Deuterium excess in precipitation of Alpine regions – moisture recycling

Abstract

The paper evaluates long-term seasonal variations of the deuterium excess (d-excess = delta(2)H - 8. delta(18)O) in precipitation of stations located north and south of the main ridge of the Austrian Alps. It demonstrates that sub-cloud evaporation during precipitation and continental moisture recycling are local, respectively, regional processes controlling these variations. In general, sub-cloud evaporation decreases and moisture recycling increases the d-excess. Therefore, evaluation of d-excess variations in terms of moisture recycling, the main aim of this paper, includes determination of the effect of sub-cloud evaporation. Since sub-cloud evaporation is governed by saturation deficit and distance between cloud base and the ground, its effect on the d-excess is expected to be lower at mountain than at lowland/valley stations. To determine quantitatively this difference, we examined long-term seasonal d-excess variations measured at three selected mountain and adjoining valley stations. The altitude differences between mountain and valley stations ranged from 470 to 1665 m. Adapting the 'falling water drop' model by Stewart [J. Geophys. Res., 80(9), 1133-1146 (1975).], we estimated that the long-term average of sub-cloud evaporation at the selected mountain stations (altitudes between about 1600 and 2250 m.a.s.l.) is less than 1 % of the precipitation and causes a decrease of the d-excess of less than 2 per thousand. For the selected valley stations, the corresponding evaporated fraction is at maximum 7 % and the difference in d-excess ranges up to 8 per thousand. The estimated d-excess differences have been used to correct the measured long-term d-excess values at the selected stations. Finally, the corresponding fraction of water vapour has been estimated that recycled by evaporation of surface water including soil water from the ground. For the two mountain stations Patscherkofel and Feuerkogel, which are located north of the main ridge of the Alps, the maximum seasonal change of the corrected d-excess (July/August) has been estimated to be between 5 and 6 per thousand, and the corresponding recycled fraction between 2.5-3 % of the local precipitation. It has been found that the estimated recycled fractions are in good agreement with values derived from other approaches.

Isotopic and hydrogeochemical characterization of high-altitude karst aquifers in complex geological settings. The Ordesa and Monte Perdido National Park (Northern Spain) case study

“…The resulting vapour increases its atmospheric deuterium excess at the local scale. The low night temperatures at high elevation cause the atmospheric water vapour to condense on the snow surface, and as a result, the snow cover there increases its deuterium excess (Stichler et al, 2001;Froehlich et al, 2008). This diurnal snow sublimation and nocturnal condensation cycle could explain why the recharge due to high altitude snow melt in autumn, winter and spring has an increased deuterium excess in the PNOMP.…”

Applicability study of deuterium excess in bottled water life cycle analyses

“…In the analyses of d-excess in Slovenian bottled waters, foreign precipitation stations near the state borders must also be considered. In Austria, the mean d-excess value for the period 1973-1994 at Villacher Alpen was 9.6 ‰ (Froehlich et al, 2008) and at Graz for the period 1973-2002it was 8.8 ‰ (IAEA, 2010. In Croatia, the d-excess value for the period 1976-1996 at Zagreb was 7.8 ‰ and daily fluctuations were between -9 ‰ and 18 ‰ .…”

Karst hydrogeology of the Untersberg massif and its interaction with the porous aquifer in the adjacent Salzburg Basin

“…11). Froehlich et al (2008) showed, that sub-cloud evaporation is the reason for the lower deuterium excess of valleys stations in Austria where evaporation reaches 7 %. Mountain stations show a higher deuterium excess and the sub-cloud evaporation is less than 1 % of the precipitation.…”