Sinuosity‐Driven Hyporheic Exchange: Hydrodynamics and Biogeochemical Potentials

• Published in: Water resources research 2024-04, Vol.60 (4), p.n/a
• Main Authors: Gonzalez‐Duque, Daniel, Gomez‐Velez, Jesus D., Zarnetske, Jay P., Chen, Xingyuan, Scheibe, Timothy D.
• Format: Article
• Language: English
• Subjects: Alluvial aquifers; Alluvial channels; Alluvial deposits; Alluvium; Aquatic ecosystems; Aquifers; Biogeochemistry; Compression zone; Constraints; denitrification; Ecosystem services; Environmental impact; Environmental restoration; ENVIRONMENTAL SCIENCES; Evaluation; Exchanging; Fluid mechanics; Groundwater; Groundwater flow; groundwater‐surface water interactions; Hydrodynamics; Hydrologic processes; hyporheic exchange; Hyporheic zone; Hyporheic zones; Mathematical models; Meandering; meanders; Modulators; Nitrogen; Nitrogen cycle; Numerical models; Parameter identification; Parameters; Planforms; Pressure gradients; Remote sensing; Representations; Restoration; Restoration strategies; River meanders; River networks; River restoration; Rivers; Shielding; Solutes; Topology; Water flow; Water quality; Water quality models
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2023WR036023

Hydrologic exchange processes are critical for ecosystem services along river corridors. Meandering contributes to this exchange by driving channel water, solutes, and energy through the surrounding alluvium, a process called sinuosity‐driven hyporheic exchange. This exchange is embedded within and modulated by the regional groundwater flow (RGF), which compresses the hyporheic zone and potentially diminishes its overall impact. Quantifying the role of sinuosity‐driven hyporheic exchange at the reach‐to‐watershed scale requires a mechanistic understanding of the interplay between drivers (meander planform) and modulators (RGF) and its implications for biogeochemical transformations. Here, we use a 2D, vertically integrated numerical model for flow, transport, and reaction to analyze sinuosity‐driven hyporheic exchange systematically. Using this model, we propose a dimensionless framework to explore the role of meander planform and RGF in hydrodynamics and how they constrain nitrogen cycling. Our results highlight the importance of meander topology for water flow and age. We demonstrate how the meander neck induces a shielding effect that protects the hyporheic zone against RGF, imposing a physical constraint on biogeochemical transformations. Furthermore, we explore the conditions when a meander acts as a net nitrogen source or sink. This transition in the net biogeochemical potential is described by a handful of dimensionless physical and biogeochemical parameters that can be measured or constrained from literature and remote sensing. This work provides a new physically based model that quantifies sinuosity‐driven hyporheic exchange and biogeochemical reactions, a critical step toward their representation in water quality models and the design and assessment of river restoration strategies. Plain Language Summary Meandering causes pressure gradients that induce water flow from the channel to the alluvial aquifer and back to the channel. This circulation process is known as sinuosity‐driven hyporheic exchange, and it has traditionally been associated with ubiquitous and favorable impacts on ecosystem services. However, its presence and biogeochemical implications can vary across river networks and even result in detrimental conditions. Here, we conducted a systematic modeling study to understand the hydrodynamics of sinuosity‐driven hyporheic exchange and its implications for nitrogen transformations. Our results show that the compressing effect of RGF can