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The influence of bioturbation induced by bottom‐dwelling macrozoobenthos on nitrogen dynamics in lotic stream sediments remains unclear. In this work, we advance the understanding of faunal bioturbation in lotic environments by developing a fully‐coupled flow and multicomponent reactive transport model and investigate the influence of sediment reworking and burrow ventilation processes on nitrogenous transformations. The model results indicate that sediment reworking and burrow ventilation significantly increase nitrate (NO3−) influx, penetration depth, and reaction rates in the streambed. Denitrification rates were observed up to three times higher in beds with U‐shaped burrows compared to flatbeds. The ratio of mound height to stream water depth ratio (h/H0) is a dominant control on determining the relative importance of the sediment reworking and burrow ventilation processes in modulating nitrogenous reactions. A power‐law scaling framework is ultimately proposed to predict NO3− removal efficiency based on the Damköhler number in bioturbated lotic streambeds. Plain Language Summary: The increase in nitrate (NO3−) levels can harm rivers by causing problems like eutrophication, toxic algal blooms, and low oxygen levels. Microbes, like those involved in denitrification, can help reduce NO3− levels in the riverbed, where surface water and groundwater mix. Creatures like macroinvertebrates that live in the riverbed also play a role in how NO3− moves and is used. We wanted to know if these creatures, by disturbing the sediment and irrigating it, change how NO3− behaves in the riverbed. Our computer modeling showed that having U‐shaped burrows in the sediment can enhance the rate at which NO3− is removed, up to three times more than in flatbed sediments. As the ratio of the mound height to the total depth becomes less than 0.1, the influence of sediment reworking on NO3− influx and consumption rates decreases, and burrow ventilation becomes more important. We also came up with a way to predict NO3− removal efficiency in bioturbated riverbeds under flowing water conditions. These findings underscore the significance of bioturbation in rivers with moving water and have important implications for managing and restoring rivers. Key Points: Developing a Navier‐Stokes‐Brinkman‐Darcy‐Reaction fully‐coupled approach to study interplay between nitrogen cycling and faunal bioturbationSediment reworking and burrow ventilation processes could significantly alter the nitrogenous transformations in low flow environmentsA power‐law scaling framework can be used to predict nitrate removal efficiency within the bioturbated sediments from the Damköhler number [ABSTRACT FROM AUTHOR]

Freshwater salinization is a common yet underappreciated environmental problem in rivers, yet how this process impacts the transport of dissolved oxygen (DO) in the hyporheic zone remains unknown. Using flume experiments and numerical simulations, we have demonstrated that the morphological dynamics of the DO transition zone are controlled by the dimensionless number Da·Ra−2, a measure of the rate of aerobic respiration to free convection. At low Da·Ra−2, the oxic front breaks up into fingers which subsequently grow, and leads to accelerating of DO transport and shrinking of the anaerobic zone in the underlying sediment. As Da·Ra−2 increases, the growth rate of the instability decreases, and the DO plume fingers are suppressed and delayed compared with the saltwater‐freshwater interface, the mixing area between saltwater and freshwater. These results indicate that the freshwater salinization syndrome can have significant impacts on the functioning of aquifer ecosystems unless regulated and managed effectively. Plain Language Summary: Increases in salinity, alkalinity, and major ions occur in a wide range of freshwater ecosystems around the world, and the freshwater salinization syndrome is becoming a serious water quality problem and a major chemical signature of the Anthropocene. The goal of this study is to understand how dissolved oxygen (DO), which is beneficial to the survival of benthic invertebrates, is transported in the sediment in response to freshwater salinity fluctuation. Flume experiments and numerical simulations are performed to investigate the development of DO plume in the riverbed. The experimental outcomes, obtained through high‐resolution imagining techniques, show that the convection induced by saltwater density gradients in the hyporheic zone could influence DO plume development. Our numerical model is capable of describing the transport behaviors of DO before and after salinization in the surface water. A dimensionless number Da·Ra−2 is proposed to predict DO transport dynamics in the river with freshwater salinization syndrome. The implications and potential threats of freshwater salinization for the river ecosystem, including the biogeochemical processes and contaminant attenuation in the hyporheic zone, are also discussed. Key Points: Experiments and simulations are performed to investigate the morphology of dissolved oxygen (DO) transition zone in a salinity‐impacted bedformAsynchronous transport of salt and DO is controlled by a dimensionless number Da·Ra−2Whether density‐driven flow can be a DO pump depends on the intensity of aerobic respiration [ABSTRACT FROM AUTHOR]

• Riverbank could degrade 13.7% of the components from non-point pollution. • The riverbank can not degrade components induced by the chemical weathering. • The WQI min model performed better for river water than groundwater. • The physical-based equation was used to directly predict water quality interaction. Intensive agriculture/industrial activities as well as natural processes result in pollution in river water and groundwater. However, how riverbank groundwater responds to the components carried by different pollution sources in the river remains unclear. In this study, the surface water and riparian groundwater quality at the Laonanguan (LNG) and Hongqierzha (HQEZ) stations of the Gusong River, China, were jointly investigated via hydrochemical monitoring and water quality analyses, and the main pollution sources, i.e., anthropogenic activities and mineral weathering, were identified by principal component analysis (PCA). The absolute principal component score-multiple linear regression (APCS-MLR) revealed that anthropogenic inputs only accounted for 11.4 % of the total pollution sources for riparian groundwater, which was much lower than that for river water (24.8 %). The riverbank hence acted as the primary sink for the components (e.g., NH 4 +-N and TP) from non-point pollution and could degrade 13.7 % of the pollutants from the river water caused by anthropogenic input. Conversely, riverbank played a source role for the species (e.g., SO 4 2- and Cl-) from mineral weathering and contributed additional 19.3 % for the groundwater based on river water input. Eventually, the combination of physical-based numerical model (i.e., using an advection–dispersion-filtration transport equation) and data-driven model was proposed to directly simulate and predict groundwater quality in response to the variation of river water quality. The results showed that both models could predict the status of riparian groundwater quality, and the physical-based model could better interpret the results compared to the data-driven black-box model. This study promotes our understanding of the importance of riverbank in improving groundwater quality in the areas with intensive agriculture practices, and riverbank restoration strategies should be carefully designed to maximize their potential to degrade non-point pollutions. [ABSTRACT FROM AUTHOR]