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Noble Gas and Major Element Constraints on the Water Dynamics in an Alpine Floodplain

Summary: Noble Gas and Major Element Constraints
on the Water Dynamics in an Alpine Floodplain
by Johannes Holocher1, Vijay Matta1,3, Werner Aeschbach-Hertig1,
Urs Beyerle1, Markus Hofer1, Frank Peeters1, and Rolf Kipfer1,2
The hydrogeological system of an ecologically sensitive alpine floodplain in the Valle di Blenio, Switzerland, was investigated
using hydrochemical and 3H-3He dating methods. Water samples from six wells and from different surface locations were ana-
lyzed. The analysis of the concentrations of major ions in conjunction with age determination by the 3H-3He-method allowed the
main hydrological properties of the system to be consistently characterized. Two geochemically distinct water zones can be dis-
tinguished: Ca-SO4-dominated water from the main river and Ca-HCO3-dominated floodplain water. The floodplain water
component characterizes the whole floodplain including the surficial hillslope drainage system. Within the ground water samples,
two spatially and temporally different types of water can be determined.Ayounger (age < 1.5 years), less mineralized water is found
in the upper part of the aquifer during the summer season. The underlying aquifer zone contains older and more highly miner-
alized water. However, the general hydrochemical characterization of both types of ground water is similar. In winter, the water
ages increase with decreasing ground water levels. Because precipitation is stored temporarily in the snow cover, the contribution
of the younger near-surface ground water decreases, resulting in higher apparent water ages and higher mineralization in the upper
zone of the aquifer. Water exchange between the main river and the ground water system is limited to ground water exfiltration
from the shallow aquifer zone, whereas the hydrochemical separation of the deeper aquifer zone indicates the isolation of the deeper
ground water from the main river.


Source: Aeschbach-Hertig, Werner - Institut für Umweltphysik, Universität Heidelberg


Collections: Geosciences; Environmental Sciences and Ecology