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Zhao L.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Zhao L.,Key Laboratory of Heihe Ecohydrology and Basin Science of Gansu Province | Xiao H.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Xiao H.,Key Laboratory of Heihe Ecohydrology and Basin Science of Gansu Province | And 8 more authors.
Hydrological Processes | Year: 2012

Utilising datasets from the Global Network of Isotopes in Precipitation of the International Atomic Energy Agency, and previous isotopic studies, we investigated δ 18O spatial and temporal patterns in Chinese precipitation. Significantly positive relationships existed between precipitation δ 18O and air temperature above the north of 35°N and in high altitude regions above 32°N. Significantly negative relationships between precipitation δ 18O and the precipitation amount existed below south of 35°N. These temperature and precipitation effects became stronger with increasing altitude except in high altitude regions between 32°N and 35°N. The NCEP/NCAR reanalysis data from 1980 to 2004 showed that variations in spatial and seasonal wind fields at 700 hpa and total precipitable water from the ground to the top of the atmosphere were correlated with the monthly spatial distribution of precipitation δ 18O. Basing on this relationship, we established quantitative correlations between the mean monthly precipitation δ 18O and both latitude and temperature in different seasons. We found that spatial variations in precipitation δ 18O could be described well using the Bowen-Wilkinson model and second-order equations developed during the present study only in winter (from December to February). During the rest of the year, patterns were too complex to predict using simple models. The results suggest that it is difficult to demonstrate variations of precipitation δ 18O throughout the year and for all regions of China using a single model. Moreover, the new models for the relationships among precipitation, latitude, and temperature were better able to depict the variations in precipitation δ 18O than the Bowen-Wilkinson model. © 2011 John Wiley & Sons, Ltd. Source


Zhao L.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Zhao L.,Key Laboratory of Heihe Ecohydrology and Basin Science of Gansu Province | Xiao H.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Xiao H.,Key Laboratory of Heihe Ecohydrology and Basin Science of Gansu Province | And 9 more authors.
Rapid Communications in Mass Spectrometry | Year: 2011

As an alternative to isotope ratio mass spectrometry (IRMS), the isotope ratio infrared spectroscopy (IRIS) approach has the advantage of low cost, continuous measurement and the capacity for field-based application for the analysis of the stable isotopes of water. Recent studies have indicated that there are potential issues of organic contamination of the spectral signal in the IRIS method, resulting in incorrect results for leaf samples. To gain a more thorough understanding of the effects of sample type (e.g., leaf, root, stem and soil), sample species, sampling time and climatic condition (dry vs. wet) on water isotope estimates using IRIS, we collected soil samples and plant components from a number of major species at a fine temporal resolution (every 2 h for 24-48 h) across three locations with different climatic conditions in the Heihe River Basin, China. The hydrogen and oxygen isotopic compositions of the extracted water from these samples were measured using both an IRMS and an IRIS instrument. The results show that the mean discrepancies between the IRMS and IRIS approaches for δ18O and δD, respectively, were: -5.6% and -75.7% for leaf water; -4.0% and -23.3% for stem water; -3.4% and -28.2% for root water; -0.5% and -6.7% for xylem water; -0.06% and -0.3% for xylem flow; and -0.1% and 0.3% for soil water. The order of the discrepancy was: leaf > stem ≈ root > xylem > xylem flow ≈ soil. In general, species of the same functional types (e.g., woody vs. herbaceous) within similar habitats showed similar deviations. For different functional types, the differences were large. Sampling at nighttime did not remove the observed deviations. © 2011 John Wiley & Sons, Ltd. Source


Zhao L.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Zhao L.,Key Laboratory of Heihe Ecohydrology and Basin Science of Gansu Province | Zhao L.,Indiana University - Purdue University Indianapolis | Wang L.,Indiana University - Purdue University Indianapolis | And 7 more authors.
Hydrology and Earth System Sciences | Year: 2014

Deuterium excess (d-excess) of air moisture is traditionally considered a conservative tracer of oceanic evaporation conditions. Recent studies challenge this view and emphasize the importance of vegetation activity in controlling the dynamics of air moisture d-excess. However, direct field observations supporting the role of vegetation in d-excess variations are not well documented. In this study, we quantified the d-excess of air moisture, shallow soil water (5 and 10 cm) and plant water (leaf, root and xylem) of multiple dominant species at hourly intervals during three extensive field campaigns at two climatically different locations within the Heihe River basin, northwestern China. The ecosystems at the two locations range from forest to desert. The results showed that with the increase in temperature (T) and the decrease in relative humidity (RH), the δD-δ18O regression lines of leaf water, xylem water and shallow soil water deviated gradually from their corresponding local meteoric water line. There were significant differences in d-excess values between different water pools at all the study sites. The most positive d-excess values were found in air moisture (9.3‰) and the most negative d-excess values were found in leaf water (85.6‰). The d-excess values of air moisture (dmoisture) and leaf water (dleaf) during the sunny days, and shallow soil water (dsoil) during the first sunny day after a rain event, showed strong diurnal patterns. There were significantly positive relationships between dleaf and RH and negative relationships between dmoisture and RH. The correlations of dleaf and dmoisture with T were opposite to their relationships with RH. In addition, we found opposite diurnal variations for dleaf and dmoisture during the sunny days, and for dsoil and dmoisture during the first sunny day after the rain event. The steady-state Craig-Gordon model captured the diurnal variations in dleaf, with small discrepancies in the magnitude. Overall, this study provides a comprehensive and high-resolution data set of d-excess of air moisture, leaf, root, xylem and soil water. Our results provide direct evidence that dmoisture of the surface air at continental locations can be significantly altered by local processes, especially plant transpiration during sunny days. The influence of shallow soil water on dmoisture is generally much smaller compared with that of plant transpiration, but the influence could be large on a sunny day right after rainfall events. © 2014 Author(s). Source

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