23 Aug 2021
23 Aug 2021
Status: a revised version of this preprint is currently under review for the journal HESS.

A method for predicting hydrogen and oxygen isotope distributions across a region's river network using reach-scale environmental attributes

Bruce Dudley1, Jing Yang1, Ude Shankar1, and Scott Graham2 Bruce Dudley et al.
  • 1National Institute of Water and Atmospheric Research, 10 Kyle Street, Riccarton, Christchurch 8011, New Zealand
  • 2Manaaki Whenua - Landcare Research, 54 Gerald Street, Lincoln 7608, New Zealand

Abstract. Stable isotope ratio measurements (isotope values) of surface water provide information on hydrological processes and can be used to determine provenance of hydrogen and oxygen stored in animal and plant tissues. Development of maps of the distribution of isotope values (isoscapes) for river networks is limited by methods to interpolate point measures to values for the entire network. Isotope values of precipitation and environmental characteristics that drive fractionation processes within the catchment also affect downstream reaches via flow. Many environmental characteristics, such as man-made dams, are no more likely to affect nearby unconnected reaches than distant ones. Hence, distance-based geospatial and statistical interpolation methods used to develop isoscapes for precipitation and terrestrial systems are less appropriate for river networks. We used a water balance-based method, which represents patterns of surface flow and mixing, and added a regression-based correction step using catchment environmental predictors. We applied this method across the river network of New Zealand, comprising over 600,000 reaches and over 400,000 kilometres of rivers. Inputs to the model are national rainfall precipitation isoscapes, a digital elevation layer, a national river water isotope monitoring dataset (3 years of monthly sampling at 58 sites) and reach scale river environmental databases across the New Zealand river network. δ2H and δ18O isoscapes produced using this regression-based kriging method showed improved fit to validation data, compared to a model for which residuals were applied as a correction factor across the river network using ordinary kriging. The resulting river water isoscapes have potential applications in ecology, hydrology and provenance studies for which understanding of spatial variation between precipitation and surface water isotope values are required.

Bruce Dudley et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2021-424', Anonymous Referee #1, 16 Nov 2021
    • AC1: 'Reply on RC1', Bruce Dudley, 04 Mar 2022
  • RC2: 'Comment on hess-2021-424', Anonymous Referee #2, 08 Feb 2022
    • AC2: 'Reply on RC2', Bruce Dudley, 04 Mar 2022

Bruce Dudley et al.

Bruce Dudley et al.


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Short summary
Maps of river water stable isotope ratios provide information on flow pathways, and can aid ecological and provenance studies because the isotope values of water that plants and animals use are passed into their tissues. We used a water balance-based mapping method, which represents patterns of surface flow and mixing, and added a correction step using catchment environmental characteristics to map water isotope ratios across all the rivers of New Zealand.