Enhancement of Hyporheic Flow and Solute Transport by Random Burrow‐ and Mound‐Induced Bioturbation

Bioturbation significantly modifies sediment structure and surface roughness, thereby altering hyporheic exchange and associated biogeochemical processes. However, the role of random burrow galleries and mound arrangements in lotic environments remains unclear, particularly when considering field representative conditions. Here, we present an integrated framework combining laboratory experiments, geostatistical reconstructions, and two‐dimensional fully coupled numerical simulations to investigate the effects of bioturbation‐induced sediment structural heterogeneity. By comparing randomized morphologies to idealized uniform configurations, we assess how variations in burrow geometry and mound topography, that is, sediment accumulations around burrow openings, shape porewater flow, solute transport, and porewater age distributions. Results revealed that irregular burrow galleries promoted deeper and spatially heterogeneous solute penetration by generating tortuous and highly connected flow paths within the sediment. Among these, fully connected and open‐ended burrows were especially effective, producing localized average sediment velocities approximately 4.3–7.9 times greater than those associated with regular vertical burrows. Stochastic variations in mound height further amplified surface‐to‐subsurface pressure gradients, driving localized infiltration and expanding the extent of surface–subsurface water exchange. Neglecting such morphological heterogeneity may underestimate hyporheic exchange flux and overestimate hyporheic residence times. Our findings demonstrate that localized and stochastic bioturbation features act as critical regulators of streambed hydrodynamics, exerting strong control over surface–subsurface water interactions. Building on these insights, future studies should integrate reactive transport and faunal activity to achieve a more holistic understanding of flow–biogeochemistry interactions in bioturbation‐affected sediments.