Vegetation induced changes in the stable isotope composition of near surface humidity

Simonin, Kevin A.; Link, Percy; Rempe, D. M.; Miller, Scot M.; Oshun, J.; Bode, Collin; Dietrich, W. E.; Fung, Inez; Dawson, Todd E.

doi:10.1002/eco.1420

Cited by 44 publications

(66 citation statements)

References 59 publications

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“…Xylem water was analysed for δ 18 O and δ 2 H. We calculated the classic deuterium‐excess parameter values (Dansgaard, ) and report these for soils, for comparison to previous evaporation studies (e.g. Simonin et al ., ):

d ‐ excess = δ^{2} normalH - 8 ((), δ^{18} normalO)

…”

Section: Methodsmentioning

confidence: 99%

Insights into plant water uptake from xylem‐water isotope measurements in two tropical catchments with contrasting moisture conditions

Evaristo

McDonnell

Scholl

et al. 2016

Hydrological Processes

132

104

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Abstract:Water transpired by trees has long been assumed to be sourced from the same subsurface water stocks that contribute to groundwater recharge and streamflow. However, recent investigations using dual water stable isotopes have shown an apparent ecohydrological separation between tree-transpired water and stream water. Here we present evidence for such ecohydrological separation in two tropical environments in Puerto Rico where precipitation seasonality is relatively low and where precipitation is positively correlated with primary productivity. We determined the stable isotope signature of xylem water of 30 mahogany (Swietenia spp.) trees sampled during two periods with contrasting moisture status. Our results suggest that the separation between transpiration water and groundwater recharge/streamflow water might be related less to the temporal phasing of hydrologic inputs and primary productivity, and more to the fundamental processes that drive evaporative isotopic enrichment of residual soil water within the soil matrix. The lack of an evaporative signature of both groundwater and streams in the study area suggests that these water balance components have a water source that is transported quickly to deeper subsurface storage compared to waters that trees use. A Bayesian mixing model used to partition source water proportions of xylem water showed that groundwater contribution was greater for valley-bottom, riparian trees than for ridge-top trees. Groundwater contribution was also greater at the xeric site than at the mesic-hydric site. These model results (1) underline the utility of a simple linear mixing model, implemented in a Bayesian inference framework, in quantifying source water contributions at sites with contrasting physiographic characteristics, and (2) highlight the informed judgement that should be made in interpreting mixing model results, of import particularly in surveying groundwater use patterns by vegetation from regional to global scales.

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d ‐ excess = δ^{2} normalH - 8 ((), δ^{18} normalO)

…”

Section: Methodsmentioning

confidence: 99%

Insights into plant water uptake from xylem‐water isotope measurements in two tropical catchments with contrasting moisture conditions

Evaristo

McDonnell

Scholl

et al. 2016

Hydrological Processes

132

104

View full text Add to dashboard Cite

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“…Some of these biophysical processes may include: effects of evaporative fractionation on xylem isotopic compositions during summer months (Simonin et al, 2014), the potentially longer residence and transit times of water within the xylem (Brandes et al, 2007), or possible 15 fractionation/discrimination of 18 and 2 during root-water uptake (Ellsworth and Williams, 2007;Vargas et al, 2017).…”

Section: Ecohydrologic Controls Of Root-uptake On Soil Watermentioning

confidence: 99%

Using StorAge Selection functions to quantify ecohydrological controls on the time-variant age of evapotranspiration, soil water, and recharge

Smith

Tetzlaff

Soulsby

2018

Preprint

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Abstract. Quantifying ecohydrological controls on soil water availability is essential to understand temporal variations in catchment storage. Soil water is subject to numerous time-variable fluxes (evaporation, root-uptake, and recharge), each with 10 different water ages which in turn affect the age of water in storage. Here, we adapt StorAge Selection (SAS) function theory to investigate water flow in soils and identify soil evaporation and root-water uptake sources from depth. We use this to quantify the effects of soil-vegetation interactions on the inter-relationships between water fluxes, storage, and age. The novel modification of the SAS function framework is tested against empirical data from two contrasting soil-vegetation units in the Scottish Highlands; these are characterised by significant preferential flow, transporting younger water through the soil during 15 high soil moisture conditions. Dominant young water fluxes, along with relatively low rainfall intensities, explain relatively stable soil water ages through time and with depth. Soil evaporation sources were more time-invariant with high preference for near-surface water, independent of soil moisture conditions, and resulting in soil evaporation water ages similar to nearsurface soil waters (mean age: 50 -65 days). Sources of root-water uptake were more variable: preferential near-surface water uptake occurred in wet conditions, with a deeper root-uptake source during dry soil conditions, which resulted in more variable 20 water ages of transpiration (mean age: 56 -79 days). The simple model structure provides a parsimonious means of constraining the water age of multiple fluxes from the upper part of the critical zone during time-varying conditions improving our understanding of vegetation influences on catchment scale water fluxes.

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“…7), when precipitation is predominantly from the trade-wind orographic source. This precipitation is formed from water vapor below the atmospheric boundary layer, from approximately sea level to 2300 m (Scholl et al, 2009;Scholl and Murphy, 2014) and it likely includes local re-evaporated canopy interception and transpiration vapor (Simonin et al, 2013). The lowest d-excess values are observed June-August (Fig.…”

Section: Dissolved Solutesmentioning

confidence: 99%

Stable-isotope and solute-chemistry approaches to flow characterization in a forested tropical watershed, Luquillo Mountains, Puerto Rico

Scholl

Shanley

Murphy

et al. 2015

Applied Geochemistry

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a r t i c l e i n f oArticle history: Available online xxxx a b s t r a c tThe prospect of changing climate has led to uncertainty about the resilience of forested mountain watersheds in the tropics. In watersheds where frequent, high rainfall provides ample runoff, we often lack understanding of how the system will respond under conditions of decreased rainfall or drought. Factors that govern water supply, such as recharge rates and groundwater storage capacity, may be poorly quantified. This paper describes 8-year data sets of water stable isotope composition (d The hydrograph separation results indicated that 36% of the storm rain that reached the soil surface left the watershed in a very short time as runoff. Weathering-derived solutes indicated near-stream groundwater was displaced into the stream at the beginning of the event, followed by significant dilution. The more biologically active solutes exhibited a net flushing behavior. The d-excess analysis suggested that streamflow typically has a recent rainfall component ($25%) with transit time less than the sampling resolution of 7 days, and a more well-mixed groundwater component ($75%). The contemporaneous stream sample sets showed an overall increase in dissolved solute concentrations with decreasing elevation that may be related to groundwater inputs, different geology, and slope position. A considerable amount of water from rain events runs off as quickflow and bypasses subsurface watershed flowpaths, and better understanding of shallow hillslope and deeper groundwater processes in the watershed will require sub-weekly data and detailed transit time modeling. A combined isotopic and solute chemistry approach can guide further studies to a more comprehensive model of the hydrology, and inform decisions for managing water supply with future changes in climate and land use.Published by Elsevier Ltd.1. Introduction Forested mountain watersheds in the tropicsForested mountain watersheds in the tropics are often characterized by higher annual rainfall amounts and frequency, greater energy inputs, and faster rates of human-induced change than watersheds in temperate latitudes (Bruijnzeel, 2004;Bruijnzeel et al., 2005;Ogden and Harmon, 2012;Wohl et al., 2012). In areas with frequent, high rainfall from seasonal monsoons or wet-season weather patterns, weathering is intense and bedrock evolves to clay soils. The presence of forests on steep mountain slopes provides soil structure for the storage and purification of water, controls erosion, enhances infiltration and recharge processes compared to cleared land (Bruijnzeel et al.

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Vegetation induced changes in the stable isotope composition of near surface humidity

Cited by 44 publications

References 59 publications

Insights into plant water uptake from xylem‐water isotope measurements in two tropical catchments with contrasting moisture conditions

Insights into plant water uptake from xylem‐water isotope measurements in two tropical catchments with contrasting moisture conditions

Using StorAge Selection functions to quantify ecohydrological controls on the time-variant age of evapotranspiration, soil water, and recharge

Stable-isotope and solute-chemistry approaches to flow characterization in a forested tropical watershed, Luquillo Mountains, Puerto Rico

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