IAEA-CN-104/157 AUSTRIAN NETWORK OF ISOTOPES IN PRECIPITATION (ANIP): QUALITY ASSURANCE AND CLIMATOLOGICAL PHENOMENON IN ONE OF THE OLDEST AND DENSEST NETWORKS IN THE WORLD
-20 -18 -16 -14 -12 -10 -8
-6-20 -18 -16 -14 -12 -10 -8 -6
DELTA OXYGEN-18 1973, 1975, 1986, 1995
DELTA OXYGEN-18 2002
1973 1975 1986 1995
1973 <250 ml
FIG. 1. Control measurements of rain water in 1L polyethylene bottles store in a cellar up to 30 years. Most results were repeatable within an error
of δ O-18 0.2 %o. Just 4 samples showed larger differences (see text).
Just four samples showed an larger deviation in the direction of evaporation. Two 1L PE- bottles of 1973 filled to 200 and 250 ml only and two samples belonging to a charge of samples waiting about 3 years in 30 ml PE-bottles in laboratory environment (about 20-25° C) prior to original analysis showed larger deviations (0.7 to 2 per mil) indicating evaporation.
Wet periods are supposed to represent maritime phases. The Alps as a weather divide sharply distinguish precipitation events caused by different air flow directions. A study about the origin of the precipitating air masses in Austria showed that an Atlantic influence (moisture from NW) causes lower δ18O values (e.g. Patscherkofel and Bregenz) than a Mediterranean one (e.g. Villacher Alpe and Graz) [1].
In addition to the input measurements at the above mentioned meteorological stations 173 springs North and South of the weather divide were analysed for oxygen-18 and tritium four times a year in 1997/1998 in the framework of the Austrian Water Quality Network (AWQN).
The mean O-18 values were plotted against the altitude of the recharge area calculated statistically as the half-height between the altitude of the spring and the potential maximum altitude of the recharge area. The correlation between the weighted mean of the O-18 values (1993-1997) and the altitude of the northern meteorological stations are in fairly good agreement with the spring trend in the North (Fig. 2).
y = -482.79x - 4436.6 R2 = 0.8932
100 600 1100 1600 2100 2600
-15.00 -14.00 -13.00 -12.00 -11.00 -10.00 -9.00 -8.00 -7.00 DELTA OXYGEN - 18
ALTITUDE (m)
Meteorol. Stations South Meteorol. Stations North S. Pellegrino, N-Italy Hohenpeissenberg, Germ.
Northern Springs Southern Springs
100m ~ 0,21 %
oO-18
FIG. 2. Altitude effect at the northern front of the Eastern Alps in meteorological stations and springs (dark blue) in contrast to a very steep or nearly no altitude effect at the inner-alpine mainly Mediterranean influenced stations and springs in southern part of Austria (lighter red symbols).
It indicates a reasonable gradient of 0.21%o oxygen-18 per 100 m altitude change. However, some of the meteorological stations and the springs in the south of Austria show clearly the Mediterranean influence as indicated by the station San Pellegrino [2] in Northern Italy. Also the altitude effect is small or not existing probably caused by the shielding effect of the Southern Alpine ranges in Northern Italy and Slovenia. As indicated by the study of [1] all stations and springs are influenced by Atlantic and Mediterranean origin to a variable degree and show therefore local mixtures, which may even vary in time.
There is a significant increase of the yearly mean of the deuterium excess in the mountain station above 1500 m altitude. But moreover, the seasonal pattern of the deuterium excess is quite different. While all valley stations exhibit the expected minimum in summer, the four mountain stations above 1500m, including the S. Pellegrino station in N-Italy, show a distinct maximum (12 - 15 ‰) between May and October. This is also the period with the seasonal maximum of precipitation.
The possible physical and meteorological mechanisms causing these isotope pattern in the precipitation will be discussed.
REFERENCES:
[1] KAISER, A.; SCHEIFINGER, H.; KRALIK, M.; PAPESCH, W.; RANK &
STICHLER, W.; (2002): Links between meteorological conditions and spatial/temporal variations in long–term isotopic records from the Austrian precipitation network. Intern.
Conf. “Study of Environmental Change Using Isotope Techniques”, 23–27 Apr. 2001, C&SPaperSeries 13/P, 67–77, IAEA, Vienna.
[2] IAEA/WMO (2001). Global Network of Isotopes in Precipitation. The GNIP Database.
Accessible at: http://isohis.iaea.org.
IAEA-CN-104/158 UTILIZATION OF MONSOONAL RAINS BY PLANTS AND ISOTOPIC PARTITIONING OF EVAPOTRANSPIRATION IN TWO CONTRASTING SEMI- ARID SAVANNA ECOSYSTEMS
G. LIN
Columbia University/Biosphere 2 Center, Oracle, Arizona, USA D. WILLIAMS, E. YEPEZ
School of Renewable Natural Resources, University of Arizona, Tucson, Arizona, USA R. SCOTT
USDA–ARS, Tucson, Arizona, USA
Due to the episodic and localized nature of monsoonal precipitation, the exchange of water between the land surface and atmosphere in arid and semi-arid environments is temporally dynamic and spatially heterogeneous during the summer growing season. There are relatively few data on how monsoonal rains are used by plants and what proportions of these growing season precipitation are lost to transpiration by canopy and evaporation by vegetation surface in semi-desert ecosystem.
In this study, we applied stable isotopes of oxygen and hydrogen to study differential utilization of summer monsoonal rains by dominant plants and to partition evapotranspiration (ET) water fluxes in southern Arizona, USA and eastern Inner Mongolia, China. Both ecosystems are influenced by monsoonal rain events and threatened by invasion of woody shrubs due to climate and land-use changes.
Isotope compositions of stem water from dominant plants indicate that woody perennial plants showed limited utilization of summer rains while grasses and annual herbs rely on summer rains for their growth. In addition, “Keeling plots” (isotope mixing relationships) were generated from isotope ratios (δD and δ18O) of atmospheric water vapor collected along height profiles and the regression intercepts from these profiles to partition ET fluxes. Our results suggest that two semiarid savanna ecosystems have distinct patterns of ET fluxes following the monsoonal rain events because of differences in local climate conditions and species compositions.
IAEA-CN-104/159 STUDY ON WATER VAPOR TRANSPORT TO TIBETAN PLATEAU USING STABLE ISOTOPIC COMPOSITION OF PRECIPITATION