Search

ABSTRACT Sources of water use by 10 alluvial trees in various hydrogeological and ecological situations at the Pfyn forest (Wallis canton, Switzerland) were assessed by analysing 18O and 2H isotopes of precipitation, soil water at different depths, surface water, groundwater and xylem sap. The soil water line in a δ18O versus δ2H diagram shows evidence of kinetic fractionation related to evaporation. The tree water line is close to the soil trend; however, an additional enrichment may occur and could be related to xylem-phloem communication under water stress. At sites where the water table was at least 2 m below the ground surface, isotopic temporal variability of soils and trees was strongly linked with seasonal variation of soil water content. When soil water content was low and water table shallow, trees used both soil water and groundwater. When soil water content was high, this source was usually the dominant source for transpiration. In addition, some ecological strategies, reproduction or growth competition, could explain shifts in the utilization of different water sources, for example, from soil water to a mix of soil water and groundwater. At one site where soil water and groundwater were abundant throughout the year (next to the river course), neighbouring trees permanently used distinct water sources. This is consistent with a strategy of competition limitation, which would favour bank colonization. These results provide insight into the ecohydrological functioning of this system and will aid future management responses to both local and climate changes. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Summary: The study was carried out in the northern part of the Aquitaine Basin extending in Southwest France. The basin has been intensively exploited for various purposes for many years. Although the geological context is well known, there are still some gaps in the knowledge about the hydrogeochemical regime, groundwater average residence time and the palaeohydrological conditions prevailing during the recharge period which would help to secure sustainable exploitation of the resources. Environmental isotopes (18O, 2H, 3H, 13C) together with radiocarbon were used to evaluate hydrochemical evolution, residence time and palaeorecharge conditions for Jurassic, Cretaceous and Eocene aquifers. Radiocarbon activity in the aquifers varies widely between 0 and 94pmc. After radiocarbon corrections the ages indicate both modern and old waters sometimes exceeding the limit for 14C dating. The Fontes and Garnier model is best adapted to the specificity of the carbonate system. The content in stable isotopes of water is varying between −7.7‰ and −4.9‰ for δ18O and −52.3‰ to −29.6‰ for δ2H. The wide ranges of stable isotopic values imply variable climatic conditions. A group of isotopically depleted samples was detected, indicating colder climatic conditions during the recharge. Radiocarbon ages calculation, together with isotopic signature, point out that the depletion in stable isotopic values fits the period between 20 and 15ka B.P. and therefore indicate the Last Glacial Maximum (LGM). According to the correction model, the transition from Pleistocene to Holocene would occur between 15 and 12ka B.P. Palaeohydrological data from the Northern Aquitaine Basin does not confirm a significant hiatus in the recharge history. The recharge conditions in South Europe seem to have occurred under discontinuous permafrost conditions as documented by many palaeoclimatological archives. This is in favour of an uninterrupted recharge of the confined aquifers of Northern Aquitaine Basin. Such information should be considered by modellers in their attempts to simulate the hydrogeological functioning of large confined aquifers on the very long time range. [Copyright &y& Elsevier]

Abstract: The Bohemian Cretaceous Basin represents a complex hydrogeological system composed of several aquifers with very favourable hydrogeological properties. These aquifers have been exploited for many years. The sustainability of such resources might be guaranteed by well organised water management, which requires a detailed knowledge about the functioning of the hydrogeological system. Although many efforts have previously been made to evaluate groundwater residence time, the many intricate geochemical processes complicate groundwater dating. The current study clarifies the functioning of this complex hydrogeological basin using hydrogeochemical and isotopic investigations. Chemical data and a combination of 13C and 14C isotopes within the Cenomanian and the Turonian layers indicate groundwater interactions with deep-seated CO2, rock matrix, surface waters and fossil organic matter. Very depleted δ13C values (average δ13C∼−13.4‰) suggest interactions with fossil organic matter, whereas enriched values account for the interaction with deep CO2 gas ascending from the upper mantle via the numerous faults and fractures, and also, to a lesser extent, from calcite dissolution. Geochemical processes that take place in the system cause a clear depletion in 14C that greatly complicates groundwater residence time evaluation. Different dilution correction models have been applied considering the different C origins. The stable isotope content, mainly 18O values, indicates both the contribution of modern precipitation and the partial infiltration of palaeowaters during colder climatic conditions from the end of the Pleistocene. The apparent 14C groundwater ages range from modern to 11.1ka BP, which suggests some post glacial infiltration from melting ice sheets. Finally, all the acquired information was used to propose a conceptual model of C origin within the basin. [Copyright &y& Elsevier]