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Abstract

Understanding the impacts of forest disturbance on hydrology is critical for protecting water supply, reducing environmental risks (i.e., floods, droughts) and managing other water-related functions and services. Previous studies on forest disturbance and hydrology at the watershed scale often treat watersheds as “black boxes” with limited understanding of detailed processes governing watershed-scale hydrological behaviours. This study addresses this knowledge gap by investigating the impacts of forest disturbance on flow pathways, mean transit time (MTT), and young water fraction (Fyw) at the sub-watershed scale in the snow-dominated Peachland Creek Community Watershed (PCW), British Columbia, a key water source for the municipality of Peachland. This study addresses two research questions: (1) What are the impacts of forest disturbance on hydrological processes in PCW? and (2) How do hydrological characteristics vary between sub-watersheds, and what factors contribute to these differences? To evaluate these impacts, stream water samples were analyzed for chemical composition towards informing hydrological processes. Geochemical tracers including ions, organic material as informed by organic colour, and stable water isotopes were used to assess variations in flow pathways, MTT, and Fyw under different levels of forest disturbance (ECA: equivalent clear-cut area: a proxy quantifying forest disturbance with consideration of post-disturbance regeneration). End-member mixing analysis was applied to estimate source water components, and linear mixed effects models were created to estimate relative contributions of forest disturbance towards changes in hydrological processes. The results indicate increased forest disturbance intensity is associated with a higher proportion of model-derived snowmelt, suggesting a shift toward shallower flow pathways as forest disturbance intensifies. However, high elevations were found to be more impactful towards increasing snowmelt contributions than forest disturbance. MTT was found to increase with slope steepness, while Fyw decreases with rapidly draining soils, but there was no association between either variable and forest disturbance. These results highlight the role of forest disturbance in regulating water movement and underscore the importance of considering elevation, drainage, and slope-dependent responses when assessing hydrological changes following forest disturbance. Additional research may continue stream water monitoring and study a broader range of disturbance intensities towards understanding disturbance impacts on hydrological processes.