On the urgent need for standardization in isotope-based ecohydrological
investigations
Abstract
Ecohydrological investigations commonly use the stable isotopes of water
(hydrogen and oxygen) as a conservative ecosystem tracer. This approach
requires accessing and analyzing water constrained within plant and soil
matrices. Generally, there are six steps that researchers must pass
through to retrieve hydrogen and oxygen isotope values from these plant
and soil matrices: (i) sampling, (ii) sample storage and transport,
(iii) extraction, (iv) pre-analysis processing, (v) isotopic analysis,
and (vi) post-processing and correction. At each of these steps
cumulative errors can be introduced which sum to non-trivial magnitudes.
These errors can impact subsequent interpretations about water cycling
through the soil-plant-atmosphere continuum. But these steps in the
research ‘process chain’ are just the tip of the iceberg when it comes
to uncertainly in published findings. At each of these discreet steps,
there are multiple possible options to select from resulting in, as we
will show, tens of thousands of possible combinations used by
researchers to go from plant and soil samples to isotopic data. In a
newly emerging science, so many options can create interpretive
confusion and major issues with data comparability. This points to the
need for the development of shared standardized approaches. Here we
critically examine the state of the process chain, reflecting on the
issues associated with each step, and end with suggestions to move our
community towards standardization. We hope that critically assessing
this common approach will help us see the current problem in its
entirety and facilitate community action toward agreed upon standardized
approaches.