Vertical Heterogeneity Research Articles

Vertical heterogeneity of Gulong shale oil governed by the OM precursors and oil accumulation: Implications for shale oil exploration in the Songliao Basin, Northeastern China

Shale oil has been discovered and produced in the Cretaceous Qingshankou Formation (K2qn) of the Gulong sag in the Songliao Basin (the Gulong shale oil). However, the selection of favorable layers for shale oil development remains uncertain due to significant variations in oil production of different intervals in the Formation (Q1–Q9). In this study, the geochemical features of shale, the content and chemical features of extracted oils in different shale intervals are analyzed in detail, and the favorable intervals and mechanism for shale oil accumulation are also addressed. It is shown that the Gulong shale has total oil contents of 200–400 mg/g TOC with considerable contents of light hydrocarbons in extracted oils. In the shale, there is a “W” trend for the evolution of chemical and carbon isotopic compositions (δ13C) of shale oil with depth. It is deduced that this evolution trend of shale oil is governed by the variation of organic matter precursor associated with the deposition environment. The distributions of δ13C of mud gas and individual n-alkanes with depth reveal that the Gulong shale oil can be separated as two independent petroleum systems at the Middle–Lower Q7. Mass balance calculations imply Q2–Q3 and Q8–Q9 are two intervals with lower oil expulsion efficiency. Combined with the morphology of calcite cements and veins as well as the homogenization temperature of inclusions, an intralayer accumulation model of the Gulong shale oil was established. In addition, the statistical analysis of the oil content, lithological properties, and oil production capacity of different layers from 95 wells, demonstrates that Q2–Q3 and Q8–Q9 can be selected as the preferential target layers for future development of the Gulong shale oil. More importantly, this study may provide new insights into the enrichment of shale oil with tight shale type in China and around the world.

Micro and Macro Flooding Mechanism and Law of a Gel Particle System in Strong Heterogeneous Reservoirs.

To address the issue of ineffective injection resulting from the consistent channeling of injected water through highly permeable channels in ultra-deep, high-temperature, high-salinity, and strongly heterogeneous reservoirs during the production process, a gel particle profile control agent suitable for high-temperature and high-salinity conditions was chosen. With the help of the glass etching visual microscopic model and the heterogeneous long core model, the formation mechanism of a water flooding channeling path and the distribution law of the remaining oil were explored, the microscopic profile control mechanism of the different parameters was clarified, and the profile control effect of macroscopic core displacement was analyzed. The research shows that the formation mechanism of a water flooding channeling path is dominated by the distribution law of the permeability section and the connection mode between different penetration zones. The remaining oil types after water flooding are mainly contiguous block, parallel throats, and multi-branch clusters. The profile control effect of gel particles on reservoir vertical heterogeneity is better than that of reservoir lateral heterogeneity. It was found that 10 wt% submicron particles with a median diameter of 600 nm play a good role in profiling and plugging pores of 5-20 μm. In addition, 10 wt% micron-sized particles with a median diameter of 2.63 μm mainly play a strong plugging role in the pores of 20-30 μm, and 5 wt% micron-sized particles with a median diameter of 2.63 μm mainly form a weak plugging effect on the pores of 10-20 μm. The overall profile control effect of 10 wt% submicro particles is the best, and changes in concentration parameters have a more significant effect on the profile control effect. In the macroscopic core profile control, enhanced oil recovery (EOR) can reach 16%, and the gel particles show plugging, deformation migration, and re-plugging. The research results provide theoretical guidance for tapping the potential of the remaining oil in strong heterogeneous reservoirs. To date, the gel particles have been applied in the Tahe oilfield and have produced an obvious profile control effect; the oil production has risen to the highest value of 26.4 t/d, and the comprehensive water content has fallen to the lowest percentage of 32.1%.

Channel cross-section heterogeneity of particulate organic carbon transport in the Huanghe

Abstract. The Huanghe (Yellow River), one of the largest turbid river systems in the world, has long been recognized as a major contributor of suspended particulate matter (SPM) to the ocean. However, over the last few decades, the SPM export flux of the Huanghe has decreased over 90 % due to the high management, impacting the global export of particulate organic carbon (POC). To better constrain sources and modes of transport of POC beyond the previously investigated transportation of POC near the channel surface, SPM samples were for the first time collected over a whole channel cross-section in the lower Huanghe. Riverine SPM samples were analyzed for particle size and major element contents, as well as for POC content and dual carbon isotopes (13C and 14C). Clear vertical and lateral heterogeneities of the physical and chemical properties of SPM are observed within the river cross-section. For instance, finer SPM carry more POC in general with higher 14C activity near the surface of the right bank. Notably, we discuss how bank erosion in the alluvial plain is likely to generate lateral heterogeneity in POC composition. The Huanghe POC is millennial-aged (4020 ± 500 radiocarbon years) and dominated by organic carbon (OC) from the biosphere, while the lithospheric fraction is ca. 12 %. The mobilization of aged and refractory OC, including radiocarbon-dead biospheric OC, from deeper soil horizons of the loess–paleosol sequence through erosion in the Chinese Loess Plateau is an important mechanism contributing to fluvial POC in the Huanghe drainage basin. Altogether, anthropogenic activities can drastically change the compositions and transport dynamics of fluvial POC, consequentially altering the feedback of the source-to-sink trajectory of a river system to regional and global carbon cycles.

Effects of soil heterogeneity and preferential flow on the water flow and isotope transport in an experimental hillslope

Soil water movement plays vital roles in hillslope runoff generation and groundwater and surface water interaction. However, there are still knowledge gaps about the impacts of soil heterogeneity and preferential flow on the internal water flow and transport process. In this study, the vertical soil heterogeneity focused on the variations in soil retention capacity, and the consideration of lateral preferential flow emphasized the higher hydraulic conductivity. We combined isotopic tracing and numerical modeling in an artificial hillslope, focusing on monitored processes of the artificial rainfall and isotopic tracing experiment. The results showed that the soil moisture quickly accumulated at the bottom of the hillslope during rainfall events, while the 2H enrichment occurred in the topsoil derived from enriched isotope injection in the second artificial rainfall. The evaporation process slowed down the mixing of new water in the topsoil and old water in the lower layer. We found that the vertical soil heterogeneity had significant influences on the internal water and isotope transport paths within the hillslope. The lateral preferential flow played an important role in the water flux and transport time to the seepage face. The coupling of isotopic tracing, which reflects the water transport and mixing with the hillslope, effectively improved the model simulation and mechanism analysis of hillslope water flow. Our findings provide new insights into the mechanisms governing soil water flow and transport dynamics in hillslopes, taking into account vertical soil heterogeneity and lateral preferential flow.

Revegetation impacts on runoff generation processes in a typical loess catchment

AbstractSince 1999, large‐scale ecosystem restoration has been implemented in the Loess Plateau, effectively increasing regional vegetation coverage. Vegetation restoration has significantly elevated the saturated hydraulic conductivity (Ks) of the near‐surface soil layers and increased the vertical heterogeneity of the Ks profile. Many studies have examined the change of runoff due to revegetation, yet the impacts of Ks profile on the soil moisture distribution and runoff generation processes were less explored. In this study, numerical simulations were conducted to investigate how changes in the Ks profile caused by vegetation restoration influenced the hydrological responses at event scale. The numerical simulation results show that the increase of surface Ks caused by vegetation restoration can effectively reduce runoff at event scale. Moreover, the enhancement of vertical heterogeneity of Ks profiles can significantly change the vertical profile of soil water content, prompting more water to percolate into the deep soil layer. When rainfall exceeds a threshold, the accumulation of soil water above the relatively less permeable layer can cause short‐term saturation in shallow soil layers, resulting in a transient perched water table. As a result, after the vegetation restoration in the Loess Plateau, though Horton overland flow is still the main runoff generation mechanism, there is a possibility of the emergence of Dunne overland flow under the high vegetation coverage (e.g., NDVI larger than 0.5). This emergence of new runoff generation mechanism, saturation excess runoff, in the Loess Plateau due to the vegetation restoration could provide scientific guidance for water and sediment movement, soil and water conservation practices, and desertification control in the Loess Plateau.

Spatial Distribution of Heterogeneity of the AB Reservoir Unit of Zubair Formation in the South Rumaila Oilfield, Southern Iraq

Reservoir heterogeneity, a critical factor in fluid flow and recovery processes, manifests at various scales and is influenced by depositional facies, diagenesis, and structural features. This study aims to quantify and map the spatial heterogeneity within Unit AB of Zubair Formation, south Rumaila oilfield, utilizing the Lorenz coefficient (Lk ) for vertical heterogeneity and ordinary kriging for spatial interpolation. Analyzing porosity and permeability data from 44 boreholes using the Lk coefficient revealed that the AB reservoir unit is primarily homogeneous, with 65% of boreholes exhibiting homogeneity. However, heterogeneity is present in the central and southeastern portions of the oilfield. Without considering the reservoir’s heterogeneity, placing injection wells along the eastern flank could lead to increased water production and reduced volumetric sweep efficiency.

The geological controlling factors of the heterogeneity of a bioclastic limestone reservoir—a case study of the Cretaceous Kh2 layer in A oilfield, Iraq

Reservoir heterogeneity is one of the key factors affecting the exploration and development of oil and gas reservoirs. The Kh2 layer in the A field of Central Iraq is a major pay zone with strong longitudinal and lateral heterogeneity. The heterogeneity, controlled by geological factors, has not yet been confirmed, which seriously restricts the development of this pay zone. This study aims to establish a geological pattern for the reservoir heterogeneity of bioclastic limestone, providing a geological basis for heterogeneity evaluation. Based on the core observation, thin-section identification, and physical property analysis, the microfacies are classified, and the diagenetic sequences and the pore structure of the Kh2 layer are analyzed. Seven types of microfacies are developed in the Kh2 layer, namely, planktic foraminiferal wackestone (MFT1), lamellar bioclastic wackestone (MFT2), intraclastic–bioclastic packstone (MFT3), green algal packstone (MFT4), green alga–pelletoid packstone (MFT5), bioclastic–intraclastic packstone (MFT6), and intraclastic grainstone (MFT7). The heterogeneity of the different microfacies and heterogeneity within the same microfacies were evaluated using the variation coefficient of permeability tested from cores collected from wells and calculated by well-logging at different intervals. The highest heterogeneity was observed in the lamellar bioclastic wackestone (MFT2), with an average variation coefficient of 0.72. The lowest heterogeneity was observed in the green algal packstone (MFT4), with an average variation coefficient of 0.11. The vertical heterogeneity of the permeability is mainly controlled by sedimentation, while the lateral heterogeneity is mainly influenced by cementation, bioturbation, and the distribution of green algae. Finally, a micro-scale geological pattern for determining the reservoir heterogeneity of bioclastic limestone reservoirs is established. This study can guide the current injection development and remaining oil prediction in oilfields with similar backgrounds.

Grassland vertical height heterogeneity predicts flower and bee diversity: an UAV photogrammetric approach

The ecosystem services offered by pollinators are vital for supporting agriculture and ecosystem functioning, with bees standing out as especially valuable contributors among these insects. Threats such as habitat fragmentation, intensive agriculture, and climate change are contributing to the decline of natural bee populations. Remote sensing could be a useful tool to identify sites of high diversity before investing into more expensive field survey. In this study, the ability of Unoccupied Aerial Vehicles (UAV) images to estimate biodiversity at a local scale has been assessed while testing the concept of the Height Variation Hypothesis (HVH). This hypothesis states that the higher the vegetation height heterogeneity (HH) measured by remote sensing information, the higher the vegetation vertical complexity and the associated species diversity. In this study, the concept has been further developed to understand if vegetation HH can also be considered a proxy for bee diversity and abundance. We tested this approach in 30 grasslands in the South of the Netherlands, where an intensive field data campaign (collection of flower and bee diversity and abundance) was carried out in 2021, along with a UAV campaign (collection of true color-RGB-images at high spatial resolution). Canopy Height Models (CHM) of the grasslands were derived using the photogrammetry technique “Structure from Motion” (SfM) with horizontal resolution (spatial) of 10 cm, 25 cm, and 50 cm. The accuracy of the CHM derived from UAV photogrammetry was assessed by comparing them through linear regression against local CHM LiDAR (Light Detection and Ranging) data derived from an Airborne Laser Scanner campaign completed in 2020/2021, yielding an R^2 of 0.71. Subsequently, the HH assessed on the CHMs at the three spatial resolutions, using four different heterogeneity indices (Rao’s Q, Coefficient of Variation, Berger–Parker index, and Simpson’s D index), was correlated with the ground-based flower and bee diversity and bee abundance data. The Rao’s Q index was the most effective heterogeneity index, reaching high correlations with the ground-based data (0.44 for flower diversity, 0.47 for bee diversity, and 0.34 for bee abundance). Interestingly, the correlations were not significantly influenced by the spatial resolution of the CHM derived from UAV photogrammetry. Our results suggest that vegetation height heterogeneity can be used as a proxy for large-scale, standardized, and cost-effective inference of flower diversity and habitat quality for bees.

Aberturas de barra provocam mudanças de longa duração na dinâmica limnológica ao longo da coluna de água de uma lagoa costeira tropical

Abstract Aim In this study, we investigated the impact of an episodic marine intrusion on the water column characteristics of Jurubatiba lagoon, a tropical coastal ecosystem, for 12 months following a sandbar breaching event to elucidate the duration of its effects. Methods Monthly, we sampled the physical, chemical, and biological characteristics along the water column for one year after a sandbar breaching event and seawater inflow. We assessed the temporal (monthly) and spatial (along depth profiles) associations among these variables and the temporal correlation among vertical heterogeneities in these variables and environmental drivers of stratification. Results Marine intrusion resulted in salt wedges formation in the short-term, leading to stratification in dissolved oxygen, pH, salinity, and chlorophyll-a concentration along the water column for at least four months. However, temperature and solar incidence also emerged as crucial factors associated with vertical heterogeneity in limnological variables, influencing water density and pH throughout the study period. Precipitation and wind speed had only marginal effects on thermal and ectogenic stratifications, probably mediated by water colour, nutrient inputs, water column depth and lagoon’s orientation in the landscape. Conclusions Our data unveiled that, despite their shallowness and wind exposure, coastal lagoons can exhibit considerable vertical heterogeneities in limnological variables due to various climatic and hydrodynamic aspects. Notably, the effects of marine intrusions on salinity and ectogenic column stratification can persist for several months, affecting water quality and, probably, biotic communities and ecosystem functioning. Once human activities and climate change may intensify marine intrusions on coastal lagoons, understanding spatiotemporal dynamics and their drivers is fundamental to anticipating their effects and conserving such vulnerable ecosystems.

How can an integrated multi-method geophysical approach optimise the groundwater management in the Chalk aquifer? Case study of the Seine fault system (France, Normandy)

The Cretaceous chalk aquifer is a strategic water resource in the north of France, especially in Normandy where it faces increasing pressure in terms of its quality and availability. The effective and sustainable manage of this resource relies on a deep understanding of its complex geological and hydrogeological nature. However, modelling this hydrosystem has its limitations due to the spatial and qualitative heterogeneity of the data available. The integration of geophysical data using various methods and scales has improved the geological knowledge by identifying the different chalk formation and highlighting the geometry of the Seine fault system near Rouen. Geophysical analysis has revealed highly complex fault geometries in this area and clarified their impact on the chalk formations. Additionally, it has provided detailed information about the vertical heterogeneity of the chalk, both geologically and hydrogeologically. This new knowledge feeds into the existing 3-D regional geological model, especially in areas with limited data. Supporting hydrogeological modelling, this updated model has already enabled to drill new boreholes. In the future, it will contribute to a better understanding and management of groundwater resources in this region.

Along-strike variations of structural style in the external Western Alps (France): Review, insights from analogue models and the role of salt

The European Alps result from the closure of a former Triassic to Cretaceous rifting system in which significative accumulation of Upper Triassic salt deposited. The thickness and spatial distribution of these salts had a major impact on the morphology and dynamic of the Alpine orogen all over the Western Alps. Following a bibliographical review, four regional cross-sections are revisited over the External Western Alps to emphasise along-strike variations of the orogenic wedge influenced by the presence or absence of Triassic salts. Each section is then compared with analogue models to examine the controlling factors explaining the structural styles variations. In the Northern Subalpine Chains, the absence of salt favoured a frictional decollement which promoted a narrow and thick orogenic wedge in the Bornes, Chartreuse, and Vercors massifs. Discrepancies in the spacing between the thrusts and the number of folds were however influenced by the thickness of incompetent layers in the sedimentary column. In the Jura and the SW Alps, the occurrence of Triassic salts promoted a viscous decollement and thus a wide and relatively thin orogenic wedge. However, in the SW Alps, thicker salt deposits allowed the development of pre-orogenic salt structures. These later constituted vertical heterogeneities having exerted a strong structural inheritance during the following compression, by accommodating a substantial part of the Alpine shortening, in squeezed diapirs especially. Triassic salt remobilization during the orogeny also locally promoted the development of syn-orogenic minibasins. This review highlights the significant role played by Triassic salt in shaping the Western Alps, and paves the way for possible new interpretations of the dynamics of the Alps regarding the exhumation of crystalline basement blocks, or new structural interpretations of Alpine domains, such as the Vocontian Domain.

CALCULATION OF AN ALTERNATIVE DEVELOPMENT SYSTEM FOR THE MAIN DEPOSIT OF THE DANILOVSKOYE OIL AND GAS CONDENSATE FIELD

The article provides a calculation of an alternative development system for deposit 3 (Main deposit ) of the Danilovskoye oil and gas condensate field. At the time of the analysis, this deposit is in the pilot development stage, with six development variants proposed in the trial operation project, which assume a principled arrangement of wells along an areal homogeneous grid. At the same time, due to the need to maintain the energy of the formation (that is, certain values of thermodynamic conditions), three provide for a transition to pressure maintenance, with the resulting four-point scheme of effect on the deposit (intensity 1:2; one well for injection, two for production). In the alternative model under consideration, the development method also involves a subsequent transition to pressure maintenance, but with a more active, five-point waterflooding system (intensity 1:1, equal ratio of production and injection wells), if necessary, as will be shown in the work, easily convertible to a nine-point one. The latter is an objective advantage, since the formation has low permeability and high vertical and lateral heterogeneity, and during waterflooding, zones not affected by the impact may appear, and, consequently, zones with high residual oil saturation. When calculating the characteristics of the proposed alternative method, modeling using the Peaceman method is used. Peaceman’s method is based on determining the well-reservoir connectivity of each individually opened cell, used to calculate flow rates (taking into account different values of average water cut for wells). The method is classical and, although it includes a large number of limiting assumptions, it is applicable everywhere and can provide sufficient justification for the effectiveness of the chosen development variant. General recommendations for the development of the entire field are also given (taking into account the low viscosity and lightness of oil and the properties of reservoir rocks). Such as the use of acid fracturing technology, the use of surfactants, hydrochloric acid treatments (HAT) and a complexing phosphorus-containing reagent — AFC.

Integrated seismic-stratigraphic, sedimentological and petrophysical approaches for characterizing the reservoir potential of early Cretaceous Alam El Bueib formation in the Meleiha concession of North Western Desert, Egypt

The Early Cretaceous late syn-rift sediments of Alam El Bueib Formation host potential, however poorly-explored reservoir targets in the north Western Desert of Egypt. The controls on depositional evolution and architecture of Alam El Bueib sedimentary facies, as well as the influence of depositional attributes on reservoir facies heterogeneity, are poorly constrained. Therefore, this study integrates seismic, sedimentological, and petrophysical data from Meleiha concession in the north Western Desert to build evolutionary models for Alam El Bueib succession and predict the architecture of the potential reservoir facies. Several channel systems were observed with a notable upward transition from complex-filled to flat-filled channels. The complex-filled channels correspond to the early highstand tidally-influenced estuarine, deltaic/estuarine sediments of Alam El Bueib-IV and Alam El Bueib-IIIG units. Matruh canyon and Alam El Bueib-IIIG fluvial sand bars were developed during a phase of forced regression, and the canyon was infilled by hemiplegic mudstones during the Late Valanginian sea level rise. The late highstand and lowstand facies of Alam El Bueib-IIIG unit present the main fluid flow conduits. The minimal degree of reservoir heterogeneity occurs in the lowstand amalgamated fluvial sandstone bars, whereas lateral and vertical reservoir heterogeneity increases in the deltaic/estuarine and estuarine successions of Alam El Bueib-IIIG and Alam El Bueib-IV, respectively. The lateral compartmentalization of the Alam El Bueib-IIIG fluvial facies against Alam El Bueib Matruh canyon shales produced excellent stratigraphic traps that should be tracked throughout the entire north Western Desert.

Examining the vertical heterogeneity of aerosols over the Southern Great Plains

Abstract. Atmospheric aerosols affect the global energy budget by scattering and absorbing sunlight (direct effects) and by changing the microphysical structure, lifetime, and coverage of clouds (indirect effects). Both aerosol direct and indirect effects are affected by the vertical distribution of aerosols in the atmosphere, which is further influenced by a range of processes, such as aerosol dynamics, long-range transport, and entrainment. However, many observations of these processes are based on ground measurements, limiting our ability to understand the vertical distribution of aerosols and simulate their impact on clouds and climate. In this work, we examined the vertical heterogeneity of aerosols over the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) using data collected from the Holistic Interactions of Shallow Clouds, Aerosols and Land Ecosystems (HI-SCALE) campaign. The vertical profiles of meteorological and aerosol physiochemical properties up to 2500 m above are examined based on the 38 flights conducted during the HI-SCALE campaign. The aerosol properties over the SGP show strong vertical heterogeneity and seasonal variabilities. The aerosol concentrations at the surface are the highest due to strong emissions at ground level. In general, the mode diameter of aerosols during summer (∼ 100 nm) is larger than that during spring (∼ 30 nm), a result of enhanced condensational growth due to enriched volatile organic compounds in summer. The concentration of aerosols below 30 nm in the boundary layer (BL) (e.g., below 1000 m) during spring is higher than that during summer, a result of the stronger new particle formation (NPF) events due to the reduced condensation sink in spring. In the BL, the size of the aerosols gradually increases with altitude due to condensational growth and cloud processing. However, the chemical composition of the aerosols remained similar, with organics and sulfates representing 59.8 ± 2.2 % and 22.7 ± 2.1 %, respectively, of the total mass in the BL. Through the vertical profiles of aerosol properties, we observed NPF events in the upper BL during 7 out of 38 research flights, where the newly formed particles continue to grow as they are mixed down to the surface. There is also an indication that deep convection brings aerosols from the free troposphere (FT) to the surface, where they grow to contribute to the cloud condensation nuclei (CCN). Overall, the vertical heterogeneity of aerosols over the SGP is influenced by aerosol dynamics (new particle formation, growth, and cloud processing) and transport processes (mixing in the BL, long-range transport, entrainment, and convective downward transport). Case studies showing the influence of these factors are discussed.

Optimization Method for Water-Flooded Beach-Bar Sand Bodies: A Case Study of the Fourth Member Red Beds of the Paleogene Shahejie Formation in the Dongying Depression

As water flooding continues to advance in mature oil fields, conventional well logging curve responses exhibit anomalies, particularly in deep-seated beach-bar thin-layer sand bodies. These sand bodies exhibit strong vertical and planar heterogeneity, which hinders a clear understanding of their distribution and connectivity. This paper conducts a sensitivity analysis of the lower part of the 4th member of the Shahejie Formation in fault block C26, based on core data analysis and the integration of drilling, logging, recording, and production dynamic data. Natural potential and resistivity curves are selected as the sensitive curves for identifying sand bodies. Preliminary processing of well logging curves is carried out using the “standard layer constraint and multi-standardization method comparison” principle. Employing sedimentological research methods and the principles of wavelet transformation, the well logging curves within the study area undergo extraction of both high and low frequencies. This procedure accentuates details related to thin sand bodies and responses indicative of sedimentary cyclicity. Through a thoughtful amalgamation of multiple curves, the investigation achieves a systematic fusion of natural potential curves via multi-curve frequency division fusion, employing reconstruction optimization. This method adeptly mitigates interference stemming from water-flooded layers, effectively addressing challenges such as excessive calibration and ambiguous identification of sand bodies. As a result, a comprehensive analytical approach is established for assessing the distribution and connectivity of deep-seated, beach-bar thin sand bodies influenced by water-flooded layers, providing clarity on the connectivity relationships among the sand bodies. Additionally, in combination with the results of mercury injection experiments in the water-flooded layer segments, favorable reservoir criteria for the study area are determined, providing a scientific basis for adjusting future development plans.

Fractional derivative method for anomalous aquitard flow in a leaky aquifer system with depth-decaying aquitard hydraulic conductivity

Aquitards significantly affect groundwater flow in multi-aquifer systems through adjacent aquifer leakage. Despite this, studies focusing on their heterogeneity and the non-conventional diffusion patterns of their flow are still limited. In this study, a factional derivative approach was first extended to explore the time-dependent behavior of flow transport in the aquitard. Two analytical solutions were derived for specific discharges in independent aquitards under different boundary conditions. The findings revealed that aquitard flow exhibits obvious anomalous diffusion behaviors, characterized by slower decay and heavy-tailed specific discharge data. The fractional derivative model provided a more accurate representation of this behavior than traditional models, as evidenced by its superior agreement with experimental data. Moreover, a transient model for pumping tests in a leaky aquifer system was developed, incorporating the memory effect of anomalous flow and vertical heterogeneity in aquitards. Relevant semi-analytical solutions were derived to explore the impacts of memory factor β and decay exponent of aquitard hydraulic conductivity (K) on the leakage aquifer system. Theoretical results demonstrated that stronger memory effect reduces drawdowns in the aquitard and confined aquifer during mid-to-late times. A larger dimensionless decay exponent (Ad) decreases aquitard drawdown and increases aquifer drawdown at late times. Sensitivity analysis showed aquitard drawdown experiences two peaks in sensitivity to β and Ad at early- or mid-times, affected by memory effect and decay exponent of aquitard K, signifying maximal impact at these specific intervals. This study provides a practical model to effectively manage groundwater resources by accurately reflecting aquitard memory and heterogeneity effects.

Heterogeneous Diazotroph Communities in the Subtropical‐Subantarctic Transition and Aphotic Zones Off the Coast of Patagonia, Eastern South Pacific Ocean

AbstractSubtropical‐subpolar transition water is a potential domain for N2 fixation, but the understanding of N2 fixation in such waters remains incomplete. We simultaneously examined the N2 fixation activity and community structures of diazotrophs and all prokaryotes from the surface to just above the seafloor off Patagonia in the transitional region of the eastern South Pacific Ocean. N2 fixation activity was not detected in the surface waters, but was observed sporadically and only in subpolar bathypelagic waters (>1,000 m) at very low rates (0.02–0.06 nmol N L−1 d−1). By contrast, the nifH gene, a key gene involved in N2 fixation, was detected widely from the surface to the bottom waters. The majority of diazotrophs were classified as non‐cyanobacterial diazotrophs (NCDs), and the nifH amino acid sequences of major diazotrophs were similar to sequences detected in the Southern Ocean, the aphotic zone and sediment of other oceans, and estuarine waters, suggesting that the NCDs are distributed across diverse marine environments. The overall prokaryotic communities were generally similar to those in other open ocean regions at the phylum level (class level for Proteobacteria) and differed among water depths. Diazotrophs, in contrast, showed vertical and horizontal heterogeneity below the euphotic zone and little association with water depth, indicating a lack of cohesion within the community, which may characterize diazotroph community in the transitional surface water and aphotic zones. Elucidating this community heterogeneity may provide pivotal information about N2 fixation in these waters.

Digital divides among microenterprises: Evidence from sub‐Saharan Africa

AbstractThis paper investigates digital inequalities in usage within African informal sectors. In particular, we examine whether the uneven digital diffusion is embedded in pre‐existing socio‐economic inequalities. After identifying three segments of informal firms, we rely on multivariate and decomposition analyses to identify predictors of usage of digital technologies for business purposes and explain usage gaps between segments. Our findings suggest that digital inequalities are rooted in the vertical heterogeneity of informal sectors, with some firm characteristics significantly predicting professional use of digital technologies. In addition, we find that there are both common and segment‐specific levers for addressing digital inequalities between informal firms.

Cross‐diffusion effects on the onset of double‐diffusive convection in a rotating vertical heterogeneous porous cylinder with vertical throughflow

AbstractThe effects of vertical throughflow, rotation, cross‐diffusion, and vertical heterogeneous permeability on the onset of double‐diffusive convection in a finite vertical porous cylinder have been studied. The fluid in the cylinder is warmed and salted from below with its top and lower walls considered to be isothermal, isosolutal, and permeable. In the model, the Brinkman model was adopted, coupled with the Oberbeck–Boussinesq approximation. The normal mode technique is used for linear stability analysis and a single‐term Galerkin method is used to solve the eigenvalue problem. Further, the influence of parameters such as the thermal and solute Rayleigh, Taylor, and the Soret and Dufour numbers on the fluid system instability have been investigated. Among other results, we found that vertical heterogeneity may either stabilize or destabilize a fluid system. The stabilization of the throughflow remains consistent irrespective of the orientation in the absence of a cross‐diffusion effect. The dual effect of throughflow is observed when there are cross‐diffusion effect. We found that increasing the Dufour parameter delays the onset of both stationary and oscillatory convection. The positive Soret number has a stabilizing effect on stationary convection and a destabilizing effect on the oscillatory convection case.

Determinants of the Vertical Distribution of the Phyllosphere Differ Between Microbial Groups and the Epi- and Endosphere in a Tropical Forest

The determinants of phyllosphere microbial communities are drawing much attention given their functional importance for their plant host fitness and health. Identifying these determinants remains challenging in neotropical forests, considering the diversity of the tree hosts and the strong vertical heterogeneity of abiotic conditions within the canopy and at the scale of the leaf. Here, we studied fungal and bacterial communities living in the endophytic and epiphytic phyllosphere in tree species across vertical gradients, from the top of the canopy to the ground. We used DNA metabarcoding to characterize microbial communities and measured abiotic variables and foliar traits to characterize environmental heterogeneity. The assembly of fungal communities was more driven by deterministic processes compared with bacteria, with endo- and epiphytic communities being similarly shaped by the host identity and unmeasured parameters. In contrast, in bacterial communities, the relative importance of deterministic processes decreased from endophytic to epiphytic communities. Bacterial epi- and endophytic communities were partly and differently determined by the position within the canopy, the host identity, and leaf traits, suggesting an effect of the vertical gradient and a stronger selection in the inner tissues of the leaf than on its surface. The tree host exerts a selective pressure on microbial communities but the leaf as microhabitat also contributes significantly to the assembly of microbial communities. Discrepancies exist between fungi and bacteria that probably reflect different life-history traits and ecological strategies, emphasizing the need to study these communities jointly if we are to fully understand plant–phyllosphere interactions. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .