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Utilizing Global Network of Isotopes in Precipitation (GNIP) datasets and previous published isotopic data, we investigated δ18O spatial and temporal patterns in precipitation across China. Significantly positive relationships existed between precipitation δ18O and air temperature of the north of 35°N and in high altitude regions to the north of 32°N. Significantly negative relationships between precipitation δ18O and the precipitation amount existed to the 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 δ18O. Based on this relationship, we established quantitative correlations between the mean monthly precipitation δ18O and both latitude and temperature in different seasons.

The connectivity of ecohydrological and biogeochemical processes across time and space is a critical determinant of ecosystem structure and function. However, characterizing cross-scale connectivity is a challenge due to the lack of theories and modelling approaches that are applicable at multiple scales and due to our rudimentary understanding of the magnitude and dynamics of such connectivity.

In this article, we present a conceptual framework for upscaling quantitative models of ecohydrological and biogeochemical processes using electrical circuit analogies and the Thévenin’s theorem. Any process with a feasible linear electrical circuit analogy can be represented in larger scale models as a simplified Thévenin equivalent. The Thevenin equivalent behaves identically to the original circuit, so the mechanistic features of the model are maintained at larger scales. We present three case applications: water transport, carbon transport, and nitrogen transport.

We created a system dynamics model that represents primary ecohydrological networks to examine how connectivity between ecosystem components impacts ecosystem processes. To create the model, a set of differential equations representing ecohydrological processes were programmed into the dynamic solver Vensim. Stocks of water storage (e.g. atmospheric and soil moisture) were linked by flows that were in turn dynamically controlled by the amount of water stored. Here, we focused on the savanna ecosystems, although the analyses may be expanded to other ecosystem types in the future.

Drylands cover about 40% of the terrestrial land surface and account for approximately 40% of global net primary productivity. In this synthesis, we identify some current critical issues in the understanding of dryland systems and discuss how arid and semiarid environments are responding to the changes in climate and land use. The issues range from societal aspects such as rapid population growth, the resulting food and water security, and development issues, to natural aspects such as ecohydrological consequences of bush encroachment and the causes of desertification. We also identify some recent technical advances in terms of monitoring dryland water dynamics, water budget and vegetation water use, with a focus on the use of stable isotopes and remote sensing.

We have reported measurements and associated uncertainties for the isotope ratios of hydrogen and oxygen in water vapor surface fluxes. These measurements were made using both vapor profiling techniques and eddy covariance measurements with off axis integrated cavity output spectroscopy (ICOS). This study is the first to report eddy covariance of isotope ratios of water vapor calculated with off axis ICOS systems. We are also the first to preform a detailed study of the uncertainties inherent in these measurements. We have presented expressions for the expected uncertainty of δET measurements based on the Keeling plot, flux gradient, and eddy covariance methods. These uncertainty estimators are expressed in terms of the inherent system precision, εδ, and sampling frequency of the instrument used, as well as the variability of water vapor concentration observed during the measurement period.

The stable isotopic composition of plant transpired water (δT) is a powerful tracer used to characterize plant processes in the fields of ecology, plant physiology and hydrology. However, δT is rarely directly measured due to the general difficulty in traditional water vapor isotopic measurements.

We report a new direct method with the potential to continuously monitor δT utilizing a commercially available laser-based isotope analyzer coupled to a transparent leaf chamber in a flow-through system arrangement. The method is based on the mass balance of both water vapor and water vapor isotopes inside the chamber. The method is applicable to both steady state and non-steady state conditions. We demonstrate the applicability of our method to field observations and capture rapid (minute time scale) δT responses to shifts in transpiration driven by variation in irradiance.

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Evapotranspiration (ET) plays a critical role in the hydrological cycle and represents the process that links both the energy and water cycles. The proportion of transpiration (T) in total evapotranspiration is an important parameter that provides insight into the degree of biological influence on the hydrological cycles.  Studies addressing the effects of climatic warming on the ecosystem total water balance are scarce, and measured warming effects on the T/ET ratio in field experiments have not been seen in the literature.  In this study, we quantified T/ET ratios under ambient and warming treatments in a grassland ecosystem using a stable isotope approach. The results showed that the T/ET ratio was higher under warming. Multiple lines of evidence indicate that the increased T/ET ratio under warming is caused mainly by reduced evaporation.