The Impact of Biofilm-Induced Dynamic Layered Clogging on Hyporheic Exchange in Streambed

The hyporheic zone functions as a critical interface mediating hydrological and biogeochemical exchanges between stream water and streambed. Within shallow streambed layers, sediment transport and biofilm colonization can induce dynamic layered clogging, alter hydraulic conductivity, and foster physical stratification that significantly modulates hyporheic exchange patterns. This study develops a coupled hydrodynamic–mass transport model for a representative streambed bedform to examine the impacts of biofilm-driven dynamic clogging on hyporheic exchange dynamics. Results reveal that dynamic layered clogging reduces pore water velocity and total water flux, causing a 45.1% decline in the total inflow to the hyporheic zone. The transport of non-absorbable solutes exhibits a biphasic pattern: initial rapid penetration transitions to gradual deceleration over time, with dynamic clogging extending the penetration time of the solute center of mass distribution (CMD). Notably, when hydraulic conductivity falls below a threshold (K* < 0.25), CMD penetration time exhibits a positive correlation with hydraulic conductivity, attributed to porosity-induced changes in actual flow velocity. When considering the anaerobic growth in deeper layers, the penetration time become longer because of the clogging present there. This research clarifies the mechanistic connections between biofilm-induced clogging and hyporheic exchange, providing valuable insights for the management of hyporheic ecosystems and the modeling of biogeochemical processes.