Interstitial Pore Space Research Articles

Swiss deep drilling campaign 2019–2022: Geological overview and rock properties with focus on porosity and pore-space architecture

A recently completed deep drilling campaign, comprising 9 deep boreholes penetrating the Mesozoic sedimentary sequence of northern Switzerland, yielded >6 km of drillcore. One of the main objectives was to characterise the low-permeability sequence with the lower Jurassic Opalinus Clay in its centre, motivated by the site selection for a deep geological repository for radioactive waste. In this context, the chemical and isotopic composition of the porewater, as well as the mineralogical and petrophysical properties of the rocks, were among the main study targets. In this paper, the main objective was the characterisation of the lithologically diverse Jurassic rock sequence with focus on mineralogy, porosity and pore-space architecture. Given the large amount of data, a well constrained relationship between clay content (relating to fine-grained sheet-silicate minerals) and porosity could be established. Porosity increases with clay content along a concave curve, but in detail minor formation-specific differences of the positions relative to the best-fit curve were identified. These are attributed to the highly variable deposition rates that resulted in different times available for early diagenesis to alter the rock fabric by mineral dissolution and cementation, thereby affecting the compaction behaviour. Pore-size distributions were obtained from N2 ad-/desorption isotherms. A distinct peak at a radius of 3 nm can be clearly correlated with clay minerals, whereas limestones are dominated by pore sizes in the range of 40–100 nm, and marls show intermediate distributions. A conceptual framework is proposed distinguishing a nanometric porosity that is proportional to the clay content and a contribution of larger pores that are related to the geometric incompatibility between platy clay minerals and isometric calcite or quartz. The contribution of these larger pore is thought to explain the curvature of the clay content-porosity relationship and the more limited compaction of the clay in pressure shadows adjacent to the larger grains. A number of outliers towards high porosity at a given clay content were identified in oolites (most strongly in Fe-rich oolites), sandstones and a unit containing coral-reef material. All these units have in common the presence of competent calcite or quartz grains at the time of deposition, leading to grain-supported fabrics and therefore to a more limited compaction in the interstitial pore space.

A mechanically-derived contact model for adhesive elastic-perfectly plastic particles, Part II: Contact under high compaction—modeling a bulk elastic response

In Part I of this two part series (Zunker and Kamrin, 2024), we presented a multi-neighbor dependent contact model for adhesive elastic–plastic particles built upon the method of dimensionality reduction that is valid for the elastic and fully-plastic contact regimes. In this Part II, we complete the contact model by proposing a treatment for the bulk elastic contact regime which is characterized by a rapid stiffening in the force–displacement curve as interstitial pore spaces vanish. A simple formulation is presented for an additional bulk elastic force. A novel criterion for triggering this force (i.e. detecting the bulk elastic regime) related to the remaining free surface area of the particle is also given. This bulk elastic force is then superimposed with the force response given in Part I to achieve a contact model capable of capturing a variety of complex loadings. In this way, the methodology for treating the bulk elastic regime presented here stands independent of Part I and could be appended to any contact model. Direct comparison is made to finite element simulations showcasing bulk elastic responses, revealing the accurate predictive capabilities of the contact model. Notably, the contact model is also demonstrated to detect and evolve contacts caused purely by outward displacement of the free surface with good precision. A numerical implementation suitable for the discrete element method is provided.

Integration of Sequence Stratigraphy and Petrophysical Analysis for Reservoir Characterization: A Case Study of “ED” Field, Offshore Niger Delta

Sequence stratigraphic concept for continental settings was assessed to analyze the depositional systems of the formations penetrated by wells in ‘ED’ Field. Identification and delineation of three sequences and their bounding surfaces was carried out using well logs. Three hydrocarbon bearing reservoirs labelled as ED-R-1000, ED-R-2000 and ED-R-3000 were delineated. Computation of petrophysical properties of reservoir rocks was executed using well established relationship. The stratigraphy comprising of an alternation of sands and shales typically was of the Agbada Formation. The petrophysical analysis results give a good indication of the reservoirs’ capability of accumulating hydrocarbon in their interstitial pore spaces. Three stratigraphic surfaces were used to sub-divide the study field into three (3) depositional sequences and further subdivide the sequences into three system tracts. They are 1154ft(m), 382ft(m) and 738ft(m) thick respectively. The depositional environment of the study field includes distributary channel fill, regressive to transgressive shoreface delta, delta front and storm dominated shelf. The best quality reservoir will be found in the lowstand system tract while TST is a good sealing rock in the study field. Keywords: Stratigraphy, Depositional sequence, Petrophysical, Well logs. DOI: 10.7176/JEES/13-1-05 Publication date: January 31 st 2023

Water Vapor Transport Across an Arid Sand Surface—Non‐Linear Thermal Coupling, Wind‐Driven Pore Advection, Subsurface Waves, and Exchange With the Atmospheric Boundary Layer

AbstractAlthough vapor exchanged across hyper‐arid surfaces without free liquid affects the water budget of sand seas, its mechanism is poorly documented for want of accurate instruments with fine spatial resolution. To rectify this, we report bulk density profiles and spatiotemporal variations of vapor mass fraction just below the surface of a mobile dune, acquired with a multi‐sensor capacitance probe sensitive to tiny water films adsorbed on sand grains. We also record wind speed and direction, ambient temperature and relative humidity, net radiation flux, and subsurface temperature profiles over 2 days. The data validate a non‐linear model of vapor mass fraction. Unlike heat, which conducts through grains, vapor percolates across the interstitial pore space by advection and diffusion. On time scales longer than evaporation, adsorbed films equilibrate with their surroundings and hinder molecular diffusion. Their non‐linear coupling with subsurface temperature generates inflections in vapor profiles without counterpart in simpler diffusive systems. Pore advection arises as wind induces subtle pressure variations over the topography. During periods of aeolian transport, flowing sand dehydrates the surface intermittently, triggering evanescent vapor waves of amplitude decaying exponentially downward on a characteristic length implying an adsorption rate governed by a kinetic‐limited activated process. Finally, the probe yields diffusive and advective exchanges with the atmospheric boundary layer. During the day, their combined flux is smaller than expected, yet nearly proportional to the difference between vapor mass fraction at the surface and aloft. Under stabler stratification at night, or during aeolian sand transport, this relation no longer holds.

Hydrate growth kinetics in marine sediments

Clathrate hydrates form and grow when small gas molecules (<0.9 nm) come to contact with water at favorable pressure and temperature conditions. It happens in both the interstitial pore space between distributed marine sediments and inside their nano-meter sized pore spaces. For several thousands of years, the hydrates have occurred abundantly in permafrost and under the sea floor locking an immense amount of energy in the form of natural gas. It is estimated that the total gas reserved in hydrate deposits can meet our primary energy demand for a couple of centuries. To understand their formation and subsequent growth, several formulations have been derived at fundamental level. Various simplified assumptions still make those models really complicated and lead to provide reasonably large errors in prediction. Unfortunately, there is no direct correlation available so far that can precisely predict the hydrate kinetics with most simple way. This work introduces the development of a non-fundamental model routed through the concept of clathrate physics. To investigate the versatility and effectiveness of this growth model, it is used to predict the real-time data comparing with existing physical models.

Bankfull shear velocity predicts embeddedness and silt cover in gravel streambeds

AbstractExcess fine sediment (&lt;2 mm) deposition on gravel streambeds can degrade habitat quality for stream biota. Two measures of fine sediment deposition include embeddedness and silt cover (&lt;62.5 μm). Embeddedness measures fine sediment in interstitial pore spaces, whereas silt cover, primarily deposited during low flows, measures fine sediment draped on the streambed's surface. Here, we demonstrate that a baseline level of embeddedness and a maximum value of silt cover can be predicted from bankfull shear velocity, which can be estimated from river channel and streamflow characteristics, independently of knowing the sediment supply. We derive an equation for bankfull shear velocity that only requires knowing bankfull flow, channel width, and channel slope, which can be readily obtained in the United States from freely available, remotely sensed data. We apply this methodology to data collected at 30 sites in the Piedmont region of Virginia and North Carolina. This work is an important step in developing statistical models of stream ecosystems in which geophysical variables can predict embeddedness and silt cover, which commonly limit biotic assemblages.

Artificial flood reduces fine sediment clogging enhancing hyporheic zone physicochemistry and accessibility for macroinvertebrates

AbstractRiver regulation globally has reduced the riverine connectivity (longitudinal, lateral and vertically) with significant consequences for their abiotic and biotic components. To restore the ecological integrity of regulated rivers, artificial floods are increasingly being employed in large‐scale flow restoration efforts. Despite considerable recognition regarding the ecological and geomorphological effects of artificial floods on benthic habitats, understanding the implications for the hyporheic zone is essentially absent. This void in our management knowledge base is considerable given that one of the most widely associated consequences of flow regulation is excessive deposition of fine sediment (sedimentation; particles &lt;2 mm) that often disconnects the hyporheic zone from surface waters.In this study, we examined the effects of an artificial flood on the hyporheic zone of the River Spöl in Switzerland. Fine sediment content of shallow benthic substrates (ca. 10 cm) was significantly reduced following the flood. The flushing of fine sediment was also apparent in hyporheic substrates (depths of 0.25 and 0.50 m), resulting in a reconnection of previously clogged interstitial pathways. The opening of interstitial pore space enhanced physicochemical conditions in the hyporheic zone, such as improved dissolved oxygen concentrations, and supported greater taxa richness.Alterations in the composition of shallower hyporheic assemblages (0.25 m) were evident following the flood. These results indicated that benthic pore space became more connected to surface waters following the flood, thereby enhancing accessibility for interstitial organisms.Our results suggest that artificial floods can be an effective management tool to restore spatial heterogeneity in sediment composition and pore space and improve vertical connectivity for macroinvertebrates. We anticipate that artificial floods would be required on a regular basis given the re‐accumulation of fine sediment 10 months later in our study system. We encourage river managers and scientists to consider flow disturbance and restoration in a holistic manner that encompasses the multiple spatial dimensions of connectivity, including the hyporheic ecotone.

Localization in Flow of Non-Newtonian Fluids Through Disordered Porous Media

We combine results of high-resolution microfluidic experiments with extensive numerical simulations to show how the flow patterns inside a “swiss-cheese” type of pore geometry can be systematically controlled through the intrinsic rheological properties of the fluid. Precisely, our analysis reveals that the velocity field in the interstitial pore space tends to display enhanced channeling under certain flow conditions. This observed flow “localization”, quantified by the spatial distribution of kinetic energy, can then be explained in terms of the strong interplay between the disordered geometry of the pore space and the nonlinear rheology of the fluid. Our results disclose the possibility that the constitutive properties of the fluid can enhance the performance of chemical reactors and chromatographic devices through control of the channeling patterns inside disordered porous media.

Experimental investigation of the reactions between pyrite and aqueous Cu(I) chloride solution at 100–250 °C

Replacement of pyrite by copper-bearing sulfides is widespread in mineral deposits, with zonation of chalcocite, bornite, and chalcopyrite being a common result of this process. Copper occurs predominantly as Cu(I) in hydrothermal fluids, but the mechanistic details of reactions between pyrite and aqueous Cu(I) and their relevance to the zonation of Cu sulfides in hydrothermal deposits remain poorly understood, because of a lack of relevant experimental constraints. In this study, we investigated the reactions between pyrite and aqueous Cu(I) chloride solutions over a wide range of physicochemical conditions (100–250 °C; pH = 1–8; saturated vapor pressure). The experimental results show that Cu-bearing sulfides form at temperatures of >150 °C, and that pH exerts an important control on the mineralogy of the reaction products. In strongly acidic conditions (pH = 1.1), pyrite dissolution occurs; in acidic-to-neutral conditions (pH = 3.0–6.0), chalcopyrite and bornite are the main products; in weakly alkaline conditions (pH = 8.2), the replacement products are chalcocite and bornite. Chalcopyrite, bornite, and chalcocite generally occur in a zoned sequence outward from the pyrite reaction front to the bulk solution, and the replacement of pyrite by chalcopyrite is heterogeneous. In situ Raman observation and S isotope analyses suggest that pyrite replacement by chalcopyrite is a redox-coupled dissolution–precipitation reaction, with the oxidative dissolution of pyrite to form sulfate, generating the electrons that maintain the reductive replacement of pyrite by chalcopyrite. The sites of oxidative dissolution and reductive replacement can be spatially separated, but coupled by electron transfer. By contrast, the further replacement of chalcopyrite by bornite and chalcocite does not involve the oxidative dissolution of sulfur, but release of iron and H+, which could be promoted at higher pH. Notably, when the zonation of sulfides is established in a hydrothermal experiment of pyrite replacement by Cu(I) solution, gradients of H2S (or HS–), Cu(I), and Fe(II) are developed between the pyrite reaction front and bulk solution via diffusion through interstitial pore space. As such, the inner zones of chalcopyrite and bornite are not in equilibrium with the bulk solution as confirmed by thermodynamic calculations. The results imply that the zonation of Cu-bearing sulfides in mineral deposits records heterogeneous chemical environments, from the mineral interface- to the ore deposit-scale during dynamic mineralization processes.

The mineralogical and lithogeochemical footprint of the George Fisher Zn-Pb-Ag massive sulphide deposit in the Proterozoic Urquhart Shale Formation, Queensland, Australia

The Proterozoic Carpentaria Province (McArthur basin and Mount Isa Inlier) in northern Australia comprises a number of world class clastic dominated (CD-type) Zn-Pb massive sulphide deposits, formally known as SEDEX deposits. In order to identify the geochemical footprint of any mineralizing system it is necessary to characterize compositional variability of the host rock to mineralization. In the southern Carpentaria, establishing the baseline composition of the host rock is complicated by varying degrees of tectonic overprint, a lack of metamorphic indicator minerals, and the overall size of the ore forming systems. In this study, samples from drill-holes intersecting the main ore bodies at the world class George Fisher CD-type massive sulphide deposit have been compared to samples from a drill-hole intersecting barren, correlative lithologies of the Urquhart Shale Formation (ca. 1654 Ma). Bulk rock lithogeochemical (X-ray fluorescence, inductively coupled plasma mass spectrometry and LECO) and mineralogical (X-ray diffraction) analyses have been combined with petrographic observations to (1) establish the baseline composition of the Urquhart Shale Formation and (2) determine the geochemical and mineralogical footprint of the CD-type system at George Fisher. The absence of metamorphic indicator minerals, combined with the preservation of illite in un-mineralized Urquhart Shale, suggests that in this part of the Mount Isa area, the host rocks did not reach greenschist facies conditions (>300 °C). Chlorite in the un-mineralized Urquhart Shale is very fine grained (≤ 10 μm) within interstitial pore spaces with other phyllosilicates (e.g., illite), and is interpreted to be diagenetic in origin. Relative to the un-mineralized Urquhart Shale, the first stage of sulphide mineralization (Zn-dominated, stratabound) at George Fisher is associated with decreased abundances of albite, chlorite, and calcite, and higher abundances of dolomite and phyllosilicates (muscovite and phlogopite). These mineralogical transformations are associated with strong minor and trace element depletion (Sr and Na) and enrichment (Tl and Mn). An element index based on this suite of elements (GF index = 10400Tl+Mn10Sr+Na) is highly effective in differentiating between the background Urquhart Shale Formation and the alteration footprint at George Fisher and may provide an additional tool for geochemical exploration programmes in the Mount Isa area. This study affirms the benefit of combining lithogeochemical, mineralogical, and petrographic data in order to understand the host rock baseline composition and the alteration footprint of Carpentaria CD-type massive sulphide systems.

Flow and diffusion around and within diatom aggregates: Effects of aggregate composition and shape

AbstractDiatom aggregates constitute a significant fraction of the particle flux from the euphotic zone into the mesopelagic ocean as part of the ocean's biological carbon pump. Modeling studies of their exchange processes with the surrounding water usually assume spherical shape and that aggregates are impermeable to flow. Using particle image velocimetry, we examined flow distributions around individual aggregates of various irregular shapes formed from two different diatom species: (1) Skeletonema marinoi, known for its cell–cell stickiness, and (2) Chaetoceros affinis, exhibiting cell‐TEP (transparent exopolymeric particles) stickiness. Chaetoceros aggregates formed porous, highly irregularly shaped aggregates as compared to the more compact and near‐spherical Skeletonema aggregates, yet flow distributions around both types of aggregates were relatively similar at a millimeter scale. At a micrometer scale, the irregular shape of diatom aggregates caused velocity gradients and vorticity close to the surface to locally vary more than for spherical model aggregates (agar‐yeast spheres). Water was deflected from the surface of all aggregate types and we found no direct evidence that flow occurred within aggregates. Digital holographic imaging and Alcian blue staining revealed a substantial presence of TEP likely clogging the interstitial pore spaces in Chaetoceros aggregates. Radial oxygen concentration distributions measured by O2 microsensors within the aggregates were similar to those modeled for aggregates and spheres impermeable to flow. Thus, transport of gases, nutrients, and solutes likely occurs by diffusion, even within large, irregularly shaped diatom aggregates during sinking.

Modeling recovery of natural gas from hydrate reservoirs with carbon dioxide sequestration: Validation with I\u0121nik Sikumi field data

Fundamental understanding of guest gas replacement in hydrate reservoirs is crucial for the enhanced recovery of natural gas and carbon dioxide (CO2) sequestration. To gain physical insight into this exchange process, this work aims at developing and validating a clathrate hydrate model for gas replacement. Most of the practical concerns associated with naturally occurring gas hydrates, including hydrate formation and dissociation in interstitial pore space between distributed sand particles in the presence of salt ions and in irregular nanometer-sized pores of those particles, irregularity in size of particles and shape of their pores, interphase dynamics during hydrate formation and decay, and effect of surface tension, are addressed. An online parameter identification technique is devised for automatic tuning of model parameters in the field. This model is employed to predict the laboratory-scale data for methane hydrate formation and decomposition. Subsequently, the model is validated with the field data of the Prudhoe Bay Unit on the Alaska North Slope during 2011 and 2012. In this Iġnik Sikumi field experiment, mixed CO2 (i.e., CO2 + N2) is used as a replacement agent for natural gas recovery. It is observed that the proposed formulation secures a promising performance with a maximum absolute average relative deviation (AARD) of about 2.83% for CH4, which is even lower, 0.84% for CO2 and 1.67% for N2.

Clathrate hydrate dynamics with synthetic- and bio-surfactant in porous media: Model formulation and validation

In this contribution, we formulate a model to gain physical insight into the hydration process in presence of biosurfactant and porous media. This hydrate model addresses several practically relevant issues, including renewal of surface where hydrates form, uneven size and shape of internal pores in the porous material, hydrate formation in the interstitial and interior pore spaces of the unconsolidated porous particles, surface tension effect, and impeding nature of the salt ions present in seawater towards the hydrate formation and growth. The proposed model is illustrated by the formation and growth process of methane and carbon dioxide gases in presence of biosurfactant (the rhamnolipids solution produced from Pseudomonas aeruginosa) and porous silica gel. In addition, here we consider one of the most efficient and preferred synthetic surface active agents, namely sodium dodecyl sulfate. The proposed formulation has shown an excellent agreement (quantified with the percentage absolute average relative deviation) with the experimental data of the methane and carbon-dioxide gas hydrates formation and growth at diverse conditions.

The role of atmospheric pressure on Mars surface properties and early Mars climate modeling

The thermal inertia of a planetary surface is a compound function of the regolith thermal conductivity, density and specific heat. On planetary bodies with atmospheres, the conductivity of the surface must account for the contributions of both the solid component of the surface as well as that of atmospheric gas found in the interstitial pore spaces. Today, variations in thermal inertia and thermal conductivity on Mars affect the size and timing of areas for which surface temperatures exceed the melting point temperature of water, which is a necessary-but-not-sufficient prerequisite for surface liquid water. Models of past Mars climate, when the atmosphere may have been significantly thicker than at present, have largely neglected the potential role of interstitial atmospheric gas as a thermally conducting element of the ‘surface,’ though we show here that such underestimation of surface conductivity and thermal inertia has no appreciable effect on models of past Mars climate. In more recent Mars history, changes in obliquity have a similar effect of inflating or collapsing the Mars atmosphere, though to a lesser extent. Orbital changes will also modify surface thermal properties, leading to variations in surface conductivity (and thermal inertia) on 105–107 year cycles. We show that these variations, in fact, should not be neglected. We propose an obliquity-driven cycle of surface evolution that drives variability in surface thermal inertia, and suggest that the potential for liquid water at the surface should increase with time following large, positive excursions in Mars' obliquity.

Quantitative micro‐X‐ray fluorescence scanning spectroscopy of wet sediment based on the X‐ray absorption and emission theories: Its application to freshwater lake sedimentary sequences

AbstractMicro‐X‐ray fluorescence scanning spectroscopy of marine and lake sedimentary sequences can provide detailed palaeoenvironmental records through element intensity proxy data. However, problems with the effects of interstitial pore water on the micro‐X‐ray fluorescence intensities have been pointed out. This is because the X‐ray fluorescence intensities are measured directly at the surfaces of split wet sediment core samples. This study developed a new method for correcting X‐ray fluorescence data to compensate for the effects of pore water using a scanning X‐ray analytical microscope. This involved simultaneous use of micro‐X‐ray fluorescence scanning spectroscopy and an X‐ray transmission detector. To evaluate the interstitial pore water content from the X‐ray transmission intensities, a fine‐grained sediment core retrieved from Lake Baikal (VER99‐G12) was used to prepare resin‐embedded samples with smooth surfaces and uniform thickness. Simple linear regression between the linear absorption coefficients of the samples and their porosity, based on the Lambert–Beer law, enabled calculation of the interstitial pore spaces and their resin content with high reproducibility. The X‐ray fluorescence intensities of resin‐embedded samples were reduced compared with those of dry sediment samples because of: (i) the X‐ray fluorescence absorption of resin within sediment; and (ii) the sediment dilution effects by resin. An improved micro‐X‐ray fluorescence correction equation based on X‐ray fluorescence emission theory considers the instrument's sensitivity to each element, which provides a reasonable explanation of these two effects. The resin‐corrected X‐ray fluorescence intensity was then successfully converted to elemental concentrations using simple linear regression between the data from micro‐X‐ray fluorescence scanning spectroscopy and from the conventional analyzer. In particular, the calculated concentration of SiO2 over the depth of the core, reflecting diatom/biogenic silica concentration, was significantly changed by the calibrations, from a progressively decreasing trend to an increasing trend towards the top of the core.

Mechanical Behavior of Cemented Granular Aggregates under Uniaxial Compression

AbstractCemented granular aggregates composed of densely packed particles bound together by a matrix partially filling the interstitial pore space, connecting adjacent grains and forming cemented g...

Phase-change mechanism for evaporation in porous media using volume of fluid: Implicit formulation of interfacial temperature

In this study, a widely-utilized mechanism which relates the rate of phase change in two-phase flows to an interfacial superheat is described and modified to improve its physical consistency and overall performance when compared to the porous two-phase Stefan problem. Maintaining interface temperature at saturation temperature, the rate of phase change is taken to be proportional to the degree of superheating at the interface. The present work demonstrates how the superheat error can be made to meet the same convergence requirements already established for the temperature solution at each time step by comparing the interfacial energy balance to the present methods superheat relation at the fluid-fluid interface. The results are in good agreement with the presented analytical solution for the porous media Stefan problem using propane. The Volume of Fluid (VOF) method, incompressible Navier-Stokes and temperature equations are segregated and modified to incorporate the effects of porous media and the source terms for phase change. For low porosities, a limitation of the rate of phase change is observed due to a restriction in the availability of interstitial pore space occupied by the phase change fluid. At the other extreme, when solid content diminishes, the system is reduced to the classical Stefan problem in free flow. Between these two ranges, an optimum porosity exists where the rate of phase change is maximum.

Evidence for pore-filling gas hydrates in the sediments through morphology observation

To provide an evidence of natural gas hydrate occurrence state, a series of experiments on multiple growth and dissociation of 90.0% methane/10.0% propane hydrates at 1.3 MPa and 270.15 K were carried out in two sediments for morphology observation via a visible jacketed-reactor. The gas hydrate crystals were observed to form and grow on the surface of sediments at the initial growth. During the thermal decomposition, gas and liquid products had an unceasingly impact on the sediments, then gas/liquid–solid migration occurred, and a large number of cavitation appeared. In the later growth and dissociation experiments, the gas hydrate particles were in suspension or supporting states in the interstitial pore space between the sediment particles, indicating that the gas hydrate displayed a pore-filling characteristics. Through analyzing the distribution of gas hydrates and bubbles, it was found that the amount of gas hydrates distributed in the sediments was improved with multiple growth-dissociation cycle proceedings. Gas migration enhanced the sediment movement, which led to the appearance of the increasing quantity of gas bubbles in the sediments during cycles. Salts affected the growth of the gas hydrates and the migration of sediment grains, which also restricted the accumulation of gas bubbles in the sediments. According to the Raman analysis, the results showed that sII hydrates were formed for CH4 and C3H8 gas mixtures in different sediments and solutions with hydration number of 5.84–6.53. The Salt restricted the access of gas into the hydrate cages.

Predator, prey, and substrate interactions: the role of faunal activity and substrate characteristics

AbstractMany taxa possess a range of strategies to reduce the risk of predation, including actively seeking suitable refuge habitats; however, the global spread of invasive species may disrupt these behavioral responses. In lotic ecosystems, interstitial spaces in the substrate are important refugia for small organisms. Some predators are ecosystem engineers that exhibit zoogeomorphic agency—the ability to modify the geomorphology of their environment. It is therefore possible that direct ecological effects of predators on prey may be realized through modifications to the prey's habitat, including the availability of refugia, by predators that are zoogeomorphic agents or via external stressors such as fine sediment loading. This study examined three research questions in a mesocosm study across a gradient of sediment‐stress treatments: (1) What affects do predators (Pacifastacus leniusculus, invasive crayfish) and prey (Gammarus pulex, amphipods) have on the ingress of fine sediment into gravel substrates and therefore on available interstitial refugia? (2) Do prey taxa seek refuge from (invasive) predators in the form of vertical movement into subsurface sediments? and (3) How does fine sediment ingress influence predator–prey interactions and prey survival through predator avoidance behavior. Here, we provide direct evidence demonstrating that fine sediment ingress into gravel river beds can be facilitated by zoogeomorphic activity with P. leniusculus increasing the infiltration of fine sand particles (but not coarse sand) during foraging activities. Predator–prey interactions were found to be a primary factor mediating zoogeomorphic activity, with the isolation of crayfish from prey (G. pulex) leading to increased fine sand ingress. When present with signal crayfish, G. pulex displayed vertical avoidance behavior, entering subsurface substrates to evade predation by P. leniusculus. Coarse sand treatments resulted in higher predation rates of G. pulex, most likely due to clogging of interstitial pore spaces between gravels limiting the effectiveness of the prey's vertical avoidance behavior strategy. A new conceptual model that captures the interactions between predator, prey, zoogeomorphic processes and habitat availability is presented. This model highlights how predator–prey interactions can be strongly mediated by dynamic bi‐directional interactions between organisms and the physical environment they inhabit as ecological and geomorphological processes are intrinsically linked.

The role of fine sediment characteristics and body size on the vertical movement of a freshwater amphipod

Abstract Sedimentation and clogging (colmation) of interstitial pore spaces with fine sediment particles is widely considered to be one of the most significant threats to lotic ecosystem functioning. This paper presents the results of a running water mesocosm study examining the effect of benthic and hyporheic fine sediment loading and particle size on the vertical movement and distribution of the freshwater amphipod Gammarus pulex. A gradient of fine sediment loading and different particle sizes were used to examine the ability of G. pulex from two body size classes to access and migrate vertically within subsurface sediments. We tested three hypotheses: (a) sediment loading would modify the distribution of G. pulex by limiting vertical movement; (b) the deposition of large particles and heterogenous sediments would limit the vertical movement of individuals more than homogeneous fine‐grained sediments; and (c) large bodied individuals would be prevented from migrating vertically with increasing sediment loading and particle size/heterogeneity. Sediment loading, particle size and heterogeneity of deposited sediment had a significant effect on the vertical movement of individuals, with heterogeneous sand (0.125–4 mm) acting as the strongest barrier to the vertical movement of individuals through the infilling and clogging of interstitial spaces followed by coarse (1–4 mm) and fine sand (0.125–4 mm). Fine sediment loading and particle size acted as a filter on body size and limited the ability of large bodied individuals to migrate vertically to a greater extent than small bodied individuals. This study demonstrates that the effects of fine sediment on habitat availability and faunal movement is dependent on both sedimentological characteristics and an individual's body size. The results illustrate the importance of both abiotic and biotic factors when evaluating the ecological effects of fine sediment deposition.