Solute Flux Research Articles

Effect of pH by Manganese Salts and Natural Organic Matter on Nanofiltration Membrane Fouling

This research aimed to determine the removal performance of manganese affected from solution pH of combined manganese salts with natural organic matter (NOM) using commercial nanofiltration (NF) membrane. The filtration experiments were tested under a dead-end filtration test cell. Variational factors used in this study were the types of manganese salts (i.e. manganese chloride (MnCl2), manganese sulfate (MnSO4), and manganese nitrate (Mn(NO3)2)) with the solution pH of 3, 5, and 7, and ionic strength of 0.01 mol/L. Water samples were prepared with NOM concentration of 10 mg/L, while the operating pressure was operated constant at 60 psig. Experimental results found that the MnSO4 salt provided the highest manganese removal efficiency of 95%, while the removal efficiencies of MnCl2 and Mn(NO3)2 were about 84.86% and 70.7%, respectively. Solution fluxes were not significantly different. In the presence of NOM concentration of 10 mg/L, solution pH of 3–7, it was found that low solution pHs for all conditions provided the highest manganese removal. The removals of NOM were relatively high more than 97%. The mathematical fouling model was done with cake filtration model (CFM) due to NOM accumulation on NF membrane surface.

Separation performance enhancement of PEEKWC/PEI cross-linked ultrafiltration membranes by poly(ethylene glycol) and polyvinylpyrrolidone as polymeric additives

In order to improve both pure water flux and retention rate of the cross-linked ultrafiltration membranes based on phenolphthalein-based poly(ether ether ketone) (PEEKWC) and polyethyleneimine (PEI), poly(ethylene glycol) (PEG) and polyvinylpyrrolidone (PVP) were used as polymeric additives in non-solvent-induced phase separation process. The characterizations, separation effectiveness, and anti-fouling performance of membranes were investigated. Compared with n-butanol additive, the PEG and PVP could accelerate the phase separation rate and form thinner and denser skin layer, and then that led to an increase in the fluxes of pure water and better dye retention performance. In addition, the impact of variable additive dosage on the pure water flux and retention for dye solutions was investigated, and the pure water flux of membranes could reach 3270.8 L·m−2·h−1 and 2494.5 L·m−2·h−1 at a PEG or PVP concentration of 0.5 wt%, respectively. These membranes also exhibited excellent retention performance for Coomassie brilliant blue and Congo red greater than 98%. The simultaneous improvement of pure water flux and retention performance also could be related to the more efficient water transmission channel forming which was investigated by atomic force microscope phase images. In anti-fouling performance tests, the membranes demonstrated effective anti-fouling properties with a high flux recovery ratio after external cleaning with water only.

Buoyancy driven convection with a Cattaneo flux model

Abstract We review models for convective motion which have a flux law of Cattaneo type. This includes thermal convection where the heat flux law is a Cattaneo one. We additionally analyse models where the convective motion is due to a density gradient caused by a concentration of solute. The usual Fick’s law in this case is replaced by a Cattaneo one involving the flux of solute and the concentration gradient. Other effects such as rotation, the presence of a magnetic field, Guyer–Krumhansl terms, or Kelvin–Voigt theories are briefly introduced.

Multi-isotopic constraints on the impacts of landslide on weathering and erosion in an active mountain range

In active mountains, landslides are the primary agent of erosion that readily generates materials with high weatherability. Understanding the linkage between landslide activity, erosion, and chemical weathering is critical for assessing how tectonic uplift affects the carbon cycle and Earth's climate. However, quantifying the contribution to chemical weathering and erosion fluxes from landslides remains challenging because of the lack of effective tracers related to landslide activities. Recent studies suggest that a suite of isotopic tracers, including the U, Sr and Be isotopes, have the potential to trace solutes and materials associated with landslide activities. Here we use three isotope ratios (234U/238U, 10Be/9Be, 87Sr/86Sr) to quantify the contribution to solid and solute fluxes from landslides in the tectonic-active eastern Tibetan mountains. We focus on 22 small catchments (drainage area < 50 km2) draining the epicentral region of the 2008 Wenchuan earthquake using samples collected in 2018 and 2019. Landslide seepage water and landslide sediment samples are used to constrain the landslide-weathering end-member. Tree branch and regolith topsoil samples are used to characterize the weathering end-member of regolith. We show that the U-Be-Sr isotopes can trace the solutes and solids sourced from landslide debris and quantify that landslides contribute 33.1 ± 16.2% (1SE) to the riverine solutes and 43.4 ± 20.8% (1SE) to the riverbed silt-sized sediment. These proportions are lower than the landslide-derived proportions in high-order catchments immediately (1 to 4 years) after the Wenchuan earthquake, which may relate to changes in landslide-material inputs across drainage networks and/or weathering processes over time. We also find that across 87 catchments with variable basin areas (from <1 km2 to ∼20,000 km2) draining the broad eastern Tibetan mountains, the 234U/238U activity ratio of river water and silt-sized riverbed sediment shows distinct characteristics for the catchments grouped by mean slope angles (mean slope angles shallower versus steeper than a common threshold angle of 32°). These findings suggest that U isotopes are a promising tracer of landslide-sourced solutes and materials. Overall, our work provides a case study showing that a multi-isotope approach can be used to quantify the impacts of landslides on erosion and weathering, providing new insights into how tectonic activities could affect the carbon cycle.

Non-equilibrium molecular dynamics of steady-state fluid transport through a 2D membrane driven by a concentration gradient.

We use a novel non-equilibrium algorithm to simulate steady-state fluid transport through a two-dimensional (2D) membrane due to a concentration gradient by molecular dynamics (MD) for the first time. We confirm that, as required by the Onsager reciprocal relations in the linear-response regime, the solution flux obtained using this algorithm agrees with the excess solute flux obtained from an established non-equilibrium MD algorithm for pressure-driven flow. In addition, we show that the concentration-gradient-driven solution flux in this regime is quantified far more efficiently by explicitly applying a transmembrane concentration difference using our algorithm than by applying Onsager reciprocity to pressure-driven flow. The simulated fluid fluxes are captured with reasonable quantitative accuracy by our previously derived continuum theory of concentration-gradient-driven fluid transport through a 2D membrane [D. J. Rankin, L. Bocquet, and D. M. Huang, J. Chem. Phys. 151, 044705 (2019)] for a wide range of solution and membrane parameters, even though the simulated pore sizes are only several times the size of the fluid particles. The simulations deviate from the theory for strong solute-membrane interactions relative to thermal energy, for which the theoretical approximations breakdown. Our findings will be beneficial for a molecular-level understanding of fluid transport driven by concentration gradients through membranes made from 2D materials, which have diverse applications in energy harvesting, molecular separations, and biosensing.

Ceramic thin-film composite membranes with tunable subnanometer pores for molecular sieving

Ceramic membranes are a promising alternative to polymeric membranes for selective separations, given their ability to operate under harsh chemical conditions. However, current fabrication technologies fail to construct ceramic membranes suitable for selective molecular separations. Herein, we demonstrate a molecular-level design of ceramic thin-film composite membranes with tunable subnanometer pores for precise molecular sieving. Through burning off the distributed carbonaceous species of varied dimensions within hybrid aluminum oxide films, we created membranes with tunable molecular sieving. Specifically, the membranes created with methanol showed exceptional selectivity toward monovalent and divalent salts. We attribute this observed selectivity to the dehydration of the large divalent ions within the subnanometer pores. As a comparison, smaller monovalent ions can rapidly permeate with an intact hydration shell. Lastly, the flux of neutral solutes through each fabricated aluminum oxide membrane was measured for the demonstration of tunable separation capability. Overall, our work provides the scientific basis for the design of ceramic membranes with subnanometer pores for molecular sieving using atomic layer deposition.

Climate change projected to impact structural hillslope connectivity at the global scale

Structural connectivity describes how landscapes facilitate the transfer of matter and plays a critical role in the flux of water, solutes, and sediment across the Earth’s surface. The strength of a landscape’s connectivity is a function of climatic and tectonic processes, but the importance of these drivers is poorly understood, particularly in the context of climate change. Here, we provide global estimates of structural connectivity at the hillslope level and develop a model to describe connectivity accounting for tectonic and climate processes. We find that connectivity is primarily controlled by tectonics, with climate as a second order control. However, we show climate change is projected to alter global-scale connectivity at the end of the century (2070 to 2100) by up to 4% for increasing greenhouse gas emission scenarios. Notably, the Ganges River, the world’s most populated basin, is projected to experience a large increase in connectivity. Conversely, the Amazon River and the Pacific coast of Patagonia are projected to experience the largest decreases in connectivity. Modeling suggests that, as the climate warms, it could lead to increased erosion in source areas, while decreased rainfall may hinder sediment flow downstream, affecting landscape connectivity with implications for human and environmental health.

Zinc sulfate as a draw solute in forward osmosis and its regeneration by reagent precipitation

Forward osmosis (FO) is an emerging membrane technology that has gained huge interest for water treatment and reclamation, owing to its low energy consumption. Nevertheless, the lack of ideal draw solutions and efficient membranes hinder its large-scale applications. In this study, the potential of zinc sulfate draw solute to recover water from different brackish waters by FO was evaluated in terms of permeate water flux, reverse solute flux, and rate of water recovery. Product water having 9.8 and 360 ppm of total dissolved solids (TDS) was recovered from the diluted draw solution by employing a reagent precipitation (RP) and nanofiltration (NF) process, respectively. The draw solution was regenerated by adding a stoichiometric amount of sulfuric acid to the precipitates obtained in RP. In addition, the specific energy consumption (SEC) and water production cost for the water desalination using an FO-RP process were calculated and compared to the FO-NF and a stand-alone RO process. The SEC and water production cost for the FO-RP process were found to be about 0.5 kWh·m−3 and 0.09 $·m−3, respectively. Finally, it is suggested that zinc sulfate could be an excellent choice as a draw solute for water desalination by FO when coupled with reagent precipitation.

Electro-forward osmosis through a titanium-dioxide-modified membrane to enhance aquaculture wastewater recovery

In this study, thin-film-nanocomposite forward-osmosis membranes (TFC-FOMs) were assembled with the top polyamide layer being modified by using titanium dioxide (TiO2) nanoparticles with camphorsulfonic acid and triethylamine (CT) agents to enhance the separation performance and surface hydrophilicity. The TFC-FOMs were characterized and tested for aquaculture wastewater (AWW) recovery in a bench-scale FO system and a multilayer electro-FO (e-FO) system, respectively. Results show that the CT modified FOM had the highest selectivity, followed by the CT-TiO2 modified FOM. A considerably lower reverse solute flux (RSF) and higher permeate flux were achieved in the separation of the electrolyte from the draw feed or solution under the bipolar membrane (BPM)–BPM modes and anion-exchange-membrane (AEM)–cation-exchange-membrane (CEM). When the CT FOM was used in the e-FO system worked in the AEM–CEM mode under a voltage of 1.5 V, the water production degree reached 711.5 L m−2 in continuous AWW recovery for 6 days, and the energy consumption considerably decreased as the number of membrane sheets was raised from 1 to 4. Overall, the consequences indicated the technical viability of the designed e-FO system for achieving high and stable separation efficiency and low energy consumption in long-duration AWW recovery. Thus, this system shows promise for practical field applications.

Construction of a Two-Dimensional GO/Ti3C2TX Composite Membrane and Investigation of Mg2+/Li+ Separation Performance.

Graphene oxide (GO) two-dimensional (2D) membranes with unique layer structures and tunable layer spacing have special advantages and great potential in the field of water treatment. However, GO membranes face the issues of weak anti-swelling ability as well as poor permeability. We prepared GO/Ti3C2TX 2D composite membranes with 2D/2D structures by intercalating Ti3C2TX nanosheets with slightly smaller sizes into GO membranes. Ti3C2TX intercalation can effectively expand the layer spacing of GO, thereby substantially enhancing the flux of the composite membrane (2.82 to 6.35 L·m-2·h-1). Moreover, the GO/Ti3C2TX composite membrane exhibited a good Mg2+/Li+ separation capability. For the simulated brine, the separation factor of M2 was 3.81, and the salt solution flux was as high as 5.26 L·m-2·h-1. Meanwhile, the incorporation of Ti3C2TX nanosheets significantly improved the stability of GO/Ti3C2TX membranes in different pH environments. This study provides a unique insight into the preparation of highly permeable and ion-selective GO membranes.

Contributions to the development of crystal growth technologies

An overview of selected contributions to the development of crystal growth technology of the Laudise Prize awardee 2023 is presented. First some results on shaped crystal growth are given, such as layers with eutectic periodic structures, casting of high-resistivity CdTe sheets, growth of in situ core doped laser rods by double die EFG, and Czochralski growth of Si crystals with rectangular cross section. Then the correlation between melt structure and quality of II-VI crystals showing high bond ionicity is discussed. The importance of marked melt overheating for growth of high-quality CdTe and (Cd,Zn)Te crystals is derived. Also the in situ stoichiometry control for reducing intrinsic point defects, precipitates and inclusions is demonstrated by the examples of Bridgman and VGF CdTe growth with Cd extra source and vapor pressure controlled Czochralski method of 6 inch GaAs crystals. Next, the reason and general appearance of dislocation cell patterns in all growing thermomechanical stressed crystals and their possible prevention are explained. The contribution of point defect diffusion for dislocation climb at high temperatures to form globular cells is underlined. Finally, melt growth experiments under travelling magnetic field (TMF) generated in coil-shaped heater-magnet modules around the crucibles are discussed. The importance of global numeric modeling for optimization the TMF convection mode in the melt is accentuated. It is shown that the growing interface can be levelled, the solution flux at vertical liquid phase epitaxy can be homogenized, and the IR transmission and minority carrier live time in 640 kg mc-Si ingots for photovoltaics can be markedly enhanced and homogenize by such external field application. The close cooperation between academics, engineers and industry is particularly emphasized.

Chemical modification of reduced graphene oxide membranes: Enhanced desalination performance and structural properties for forward osmosis

Graphene oxide (GO) nanosheets can offer a breakthrough into the development of novel and efficient laminated forward osmosis membranes, with high hydrophilicity and outstanding desalination performance. However, fabrication of desirable GO-based nanocomposite membrane which can overcome the on-going trade-off between forward osmosis (FO) performance and chemical/mechanical stability, remains to be challenging in practical application. In this study, polyethyleneimine (PEI) was used to reduce GO (rGO) and crosslink and surface modify membrane's GO sheets for the performance enhancement. The crosslinked rGO was then deposited on a hydrophilic nylon support layer (modified by polydopamine, pDA, for structural stability) using vacuum filtration method. The resulting PEI:rGO/pDA membrane showed excellent water flux (25.5 LMH), high sodium chloride (NaCl) salt rejection (98.9%), and low reverse solute flux (0.91 gMH) in lab-scale tests. The combination of crosslinking GO with PEI and modifying the support layer with polydopamine (pDA) enhanced the membranes hydrophilicity and structural stability. The incorporation of PEI into GO resulted in compacted nanochannels, improving molecular/ions separation. Moreover, the pDA coating enhanced desalination performance and reduced internal concentration polarisation effects, further improving the membrane durability and integrity through the formation of numerous binding sites for firmly anchoring with the PEI:rGO nanocomposite structure.

An analytical complete model of root pressure generation: Theoretical bases for studying hydraulics of bamboo.

To better understand the dynamics and functional roles of root pressure, we represent a novel and the first complete analytical model for root pressure, which can be applied to complex roots/shoots. The osmotic volume of a single root is equal to that of the vessel lumen in fine roots and adjacent apoplastic spaces. Water uptake occurs via passive osmosis and active solute uptake ( , osmol s-1 ), resulting in the osmolyte concentration Cr (mol·kg-1 of water) at a fixed osmotic volume. Solute loss occurs via two passive processes: radial diffusion of solute Km (Cr - Csoil ) from fine roots to soil, where Km is the diffusional constant and Csoil is the soil-solute concentration, and the mass flow of solute and water into the plant from the fine roots. The proposed model predicts the quadratic function of root pressure (Pr ), , where b and c are the functions of plant hydraulic resistance, soil water potential, solute flux and gravitational potential. The model demonstrates the root pressure-mediated distribution of water through the hydraulic architecture of a 6.8-m-tall bamboo shoot. This model provides a theoretical basis to test the functional roles of root pressure in shaping the hydraulic architecture and refilling potential xylem embolisms.

Ecosystem function modified by an invasive species: Density and distance dependent changes in sediment characteristics, fluxes, and benthic communities

Coastal marine benthic ecosystems are considered hotspots for biodiversity and productivity. However, the introduction of bio-engineering non-indigenous species can alter the delivery of key functions and services provided by these systems. Here, we investigated the influence of Sabella spallanzanii, a large structure-forming invasive polychaete, on a marine soft-sediment system in New Zealand, examining effects on sediment characteristics (organic matter and chlorophyll a content), solute fluxes, and benthic communities near and far from low-, medium-, and high-density clumps of Sabella. Fluxes of dissolved oxygen and inorganic nitrogen near (<10 cm) Sabella clusters were significantly lower to those 1 m away, and fluxes differed between low-, medium-, and high-density clumps. Larger densities of Sabella and clumps with greater overall biomass were associated with increased sediment oxygen consumption, particularly in areas 1 m distant from the Sabella clumps. Similarly, ammonium production (efflux from the sediment) increased with increasing Sabella biomass at the 1 m ‘distal’ sites (from 0 μ to 40 μmol/m2/h), but NOx efflux decreased (from 5 to 0 μmol/m2/h) with distance. The flux results were consistent with findings of higher organic matter content and finer grain size sediment in ‘distal’ plots to Sabella clusters. We also showed how benthic diversity and abundance increased with increasing Sabella clump biomass. Our investigation suggests that the building of biogenic structures and the filter feeding activity by Sabella may alter near-bed flows and concentrations of organic rich biodeposits in surrounding sediments, with ramifications for organic matter distribution and nutrient recycling rates. The continuous expansion and colonisation of Sabella could reshape local benthic communities and increase oxygen consumption rates in affected marine sediments.

Lymphatic Vascular Permeability Determined from Direct Measurements of Solute Flux.

The permeability of the lymphatic vasculature is tightly regulated to prevent the excessive leakage of lymph into the tissues, which has profound consequences for edema, immune responses, and lipid absorption. Dysregulated lymphatic permeability is associated with several diseases, including life-threatening chylothorax and pleural effusion that occur in patients with congenital lymphedema and lymphatic malformations. Due to a growing interest in uncovering new mechanisms regulating lymphatic vascular permeability, we recently pioneered methods to quantify this aspect of lymphatic function. Here, we detail our ex vivo method to determine the permeability of mouse collecting lymphatic vessels from direct measurements of solute flux. This method is modified from a similar ex vivo assay that we described for studying the contractile function of murine collecting lymphatic vessels. Since this method also uses the mouse as a model, it enables powerful genetic tools to be combined with this physiological assay to investigate signaling pathways regulating lymphatic vascular permeability.

Modeling of transport phenomena in a hybrid forward osmosis-directional freeze crystallization process for clean water recovery from hydrometallurgical effluents.

Sustainable water recovery and reuse are critical yet challenging, especially from industrial effluents in cold regions. This work presents a robust numerical model of the transport phenomena in a hybrid two-step forward osmosis (FO)-directional freeze crystallization (DFC) desalination process, whose application in areas with cold climates is advantageous. Deionized (DI) water and a hydrometallurgical effluent were considered as the feed solution in the FO step, while three aqueous solutions of inorganic salts were considered as the draw solutions (DS): NaCl, CaCl2, and MgCl2. The effects of temperature and initial DS concentration were investigated on water flux, reverse solute flux, and specific water flux using computational fluid dynamics (CFD). Based on the simulation results, the highest water flux (18 L/m2/h for DI water and 5 L/m2/h for the hydrometallurgical effluent) and lowest reverse solute flux (consistently below 0.3 mol/m2/h) were obtained when MgCl2 was used as the DS. The effect of solute type in the DS on both water recovery yield and purity was in turn studied in the subsequent DFC step, allowing to visualize the solute distribution during the freezing process.

Exogenous methyl jasmonate promotes wound healing of Chinese yam tubers (Dioscorea opposita) through the deposition of suberin polyaliphatics at the wound sites

Suberin polyaliphatics (SPA) is an important component of suberin, which plays a pivotal role in controlling water loss and solute fluxes during wound healing of fruit and vegetables. The objective of this study was to investigate the effect of exogenous methyl jasmonate (MeJA) on wound-induced SPA deposition in Chinese yam tubers. The results exhibited that MeJA treatment accelerated the deposition of SPA and the wound healing process. The gene expressions of β-ketoacyl-CoA synthases (DoKCS2, DoKCS6), CYP86 subfamily of cytochrome P450 monooxygenases (DoCYP86A1, DoCYP86B1) and Glycerol-3-phosphate acyltransferases (DoGPAT5, DoGPAT7) and their corresponding protein content (i.e. KCS, CYP, GPAT) associated with SPA monomer biosynthesis were notably increased by MeJA application. Meanwhile, MeJA also enhanced gene expressions of ATP-binding cassette transporter subfamily G proteins (DoABCG2, DoABCG6) and GDSL-type esterase/lipases (DoGELP38, DoGELP51, DoGELP96) and increased ABCG content, which might participate in the trafficking and polymerization of SPA monomer. Noteworthily, application of diethyldithiocarbamic acid (DICA), an inhibitor of jasmonic acid (JA) synthesis, showed an opposite effect to MeJA treatment. These results suggest that MeJA could promote SPA deposition by positively regulating relevant gene expression and corresponding protein content, thereby accelerating wound healing of Chinese yam tubers.

Sampling frequency, load estimation and the disproportionate effect of storms on solute mass flux in rivers

Riverine discharge (Q) and dissolved concentrations (C) dictate solute mass export from watersheds. Commonly Q is tracked at a much higher frequency than C for most major solutes, leading to the necessity of load estimation algorithms which are often based on sparse data. The result is that the disproportionate effects of short-duration events (e.g., storms) on solute mass fluxes are poorly known. Here we use novel lab-in-the-field instrumentation to compare high temporal-resolution (∼30 min to 7 h) datasets of major ion chemistry collected over a year of continuous monitoring in three watersheds ranging over four orders of magnitude in drainage area. In these diverse settings, we quantify the errors associated with common load estimation algorithms and reduced sampling frequencies. When sample frequencies are coarsened, the mass flux of solutes which are diluted by storm events (i.e., Ca2+, Mg2+, Na+, Cl− and SO42−) are systematically overestimated, while nutrients which become mobilized by these events (K+ and NO3−) are underestimated. This is most pronounced in the largest river, and strongly tied to the increasing likelihood that storm events are missed as sampling frequencies decrease. Coarsening our high-resolution data to monthly sampling frequency yields an average overestimate of 8 % for Na+ and an average underestimate of 32.5 % for K+ across the three watersheds, illustrating clear implications for estuary and coastal water eutrophication, chemical weathering budgets, and agricultural land management practices. SynopsisA new ‘lab-in-the-field’ technology produces continuous high-frequency records of the full suite of major ions in rivers. These data highlight the disproportionate effect of large storms on catchment solute exports and the error associated with temporally coarse monitoring.

Desalination and extraction of high value bio-products from algal-rich seawater using Rhamnolipid as a bio draw solution in forward osmosis

In this research, Rhamnolipid has been investigated as a novel bio-draw solution (BDS) for the extraction of high value bio-products and desalination of algal-rich seawater using FO membrane. First, Rhamnolipid was characterized using FTIR, surface tension, osmotic pressure and flux generation analyses. Then, the performance of Rhamnolipid was evaluated and compared with NaCl in terms of microalgae dewatering, seawater desalination and fouling behavior. The results revealed that Rhamnolipid has a high osmotic pressure (up to 29 bar) due to its high diversity of molecular species and solubilization feature. During the microalgae dewatering, water flux of 7.7 and 8.6 LMH were recorded by using 0.2 and 70 g/L of Rhamnolipid and NaCl, respectively. Rhamnolipid showed much less reverse solute flux (∼0.01 GMH) in comparison with NaCl (4.8 GMH). Biomass recovery of 66 % and 48 % was achieved using Rhamnolipid and NaCl, respectively after 60 min FO process. The SEM-EDX analysis revealed that Rhamnolipid leads to less irreversible fouling (13.7 %) than NaCl (26 %). A satisfactory desalination of 99 % was obtained using Rhamnolipid at the optimum concentration of 0.2 g/L. Given to the organic nature of Rhamnolipid the final diluted DS can be utilized as a reuse water for agricultural applications.

The low permeability of the Earth’s Precambrian crust

The large volume of deep groundwater in the Precambrian crust has only recently been understood to be relatively hydrogeologically isolated from the rest of the hydrologic cycle. The paucity of permeability measurements in Precambrian crust below 1.3 km is a barrier to modeling fluid flow and solute transport in these low porosity and permeability deep environments. Whether permeability-depth relationships derived from measurements shallower than 1.3 km can be extended to greater depths in unclear. Similarly, application of a widely-used permeability-depth relationship from prograde metamorphic and geothermal systems to deep Precambrian rocks may not be appropriate. Here, we constrain permeabilities for Precambrian crust to depths of 3.3 km based on fluid residence times estimated from noble gas analyses. Our analysis shows no statistically significant relationship between permeability and depth where only samples below 1 km are considered, challenging previous assumptions of exponential decay. Additionally, we show that estimated permeabilities at depths >1 km are at least an order of magnitude lower than some previous estimates and possibly much lower. As a consequence, water and solute fluxes at these depths will be extremely limited, imposing important controls on elemental cycling, distribution of subsurface microbial life and connections with the near-surface water cycle.