• Nanoindentation experiments on a high-angle grain boundary (60 • misorientation) in a pure forsterite bicrystal reveal that the interface acts as a source of dislocations. • Nanoindentation experiments on a high-angle grain boundary (60 • misorientation) in a pure forsterite bicrystal reveal that the interface acts as an obstacle to incoming dislocations, leading to pileups of dislocations. • Nanoindentation experiments on a subgrain boundary (13 • misorientation) in a pure forsterite bicrystal do not detect the impact of the interface on dislocations.

Large-scale convection associated with the Madden-Julian Oscillation (MJO) initiates over the Indian Ocean and propagates eastward across the Maritime Continent (MC). Over the MC, MJO events are generally weakened due to complex interactions between the large-scale MJO and the MC landmass. The MC barrier effect is responsible for the dissipation of 40-50\% of observed MJO events and is often exaggerated in weather and climate models. We examine how MJO propagation over the MC is affected by two aspects of the MC - its land-sea contrast and its terrain. To isolate the effects of mountains and land-sea contrast on MJO propagation, we conduct three high-resolution coupled atmosphere-ocean model experiments: 1) control simulation (CTRL) of the 2011 November-December MJO event, 2) flattened terrain without MC mountains (FLAT), and 3) no-land simulation (WATER) in which the MC islands are replaced with 50 m deep ocean. CTRL captures the general properties of the diurnal cycle of precipitation and MJO propagation across the MC. The WATER simulation produces a more intense and smoother-propagating MJO compared with that of CTRL. In contrast, the FLAT simulation produces much more convection and precipitation over land (without mountains) than CTRL, which results in a stronger barrier effect on MJO propagation. The land-sea contrast induced land-locked convection weakens the MJO’s convective organization. The land-locked convective systems over land in FLAT are more intense, grow larger, and last longer, which is more detrimental to MJO propagation over the MC, than the mountains that are present in CTRL.

A proper understanding of sediment transport dynamics, critically including resuspension and deposition processes of suspended sediments, is key to the morphodynamics of shallow tidal environments. Aiming to account for deposition mechanics in a synthetic theoretical framework introduced to model erosion dynamics (D’Alpaos et al., 2022), here we investigated suspended sediment dynamics. A complete spatial and temporal coverage of suspended sediment concentration (SSC) required to effectively characterize resuspension events is hardly available through observation alone, even combining point measurements and satellite images, but it can be retrieved by properly calibrated and tested numerical models. We analyzed one-year-long time series of SSC computed by a bi-dimensional, finite-element model in six historical configurations of the Venice Lagoon in the last four centuries. Following the peak over threshold theory, we statistically characterized suspended sediment dynamics by analyzing interarrival times, intensities and durations of overthreshold SSC events. Our results confirm that, as for erosion events, SSC can be modeled as a marked Poisson process in the intertidal flats for all the considered historical configurations of the Venice Lagoon because exponentially distributed random variables well describe interarrival times, intensity and duration of overthreshold events. Moreover, interarrival times, intensity and duration describing local erosion and overthreshold SSC events are highly related, although not identical because of the non-local dynamics of suspended sediment transport related to advection and dispersion processes. Owing to this statistical characterization of SSC events, it is possible to generate synthetic, yet realistic, time series of SSC for the long-term modeling of shallow tidal environments.

We present the first investigation of subsidence due to sediment compaction and consolidation in two laboratory-scale river delta experiments. Spatial and temporal trends in subsidence rates in the experimental setting may elucidate behavior which cannot be directly observed at sufficiently long timescales, except for in reduced scale models such as the ones studied. We compare subsidence between a control experiment using steady boundary conditions, and an otherwise identical experiment which has been treated with a proxy for highly compressible marsh deposits. Both experiments have non-negligible compactional subsidence rates across the delta-top, comparable in magnitude to our boundary condition relative sea level rise of 250 μm/h. Subsidence in the control experiment (on average 54 μm/h) is concentrated in the lowest elevation (<10mm above sea level) areas near the coast and is likely due to creep induced by a rising water table near the shoreface. The treatment experiment exhibits larger (on average 126 μm/h) and more spatially variable subsidence rates controlled mostly by compaction of recent marsh deposits within one channel depth (_10 mm) of the sediment surface. These rates compare favorably with _eld and modeling based subsidence measurements both in relative magnitude and location. We find that subsidence “hot spots” may be relatively ephemeral on longer timescales, but average subsidence across the entire delta can be variable even at our shortest measurement window. This suggests that subsidence rates in a given decade or century may exceed thresholds for marsh platform drowning, even if the long term trend does not.

Wave-induced bottom shear stress is one of the leading processes that control sediment erosion dynamics in shallow tidal environments, because it is responsible for sediment resuspension and, jointly with tidal currents, for sediment reworking on tidal flats. Reliable descriptions of erosion events are foundational to effective frameworks relevant to the fate of tidal landscape evolution. However, the absence of long-term, measured time series of bottom shear stress (BSS) prevents a direct analysis of erosion dynamics. Here we adopted a fully-coupled, bi-dimensional numerical model to compute BSS generated by both tidal currents and wind waves in six historical configurations of the Venice Lagoon in the last four centuries. e one-year-long time series of the total BSS were analysed based on the peak over threshold theory to statistically characterize events that exceed a given erosion threshold and investigate the effects of morphological modifications on spatial and temporal erosion patterns. Our analysis suggests that erosion events can be modeled as a marked Poisson process in the intertidal flats for all the considered configurations of the Venice Lagoon, because interarrival times, durations and intensities of the over-threshold exceedances are well described by exponentially distributed random variables. Moreover, while the intensity and duration of over-threshold events are temporally correlated, almost no correlation exists between them and interarrival times. The resulting statistical characterization allows for a straightforward computation of morphological indicators, such as erosion work, and paves the way to a novel synthetic, yet reliable, approach for long-term morphodynamic modeling of tidal environments.

Compositional stratigraphy, consisting of Al-rich kaolinite overlying Fe/Mg-richnontronite, is sporadically distributed within 40{degree sign}S to 30{degree sign}N on Mars. The compositional stratigraphy was considered a typical product of a warm and wet climate, and a window into understanding the atmospheric conditions of early Mars. However, the question remains as to whether the compositional stratigraphy was formed by chemical weathering or sedimentation. Variations in mineralogical/ geochemical properties along the compositional stratigraphy can provide important clues for interpreting the genesis of the compositional stratigraphy. Visible to near infrared (VNIR) reflectance spectroscopy has been used as an effective tool to quantitatively characterize the abundance of kaolinite, nontronite, and weathering intensity in a basaltic weathering succession, as demonstrated by a terrestrial regolith profile. Nevertheless, the VNIR spectra could be influenced by primary minerals and organics in a basalt succession. To test the effectiveness of spectral parameters, the stepwise transformation of nontronite to kaolinite was experimentally modeled and quantitatively investigated using thermogravimetric (TG) and VNIR. The correlation between BD1400 and the content of OH, BD1900 and the H2O content, and BD1400/BD1900 and the OH/H2O ratio were quantitatively constrained to demonstrate their effectiveness as spectral proxies. The obtained data set was also compared with the VNIR spectra from the compositional stratigraphy on Mars, and the continuous variations of the spectral proxies suggest the compositional stratigraphy is formed by a surface chemical weathering process. Accordingly, Mars likely had a warm and wet climate that could maintain liquid water on its surface over a geologic time span.

The possibility to exploit the muon scattering for the elemental discrimination of materials in a given volume is well known. When more than one material is present along the muon path, it is often important to discern the order in which they are stacked. The scattering angle due to the target volume can be split into two interior angles in the tomographic setups based on the muon scattering, and we call this property as the triangular correlation where the sum of these two interior angles is equal to the scattering angle. In this study, we apply this triangular correlation for a multi-block material configuration that consist of concrete, stainless steel, and uranium. By changing the order of this material set, we employ the GEANT4 simulations and we show that the triangular correlation is valid in the multi-block material setups, thereby providing the possibility of supportive information for the coarse prediction of the material order in such configurations.

This research examines the historical record of the 1886 Tarawera eruption and the Pink and White Terraces, into the death of the only English tourist killed in the eruption, Mr. Edwin Bainbridge. While his immediate cause of death is accepted as accidental i.e. being crushed by a falling balcony: the proximate cause i.e. hydrogen sulfide poisoning from Whatapoho fumarole was misdiagnosed at the time, as alcohol intoxication. This proximate cause was concealed at the time in 1886, probably to ease his family distress in the UK and to protect the publican from criticism or liability. A Dying Declaration made fifty-one years later is analysed together with firsthand evidence from Bainbridge’s tourist guide, who also became ill. It is suggested the H2S inhalation later impeded Bainbridge’s ability to dodge the falling balcony, which the person beside him survived. Bainbridge’s teetotal belief was overlooked at the time. This research now corrects the historical record.

Albeit slow and not without its challenges, lead (Pb) emissions and sources in the United States (U.S.) have decreased immensely over the past several decades. Despite the prevalence of childhood Pb poisoning throughout the 20th century, most U.S. children born in the last two decades are significantly better off than their predecessors in regards to Pb exposure. However, this is not equal across demographic groups and challenges remain. Modern atmospheric emissions of Pb in the U.S. are nearly negligible since the banning of leaded gasoline in vehicles and regulatory controls on Pb smelting plants and refineries. This is evident in the rapid decrease of atmospheric Pb concentrations across the U.S over the last four decades. One of the most significant remaining contributors to air Pb is aviation gasoline (avgas), which is minor compared to former Pb emissions. However, continual exposure risks to Pb exist in older homes and urban centers, where leaded paint and/or historically contaminated soils+dusts can still harm children. Thus, while effective in eliminating nearly all primary sources of Pb in the environment, the slow rate of U.S. Pb regulation has led to legacy, secondary sources of Pb in the environment. More proactive planning, communication, and research of commonly used emerging contaminants of concern that can persist in the environment long after their initial use (i.e., PFAS) should be prioritized so that the same mistakes are not made again.

1. This study combines two approaches to explore the utility of Monod growth kinetics to predict competition outcomes between freshwater cyanobacteria and chlorophytes at low iron Fe. Fe threshold concentrations (FeT) below which growth ceases, and growth affinities (slope of Fe concentration vs growth rate near FeT) were estimated for three large-bodied cyanobacteria (two N-fixers and Microcystis) and two chlorophytes in batch cultures. 2. Mean FeT for N-replete cyanobacteria, N-deplete (when N-fixing) cyanobacteria and chlorophytes were 0.076, 0.736 and 0.245 nmol L-1 , respectively. Mean affinities were 0.937, 0.597 and 0.412 L nmol-1 d-1 , respectively. Assuming that the mean affinities are representative of their groups, affinities predict that N-replete cyanobacteria are more efficient at acquiring Fe than chlorophytes and should dominate when Fe is low but greater than their FeT. 3. A second study evaluated the competitive abilities of a pico-cyanobacterium and a third chlorophyte in dual species, serial dilution culture. The pico-cyanobacterium was dominant at 50 nmol L-1 total Fe (which limited both taxa) and 500 nmol L-1 total Fe. At 0.5 nmol L-1 total Fe, a stressful concentration below FeT during most of the incubation, growth rates and cell densities were extremely low but neither had washed out after several months. 4. These results show that Monod kinetics can successfully predict competition outcomes in laboratory settings at low Fe. While important, Monod kinetics are only one mechanism governing competition between cyanobacteria and eukaryotes in natural systems. Observed deviations from Monod predictions can be partially explained with known mechanisms.

We use in situ measurements of suspended mud to assess the flocculation state of the lowermost freshwater reaches of the Mississippi River. The goal of the study was to assess the flocculation state of the mud in the absence of seawater, the spatial distribution of floc sizes within the river, and to look for seasonal differences between summer and winter. The data was also used to examine whether measured floc sizes could explain observed vertical distributions of suspended sediment concentration through a Rouse profile analysis. The surveys were conducted at the same location during summer and winter at similar discharges and suspended sediment concentrations, and in situ measures of the size distribution of the mud over the longitudinal, transverse, and vertical directions within the river were obtained using a specially developed underwater imaging system. These novel observations show that mud in the Mississippi is flocculated with median floc sizes ranging from 50 to 200 microns depending on location and season. On average flocs were found to be 40 microns larger during summer than in winter and to slightly increase in size moving downriver from the Bonnet Carré Spillway to Venice, LA. Floc size statistics varied little over the depth or laterally across the river at a given station. Bulk settling velocities calculated from size measurements matched values obtained from a Rouse profile analysis at stations with sandy beds, but underestimated settling velocities using the same equation parameters for measurements made during winter over muddy beds.

To increase drought preparedness in semi-arid regions many small and medium reservoirs have been built in recent decades. Together these reservoirs form a Dense Reservoir Network (DRN) and its presence generates numerous challenges for water management. Most of the reservoirs that constitute the network are unmonitored and unregistered, posing questions on their cumulative effects on strategic reservoirs and water distribution at watershed scale. Their influence on hydrological drought propagation is thus largely unexplored. The objective of this study is then to assess the DRN effects on droughts both in time and space. This study utilized a mesoscale semi-distributed hydrological model to reproduce the DRN in a large-scale tropical semiarid watershed (19,530 km2), which presents both a network of large strategic reservoirs and a DRN. To investigate the effects in time and space generated by the network’s presence, the differences between multiple network scenarios were analyzed. Results show that the presence of the DRN accelerates the transition from meteorological to hydrological drought phases by 20% on average and slows down the recharge in strategic reservoirs by 25%, leading to a 12% increase of periods in hydrological drought conditions in a highly strategic basin and 26% without strategic reservoirs. In space, the DRN shifts upstream the basin’s water storage capacity by 8%, but when both large and small reservoirs are present the stored volume distribution behavior is not straightforward. The findings confirm the need to consider small reservoirs when addressing drought management policies at regional scale.

The results of a study aimed at assessing the utility of transionospheric 35 MHz scintillation measurements toward cosmic radio sources for estimating the level of spatial coherence in high frequency (HF) skywave systems are presented. This was done using an array of four antennas in southern Maryland called the Deployable Low-band Ionosphere and Transient Experiment (DLITE). Two of the antennas within a ~350-m north/south baseline were used to monitor 35-MHz intensity variations of two bright cosmic sources, Cynus A and Cassiopeia A. The other two antennas, which were within a ~420-m east/west baseline, recorded the 7.85 MHz skywave from the CHU radio station near Ottawa, Ontario. These HF measurements were used to quantify the level of spatial coherence by measuring the amplitudes of the cross correlation of the two antennas’ recorded voltages relative to the received power, which were typically ~0.5-0.9, but occasionally near zero. A method was developed to estimate the expected cross-correlation amplitude based on the 35-MHz scintillations. This method assumes the case of weak scattering, which is generally appropriate for mid-latitudes, and that the irregularity distribution follows that of the background electron density. These calculations typically captured the day-to-day variations in spatial coherence quite well (correlation coefficient r≈0.6) while only marginally reproducing hour-to-hour variations (r≈0.2). Thus, this method holds promise as an economical and passive means to assess the spatial coherence expected for skywave propagation within a given mid-latitude region.

Mantle convection models based on geophysical constraints have provided us with a basic understanding of the forces driving and resisting plate motions on Earth. However, existing studies computing the balance of underlying forces are contradicting, and the impact of plate boundary geometry on surface deformation remains unknown. We address these issues by developing global instantaneous 3-D mantle convection models with a heterogeneous density and viscosity distribution and weak plate boundaries prescribed using different geometries. We find that the plate boundary geometry of the Global Earthquake Model (GEM, Pagani et al., 2018), featuring open plate boundaries with discrete lithospheric-depth weak zones in the oceans and distributed crustal faults within continents, achieves the best fit to the observed GPS data with a directional correlation of 95.1% and a global point-wise velocity residual of 1.87 cm/year. A good fit also requires plate boundaries being 3 to 4 orders of magnitude weaker than the surrounding lithosphere and low asthenospheric viscosities between 5e17 and 5e18 Pa s. Models without asthenospheric and lower mantle heterogeneities retain on average 30% and 70% of the plate speeds, respectively. Our results show that Earth’s plate boundaries are not uniform and better described by more discrete plate boundaries within the oceans and distributed faults within continents. Furthermore, they emphasize the impact of plate boundary geometry on the direction and speed of plate motions and reaffirm the importance of slab pull in the uppermost mantle as a major plate driving force.

El Niño-Southern Oscillation (ENSO) is the most prominent interannual climate variability in the tropics and exhibits diverse features in spatiotemporal patterns. This paper develops a simple multiscale intermediate coupled stochastic model to capture the ENSO diversity and complexity. The model starts with a deterministic and linear coupled interannual atmosphere, ocean, and sea surface temperature (SST) system. It can generate two dominant linear solutions representing the eastern Pacific (EP) and the central Pacific (CP) El Niños, respectively. In addition to adopting a stochastic model for characterizing the intraseasonal wind bursts, another simple stochastic process is developed to describe the decadal variation of the background Walker circulation. The latter links the two dominant modes in a simple nonlinear fashion and advances the modulation of the strength and occurrence frequency of the EP and the CP events. Finally, cubic nonlinear damping is adopted to parameterize the relationship between subsurface temperatures and thermocline depth. The model succeeds in reproducing the spatiotemporal dynamical evolution of different types of ENSO events. It also accurately recovers the strongly non-Gaussian probability density function, the seasonal phase locking, the power spectrum, and the temporal autocorrelation function of the SST anomalies in all the three Niño regions (3, 3.4 and 4) across the equatorial Pacific. Furthermore, both the composites of the SST anomalies for various ENSO events and the strength-location bivariate distribution of equatorial Pacific SST maxima for the El Niño events from the model simulation highly resemble those from the observations.

Detailed pathway of wave energy exchange between the Pacific and Indian Oceans through the Indonesian archipelago and associated energy dissipation are investigated by using a reduced gravity model with realistic coastline. The wave energy flux analysis that can be applicable for all latitudes in a linear shallow water system is adopted. The energy fluxes diagnosed from the model outputs for the incoming Rossby waves from the Pacific clearly indicate two major energy pathways to the Indian Ocean; one turning southward in the Halmahera Sea and reaches the Indian Ocean via the Banda Sea and the Timor Passage, the other passing through the Makassar and Lombok Straits. The former route, however, is shifted to the western side of the island chain within the Banda Sea due to energy trapping around the island chain. It is also found that strong energy dissipation occurs along the northern coast of New Guinea when the period of the incoming Rossby wave is shorter than 1.5 year. In the case of the Kelvin waves from the Indian Ocean, it is found that the major energy pathway is through the Lombok and Makassar Straits to the Pacific Ocean. However, there appears another pathway along the eastern side of the Sulawesi Island in the Banda Sea to exit through the Molucca Sea only when the wave period is shorter than about one month. This secondary pathway makes it easier for the wave energy from the Indian Ocean to reach the western Pacific Ocean for the short period waves.

Much information about the North American lithosphere has been gained by imaging seismic wave velocities. Additional constraints on the state of the subsurface can be gained by studying seismic attenuation, which has different sensitivity to physical properties. We produce a model of lateral variations in attenuation across the conterminous U.S. by analyzing P waveforms from deep earthquakes recorded by the EarthScope Transportable Array using a time-domain waveform matching approach. We divide the study area into 12 overlapping tiles and differential attenuation is measured in each tile independently; with analysis being repeated independently for 4 of the tiles. Measurements are combined into a smooth map using a linear inversion. Comparing results for adjacent tiles and for repeated tiles shows that the imaged features are robust. The final map is produced by combining all the measurements and shows generally higher attenuation west of the Rocky Mountain Front than east of it, with significant small length scale variations superimposed on that broad pattern. In general, there is a strong anticorrelation between differential attenuation and shear wave velocities at 90 km depth. However, a given change in velocity may correspond to large or small change in attenuation, depending on the area; suggesting that different physical mechanisms are operating. In some cases, most notably in the Snake River Plain, attenuation and velocity do not show the expected anticorrelation. The southern Intermountain Seismic Belt coincides with a high gradient in the attenuation signal, but even larger gradients further inland do not show any association with seismicity.

Jet streams are important sources of non-orographic internal gravity waves and clear air turbulence (CAT). We analyze non-orographic gravity waves and CAT during a merging of the polar front jet stream (PFJ) with the subtropical jet stream (STJ) above the southern Atlantic. Thereby, we use a novel combination of airborne observations covering the meso-scale and turbulent scale in combination with high-resolution deterministic short-term forecasts. Coherent phase fronts stretching along a highly sheared tropopause fold are found in the ECMWF IFS (integrated forecast system) forecasts. During the merging event, the PFJ reverses its direction from antiparallel to parallel with respect to the STJ, going along with strong wind shear and horizontal deformation. Temperature perturbations in limb-imaging and lidar observations onboard the research aircraft HALO in the framework of the SouthTRAC campaign show remarkable agreement with the IFS data. Ten hours earlier, the IFS data show a new “X-shaped” phase line pattern emanating from the sheared tropopause fold. The analysis of tendencies in the IFS wind components shows that these gravity waves are excited by a local body force as the PFJ impinges the STJ. In situ observations of temperature and wind components at 100 Hz confirm upward propagation of the probed portion of the gravity waves. They furthermore reveal embedded episodes of light-to-moderate CAT, Kelvin Helmholtz waves, and indications for partial wave reflection. Patches of low gradient Richardson numbers in the IFS data coincide with episodes where CAT was observed, suggesting that this event was well accessible to turbulence forecasting.

The debate over the historical and future evolution of the Atlantic Meridional Overturning Circulation (AMOC) has united scientists around a single topic, but this community has yet to unite around a single definition of the AMOC. In an effort to focus the debate around dynamics rather than semantics, we recommend that the community universally adopt a definition of the AMOC in density coordinates. We present evidence that the traditional depth space definition is insufficient at capturing elements of this circulation, especially at high latitudes where the northward and southward limbs of the AMOC are separated horizontally rather than vertically. Instead, the AMOC in density coordinates more realistically captures the water mass transformation process at high latitudes, shifts the maximum AMOC from the subtropical to the subpolar North Atlantic where the majority of the deep waters are formed, and depicts the peak in meridional heat transport associated with the subtropical gyre.

A current along a sloping bottom gives rise to upwelling, or downwelling Ekman transport within the stratified bottom boundary layer (BBL), also known as the bottom Ekman layer. In 1D models of slope currents, geostrophic vertical shear resulting from horizontal buoyancy gradients within the BBL is predicted to eventually bring the bottom stress to zero, leading to a shutdown, or \lq arrest \rq \, , of the BBL. Using 3D ROMS simulations, we explore how the dynamics of buoyancy adjustment in a current-ridge encounter problem differs from 1D and 2D temporal spin up problems. We show that in a downwelling BBL, the destruction of the ageostrophic BBL shear, and hence the bottom stress, is accomplished primarily by nonlinear straining effects during the initial topographic counter. As the current advects along the ridge slopes, the BBL deepens and evolves toward thermal wind balance. The onset of negative potential vorticity (NPV) modes of instability and their subsequent dissipation partially offsets the reduction of the BBL dissipation during the ridge-current interaction. On the upwelling side, although the bottom stress weakens substantially during the encounter, the BBL experiences a horizontal inflectional point instability and separates from the slopes before sustained along-slope stress reduction can occurred. In all our solutions, both the upwelling and downwelling BBLs are in a partially arrested state when the current separates from the ridge slope, characterized by a reduced, but non-zero bottom stress on the slopes.

Winter warming events (WWEs) are short-lasting events of unusually warm weather, occasionally combined with rainfall, which can cause severe ecosystem impacts by altering ground temperatures and water fluxes. These impacts are generally overlooked in large-scale ecosystem models. The frequency and intensity of WWEs will likely increase further in the future. We used an ecosystem model, LPJ-GUESS, to investigate the responses of four subarctic ecosystems to different levels of predicted WWEs, and identify model gaps hindering accurate estimates of these responses. In response to WWEs, the model simulated substantial ground cooling (up to 2 °C in winter) in contrast to the observed warming, leading to changes in biogeochemical fluxes often comparable in magnitude to those from altered winter climatologies. The mismatch between the modelled and the observed ground temperature changes may be due to the 1) lacking surface energy balance, 2) daily timestep, and 3) simplistic water retention scheme in LPJ-GUESS.

Simulating magma propagation pathways requires both a well-calibrated model for the stress state of the volcano and models for dike advance within such a stress field. With the purpose of establishing a framework for calculating computationally efficient and flexible shallow magma propagation scenarios, we develop three-dimensional models for the stress state of volcanoes with complex topographies and edifice histories as well as a new simplified three-dimensional model of dike propagation using the stress state of the volcano as input. Next, we combine all these models to calculate shallow dike propagation scenarios for complex caldera settings. The resulting synthetic magma pathways and eruptive vent locations broadly reproduce the variability observed in natural calderas.

Salmonids bury their eggs in hyporheic streambed gravel, forming an egg nest, called a redd, characterized by a pit and a hump topography resembling a dune. Embryos’ survival depends on downwelling oxygen-rich stream water fluxes, whose magnitudes are expected to depend on the interactions among redd shape, stream hydraulics, and the hydraulic conductivity of the streambed sediment. Here, we hypothesize that downwelling fluxes increase with stream discharge and redd aspect ratio, and such fluxes can be predicted using a set of dimensionless numbers, which include the stream flow Reynolds and Froude numbers, the redd aspect ratio, and the redd relative submergence. We address our goal by simulating the surface and subsurface flows with numerical hydraulic models linked through the near-bed pressure distribution quantified with a two-phase (air-water) two-dimensional surface water computational fluid dynamics model, validated with flume experiments. We apply the modeling approach to three redd sizes, which span the observed range in the field (from ~1 to ~4 m long), and by increasing discharge from shallow (0.1 m) and slow (0.15 m/s) to deep (8m) and fast (3.3 m/s). Results support our hypothesis of downwelling fluxes increasing with discharge and redd aspect ratio due to the increased near-bed head gradient over the redd. The derived equation may help evaluate the effect of regulated flow (e.g., hydroelectric and flood control dams) on redd-induced hyporheic flows.

In this paper a set of equations governing the electromagnetic/acoustic coupling in partially-saturated porous rocks in the low-frequency regime is derived. The equations are obtained by volume averaging of fundamental electromagnetic and mechanical equations valid at the porescale, following the same procedure as the one developed in the seminal paper of S. Pride for porous media where the fluid electrolyte fully saturates the pore space. In the present approach it is assumed that the porous rock is partially saturated with a wetting-fluid electrolyte