitoring and data analysis techniques. Interdisciplinarity will be sought by increased efforts to connect with the socio-economic sciences and geosciences in general. This paper presents a summary of the Science Plan of Panta Rhei, its targets, research questions and expected outcomes. Editor Z.W. Kundzewicz Citation Montanari, A., Young, G., Savenije, H.H.G., Hughes, D., Wagener, T., Ren, L.L., Koutsoyiannis, D., Cudennec, C., Toth, E., Grimaldi, S., Blöschl, G., Sivapalan, M., Beven, K., Gupta, H., Hipsey, M., Schaefli, B., Arheimer, B., Boegh, E., Schymanski, S.J., Di Baldassarre, G., Yu, B., Hubert, P., Huang, Y., Schumann, A., Post, D., Srinivasan, V., Harman, C., Thompson, S., Rogger, M., Viglione, A., McMillan, H., Characklis, G., Pang, Z., and Belyaev, V., 2013. “Panta Rhei—Everything Flows”: Change in hydrology and society—The IAHS Scientific Decade 2013–2022. Hydrological Sciences Journal. 58 (6) 1256–1275.

Theoretical Chemical Thermometry on Geothermal Waters: Problems and Methods

Using a synthetic geothermal water, we examine the effect of errors in Al analyses on theoretical chemical geothermometry based on multicomponent chemical equilibrium calculations of mineral equilibria. A new approach named FixAl that entails the construction of a modified Q/K graph eliminates problems with water analyses lacking Al or with erroneous analyses of Al. This is made possible by forcing the water to be at equilibrium with a selected Al-bearing mineral, such as microcline. In a FixAl graph, a modified Q/K value is plotted against temperature for Al-bearing minerals. Saturation indices of nonaluminous minerals are plotted in the same way as in an ordinary Q/K graph. In addition to Al concentration errors, degassing of CO2 and dilution of reservoir water interfere with computed equilibrium geothermometry. These effects can be distinguished in a Q/K graph by comparing curves for nonaluminous minerals to those of aluminous minerals then correcting for CO2 loss and dilution by a trial and error method. Example geothermal waters from China, Iceland, and the USA that are used to demonstrate the methods show that errors in Al concentrations are common, and some are severe. The FixAl approach has proved useful for chemical geothermometry for geothermal waters lacking Al analysis and for waters with an incorrect Al analysis. The equilibrium temperatures estimated by the FixAl approach agree well with quartz, chalcedony, and isotopic geothermometers. The best choice of mineral for forced equilibrium depends on pH. For most neutral pH waters, microcline and albite work well; for more acidic waters, kaolinite or illite are good choices. Measured pH plays a critical role in computed equilibria, and we find that the best pH to use is the one to which the reported carbonate also applies. Commonly this is the laboratory pH instead of field pH, but the field pH is still necessary to constrain CO2 degassing. Calculations on numerous waters in the 80–180°C reservoir temperature range indicate that mineral-aqueous equilibrium is probably nearly always achieved, but is obscured by short time-scale processes of dilution or degassing of CO2 in the near-surface environment.

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.

Integrated assessment on groundwater nitrate by unsaturated zone probing and aquifer sampling with environmental tracers

By employing chemical and isotopic tracers ((15)N and (18)O in NO(3)(-)), we investigated the main processes controlling nitrate distribution in the unsaturated zone and aquifer. Soil water was extracted from two soil cores drilled in a typical agricultural cropping area of the North China Plain (NCP), where groundwater was also sampled. The results indicate that evaporation and denitrification are the two major causes of the distribution of nitrate in soil water extracts in the unsaturated zone. Evaporation from unsaturated zone is evidenced by a positive correlation between chloride and nitrate, and denitrification by a strong linear relationship between [Formula: see text] and ln(NO(3)(-)/Cl). The latter is estimated to account for up to 50% of the nitrate loss from soil drainage. In the saturated zone, nitrate is reduced at varying extents (100 mg/L and 10 mg/L at two sites, respectively), largely by dilution of the aquifer water.

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.

Origin and evolution characteristics of geothermal water in the Niutuozhen geothermal field, North China Plain

Statistical study of analyses of water from 43 samples from geothermal wells, three groundwater wells, and one sample of local rainwater along with rainwater data from the Global Network of Isotopes in Precipitation has been used to identify the origin and evolution of geothermal water in the Niutuozhen (牛驼镇) geothermal field and estimate the renewability rate of its geothermal resource. The results show that the geothermal waters of the Jixianian Wumishanian dolomite reservoir and the Ordovician limestone reservoir are of Cl-Na type, the geothermal water of the Pliocene Minghuazhen (明化镇) Formation sandstone reservoir are Cl-Na type and HCO3-Na type and the groundwater of the Quaternary aquifer is HCO3-Na and HCO3-Na·Mg·Ca type. A linear relationship between silica concentration and temperature indicates that higher temperature probably enhances concentration of silica in Jixianian geothermal water. δ18O shift in Wumishanian geothermal water averaged 1.57‰, and was less than 1‰ in the other geothermal waters. The minimum and maximum 14C ages of Wumishanian geothermal water are 17 000 and 33 000 years from north to the south of the Niutuozhen geothermal field. Geothermal water and Quaternary groundwater belong to different groundwater systems with no hydraulic connections. Although the geothermal field receives some recharge from the Yanshan and Taihang mountains outside the northern and western boundaries of the geothermal field respectively, the renewability rate of geothermal water is on the scale of 10 000 years.

Groundwater recharge in an arid grassland as indicated by soil chloride profile and multiple tracers

&NA; Previous studies have shown that shallow groundwater in arid regions is often not in equilibrium with near‐surface boundary conditions due to human activities and climate change. This is especially the case where the unsaturated zone is thick and recharge rate is limited. Under this nonequilibrium condition, the unsaturated zone solute profile plays an important role in estimating recent diffuse recharge in arid environments. This paper combines evaluation of the thick unsaturated zone with the saturated zone to investigate the groundwater recharge of a grassland in the arid western Ordos Basin, NW China, using the soil chloride profiles and multiple tracers (2H, 18O, 13C, 14C, and water chemistry) of groundwater. Whereas conventional water balance and Darcy flux measurements usually involve large errors in recharge estimations for arid areas, chloride mass balance has been widely and generally successfully used. The results show that the present diffuse recharge beneath the grassland is 0.11–0.32 mm/year, based on the chloride mass balance of seven soil profiles. The chloride accumulation age is approximately 2,500 years at a depth of 13 m in the unsaturated zone. The average Cl content in soil moisture in the upper 13 m of the unsaturated zone ranges from 2,842 to 7,856 mg/L, whereas the shallow groundwater Cl content ranges from 95 to 351 mg/L. The corrected 14C age of shallow groundwater ranges from 4,327 to 29,708 years. Stable isotopes show that the shallow groundwater is unrelated to modern precipitation. The shallow groundwater was recharged during the cold and wet phases of the Late Pleistocene and Holocene humid phase based on palaeoclimate, and consequently, the groundwater resources are nonrenewable. Due to the limited recharge rate and thick unsaturated zone, the present shallow groundwater has not been in hydraulic equilibrium with near‐surface boundary conditions in the past 2,500 years.