Preprints
https://doi.org/10.5194/hess-2020-648
https://doi.org/10.5194/hess-2020-648

  26 Jan 2021

26 Jan 2021

Review status: a revised version of this preprint is currently under review for the journal HESS.

Technical note: Evaporating water is different from bulk soil water in δ2H and δ18O

Hongxiu Wang1,2, Jingjing Jin1, Bingcheng Si1,2, Xiaojun Ma3, and Mingyi Wen1 Hongxiu Wang et al.
  • 1Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas, Ministry of Education, Northwest A&F University, Yangling, Shaanxi Province 712100, China
  • 2Department of Soil Science, University of Saskatchewan, Saskatoon SK S7N 5A8, Canada
  • 3Gansu Provincial Department of Water Resources, Lanzhou, Gansu Province 730000, China

Abstract. Soil evaporation is a key process in the water cycle and can be conveniently quantified with δ2H and δ18O in bulk surface soil water (BW). However, recent research shows that larger soil pore water evaporates first and differs from small pore water in δ2H and δ18O, which disqualifies quantification of evaporation from BW δ2H and δ18O. We hypothesize that BW has different isotopic compositions than evaporating water (EW). Therefore, our objectives are to test the hypothesis, and to evaluate if the difference alters the calculated evaporative water loss. We measured isotopic composition in soil water in two continuous evaporation periods in a summer maize field. Period Ⅰ had a duration of 32 days following a precipitation event and Period Ⅱ lasted 24 days following an irrigation event with a 2H-enriched water. BW was obtained by cryogenically extracting water from samples of 0–5 cm soil taken every three days; EW was derived from condensation water collected every two days on plastic film placed on soil surface. Results showed that when newly added water was heavier than pre-event BW, δ2H of BW in Period Ⅱ decreased with the increase of evaporation time, indicating evaporation of heavy water; when newly added water was lighter than pre-event BW, δ2H and δ18O of BW in Period Ⅰ and δ18O of BW in Period Ⅱ increased with increasing evaporation time, suggesting evaporation of light water. Moreover, relative to BW, EW had significantly smaller δ2H and δ18O in Period Ⅰ and significantly smaller δ18O in Period Ⅱ (p < 0.05). This suggests that evaporating water was newly added water, both of which were different from bulk soil water. Further, the newly added water may be in large pores, from which evaporation takes precedence. We also calculated soil evaporation losses from using water isotopes from EW and BW and they did not differ significantly (p > 0.05). Our results have important implication for quantifying evaporation process with water stable isotopes.

Hongxiu Wang 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-2020-648', Anonymous Referee #1, 27 Feb 2021
    • AC1: 'Reply on RC1', Hongxiu Wang, 23 Mar 2021
  • RC2: 'Comment on hess-2020-648', Anonymous Referee #2, 01 Mar 2021
    • AC2: 'Reply on RC2', Hongxiu Wang, 23 Mar 2021

Hongxiu Wang et al.

Hongxiu Wang et al.

Viewed

Total article views: 444 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
335 95 14 444 14 6 6
  • HTML: 335
  • PDF: 95
  • XML: 14
  • Total: 444
  • Supplement: 14
  • BibTeX: 6
  • EndNote: 6
Views and downloads (calculated since 26 Jan 2021)
Cumulative views and downloads (calculated since 26 Jan 2021)

Viewed (geographical distribution)

Total article views: 386 (including HTML, PDF, and XML) Thereof 385 with geography defined and 1 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 24 Jul 2021
Download
Short summary
Evaporation led to progressively more heavy-isotope enriched bulk soil water (BW) following precipitation/irrigation of heavy isotope depleted new water but causes progressively more heavy-isotope depleted BW following irrigation of heavy isotope enriched new water. The results indicated that δ2H and δ18O in evaporating water (EW) were similar to new water and differed from BW. However, the evaporative water loss calculated from BW did not differ significantly from that of EW.