A multirate mass transfer model to represent the interaction of multicomponent biogeochemical processes between surface water and hyporheic zones (SWAT-MRMT-R 1.0)

Abstract

Abstract. Surface water quality along river corridors can be modulated by hyporheic zones (HZs) that are ubiquitous and biogeochemically active. Watershed management practices often ignore the potentially important role of HZs as a natural reactor. To investigate the effect of hydrological exchange and biogeochemical processes on the fate of nutrients in surface water and HZs, a novel model, SWAT-MRMT-R, was developed coupling the Soil and Water Assessment Tool (SWAT) watershed model and the reaction module from a flow and reactive transport code (PFLOTRAN). SWAT-MRMT-R simulates concurrent nonlinear multicomponent biogeochemical reactions in both the channel water and its surrounding HZs, connecting the channel water and HZs through hyporheic exchanges using multirate mass transfer (MRMT) representation. Within the model, HZs are conceptualized as transient storage zones with distinguished exchange rates and residence times. The biogeochemical processes within HZs are different from those in the channel water. Hyporheic exchanges are modeled as multiple first-order mass transfers between the channel water and HZs. As a numerical example, SWAT-MRMT-R is applied to the Hanford Reach of the Columbia River, a large river in the United States, focusing on nitrate dynamics in the channel water. Major nitrate contaminants entering the Hanford Reach include those from the legacy waste, irrigation return flows (irrigation water that is not consumed by crops and runs off as point sources to the stream), and groundwater seepage resulting from irrigated agriculture. A two-step reaction sequence for denitrification and an aerobic respiration reaction is assumed to represent the biogeochemical transformations taking place within the HZs. The spatially variable hyporheic exchange rates and residence times in this example are estimated with the basin-scale Networks with EXchange and Subsurface Storage (NEXSS) model. Our simulation results show that (1), given a residence time distribution, how the exchange fluxes to HZs are approximated when using MRMT can significantly change the amount of nitrate consumption in HZs through denitrification and (2) source locations of nitrate have a different impact on surface water quality due to the spatially variable hyporheic exchanges.

Spatial Microbial Respiration Variations in the Hyporheic Zones Within the Columbia River Basin

“…The NEXSS model couples NHDPLUS‐based geomorphologic model with physics‐based surrogate models for hyporheic exchange to compute the exchange flux, residence time distribution, and median residence time via a bedform‐driven (or vertical) and sinuosity‐driven (or lateral) exchange (Gomez‐Velez et al., 2015; Gomez‐Velez & Harvey, 2014). Details of the NEXSS model can be found in the papers of (Fang et al., 2020; Gomez‐Velez & Harvey, 2014).…”

Groundwater–Stream Connectivity Mediates Metal(loid) Geochemistry in the Hyporheic Zone of Streams Impacted by Historic Mining and Acid Rock Drainage

“…The transient storage model OTIS, in combination with geochemical data from the hyporheic zone well clusters, highlighted distinct differences in metal fate and transport at Mineral and Cement Creeks, yet the parameters estimated in OTIS do not necessarily capture the full complexity of physical and chemical processes occurring in the hyporheic zone, particularly for highly advective streams such as Mineral Creek. Future work could implement multi-rate mass transfer models (e.g., Fang et al, 2020), physical and advective models that consider channel morphology (e.g., Cardenas and Wilson, 2007;Marzadri et al, 2012Marzadri et al, , 2013Boano et al, 2014), or coupled reactive transport-hyporheic models (Zarnetske et al, 2012;Trauth et al, 2014) to understand finer-scale processes affecting the metal dynamics in poorly connected and well-connected stream-groundwater systems.…”

On the Reliability of Parameter Inferences in a Multiscale Model for Transport in Stream Corridors

“…Another approach capable of full multicomponent nonlinear geochemistry is the multirate Transient Storage Models (mTSMs) by Fang et al. (2020). mTSM uses multiple transient storage zones with individual coefficients for first‐order mass exchange with the stream channel.…”