How Well Bucket Lysimeters Correspond with Whole-catchment Runoff and its Chemistry: A Case Study of Artificial Experimental Catchments at a Post-mining Site

This study evaluated efficiency of bucket lysimeters for measuring water fluxes and ion transport in four hydrologically isolated experimental catchments representing reclaimed (levelled and planted by alder) and unreclaimed (wave like topography, unvegetated) post-mining sites near Sokolov, Czech Republic. Weekly measurements of leachate from lysimeters and surface/subsurface runoff from experimental catchments, in which lysimeters were installed, were collected from 2021 to 2024. Ion concentrations (Ca²⁺, Na⁺, Li⁺, NH₄⁺, K⁺) were quantified using ion-selective electrodes. Upscaled estimates showed higher accuracy at the unreclaimed site (R² = 0.81 for total runoff, R² = 0.88 for evapotranspiration) than at the reclaimed site (R² = 0.72 and R² = 0.77). Lysimeter leachate explained surface runoff variance at unreclaimed (R² = 0.75) and reclaimed (R² = 0.47) sites, but was not predictive for subsurface flow. Among ions, Li⁺ showed the highest predictive capacity (R² = 0.44 - 0.56), while NH₄⁺ showed consistent patterns across sites. K⁺, Na⁺, and Ca²⁺ showed variable transport influenced by soil and vegetation development. Lysimeters captured surface water fluxes and evapotranspiration but did not represent subsurface flow or solute transport well. Better lysimeter performance at the unreclaimed site suggests that vegetation development reduces hydrological predictability during ecosystem recovery.