Advective Transport Rates Research Articles

Textile Washing Conveys SVOCs from Indoors to Outdoors: Application and Evaluation of a Residential Multimedia Model.

Indoor environments have elevated concentrations of numerous semivolatile organic compounds (SVOCs). Textiles provide a large surface area for accumulating SVOCs, which can be transported to outdoors through washing. A multimedia model was developed to estimate advective transport rates (fluxes) of 14 SVOCs from indoors to outdoors by textile washing, ventilation, and dust removal/disposal. Most predicted concentrations were within 1 order of magnitude of measurements from a study of 26 Canadian homes. Median fluxes to outdoors [μg·(year·home)-1] spanned approximately 4 orders of magnitude across compounds, according to the variability in estimated aggregate emissions to indoor air. These fluxes ranged from 2 (2,4,4'-tribromodiphenyl ether, BDE-28) to 30 200 (diethyl phthalate, DEP) for textile washing, 12 (BDE-28) to 123 200 (DEP) for ventilation, and 0.1 (BDE-28) to 4200 (bis(2-ethylhexyl) phthalate, DEHP) for dust removal. Relative contributions of these pathways to the total flux to outdoors strongly depended on physical-chemical properties. Textile washing contributed 20% tris-(2-chloroisopropyl)phosphate (TCPP) to 62% tris(2-butoxyethyl)phosphate (TBOEP) on average. These results suggest that residential textile washing can be an important transport pathway to outdoors for SVOCs emitted to indoor air, with implications for human and ecological exposure. Interventions should try to balance the complex tradeoff of textile washing by minimizing exposures for both human occupants and aquatic ecosystems.

Geochemical conditions of natural wetland and paddy fields in the Poyang Lake area, China

During the last several decades, wetlands are losing their ecological functions due to increasing anthropogenic loads. One of these functions is the ability to bind elements forming geochemical barriers. The research aimed to study the geochemical conditions of natural wetlands and flooded paddy fields (artificial wetlands) in the Ganjiang River basin to trace geochemical barriers. The research approach was based on a comprehensive analysis of water and aqueous extracts from bottom sediments and paddy soils, including chemical and mineral composition. The samples were collected in November 2019, during the dry season at the end of harvesting. Chemical analysis was performed using standard methods for natural substances: titrimetry, photometry, ionic chromatography, high-temperature oxidation, ICP-MS, and ICP-AES. The mineral composition of the soils and sediments was determined by XRD. It was found that the main physicochemical characteristics (TDS, pH, main component concentrations) of the natural wetland water correspond to the surface water of the study area, whereas the irrigation water is similar to shallow groundwater. The content of trace elements in the irrigation water is higher than in the natural wetland water. Generally, the trace element composition of the natural wetland water corresponds to the geochemical background of the study area. Analysis of the mineral and chemical composition of the paddy soils and sediments indicates the geochemical barriers that accumulate a wide range of elements. In the natural wetland, the geochemical barrier is likely associated with a decrease in oxygen content and advective transport rate in the sediments, whereas in the paddy fields, the precipitation of clay minerals in the soil profile forms the geochemical barrier related to a decrease in filtration properties and advection–diffusion transport.Graphic abstract

Flow uniformity metrics for quantifying the hydraulic and treatment performance of constructed wetlands

The treatment efficiency of constructed wetlands is strongly related to hydraulic conditions. The occurrences of a dead zone and short-circuiting flow decrease flow uniformity and might decrease hydraulic performance. This study aims to investigate the relationship between spatial flow characteristics and wetland treatment performance. A hydrodynamic and contaminant transport model conducted ten sets of simulations with different water depths and five sets of simulations with varying numbers of emergent obstructions. Each experiment had a variant number, dimension, and allocation of obstructions. A metric of flow uniformity was proposed and discussed. We demonstrated how the dead zone and short-circuiting alter flow conditions and affect the hydraulic performance and pollutant treatment efficiency by examining the flow characteristics. The order-of-magnitude of time scales between the advective transport rate and diffusive transport rate was analyzed by calculating the Peclet number. The first-order model was used to calculate the pollutant removal ratio. The results revealed that the values of advection were approximately tens to hundreds of times those of diffusion, indicating that the flow velocity dominated the dispersion behavior. The significant improvement in flow uniformity was found when emergent obstructions were installed. The index value of the dead zone was 2 to 69 times that of the short-circuiting flow, which shows that the dead zone significantly affected the uniformity of the flow. In addition, we discovered that when the coverage ratio of the dead zone was less than 50%, the hydraulic efficiency increased from 0.55 to 1.00. Nevertheless, the short-circuiting flow was found to have minor effects on the hydraulic efficiency. The new methodology for distinguishing dead zones and short-circuiting flow areas is useful for evaluating hydraulic performance directly instead of executing water quality modeling or tracer experiments.

Spatial and temporal distributions of turbulence under bichromatic breaking waves

The present study aims to extend insights of surf zone turbulence dynamics to wave groups. In a large-scale wave flume, bichromatic wave groups were produced with 31.5 s group period, 4.2 s mean wave period, and a 0.58 m maximum wave height near the paddle. This condition resulted in plunging-type wave breaking over a fixed, gravel-bed, barred profile. Optic, acoustic and electromagnetic instruments were used to measure the flow and the spatial and temporal distributions of turbulent kinetic energy (TKE). The measurements showed that turbulence in the shoaling region is primarily bed-generated and decays almost fully within one wave cycle, leading to TKE variations at the short wave frequency. The wave breaking-generated turbulence, in contrast, decays over multiple wave cycles, leading to a gradual increase and decay of TKE during a wave group cycle. In the wave breaking region, TKE dynamics are driven by the production and subsequent downward transport of turbulence under the successive breaking waves in the group. Consequently, the maximum near-bed TKE in the breaking region can lag the highest breaking wave by up to 2.5 wave cycles. The net cross-shore transport of TKE is in the shoaling region primarily driven by short-wave velocities and is shoreward-directed; in the wave breaking region, the TKE transport is seaward-directed by the undertow and the long-wave velocities. Downward transport of TKE is driven by the vertical component of the time-averaged flow. The cross-shore and vertical diffusive transport rates are small relative to the advective transport rates.

The impact of hydrodynamics on viscosity evolution in colloidal dispersions: Transient, nonlinear microrheology

Evolution of microstructure and rheology during flow startup, and its connection to microscopic transport processes, is studied theoretically via active microrheology. At steady state, the balance between entropic, hydrodynamic, and other forces changes with flow strength, producing sustained microstructural asymmetry and non‐Newtonian rheology. However, the transition from equilibrium to steady flow is sometimes marked by overshoots in viscosity that suggests a temporally evolving competition between these rate processes. Here, we formulate and solve a Smoluchowski equation for the time‐dependent evolution of particle microstructure induced by the motion of a colloidal probe driven through a bath of colloidal spheres. The structure is then utilized to compute the time‐dependent microviscosity. Brownian diffusion always sets short‐time particle dynamics, which hinders maturation of the boundary layer. The disparity in Brownian and advective transport rates produces a reversal from flow thinning to flow thickening during startup, revealing that non‐Newtonian flow phenomenology is not instantaneously established. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3198–3214, 2018

Particle diffusion in non-equilibrium bedload transport simulations

This paper examines the importance of particle diffusion relative to advection in bedload transport. Particle diffusion is not included in existing approaches to bedload transport. Based on recent advances in the probabilistic theory of sediment transport, this paper emphasizes the part played by particle diffusion in bedload transport. The proposed model consists of the classic Saint-Venant–Exner equations supplemented by an advection–diffusion equation for particle activity (solid volume of particles in motion per unit streambed area). The model is solved numerically using standard finite-volume techniques. Our numerical simulations consider two case studies: (i) bed degradation under subcritical flow conditions and (ii) anti-dune development in supercritical flows on sloping gravel beds. These simulations show that particle diffusion plays a key role in bedload transport under non-uniform flow conditions. The diffusive sediment transport rate may be as large as the advective transport rate. When anti-dunes develop and migrate upstream, particle diffusion can create fluctuations in the sediment transport rate, whose amplitude compares with the capacity transport rate. Non-uniform flows can be characterized by a typical length, referred to as the adaptation length, which represents the distance that a particle dislodged from the bed travels before it reaches steady-state velocity. We show that the adaptation length is controlled by the particle advection velocity, particle diffusivity, and entrainment/deposition rates, but is independent of the bedform wavelength (contrary to common belief). For simulating bed degradation and anti-dune migration in gravel-bed rivers, a benchmark analysis of different bedload transport models provides evidence that those including particle diffusion perform better than classic models.

Modeling the coupled effects of pore space geometry and velocity on colloid transport and retention

Recent experimental and theoretical work has demonstrated that pore space geometry and hydrodynamics can play an important role in colloid retention under unfavorable attachment conditions. Conceptual models that only consider the average pore water velocity and a single attachment rate coefficient are therefore not always adequate to describe colloid retention processes, which frequently produce nonexponential profiles of retained colloids with distance. In this work, we highlight a dual‐permeability model formulation that can be used to account for enhanced colloid retention in low‐velocity regions of the pore space. The model accounts for different rates of advective and dispersive transport, as well as first‐order colloid retention and release in fast and slow velocity regions of the pore space. The model also includes provisions for the exchange of colloids from fast to slow regions in the aqueous phase and/or on the solid phase. A sensitivity analysis performed with the dual‐permeability model parameters indicated that low rates of advective transport to low‐velocity regions had a pronounced influence on colloid retention profiles, especially near the inlet. The developed model provided a good description of measured colloid breakthrough curves and retention profiles that were collected for a variety of conditions.

A boundary layer analysis for entrance region heat transfer in vertical microchannels within the slip flow regime

A boundary layer integral analysis has been executed to investigate the heat transfer characteristics of natural convection gas flows in symmetrically heated vertical microchannels, under the conditions of large channel aspect ratios, in the slip flow regime. It has been revealed that for low values of Rayleigh number, the entrance region length is only a small fraction of the total channel extent. For higher values of Rayleigh number, however, effects of the developing region are non-trivial, and two counteracting heat transfer mechanisms need to be aptly taken into consideration for interpreting the Nusselt number values. In the present study, the proportionate enhancement in the average Nusselt number with wall-slip effects has been observed to become more prominent for higher values of Knudsen number. However, the relative augmentation in the rate of heat transfer tends to get somewhat arrested for higher values of Rayleigh number, as attributable to the counteracting influences of augmented rates of advective transport and reduced wall-adjacent temperature gradients. For all cases, the boundary layer theory based predictions have been found to agree excellently with the corresponding results obtained from full-scale numerical predictions.

Surface and Pore Water Mixing in Estuarine Sediments: Implications for Nutrient and Si Cycling

Abstract Dissolved constituent fluxes from the sediment to the water column are important in estuarine environments. Benthic nutrient source depends on the mechanisms driving advection, the advective transport rate, and the concentration of nutrients in the discharged water, all of which depend on the source of discharged water and water-solid reactions along its flow. Pore water advection has been measured at rates of 3 to 6 cm/d using seepage meters in the Banana River Lagoon, Florida. Diffusion, advection, and reaction modeling of SiO2 profiles in pore water indicate that advection and reactions are more important than diffusion in the upper 1 m of the sediments. Advection results from the recirculation of the overlying water column through the bottom sediments, oxygenating the lagoon water, while pore water lacks oxygen. As lagoon water recirculates through sediments, the subsequent loss of oxygen enhances regeneration of buried organic matter. Using measured seepage rates and average pore water conce...

Organic matter remineralization and porewater exchange rates in permeable South Atlantic Bight continental shelf sediments

South Atlantic Bight (SAB) continental shelf sediments are characterized by high permeabilities, substantial benthic microalgal photosynthesis, and rapid tidally driven bottom currents. Primary productivity by benthic microalgae rivals water column production for much of the shelf area for most of the year and porewater exchange proceeds at rates of 2–100 (mean 34) times that of molecular diffusion. In this environment, traditional techniques of porewater diffusion calculations and benthic flux chamber incubations do not yield accurate estimates of integrated sedimentary reaction and metabolic rates. Between 1995 and 2001, porewater nutrient distributions have been determined on sediment cores recovered on 24 separate expeditions to the central shelf. Measurements demonstrate that standing stocks of porewater nutrients vary significantly seasonally. Replicate whole core incubations from 1999–2001 conducted over a seasonal cycle reveal that remineralization rates vary seasonally by more than a factor of 18, in response to changes in bottom temperature and possibly organic carbon input. These results suggest that changes in remineralization rate and not changes in porewater advective transport rate are the primary factor accounting for the observed seasonal differences in porewater nutrient inventories. Integrating the observed remineralization rates over the shelf area and throughout an annual cycle implies that approximately 3.8 Tg C, equivalent to 17% of the integrated mid-shelf water column production, is recycled annually in the sediments below the surface benthic microalgal layer of the South Atlantic Bight. Including respiration associated with the sediment surface photosynthetic community implies that the sediments account for approximately half of the total metabolic carbon turnover in this shelf system.

Rapid physical and biological particle mixing on an intertidal sandflat

Sediment mixing processes were investigated using inert tracer experiments, benthic macrofaunal community analysis, and surveys of ray feeding pits to quantify the relative rates and controls of physical and biological reworking on Debidue Flat, an intertidal sande at in South Carolina. Sediment reworking on Debidue Flat was rapid, with both advective and biodiffusive mixing operating over different vertical spatial scales. Physical reworking by tidal currents dominated initial transport of the tracer in the top 5‐ 10 cm on timescales of ;30 days. Although the exact mechanism of tracer transport is unclear, it is most likely due to active e uidization of surface sediments during stages of the tide followed by a density-driven settling of tracer resulting in a steady downward transport to the depth of bedform reworking. Biodiffusive mixing was evident throughout the sampled interval (;30 cm) and dominated reworking at depths greater than 10 cm. Estimated biodiffusive mixing coefe cients ( D b) were high all year (0.15‐ 0.28 cm 2 d 2 1 ), and were comparable to values reported for coastal bioturbated muds. The haustoriid amphipod Pseudohaustorius caroliniensis was most likely responsible for tracer dispersal in the 10‐ 30 cm interval based on its distribution, abundance, size, and observed burrow structures. Ray pit excavation and ine lling were seasonal disturbances that contributed ;12‐ 22% to spatially averaged advective transport rates but were locally intense and capable alone of turning over the entire upper ;15 cm of the e at in ;100‐ 1000 d. We propose that the mixing processes on Debidue Flat promote an unconstricted, open sediment matrix that maintains the high permeability required for the rapid porewater exchange to 25 cm noted for this system. Thus, in addition to redistributing organic substrates, physical and biological particle mixing play important roles in controlling permeability of e at deposits and quantie cation of these processes is important to understand controls on permeability and biogeochemical cycling of solutes in sandy systems.

Influence of diameter on particle transport in a fractured shale saprolite

Experiments in an undisturbed, saturated column of weathered and fractured shale saprolite using fluorescent carboxylate-coated latex microspheres as tracers indicate that particle diameter plays a major role in controlling transport. In this study the optimum microsphere diameter for transport was approximately 0.5 μm. Microspheres larger than the optimum size were present in the effluent at lower relative concentrations, apparently because of greater retention due to gravitational settling and/or physical straining. The smaller than optimum microspheres also experienced greater retention, apparently related to their higher rates of diffusion. Faster diffusion can lead to more frequent collisions with, and attachment to, fracture walls and may also lead to movement of particles into zones of relatively immobile pore water in the fractures or in the fine pore structure of the clay-rich matrix between fractures. Dismantling of the soil column and mapping of the distribution of retained microspheres indicated that there was substantial size-segregation of the microspheres between different fractures or in `channels' within a fracture. Examination of small core samples showed that the smallest microspheres (0.05–0.1 μm) were present in the fine pores of the matrix at distances of up to 3–4 mm from the nearest fracture, which supports the hypothesis that small particles can be retained by diffusion into the matrix. Calculations of settling velocity and diffusion rate using simple 1D approaches suggest that these processes could both cause significant retention of the larger and smaller particles, respectively, even for the fast advective transport rates (up to 32 m/day) observed during the experiments.

Sediment nutrient dynamics on the South Atlantic Bight continental shelf

Continental shelf sediments on the South Atlantic Bight (SAB) consist of relict sands that, at depths ranging from 14–45 m, fall within the photic zone and are sites in which significant rates of benthic primary production are observed. Thus, SAB seafloor sediments are a source of organic matter to the shelf system and are possibly a sink for nutrients regenerated within the sediments. We have investigated the nutrient dynamics in SAB shelf sediments along two transects (off the coasts of Georgia and Florida) as part of a study that addresses the significance of benthic primary production in terms of overall shelf biogeochemistry. Sandy sediments were sampled with a newly designed corer that permits retention of pore water in highly permeable sands and thus avoids commonly encountered “washout” problems. Nutrient (ammonium, silicate, nitrate + nitrite, and phosphate) distributions from sediments along both transects show substantial variation in concentration magnitudes and profile shapes over short horizontal spatial scales (meters). Laboratory experiments and numerical models of diagenetic processes in these sediments suggest that (1) pore‐water advection, driven by current flows over wave ripples and bioturbational features, is likely an important transport process in promoting nutrient exchange in these porous sands (more so than irrigation), and (2) reaction rates in SAB sediments are rapid and are comparable to those in nearshore muddy habitats. In spite of this variation and the apparently high rates of advective transport, time series measurements show a gradual increase in depth‐integrated nutrient concentrations at one station along the Georgia transect from the spring through the fall. This increase is probably related to elevations in temperature and metabolic rates in sediments during the warmer summer months.Measured oxygen and nutrient fluxes across the sediment‐water interface in paired transparent “light” chambers and opaque “dark” chambers did not conform to trends observed in shallow water systems, where oxygen is typically evolved and nutrients are consumed in the light (versus oxygen that is consumed and nutrients that are evolved in the dark). The absence of measurable or consistent fluxes on the SAB shelf is likely the result of low concentrations of nutrients in both the water column and the upper sediment layers. However, rapid regeneration rates in sediments and generally higher nutrient concentrations in deeper sediment layers suggest that sediments are an important source of the nutrients that fuel benthic primary production. Although ammonium is rapidly produced in these oxic sands, nitrate concentrations are uniformly low, and measurable nitrate generally appears in the oxic sedimentary layers. The absence of high nitrate concentrations in the suboxic or anoxic zone suggests that denitrification may not be an important process in SAB shelf sediments.

Injection of Nutrients and TEAs in Clayey Soils Using Electrokinetics

Bioremediation is a cost-effective and attractive technique for cleanup of organic contaminants in high-permeable soils. Difficulties in providing sufficient nutrients and terminal electron acceptors (TEAs) (e.g., nitrate and sulfate) to subsurface contaminant locations preclude its use for in situ biodegradation of organic contaminants in clayey soils. Electrokinetics is shown to be an effective means to inject necessary ionic nutrients and TEAs in clayey soils. Theoretical analysis and experimental results show that electromigration is a significant factor compared with advective transport rate of ions by electroosmosis. Negatively charged nutrients and TEAs could be injected via introducing them at the cathode and vice versa for positively charged ions. Results also indicate that the concentration achievable in the soil depends on the conductivity of the soil and the inlet concentration of the ion to be injected. The higher the soil conductivity and the inlet concentration the higher is the concentration of ionic nutrients and TEAs achievable in the soil. The pH conditions in the soil could be maintained within the range of approximately 6--9 by placing a calcium carbonate layer in the vicinity of the anode.

田辺湾における１９９０年ギムノディニウム赤潮の１層ボックスモデルによるシミュレーション

The temporal change in the algal population growth of Gymnodinium mikimotoi bloom in Tanabe Bay 1990 was simulated using a one-layer box model which consisted of two submodels for algal proliferation and transport. The algal proliferation process was modeled with daily proliferation rates that depended on its own maximal proliferation rates, light intensities and nutrients in the surrounding waters. The transport process was modeled with advective transport rates between inshore and offshore waters. It was assumed that water movements were induced by wind stress and came immediately to a steady state, with the gradient of sea surface level balanced with vertical eddy viscosity. Inshore cell densities were calculated at a daily interval, starting from an initial cell density of the dinoflagellates in the motile form which had overwintered, and varied according to both the daily proliferation rates and the transport rates associated with the offshore cell densities. Calculated cell densities were in general accord with the observed ones.

Numerical modeling of advective transport of saturated deforming sediment beneath the Lake Michigan Lobe, Laurentide Ice Sheet

We investigated the dynamics of advective transport of saturated, fine-grained deforming sediment beneath the Late Wisconsinan Lake Michigan Lobe (LML) of the Laurentide Ice Sheet using a numerical flowline model. Sediment rheology is modeled using a general constitutive law for mass movement of fine-grained material. Geotechnical tests on selected tills deposited by the LML in northern Illinois suggest an effective viscosity of about 5 × 10 9 Pa-s for fully saturated sediment and mild nonlinearity in the stress-strain relation. Numerical calculations of sediment flux, based on conservative parameters and assumptions, yield estimates on the order of 100 m 3/y/meter width of the lobe, suggesting that advective transport could account directly for at least 25% of the total sediment flux estimated on the basis of field evidence. Less restrictive parameters and assumptions would increase sediment flux attributable to both advective transport as well as other ice-velocity-dependent sediment transport processes. Modeling results also suggest that maximum advective transport rates might be associated with viscosities up to an order of magnitude higher than the viscosity exhibited by fully saturated sediment. These results thus suggest that subglacial sediment deformation could account for a substantial portion of total sediment flux in areas with fine-grained glacial till, and that transport rates are strongly sensitive to the subglacial hydrologic processes that control basal water pressure and sediment viscosity.

Influence of laminar flow velocity and nutrient concentration on attachment of marine bacterioplankton

A two‐stage continuous culture system was employed to study the influence of laminar flow velocity and nutrient concentration on the attachment of marine bacterioplankton to Pyrex surfaces. Both instantaneous Sorption and accumulation rates of bacterioplankton were significantly greater at high than low nutrient concentrations over a range of flow velocities, from 0.5 to 8.5 cm‐s‐1. Bacterial accumulation generally increased as a function of laminar flow velocity during 12 h trials. Under low flow — low nutrient regimes, concentrations of epibacteria were very low, probably due to low rates of advective transport to the surface and nutrient depletion within surface boundary layer. Experimental results demonstrate that both laminar flow velocity and nutrient concentration affect not only bacterial attachment but also subsequent growth, metabolic activity, and removal of epibacteria. To explain the observed accumulations of epibacteria, a model based on empirical results is presented to estimate rates of attachment and removal. This model is consistent with the hypothesis that the attachment rate is a function of laminar flow velocity, i.e. delivery of cells to the interface. However, removal rate, described as a shear‐related function under nutrient replete conditions, appears to be controlled by nutrient supply to the interface and the metabolic state of epibacteria under nutrient limiting conditions.

Evidence for Large-Scale Vertical Migration of Dissolved Fatty Acids in Louisiana Oil Field Brines: Iberia Field, South-Central Louisiana: ABSTRACT

ABSTRACT There is considerable interest at the present time in the origin and distribution of dissolved volatile fatty acids (VFAs) in oil-field brines. This interest has developed as a result of the recognition of the role these compounds may play: 1) in subsurface acid attack and porosity enhancement, 2) as precursors of natural gas, and 3) as possible proximity indicators of hydrocarbon accumulations. The detailed study of the distribution of dissolved VFAs on a field scale provides much useful information on processes of generation, transport, and degradation of these compounds. At the Iberia oil field, one of several fields we have studied in the Tertiary section of South-Central Louisiana, spatial variations in pore water compositions and temperatures indicate the presence of an on-going, dynamic, subsurface circulation system. Deep brines with VFA levels in excess of 150 mg/1 are migrating up the south flank of the Iberia salt dome a vertical distance of at least 2 km (6000 ft). The VFAs in these waters are dominated by acetate and propionate. As these waters ascend, they mix with an ambient mass of water having total VFA concentrations of 20 mg/1 or less and dominated by n-butyrate. Preferential decarboxylations of acetate and propionate relative to iso- and n-butyrate and iso- and n-valerate are occurring in this system. The byproducts of these decarboxylation reactions should be methane, ethane, and bicarbonate. Temperatures are cool enough (<80°C) in the shallower parts of the sequence to permit the existence of bacteria that coud break down acetate through fermentation. The spatial distribution of individual dissolved VFA's is complex but systematic, and must ultimately be related to the rates of advective transport, dispersive mixing, and chemical reaction. We believe that a potential new application of the study of these dissolved organic compounds lies in helping to unravel the dynamics of some types of subsurface flow systems.

High fluid pressures during regional metamorphism and deformation: Implications for mass transport and deformation mechanisms

Evidence is presented to support the conclusion that pore fluid pressures tresses PF during regional metamorphism are generally greater than or equal to the minimum principal compressive stress S3. The resultant very low effective stresses σ lead to significantly increased porosity and permeability, even at moderate to high metamorphic temperatures. Permeabilities between 10−18 and 10−15 m2 and are considered to be common, resulting in rapid fluid migration and the dominance of advective (infiltrative) over diffusive mass transport, even over relatively small distances. In view of the importance of intergranular mass transport to rock deformation during metamorphism, a mobile, high‐pressure fluid will have substantial rheological effects, especially in polyphase rocks. The fluid is capable of influencing the rate of dislocation creep in a number of ways. More importantly, advective mass transport along fluid pressure gradients can give rise to a solution transfer deformation mechanism that competes with conventional pressure solution. The rate of deformation by advective mass transport could be controlled by a number of processes, including dissolution kinetics, advective transport rates, and the rate of crack growth. A specific deformation model, based on advective transport rate control,is developed, which can produce strain at competitive rates but with stress and temperature dependences of unusual form.