A stable isotope study of soil water: evidence for mixing and preferential flow paths

Gazis, Carey; Feng, Xiahong

doi:10.1016/s0016-7061(03)00243-x

Cited by 323 publications

(259 citation statements)

References 29 publications

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“…One possible reason is that forests with high stock volume density could be older, and old trees can counter meteorological drought by accessing underground water from greater depths (at which moisture from earlier precipitation is stored) [66,67]. On the other hand, forests with low stock volume density could be younger, and the root systems of young trees are shallower, therefore allowing young trees to respond to drought faster [68].…”

Section: Differences In Response Due To Differences In Stock Volume Dmentioning

confidence: 99%

Stock Volume Dependency of Forest Drought Responses in Yunnan, China

Luo

Zhou

et al. 2018

Forests

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Abstract:Revealing forest drought response characteristics and the potential impact factors is quite an important scientific issue against the background of global climate change, which is the foundation to reliably evaluate and predict the effects of future drought. Due to the high spatial heterogeneity of forest properties such as biomass, forest age, and height, and the distinct differences in drought stress in terms of frequency, intensity, and duration, current studies still contain many uncertainties. In this research, we used the forests in Yunnan Province in Southwest China as an example and aimed to reveal the potential impacts of forest properties (i.e., stock volume) on drought response characteristics. Specifically, we divided the forest into five groups of stock volume density values and then analyzed their drought response differences. To depict forest response to drought intensity, the standardized precipitation evapotranspiration index (SPEI) was chosen as the explanatory variable, and the change in remote sensing-based enhanced vegetation index (deficit of MODIS-EVI, dEVI) was chosen as the response variable of drought stress. Given that the SPEI has different time scales, we first analyzed the statistical dependency of SPEIs with different time scales (1 to 36 months) to the response variable (i.e., dEVI). The optimal time scale of SPEI (SPEI opt ) to interpret the maximum variation of dEVI (R-square) was then chosen to build the ultimate statistical models for the five groups of stock volume density. The main findings were as follows: (1) the impacts of drought showed hysteresis and cumulative effects, and the length of the hysteresis increased with stock volume densities; (2) forests with high stock volume densities required more soil water and were therefore more sensitive to the changes in water deficit; (3) compared with the optimal time scale of SPEI (SPEI opt ), the SPEI with the commonly used time scale (e.g., 1, 6, and 12 months) could not well reflect the impacts of drought on forests and the simulation error of dEVI increased with stock volume densities; and (4) forests with higher stock volume densities were likely to experience a greater risk of degradation following higher atmospheric concentrations of greenhouse gases (Representative Concentration Pathway (RCP) 8.5). As a result, both the time scale of the meteorological drought index and the spatial difference in forest stock volumes should be considered when evaluating forest drought responses at regional and global scales.

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Section: Differences In Response Due To Differences In Stock Volume Dmentioning

confidence: 99%

Stock Volume Dependency of Forest Drought Responses in Yunnan, China

Luo

Zhou

et al. 2018

Forests

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“…Isotope composition of soil water provides information about mixing and residence time in soil (Gazis and Feng, 2004), demonstrating that soil water comprises both stationary and mobile fractions. Water movement in solids can be by preferential (macropore) flow, which would allow mobile event water to pass old stationary water, fingered flow due to wetting front instability, or piston flow, which would result in movement of an isotope front of relatively stationary water within the soil.…”

Section: Oxygen Isotopes and Water Infiltration Through Soilsmentioning

confidence: 99%

“…At depth, there is a higher proportion of water replenished from storm events or snowmelt. Variations in soil structure can lead to significant spatial isotope variability; Gazis and Feng (2004) show two soil water profiles within 200 m differ by 1.5 to 3 o / oo at the same depth, purely due to topographic differences.…”

Section: Oxygen Isotopes and Water Infiltration Through Soilsmentioning

confidence: 99%

Modification and preservation of environmental signals in speleothems

Fairchild

Smith

Baker

et al. 2006

Earth-Science Reviews

729

506

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Speleothems are primarily studied in order to generate archives of climatic change and results have led to significant advances in identifying and dating major shifts in the climate system. However, the climatological meaning of many speleothem records cannot be interpreted unequivocally; this is particularly so for more subtle shifts and shorter time periods, but the use of multiple proxies and improving understanding of formation mechanisms offers a clear way forward.An explicit description of speleothem records as time series draws attention to the nature and importance of the signal filtering processes by which the weather, the seasons and longer-term climatic and other environmental fluctuations become encoded in speleothems. We distinguish five sources of variation that influence speleothem geochemistry: atmospheric, vegetation/soil, karstic aquifer, primary speleothem crystal growth and secondary alteration and give specific examples of their influence. The direct role of climate diminishes progressively through these five factors.We identify and review a number of processes identified in recent and current work that bear significantly on the conventional interpretation of speleothem records, for example: 1) speleothem geochemistry can vary seasonally and hence a research need is to establish the proportion of growth attributable to different seasons and whether this varies over time.2) whereas there has traditionally been a focus on monthly mean δ 18 O data of atmospheric moisture, current work emphasizes the importance of understanding the synoptic processes that lead to characteristic isotope signals, since changing relative abundance of different weather types might 1 Corresponding author, fax +44(0)1214145528, E-mail: i.j.fairchild@bham.ac.uk control their variation on the longer-term. 3) the ecosystem and soil zone overlying the cave fundamentally imprint the carbon and trace element signals and can show characteristic variations with time. 4) new modelling on aquifer plumbing allows quantification of the effects of aquifer mixing. 5) recent work has emphasized the importance and seasonal variability of CO 2 -degassing leading to calcite precipitation upflow of a depositional site on carbon isotope and trace element composition of speleothems. 6) Although much is known about the chemical partitioning between water and stalagmites, variability in relation to crystal growth mechanisms and kinetics is a research frontier. 7) Aragonite is susceptible to conversion to calcite with major loss of chemical information, but the controls on the rate of this process are obscure.Analytical factors are critical to generate high-resolution speleothem records. A variety of methods of trace element analysis are available, but standardization is a common problem with the most rapid methods. New stable isotope data on Irish stalagmite CC3 compares rapid laser-ablation techniques with the conventional analysis of micromilled powders and ion microprobe methods. A high degree of comparability between techniques ...

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“…Several studies have demonstrated the usefulness of stable isotopes for analysing transport phenomena in the unsaturated zone (Barnes & Allison, 1983;Fontes et al, 1986;Walker & Richardson, 1991;Komor & Emerson, 1994;Abbott et al, 2000;McGuire et al, 2002;Gazis & Feng, 2004;O'Driscoll et al, 2005). In most cases the experiments were performed in arid zones where the vertical distributions of environmental tracer concentrations were analysed.…”

Section: Introductionmentioning

confidence: 99%

Modelling of water flow through typical Bavarian soils: 2. Environmental deuterium transport

Małoszewski

Maciejewski

Stumpp

et al. 2006

Hydrological Sciences Journal

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Seven experimental lysimeters were filled with different soil materials and used to study water flow and tracer transport through the unsaturated zone under natural atmospheric conditions during an eight year period (1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991). The study of soil characteristics and water flow was presented in Part 1. The present paper focuses on environmental deuterium transport. The concentrations of environmental deuterium were measured in both precipitation and the water outflowing from the lysimeters. Two model approaches were used to describe tracer transport. The numerical solution of water flow and twophase mass transport equations, referred to here as the variable flow dispersion model (VFDM), can exactly simulate spatial and temporal distribution of flow and transport parameters. The fitting parameters of VFDM are the soil characteristics, the longitudinal dispersivity, the fraction of immobile water and the transfer constant between mobile and immobile water. However, the application of the VFDM for detailed transport simulations requires an adequate database, which is typically not available. That was the reason to introduce a second model, the lumped-parameter steady-state dispersion model (DM). This model assumes dispersive distribution of the transit time of a tracer particle between input and output from the system, has two fitting parameters: the apparent dispersion constant and the mean transit time of the tracer, and requires only input and output concentrations of tracer as a function of time. Both models were calibrated to the experimental data with similar accuracy. Using the VFDM it was possible to fit output concentrations with the same accuracy assuming that the entire volume of water takes part in motion. The results obtained with the DM demonstrated that this simple steady-state approach can be applied successfully to describe tracer transport under variable flow conditions. Both models have shown that, under applied experimental conditions, it is practically impossible to discover the existence of immobile water in the system. Key words environmental deuterium; lumped-parameter approach; lysimeter experiments; mathematical modelling; transport parameters; unsaturated zone Modélisation de transfert hydrique dans des sols typiques de Bavière: 2. Transport de deutérium environnemental Résumé Sept lysimètres expérimentaux ont été remplis de différents matériaux de sols et suivis pour étudier les transferts hydriques et le transport d'un traceur à travers la zone non saturée, sous conditions atmosphériques naturelles, pendant une période de huit ans (1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991). L'étude des caractéristiques des sols et des transferts hydriques a été présentée dans la Partie 1. Cet article est centré sur le transport de deutérium environnemental. Les concentrations de deutérium environnemental ont été mesurées dans les précipitations et dans l'eau sortant des lysimètres. Aucun enrichissement isotopique du deutérium lié à l'évaporation ou à un...

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A stable isotope study of soil water: evidence for mixing and preferential flow paths

Cited by 323 publications

References 29 publications

Stock Volume Dependency of Forest Drought Responses in Yunnan, China

Stock Volume Dependency of Forest Drought Responses in Yunnan, China

Modification and preservation of environmental signals in speleothems

Modelling of water flow through typical Bavarian soils: 2. Environmental deuterium transport

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