title: Noble gas and major element constraints on the water dynamics in an alpine floodplain.
abstract: 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 analyzed. 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 distinguished: 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. A younger (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 mineralized 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.
authors.affiliation: Department of Water Resources and Drinking Water, Swiss Federal Institute of Environmental Science and Technology, Duebendorf. johannes.holocher@eawag.ch
authors.forename: J
authors.initials: J
authors.lastname: Holocher
authors.forename: V
authors.initials: V
authors.lastname: Matta
authors.forename: W
authors.initials: W
authors.lastname: Aeschbach-Hertig
authors.forename: U
authors.initials: U
authors.lastname: Beyerle
authors.forename: M
authors.initials: M
authors.lastname: Hofer
authors.forename: F
authors.initials: F
authors.lastname: Peeters
authors.forename: R
authors.initials: R
authors.lastname: Kipfer
mesh_terms: D055593:Geological Phenomena; D005844:Geology; D007477:Ions; D008903:Minerals; D005741:Noble Gases / Q000737:chemistry*; D011891:Rain; D012621:Seasons; D012987:Soil; D014867:Water / Q000737:chemistry*; D014872:Water Movements
chemical_list: D007477:Ions; D008903:Minerals; D005741:Noble Gases; D012987:Soil; D014867:Water