Groundwater Movement in a Quarry: Change in Landscapes Effect on Recharge, and Evaluation of Pastas Model

Sammanfattning

Clear-cutting of forest for land-use development can significantly alter local geohydrology by reducing evaporation and increasing groundwater recharge. This study investigates groundwater responses to land-cover change at the Almby Quarry outside Uppsala, Sweden, and evaluates open-source Transfer function-noise model, Pastas, as a modelling tool. Field work was conducted including continuous daily groundwater head logging over March-April 2025 and quarterly measurements since 2020. Stable water isotopes from groundwater, surface water and rain were analyzed to categorize groundwater storage and recharge. Potential evaporation under different vegetation-scenarios was calculated using a modified Penman-Monteith approach to be further analyzed with Pastas. Results indicate that clear-cutting reduces the actual evaporation by approximately 60%, leading to an increase of ~40% in effective precipitation, in line with literature values. Groundwater head in both bedrock and till-aquifer showed rapid response to precipitation, suggesting quick infiltration. The Pastas model simulated groundwater fluctuations well (NSE ~0.6) but tended to overestimate lows and peaks, likely due to simplified snow-modelling. Isotopic analysis of groundwater showed low amounts of fractionation, indicating quick infiltration and low evaporation. Isotopic signatures in rainwater showed that the majority of recharge originated from autumn rain and snow melt. The findings provide an understanding of the recharge dynamics of the study area, the transpirations part in total evaporation, and illustrate how time-series modelling combined with field and isotopic data can supplement traditional groundwater surveying, as well as data scarce regions and exploratory studies.