Driving forces for solute transport in the hyporheic zone of the River Lahn (Germany): numerical simulations

摘要

Hydraulic exchange processes between the surface water and the hyporheic zone play an important role for the hyporheic fauna, since they supply the habitat with nutrients and oxygen. The dynamic hydraulic exchange processes were inspected in situ along a riffle-pool sequence at the River Lahn, Germany Hydraulic heads and tracer concentrations were reproduced with numerical models in order to simulate the solute transport in the hyporheic zone. As transport mechanisms act on different scales, the influence of the groundwater aquifer, the morphological structure of the riffle and the small-scale exchange due to local irregularities were differentiated. The small-scale exchange was described cumulatively by a so-called exchange coefficient, which is based on a diffusion concept Results show that the hyporheic flow is controlled by the riffle morphology and the groundwater table An increased groundwater table due to the enlargement of a pond had a strong impact on the hyporheic habitat. Small-scale exchange is the driving force for the solute exchange of the upper decimeter of the sediment As most biogeochemical processes occur here, the small-scale exchange is important for the metabolism of the hyporheic zone and the surface water.