Aerobic respiration in riparian exchange zones of regulated river corridors

Abstract

River stage fluctuations drive surface water‐groundwater exchanges within river corridors. This study evaluates how repeated daily stage fluctuations, representative of hydropeaking conditions, influence aerobic respiration of river‐sourced dissolved organic carbon (DOC) in the riparian exchange zone using reactive flow and transport simulations. Over 50 hypothetical scenarios were modelled to evaluate how the duration of the daily flood signal, river DOC concentration, aquifer hydraulic conductivity and ambient groundwater flow condition affect the fate and transport of DOC and DO in the riparian aquifer. Time series subsurface snapshots highlight how the various factors influence the subsurface distribution of DOC and DO. The total mass of DOC respired per meter of river had a wide range depending on the parameters, spanning from 1.4 to 71 g over 24‐h, with high hydraulic conductivity and losing ambient groundwater flow conditions favouring the largest amount of DOC respired. The ratio of DOC mass entering the riparian zone with the mass returning to the river showed that as little as 5% to as much as 76% of the DOC that enters the bank during stage fluctuations returns to the river. This return ratio is dependent on river DOC concentration, hydraulic conductivity and ambient groundwater flow. The results illustrate that stage variations due to river regulation can be a significant control on aerobic respiration in riparian exchange zones.

Numerical simulation of hyporheic exchange driven by an emergent vegetation patch

“…Previous research on flow‐vegetation interactions concentrated mainly on channel hydrodynamics and sediment transport processes. In particular, we noticed that the presence of vegetation patches increases flow resistance (Caroppi et al, 2021), which increases the pressure gradient of local channels (Västilä et al, 2013), thus forming an uneven pressure distribution at the bed surface and driving hyporheic exchange (Dudunake et al, 2020; Ferencz et al, 2021; Moreto et al, 2022). The mechanism of hyporheic exchange between the bed morphology and the vegetation patch is similar and is derived from an uneven pressure distribution at the bed surface.…”