Technical note: Isotopic fractionation of evaporating waters: effect of sub-daily atmospheric variations and eventual depletion of heavy isotopes
<p>Isotopic fractionation of evaporating waters has been studied constantly in recent decades, particularly because it enables calculation of both the volume of water evaporated from a water body and the isotopic composition of its source water. We studied the stable water isotopic composition...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2024-01-01
|
| Series: | Hydrology and Earth System Sciences |
| Online Access: | https://hess.copernicus.org/articles/28/229/2024/hess-28-229-2024.pdf |
| _version_ | 1797354147198009344 |
|---|---|
| author | F. Gallart S. González-Fuentes P. Llorens |
| author_facet | F. Gallart S. González-Fuentes P. Llorens |
| author_sort | F. Gallart |
| collection | DOAJ |
| description | <p>Isotopic fractionation of evaporating waters has been studied constantly in recent decades, particularly because it enables calculation of both the volume of water evaporated from a water body and the isotopic composition of its source water. We studied the stable water isotopic composition of an artificial pan filled with water and subject to total evaporation in a sub-humid environment, in order to put into practice an operational method for estimating the time since disconnection of riverine pools when these are sampled for the quality of aquatic life.</p>
<p>Results indicate that (i) when about 70 % of pan water had evaporated and its isotopic composition had become enriched in heavy isotopes, some subsequent periods of depletion instead of enrichment happened; and (ii) the customary application of isotopic fractionation equations to determine the isotopic composition of the water in the pan using weekly averaged atmospheric conditions (temperature and relative humidity) strongly underestimated the changes observed but predicted an early depletion of heavy isotopes. The first result, rarely reported in the literature, was found to be fully consistent with the early studies of the isotopic composition of evaporating waters. The second one could be attributed to the fact that weekly averages of temperature and relative humidity strongly overestimated air relative humidity during daylight periods of active evaporation. However, when the fractionation equations were parameterized using temperature and relative humidity weighted by potential evapotranspiration at sub-hourly time steps, they adequately reproduced the observed isotopic composition of the water in the pan, including the late periods of heavy isotope depletion.</p>
<p>We demonstrate how weekly increases in air relative humidity when the pan water was already enriched in heavy isotopes led to their depletion. We also analyse the errors that can be incurred if time averages are used instead of flux-weighted meteorological data for model parameterization and if unidentified periods of heavy isotope depletion occur. Our results should be taken into account when applying fractionation equations, particularly in conditions or areas with high air relative humidity.</p> |
| first_indexed | 2024-03-08T13:45:20Z |
| format | Article |
| id | doaj.art-48a574e18a154531add5946d1ed081a9 |
| institution | Directory Open Access Journal |
| issn | 1027-5606 1607-7938 |
| language | English |
| last_indexed | 2024-03-08T13:45:20Z |
| publishDate | 2024-01-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Hydrology and Earth System Sciences |
| spelling | doaj.art-48a574e18a154531add5946d1ed081a92024-01-16T09:32:25ZengCopernicus PublicationsHydrology and Earth System Sciences1027-56061607-79382024-01-012822923910.5194/hess-28-229-2024Technical note: Isotopic fractionation of evaporating waters: effect of sub-daily atmospheric variations and eventual depletion of heavy isotopesF. Gallart0S. González-Fuentes1P. Llorens2Surface Hydrology Ecology and Erosion group, IDAEA, CSIC, 08034 Barcelona, SpainGroundwater and Hydrogeochemistry group, IDAEA, CSIC, 08034 Barcelona, SpainSurface Hydrology Ecology and Erosion group, IDAEA, CSIC, 08034 Barcelona, Spain<p>Isotopic fractionation of evaporating waters has been studied constantly in recent decades, particularly because it enables calculation of both the volume of water evaporated from a water body and the isotopic composition of its source water. We studied the stable water isotopic composition of an artificial pan filled with water and subject to total evaporation in a sub-humid environment, in order to put into practice an operational method for estimating the time since disconnection of riverine pools when these are sampled for the quality of aquatic life.</p> <p>Results indicate that (i) when about 70 % of pan water had evaporated and its isotopic composition had become enriched in heavy isotopes, some subsequent periods of depletion instead of enrichment happened; and (ii) the customary application of isotopic fractionation equations to determine the isotopic composition of the water in the pan using weekly averaged atmospheric conditions (temperature and relative humidity) strongly underestimated the changes observed but predicted an early depletion of heavy isotopes. The first result, rarely reported in the literature, was found to be fully consistent with the early studies of the isotopic composition of evaporating waters. The second one could be attributed to the fact that weekly averages of temperature and relative humidity strongly overestimated air relative humidity during daylight periods of active evaporation. However, when the fractionation equations were parameterized using temperature and relative humidity weighted by potential evapotranspiration at sub-hourly time steps, they adequately reproduced the observed isotopic composition of the water in the pan, including the late periods of heavy isotope depletion.</p> <p>We demonstrate how weekly increases in air relative humidity when the pan water was already enriched in heavy isotopes led to their depletion. We also analyse the errors that can be incurred if time averages are used instead of flux-weighted meteorological data for model parameterization and if unidentified periods of heavy isotope depletion occur. Our results should be taken into account when applying fractionation equations, particularly in conditions or areas with high air relative humidity.</p>https://hess.copernicus.org/articles/28/229/2024/hess-28-229-2024.pdf |
| spellingShingle | F. Gallart S. González-Fuentes P. Llorens Technical note: Isotopic fractionation of evaporating waters: effect of sub-daily atmospheric variations and eventual depletion of heavy isotopes Hydrology and Earth System Sciences |
| title | Technical note: Isotopic fractionation of evaporating waters: effect of sub-daily atmospheric variations and eventual depletion of heavy isotopes |
| title_full | Technical note: Isotopic fractionation of evaporating waters: effect of sub-daily atmospheric variations and eventual depletion of heavy isotopes |
| title_fullStr | Technical note: Isotopic fractionation of evaporating waters: effect of sub-daily atmospheric variations and eventual depletion of heavy isotopes |
| title_full_unstemmed | Technical note: Isotopic fractionation of evaporating waters: effect of sub-daily atmospheric variations and eventual depletion of heavy isotopes |
| title_short | Technical note: Isotopic fractionation of evaporating waters: effect of sub-daily atmospheric variations and eventual depletion of heavy isotopes |
| title_sort | technical note isotopic fractionation of evaporating waters effect of sub daily atmospheric variations and eventual depletion of heavy isotopes |
| url | https://hess.copernicus.org/articles/28/229/2024/hess-28-229-2024.pdf |
| work_keys_str_mv | AT fgallart technicalnoteisotopicfractionationofevaporatingwaterseffectofsubdailyatmosphericvariationsandeventualdepletionofheavyisotopes AT sgonzalezfuentes technicalnoteisotopicfractionationofevaporatingwaterseffectofsubdailyatmosphericvariationsandeventualdepletionofheavyisotopes AT pllorens technicalnoteisotopicfractionationofevaporatingwaterseffectofsubdailyatmosphericvariationsandeventualdepletionofheavyisotopes |