Research activity associated with various observations at the Strengbach catchment in the Vosges Massif (880-1150 m) addresses many questions in the domains of hydrology and geochemistry. The catchment is the observation and experimental site of the Observatoire Hydro-Géochimique de l'Environnement appointed by the Centre National de la Recherche Scientifique. It also belongs to the research facilities that form the French Network of Critical Zone Observatories (OZCAR), which supports a network of critical zone observatories. The catchment is small (0.8 km 2 ) with steep slopes (20-30%) on granitic bedrock that mainly allow for forestry (spruce and beech stands) as the main land cover. Meteorological, hydrological, and geochemical data have been monitored since 1986. The first studies conducted were dedicated to the elucidation of acid rain effects on forest ecosystems and particularly on forest decline. Multidisciplinary research studies conducted on the Strengbach catchment enable exploration of the following issues: (i) hydrological functioning at the scale of a small catchment and questions regarding the evolution and preservation of the water resources in mountainous environments (stock, recharge, infiltration, and water pathways), (ii) exchange processes observed at the soil-plant-atmosphere continuum and in particular weathering processes and the evolution of soil mineral fertility (Ca, Mg, K, P), (iii) processes responsible for the export of water and for associated fluxes (dissolved chemicals, suspended materials, bed loads) and their dynamic at the outlet, and (iv) responses of the ecosystems to environmental disturbances (acid rain, forest management, and climate change) and their current and future modeling. University of Strasbourg), is well suited for addressing such issues owing to (i) a long-term dataset available for the area (from 1985;Probst et al., 1987), (ii) the availability of field equipment and monitoring devices, and (iii) numerous scientific studies that have been performed on the area. Research performed at this catchment, which is located in the Vosges Mountains in northeastern France, has focused on the evaluation of water and soil resources in relation to climatic changes (i.e., rainfall regimes and atmospheric chemistry trends) and anthropogenic patterns (e.g., forest management and acid precipitation) occurring in this moderate-altitude mountainous region.Usually, in this type of ecosystem, water is scarce and not evenly distributed, and stocks may rapidly vary over time. In addition, although wood production is an economically important activity in these regions, soil degradation (e.g., from acidification and nutrient depletion) modifies soil fertility features and thus affects the development of forests.The scientific objective of the OHGE is to develop a detailed understanding of water transport processes and of related chemical fluxes (including nutrients and contaminants) through the critical zone extending from the near atmosphere to the near subsurface. The main purposes of...

The performance of the Magnetic Resonance Sounding (MRS) method applied to the investigation of heterogeneous hard-rock aquifers was studied. It was shown using both numerical modeling and field measurements that MRS could be applied to the investigation of the weathered part of hard-rock aquifers when the product of the free water content multiplied by the thickness of the aquifer is >0.2 (for example, 10-m-thick layer with a 2% water content). Using a currently available one-dimensional MRS system, the method allows the characterization of two-dimensional subsurface structures with acceptable accuracy when the size of the subsurface anomaly is equal to or greater than the MRS loop. However, the fractured part of hard-rock aquifers characterized by low effective porosity (<0.5%) cannot be resolved using currently available MRS equipment. It was found that shallow water in the weathered part of the aquifer may screen MRS signals from deeper water-saturated layers, thus further reducing the possibility of investigating deeper fractured aquifers. A field study using the NUMIS(plus) MRS system developed by IRIS Instruments was carried out on an experimental watershed in southern India. A heterogeneous unconfined aquifer in a gneissic formation was successfully localized, and MRS results were confirmed by drilling shortly after the geophysical study. The top of the aquifer revealed by MRS was found to be in a good agreement with observed static water level measurements in boreholes.

A new methodology for Magnetic Resonance Sounding (MRS) data acquisition and interpretation was developed for locating water-filled karst cavities. This methodology was used to investigate the Ouysse karst system in the Poumeyssens shaft in the Causse de Gramat (France). A new 2D numerical MRS response model was designed for improved accuracy over the previous 1D MRS approach. A special survey performed by cave divers confirmed the accuracy of the MRS results. Field

 Magnetic resonance soundings are used to condition hydrological model parameters.  The output of hydrological model simulations provides the subsurface water content.  The estimated water content is then used to simulate the MRS signal.  The comparison with observations allows selecting sets of model parameters.  The approach is applied on a hard-rock headwater catchment.