Spatiotemporal variations in water sources and mixing spots in a riparian zone

Abstract. Riparian zones are known to modulate water quality in stream corridors. They can act as buffers for groundwater-borne solutes before they enter the at harmful, high concentrations or facilitate solute turnover and attenuation where (SW) groundwater (GW) mix. This natural capacity is strongly controlled by dynamic exchange of between adjoining aquifer, creating potential mixing-dependent reactions take place. Here, we couple a previously calibrated transient fully integrated 3D surface–subsurface numerical flow model with hydraulic mixing cell (HMC) method map source composition along net losing reach (900 m) fourth-order Selke track its spatiotemporal evolution. allows us define aquifer more balanced fractions different sources per volume (called hot spots), which have and, turn, enhance turnover. We further evaluated HMC results against hydrochemical monitoring data. Our show that, on average, about 50 % alluvial consists infiltrating SW. Within 200 m around stream, almost entirely made up infiltrated SW practically no significant amounts other mixed in. On 9 domain could be characterized spots, were mainly located fringe geochemical hyporheic zone rather than below immediate vicinity streambed. percentage rise values nearly 1.5 times higher following large discharge events. Moreover, event intensity (magnitude peak flow) was found important increase duration. modeling suggest that events significantly greater distances from stream. In contrast near rapid influx shifts ratio SW, reducing associated reactions. With this easy-to-transfer framework, seek applicability complementary approach identification spots corridors, while showing controls SW–GW process implications riparian biogeochemistry processes.