View article

In their reexamination of an earlier study (1) in which water isotope data from globally distributed sites were compiled, Evaristo et al.(2) show that, after accounting for extraction artifacts, precipitation offsets of xylem water (dxylem_c) are still statistically distinct from those of stream (dstream)/groundwater (dgw) in a majority of the sampling sites. In agreement, our own analysis on the dataset of ref. 1 also revealed a significant dxylem_c versus dgw/dstream difference at the global scale (Table 1). However, we would like to point out that these analyses miss a crucial point: By removing the∼ 8‰ stem water extraction-associated error, there is as much “ecohydrological separation” from xylem water to groundwater as there is between stream and groundwater.

In our opinion, assessment of ecohydrological separation based solely on statistical significance in “offset” differences—as done here by Evaristo et al.(2)—is …