Evaluate the impact of climate change on the groundwater reserves and ecology of a karst aquifer flooding intermittently: the Upper Pivka Valley

Karst aquifers supply a quarter of the world and half of Slovenia with drinking water. Due to the global increase of population, this demand is expected to grow in the future. On the meantime, extreme hydrological events are forecasted to increase with climate change. This poses a threat on the quantity and quality of the water stored in karst aquifers. In addition, many peculiar ecosystems relying on karst waters could be affected by a decrease of the water resources. Therefore, current characterization techniques of karst aquifers need to be improved to evaluate their vulnerability to climate change. However, one difficulty is that the aquifer geometry remains largely unknown. Moreover, karst aquifers often belong to larger hydrogeological systems where temporary processes such as inter-catchment flow, overflow, or inversion of flow direction occur. This may affect the water quality.

The karst aquifer of the Upper Pivka Valley (Pivka Karst Aquifer) is very good example of the two problematics exposed above. While the valley lower part is constituted of flysch, its upper part is made of limestone and dry during most of the year. When a flood occurs, the water level rise up to 45 m and the Pivka River emerges at the surface. While most of the conduit system in the Pivka Karst Aquifer is unknown, the Pivka Karst Aquifer is connected to a larger aquifer named Javorniki Karst Aquifer that is well characterized. Under low water conditions, water from the Pivka Karst Aquifer drains through the Javorniki Karst Aquifer towards the Unica and Malenščica Springs. Under high-water situations, the flow direction is modified. The Pivka Karst Aquifer receives water from the Javorniki Karst Aquifer, which provides also autogenic water to the Unica and Malenščica springs. Therefore, characterizing the interaction between both aquifers is a pre-requisite before evaluating the sensitivity of the Pivka Karst Aquifer to climate change. Finally, 17 temporary lakes appear in the Upper Pivka Valley when a flood occurs. The wetland ecosystem linked to these lakes is peculiar, with many species depending on the presence of water. As the appearance of the lakes is controlled by water level oscillations in the Pivka Karst Aquifer, a decrease of the yearly total precipitation could modify their ecosystem in a short time span.

This project aims evaluating the effect of climate change on the groundwater reserves and water quality of the Pivka Karst Aquifer. To do so, a combination of several hydrogeological methods will be used. The monitoring network already installed in the Pivka Karst Aquifer will be extended, and two multi-tracers tests will be implemented to assess the flow directions and travels times. Analyses of water chemistry and microbiology will support the hydrogeological assessment, with a combined field-laboratory experiment to see the effect of an increase of air temperature on the water quality. A conceptual hydrogeological model of the Pivka Karst Aquifer and its relationship to the Javorniki Karst Aquifer will be built using the 3D software platform Visual KARSYS. This model will be then validated using discretized numerical flow and transport modelling at both local and regional scales. The numerical models aim reproducing the behaviour of the Pivka Karst Aquifer and the Javorniki Karst Aquifer under different hydrogeological situations. After a reasonable calibration will be reached, the models will test different climate scenarios to see how a change of precipitations and air temperature might influence the groundwater reserves. Finally, the models will be combined to a statistical analysis of the data measured in the Pivka temporary lakes to assess their hydrological regime and forecast how climate change might influence them.

Petelinjsko jezero, photo C. Mayaud

Petelinjsko jezero, photo C. Mayaud