262 Advances in Ecohydrogeology (Posters)

Ecohydrogeology is the unifying, synthetic field of study integrating the approaches from the ecological and hydrogeological sciences in the study of groundwater-related ecosystems, habitats, and organisms. We encourage submissions of research that advances the science, stewardship, and policy at the intersection of ecology and hydrogeology.

Wednesday, 22 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Hydrogen isotope evidence for biased uptake of winter- spring precipitation by plants in Montana, USA

Paper number: 262-6
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Current understanding of water partitioning and assimilation in plants has been gained mostly from growth chambers and field-based experiments with controlled variables. Uncontrolled field-based studies of water partitioning and assimilation in plants face challenges in constraining temporal variations in climate at relevant spatial scales and uncertainties in plant source water usage. This study employs a stable isotope-based approach to constrain the plant water use and biosynthetic fractionation of hydrogen isotopes in leaf waxes produced by five plant types (broadleaf, grass, pine, forbs, and shrubs) along a moisture gradient in Montana, USA. We first conducted Monte-Carlo based source water modelling following the Craig-Gordon model, which assumes that any isotopic offset of plant water from meteoric conditions is a result of evaporative fractionation of the source water. We applied constrained single-source and unconstrained multi-source water likelihood modeling, assuming mean annual precipitation and a range of monthly precipitation values as the respective source waters. Considering multiple scenarios of climatic parameters and uncertainties, we modeled source water δD values that best explained the observed leaf water δD values. Our results show that shrubs, forbs, grasses, and pines have source water most likely from late winter-spring precipitation, but broadleaf trees have a dominant source from early winter precipitation. Because these models are sensitive to the ambient relative humidity and temperature during leaf water evaporation and assimilation, two scenarios, evaporation biased to growth season and summer (within two weeks before sampling), were tested to see which group yields the most realistic source water δD values. We then used the modeled source water from both scenarios and measured leaf wax δD values to calculate the range of biosynthetic fractionation (εbio). The εbio values derived from both scenarios broadly corresponds to the εbio estimated from leaf water and wax δD values for grass, pine, forbs, and shrubs. However, neither scenario yields a good correlation for broadleaf trees. Our model corroborates previous controlled experiments suggesting that in cold climate, the source water for most vegetation is winter precipitation, with focused leaf water evaporation occurring in late summer season when it is hot and dry; and leaf wax δD likely assimilated throughout the growing season, except for broadleaf trees, which assimilated winter precipitation during the leaf flushing.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-414884

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