Abstract. Exchange of water in the parafluvial zone, located along the boundaries of meandering streams, arises in response to seasonal variation and spatial distribution. Remarkably, few studies have applied multi-tracer 10 methods for qualitative scrutiny of losing (recharge) or gaining (discharge) reaches along the parafluvial zone.Hence, the main objective of this study is to qualitatively characterize the spatio-temporal alteration in parafluvial exchange within the hyporheic zone (PEHZ) by simultaneous application of multi-tracer methods. cm) are affected by large-scale regional flow-field which is embedded within. The synthesized approaches used in this study provide a useful insight into the spatiotemporal changes of stream-aquifer connectivity which make 5 the more efficient monitoring and interpretation of hydrological processes possible. They can be, furthermore, utilized to pinpoint the losing/gaining reaches accurately to tackle environmental problems such as monitoring the transport of anthropogenic contaminants in a system.

Abstract. Riffle-pool sequences in the thalweg paths of meandering streams are of pivotal importance to the hyporheic exchange pattern in a fluvial network, but the complex hydrodynamic, morphological, and sedimentary features of riverbed sediments increase the difficulties associated with vertical hyporheic exchange (VHE) quantification. This study applied depth-dependent radon (222Rn) and diel temperature variations to quantify VHE and residence time (tr). The study was conducted in four different hyporheic areas with riffle-pool sequences in the third-order Ghezel-Ozan River, located in north-west Iran. The mean values of temperature-derived VHE (VHET) and radon-derived VHE (VHERn) were 0.67±0.32 m/day and 0.63±0.36 m/day, respectively. Due to effects of sediment bed heterogeneity on temperature variation and 222Rn activity at downwelling and upwelling points, there were discrepancies between radon-derived (trRn) and temperature-derived residence time (trT), with mean values of 2.11±1.17 days and 1.87±1.26 days, respectively. The value of trT was well within uncertainty boundaries at a 95 percent confidence interval (p<0.05) and was lower than trRn at the downwelling points. The analysis of vertical diel temperature, radon and electrical conductivity variations revealed subsurface water exchange to be greatly affected by larger scale regional flow. The comparison between VHET and VHERn with VHE obtained from PHAST model simulation (VHEPHAST) revealed a higher correlation between VHET and VHEPHAST (R2=0.96) than with VHERn (R2=0.76). Furthermore, vertical hydraulic conductivity (Kv) of the sediment-bed materials, calculated in situ by the permeameter test, indicated not only that Kv was up to 21 % higher in areas dominated by upward movement than at downwelling points, but also principle component analysis (PCA) demonstrated the dependence of Kv on porosity, VHE, and %sand of the stream-bed materials. This study provides evidence that vertical flux in the hyporheic zone is mainly affected by stream sinuosity and regional subsurface flow, and that the temperature method is more suitable than radon activity to quantify hyporheic exchange patterns.

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