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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]

As floodplains are inundated during floods in a compound channel, solutes in the surface water column reach the hyporheic zone and react with solutes upwelled from the groundwater. These biogeochemical reactive processes, such as aerobic respiration, nitrification, and denitrification, need more clarification. In this study, a 3D hydrodynamic model combined with a 2D groundwater and biogeochemical model was used to examine the influence of bank slope angle and ambient groundwater discharge on these processes. A denitrification zone was found under the interface between the main channel and the floodplain when the bank slope angle was 90°, while lower angles extended that zone horizontally. In addition, a lower bank angle decreased N entry into the streambed and enhanced nitrogen removal. A decrease in ambient groundwater had a negative impact on both aerobic respiration and denitrification. When the ambient groundwater discharge reached below −0.9 m/d, nitrification was dominant in the model domain, and the hyporheic zone turned into a NO3− source. The greatest removal efficiency, equal to 0.8, was attained at a discharge rate of −0.5 m/d for ambient groundwater and a bank slope angle of 30°. The hyporheic zone should lose its ability to remove N when ambient groundwater discharges exceed 0.25 m/d and removal efficiency fluctuates by 0. In conclusion, our findings indicate that bank slope angle and ambient groundwater discharge have a substantial impact on solute transport and biogeochemical activities in the hyporheic zone of a compound channel. [ABSTRACT FROM AUTHOR]

High-enthalpy and high-density inductively coupled plasmas (ICPs) have the capability to generate continuous, high-temperature, and high-enthalpy plasma gas flows. They find extensive applications in various fields including material processing and aerospace engineering. This work aims to provide a theoretical basis for the better utilization and improvement of high-power ICP plasma generation devices developed by the Xidian University. The discharge characteristics of argon gas, heat exchange properties, and flow field characteristics are investigated through modeling. According to the simulations (50–250 kW coil power input), the increase in ignition input power and the gas intake leads to an increase in the internal temperature of the generator, gas outlet velocity, and electron number density. A noticeable high-pressure region gradually forms in the middle of the pipeline during the ignition, which gradually controls the internal flow field. Surrounding this high-pressure region, thermal exchange recirculation vortices are formed inside the plasma tube, which damages the flow field quality at the generator outlet. We propose to use shrink nozzles to improve the outlet flow quality. The simulation of ICP generator can guide facility utilization and further development. [ABSTRACT FROM AUTHOR]

Hyporheic zone plays a key role in the release of greenhouse gas nitrous oxide (N2O) to the stream water, and the variable‐density flow induced by salinity from stream water can increase the hyporheic exchange flux. However, the nitrogen dynamics in a salinity‐impacted hyporheic zone under different saltwater concentrations still remain unclear. In this study, a numerical model coupling the hyporheic flow, salt transport and nitrogen transformations is proposed to investigate how density gradients affect the N2O production and consumption processes in the streambed. The results show that density gradients between infiltrating saltwater and ambient groundwater create gravitational instabilities that significantly accelerate the downward flow of pore water. Such density gradients enhance the species (e.g., dissolved organic carbon and NO3−) mixing efficiency and increase the reaction area, leading to the formation of N2O fingers and promoting the N2O production‐consumption rate. The variable‐density flow also drags more reactants infiltrating deeper area with longer residence times and increase the frequency of the Damköhler number Da > 1 in the streambed, facilitating the conversion of NO3− to the final product N2 through stepwise denitrification processes. Therefore, the NO3− removal efficiency and N2O yield are increased by 24% and reduced by 3% at low‐density gradients (Δρ/ρf = 7 × 10−4), respectively. The possible implications and applications about the effects of hydrodynamic changes due to the density effect are also presented. However, further biogeochemical experiments and river restoration strategies are needed to validate the results of this study. Plain Language Summary: The salinization of river water ecosystems as a result of salt pollution such as road deicers, irrigation runoff, sewage and potash is becoming a worldwide problem. Rivers with excess nitrogen resulting from agricultural practices also have become an active source of N2O emissions. We hypothesized that the bedform, as stream water with different salinization flows through them, can affect the N2O production and consumption processes in the streambed. We tested this idea by using computational simulations of density‐dependent hyporheic flow through bedform and then linked these with simulations of N2O production and consumption processes. We found that the density differences between saltwater and pore water in the streambed can modify the dissolved organic carbon, oxygen (O2) and nitrate (NO3−) supply rate from stream water. How much N2O produces, consumes and releases in the hyporheic zone, how does river salinity affect these changes, and how much can be changed are all determined by the different salinity input. In response to these findings, we also give some strategies for river nitrogen removal and emission reduction. Key Points: A density‐dependent model was proposed to describe nitrous oxide (N2O) production and consumption processes in a salinity‐impacted hyporheic zoneThe variable‐density flow leads to unstable N2O plume development in streambed and strengthen the role of the HZ as a NO3− and N2O sinkThe mass percentage of N2O released from the bed to the stream water is decreased by 25% as the density effect is increased to 1.4 × 10−3 [ABSTRACT FROM AUTHOR]