Alternative methods to determine the δ2H-δ18O relationship: An application to different water types

Amin

Frentress

et al. 2020

Preprint

Self Cite

Abstract. Recent tracer-based studies using stable isotopes of hydrogen and oxygen showed that different methods for extracting water from plant tissues can return different isotopic composition due to the presence of organic compounds and the extraction of different plant water pools. One of the most used methods to extract plant water is the cryogenic vacuum distillation (CVD), which tends to extract total plant water. Conversely, the Scholander-type pressure chamber (SPC), which is commonly used by tree physiologists to measure shoot water potential and determine plant water stress, has been rarely applied to extract plant water for isotopic analyses. In this work, we analyzed the variability in the isotopic composition of plant water extracted by SPC and CVD, also considering the potential variability in the isotopic signature of the plant tissues (i.e., leaves, twig without bark, twig with bark, twig close to the trunk of the tree, and wood core) and plant species (i.e., alder, apple, chestnut and beech). The extraction of plant water by SPC is simple, can be carried out in situ, and it does not require specific laboratory work as in case of CVD. However, the main limitation of SPC is the very small water volume that can be extracted from the lignified shoots during conditions of water deficit, compared to CVD. Our results indicated that plant water extracted by SPC and CVD were significantly different. The difference in the isotopic composition obtained by the two extraction methods was smaller in the beech samples compared to alder, apple and chestnut samples. The isotopic signature of alder, apple and chestnut plant water extracted by SPC was more enriched in δ2H and δ18O, respectively, than the samples obtained by CVD. We conclude that plant water extraction by SPC is not an alternative for CVD, as SPC likely extracts only water within the xylem (dead cells), whereas CVD tends to retrieve all water stored in the sampled tissue, from both living and dead cells. However, studies aiming to quantify the relative contribution of the water sources to transpiration should rely more on the isotopic composition of xylem water transpiring during the sampling day (which is theoretically sampled by SPC), than the isotopic composition of total plant water (sampled by CVD), which also contains a fraction of water that could be stored in plant tissues for long time.

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

A comparative study of plant water extraction methods for isotopic analyses: Scholander-type pressure chamber vs. cryogenic vacuum distillation

Amin

Frentress

et al. 2020

Preprint

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“…All samples are injected eight times (the first two injections are discarded from the computation of the mean isotopic composition in order to minimize memory effects, seePenna et al, 2012) and calibrated with standards relative to Vienna Standard Mean Ocean Water. The analytical uncertainty is better than 1.0 and 0.20‰ for δ 2 H and δ 18 O, respectively; the average standard deviation for 2094 samples was 0.5‰ for δ 2 H and 0.08‰ for δ 18 O(Marchina et al, 2020).Concentrations of chloride (Cl − ), nitrate (NO −3 ), sulphate (SO 2− 4 ), calcium (Ca 2+ ), magnesium (Mg 2+ ), sodium (Na + ), and potassium (K + ) are measured by ion chromatography using a 930 Compact IC Flex(Metrohm AG, Switzerland), with an in-line filtration system (0.45 μm) and a single column system: Metrosep A Supp 5-250/4.0 for anions and Metrosep C 6-250/4.0 for cations. The ion analyses are carried out on an aliquot (6 mL) of the sample collected in the field.…”

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confidence: 86%

“…Relation between the sum of the antecedent soil moisture index (ASI; Haga et al, 2005), computed for the 0-30 cm depth, plus event precipitation (P) and event runoff (a), and dual-isotope plot for stream water, groundwater and soil water samples collected at Ressi between 2012 and 2018 (b). The plotted local meteoric water line (LMWL) for Ressi is: δ 2 H = 8.12 × δ 18 O + 14.75 (Marchina et al, 2020) T A B L E 1 Eco-hydro-meteorological variables measured in the Ressi experimental catchment, data availability and description of the instruments. Depth to water table is monitored in six piezometers (four located in the riparian zone and two on the hillslopes; Figure 2e) using pressure transducers (Table 1).…”

Section: F I G U R Ementioning

confidence: 99%

“…Relation between the sum of the antecedent soil moisture index (ASI; Haga et al, 2005), computed for the 0–30 cm depth, plus event precipitation (P) and event runoff (a), and dual‐isotope plot for stream water, groundwater and soil water samples collected at Ressi between 2012 and 2018 (b). The plotted local meteoric water line (LMWL) for Ressi is: δ 2 H = 8.12 × δ 18 O + 14.75 (Marchina et al, 2020)…”

Section: Introductionmentioning

confidence: 99%

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Ressi experimental catchment: Ecohydrological research in the Italian pre‐Alps

Marchina

Gelmini

et al. 2021

Hydrological Processes

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Ressi is a small (2.4 ha) forested catchment located in the Italian pre-Alps. The site became an experimental catchment to investigate the water fluxes in the soil-plantatmosphere continuum and the impact of vegetation on runoff generation in 2012. The elevation of the catchment ranges from 598 to 721 m a.s.l. and the climate is humid temperate. The bedrock consists of rhyolites and dacites; the soil is a Cambisol. The catchment is covered by a dense forest, dominated by beech, chestnut, maple, and hazel trees. The field set up includes measurements of the rainfall in an open area, streamflow at the outlet, soil moisture at various depths and locations, and depth to water table in six piezometers at a 5-or 10-min interval. Samples of precipitation, stream water, shallow groundwater and soil water are collected monthly for tracer analysis (stable isotopes (2 H and 18 O), electrical conductivity and major ions), and during selected rainfall-runoff events to determine the contribution

Hysteresis in streamflow‐water table relation provides a new classification system of rainfall‐runoff events

Gelmini

Zaramella

et al. 2022

Hydrological Processes

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Rainfall-runoff event types can be used to better understand the hydrological functioning of catchments. In this study, we propose a framework to characterize and classify runoff events relying on the hysteresis analysis of the relation between streamflow (independent variable) and depth to water table (dependent variable). We evaluated hysteresis for 112 rainfall-runoff events occurred in the period 2012-2016 in a small forested catchment in the Italian Pre-Alps. Three main groups of rainfall-runoff events were identified, each associated with specific hydro-meteorological characteristics of the events. A first group, identified by a faster response of streamflow compared to the groundwater level (which led to a clockwise hysteretic loop), was characterized by dry antecedent conditions, short rainfall events, low streamflow peaks and small runoff coefficients. A second group had characteristics similar to the first group, that is, faster response of streamflow compared to the groundwater level (clockwise hysteretic loop), but on average displayed a narrower hysteretic loop. A third group, identified by a faster response of the groundwater level compared to streamflow (which led to an anticlockwise loop), was characterized by wet antecedent conditions, long rainfall events, high streamflow peaks and large runoff coefficients. Results showed statistically significant differences among the groups, corroborated by an analysis based on environmental tracers ( 2 H and electrical conductivity). This study shows how the analysis of the hysteretic relation between streamflow and depth to water table can be used for grouping rainfall-runoff events and to better identify the catchment's hydrological response to rainfall inputs.