> Observatoire SO Karst


Karst is a complex hydrogeologic entity whose study requires specific and original models and approaches. The goal of SNO KARST is to bring out scientific questions and advances, specifically in terms of hydrogeochemical flux modeling at karst hydrosystem outlets and the links between global changes and the physico-chemical composition of water at the interface between hydrologic and hydrogeologic compartments. Particular attention is focused on the data-model link so as to understand better the physics and chemistry of the medium and to enhance modeling capacity to reproduce variations of flux and matter. We also point out that carbonate rocks that host karst systems are materials eminently "susceptible" to erosion and weathering and that these processes are themselves highly dependent on by expected modifications of climate, and of the hydrologic and rainfall regime. Because of these factors, karst is even more vulnerable over short time scales, which is a characteristic that is generally less meaningful in deeper non-karst hydrosystems or those that have slower hydric dynamics. The aspect of material transfer and participation in major biogeochemical cycles is also a primary preoccupation of this SNO, especially because karst systems are more vulnerable to modifications of conditions at surface boundaries.

SNO KARST is a suitable place to merge the powers of observation and current research on karst aquifers to compare, organize, and standardize approaches (tools, methods, concepts). Here team members work to develop tools to characterize and model water resource evolution (qualitative, quantitative) in response to forcing of short, medium, and long wavelength, within different physiographic, geologic, and climatic contexts. We hope to move toward a "synthetic" approach at the scale of large karst typologies, from characterizing their structure and operation to hydrodynamic and hydrogeochemical modeling of transfers. To accomplish this, it is necessary to perpetuate the temporal surveillance of various natural laboratories.

For example, one goal is to identify the intrinsic variability of water resources in these hydrosystems while trying to separate the impact of climate variability from the impact of global change, on the scale of a karst basin. To accomplish this, it is necessary to characterize the specific non-linearity of karst in its hydrodynamic and hydrochemical response to external stress and to characterize the role of various compartments in this non-linearity. The existence of long records maintained by the observatories specific to one or another of the karst compartments and the expertise of each team participating in this SNO make it possible to address this issue.

Another issue/challenge for SNO KARST is to propose a systematic and generic approach to karst. In many ways, this generic mission can be compared to what is being built at the meso-scale for the 3D surface-underground integration of fluid dynamics and material fluxes in drainage basins. In the specific case of karst, flows in the unsaturated zone (ZNS) and the saturated zone (ZS) cannot be grasped by simple physics/physics alone because we lack knowledge of the geometry of flows and their channelization [or: flow geometry and channelization]. Thus, it seems necessary that at least for flows, this part of the ZNS-ZS of the system must be understood in a homogenized, even systemic, form.

SO KARST, a National Observing Service of INSU