Depth Position Research Articles

Subsurface fracture characterization in a folded ultra-deep tight-gas sandstone reservoir: A case study from the Keshen gas field, Tarim Basin, China

In the Keshen gas field in the northern Tarim Basin, the main production interval is the ultra-deep (>6000 m), ultra-high pressure Lower Cretaceous Bashijiqike Formation. Understanding the characteristics and role of natural fractures in the reservoir is essential for efficient exploration and development. Data from borehole images (42 vertical wells) and cores (12 vertical wells) enabled a comprehensive characterization of fracture attributes, including mode, orientation, fill, density, and clustering as well as variations with respect to depth and structural position. Using image logs from 20 vertical wells and cores from 12 wells, we find that steeply dipping (>60°), E-W and N–S-striking fractures are the most common across the studied anticline. Fracture density is highest in the forelimb and near faults (2.85 fractures/m), compatible with fracture formation during folding and associated faulting. Fracture clusters 10+ m wide are also preferentially located within these structural zones and are spaced around 5–15 m apart. Fracture orientations, fill, and density varies with depth. We identify a depth transition horizon above and below which fracture characteristics, specially strike, dip, and resistivity change dramatically. We infer those changes are due to fold geometry, rheological differences associated with increasing pressure and temperature at extreme depths. We observe anhydrite-filled fractures located near the top of the formation, whose presence is associated with overlying evaporites. Vertical and lateral variations of fracture characteristics and distribution discovered in this reservoir may aid the interpretation and prediction of the fracture network in other ultra-deep sandstone reservoirs with a comparable setting or well performance.

Active morphological factors determining the locations of sand mines in dry-river channels

In Kenya, most of the construction sand is derived from dry riverbeds. Due to rampant nature in which sand mining is carried out in these rivers, adverse environmental and social effects have been reported. In order to ensure sustainable sand mining activities, this study assessed active morphological factors determining sand abundance in the seasonal river Tyaa in Kitui, Kenya. The study adopted quantitative research design. Purposive sampling was used to select river Tyaa due to uncontrolled sand mining that was taking place there. Systematic sampling at 20 meter intervals was used while collecting data at the stretches of the river channel, thus constituting 2,000 meters in total. Data on independent variables, namely the river channel’s width, depth, slope angles, bank position, weathering status, vegetation status, and erosion status was collected using physical measurements and logic guided observation. Binary logistic regression analysis was used to analyze the data, giving marginal effects and respective p-values. The study established four statistically significant factors responsible for sand abundance in the dry river channel’s namely depth (p=0.001), width (p=0.001), slope angles (p=0.001) and bank position (p=0.001). The study concluded that these factors should be observed while siting sand mines along dry river channels to mitigate adverse environmental effects. The study recommended that National Environmental Management Authority of Kenya should apply the findings of this study in the establishment of the locations of sand mines and monitoring of the mining process in line with the existing guidelines and regulations.

Marine protected areas in the southern south‐west Atlantic: Insights from marine top predator communities

AbstractThe marine ecosystem provides numerous goods and services, dampens the impacts of floods and storms, and provides climate control, through the regulation of carbon fluxes, nutrient cycling, and the bioremediation of human waste and tourism. However, the ocean is vulnerable to anthropogenic threats and has been severely altered by humans.Seabirds and marine mammals are long lived, highly mobile, easily identifiable, and occupy the upper levels of trophic webs. These ecological features make them suitable as sentinels of the marine ecosystem.Sighting data collected during eight oceanographic surveys were analysed to describe and compare the biodiversity of the communities of top predators within the marine protected areas (MPAs) of Namuncurá/Burdwood Bank I and II and the surrounding areas in two contrasting seasons (summer and winter). Data were grouped into six zones based on depth and geographic position.Twenty‐five species of seabirds and 13 species of marine mammals were recorded in 113 days of surveys between 2014 and 2018. Top predator community composition varied seasonally in the different zones.A suite of indicator species was identified according to their specificity and fidelity to a particular zone. Most of the species identified as potentially useful indicators differed between summer and winter, highlighting the importance of conducting systematic surveys in both periods.The MPAs Namuncurá/Burdwood Bank I and II are key areas for top predator communities in the region, mainly in summer when the number and abundance of species increase. However, the waters around Isla de los Estados and the channel between Isla de los Estados and Burdwood Bank were also identified as a relevant habitat for many species. This knowledge should be included to create a regional network of areas under special management considerations that connect the established MPAs with other key pelagic and coastal areas (as found in this study) for the conservation of subantarctic marine megafauna.

Context-based modulations of 3D vision are expertise dependent.

An object's identity can influence depth-position judgments. The mechanistic underpinnings underlying this phenomenon are largely unknown. Here, we asked whether context-dependent modulations of stereoscopic depth perception are expertise dependent. In 2 experiments, we tested whether training that attaches meaning (i.e. classification labels) to otherwise novel, stereoscopically presented objects changes observers' sensitivity for judging their depth position. In Experiment 1, observers were randomly assigned to 3 groups: a Greeble-classification training group, an orientation-discrimination training group, or a no-training group, and were tested on their stereoscopic depth sensitivity before and after training. In Experiment 2, participants were tested before and after training while fMRI responses were concurrently imaged. Behaviorally, stereoscopic performance was significantly better following Greeble-classification (but not orientation-discrimination, or no-) training. Using the fMRI data, we trained support vector machines to predict whether the data were from the pre- or post-training sessions. Results indicated that classification accuracies in V4 were higher for the Greeble-classification group as compared with the orientation-discrimination group for which accuracies were at chance level. Furthermore, classification accuracies in V4 were negatively correlated with response times for Greeble identification. We speculate that V4 is implicated in an expertise-dependent, object-tuning manner that allows it to better guide stereoscopic depth retrieval.

Magnetic characteristics and tectonic structure of the Earth's crust of the Carpathian oil and gas region as a component of complex hydrocarbon criteria

For the first time, a qualitative and quantitative analysis of the geomagnetic field and oil and gas capacity was performed for the territory of the Carpathian region, which made it possible to reveal the connection of hydrocarbon deposits with the magnetization of the Earth’s crust at the regional and local levels and the features of the deep structure of the Earth’s crust according to seismic data. The regularity of the distribution of oil and gas deposits of the Carpathian oil and gas-bearing region revealed by geomagnetic criteria is confirmed by their connection with regional and local anomalies of the gravity field and heat flow density. According to the analysis of the regional geomagnetic field and magnetic models along the PANCAKE and RomUkrSeis geotraverses, gas fields are located above the magnetic blocks of the middle and lower parts of the Earth’s crust or in their marginal parts, and oil fields are located above practically non-magnetic deep blocks. Under the thrust part of the Carpathian arc, the regional features of the Earth’s crust structures are clearly manifested, namely, starting from the longitude of the city of Rakhiv, the submeridional direction of extension of regional anomalies of magnetic, gravity, and thermal fields and their horizontal gradient zones prevails. The oil and gas potential of the region is in good agreement with this — the gas fields are timed to the minimum values of the regional horizontal gradient of the regional magnetic field, to the increased gradient of Bouguet anomalies, as well as to the minimum values of the horizontal gradient of heat flow density anomalies. In local geophysical fields, gas fields are gravitating: to weakly negative magnetic anomalies and their gradient zones; to negative anomalies of the gravitational field predominantly; to positive anomalies of heat flow density in the northwest, within the area of Trans-European suture zone (without the middle of the Krakovets fault), and negative anomalies in the Carpathian trough. Oil and oil condensate deposits are correlated with a band of positive magnetic field anomalies, negative gravity field anomalies, and increased heat flux density values. The main deep faults of the Carpathian region and the marginal part of the Platform in the first approximation can be considered Velikomostivsko-Chernivetsky, which characterizes the change in the character of magnetic and gravity fields and heat flow density, Rava-Rusky, which reflects the zone of articulation of the Eastern and Western European platforms, Pre-Carpathian — the border of the Pre-Carpathian trough and the Folded Carpathians on the Earth’s surface (as well as the boundary of the Archaean(?)-Paleoproterozoic and Meso-Neoproterozoic crust according to the modern international chronostratigraphic scale), as well as the Transcarpathian fault. On the basis of magnetic and seismic data, the hypothetical depth position of these faults and the possible connection with them of hydrocarbon flows into the upper part of the Earth’s crust are proposed. Therefore, the geomagnetic criteria of the oil and gas bearing capacity of the Earth’s crust of the Carpathian region are agreed based on the results of the study of the gravity field and heat flow density anomalies, which makes it possible to predict the spread of oil and oil condensate and gas and gas condensate deposits according to the regional and local features of these fields in a first approximation.

Transmucosal abutments in the esthetic zone: Surgical and prosthetic considerations.

This article describes an updated step-by-step protocol for transmucosal abutment selection and treatment sequencing after immediate implant placement in the esthetic zone. Current surgical and prosthetic concepts strive to preserve hard and soft-tissues to provide optimal esthetics at the implant-abutment interface. Consequently, restoring implants in the esthetic zone with transmucosal abutments presents a great challenge and must take into consideration implant depth, angulation, and bucco-lingual position as well as transmucosal height and space for an optimized emergence profile of the restoration and the dimensions of the anterior tooth to be restored. The proper selection of the type, shape, and dimensions of implant components and connections, determined by the product portfolio offered by the implant manufacturer, play a critical role in the ability to adequately address these challenges. This article provides an update on surgical and prosthetic workflows for single implant restorations in the esthetic zone. Following esthetic, mechanical, and biologic principles, the long-term success of implant-supported restorations in the esthetic zone is directly correlated to proper execution and sequencing of surgical and prosthetic treatment steps, especially after immediate implant placement. These steps must be critically assessed based on the current scientific evidence to achieve the desired clinical outcomes on a predictable and consistent basis. Selection of surgical and prosthetic treatment protocols to achieve ideal esthetic outcomes and emergence profiles in implant dentistry is often a great challenge, not only determined by technical and clinical skills of the provider but also by the type and dimensions of implant components and connections offered by the manufacturer. Following certain decision-making principles and workflows are key for clinical success with implant-supported restorations after immediate implant placement the esthetic zone.

Variability and driving factors of the soil saturated hydraulic conductivity along the horizontal and vertical directions in the upper catchment of Benggang

Benggang is a unique soil erosion landform in the subtropical hilly granite area of South China that seriously endangers the local ecology and environment. In this study, a developing Benggang in South China was selected to explore the spatial variability and the driving factors of the soil saturated hydraulic conductivity (Ks). The results demonstrated that the soil properties of Benggang landforms varied with the soil layer depth and slope position. Only the sand content increased with decreasing distance from the collapsing wall, while the soil organic matter (SOM) content, free iron oxide (Fed) content and cation exchange capacity (CEC) exhibited the opposite trend. Particularly, these parameters exhibited the most significant variation between the middle slope (MS) and lower slope (LS) I and II positions. The Ks values at the LS positions were significantly higher than those at the upper slope (US) and middle slope (MS) positions, and the Ks values first decreased and then increased as the soil layer depth increased. Among the slope positions, the variation in Ks values followed the order of LS II > LS I > US > MS. The Ks values in different directions exhibited notable multifractal characteristics, and the heterogeneity was stronger in the vertical direction than in the horizontal direction. The soil Ks values significantly differed between the different directions at four slope positions, and the values along the vertical direction were higher than those along the horizontal direction at the US and MS sites. However, the values along the horizontal direction were higher than those along the vertical direction at the LS I and LS II sites. Especially at the LS II site, the difference in the soil Ks values between the two directions was extremely significant (P < 0.01). The correlation coefficient values between Ks and the number, area ratio and mean volume of soil macropores were > 0.8. Path analysis revealed that the mean volume of macropores was the main factor affecting the Ks variation. The difference in the soil Ks values at the LS positions could effectively explain the mechanism of headward erosion on the Benggang slope. This study provides a theoretical basis for Benggang erosion control and the prevention of soil erosion in South China.

Theoretical and experimental study on sound absorption performance of Al2O3-polyurethane foam and microperforated plate composite structure

Low-frequency noise pollution in substations has a significant impact on the physical and mental health of workers. Reduction low-frequency noise pollution is an urgent problem to solve for researchers. In this paper, the different structures of Al2O3-polyurethane composites and micro-perforated plate were constructed, and the effects of cavity depth, perforated plate, and foam position on sound absorption properties were comprehensively investigated. The results showed that the position of perforated plate and the arrangement of resonance structure were the two most important factors affecting sound absorption performance. When the sound wave passed through the plexiglass plate–cavity–composites foam–perforated plate in turn, the peak position of sound absorption coefficient was located in the ultra-low frequency range. Meantime, the simulation study showed that the friction between the air column and the cavity wall in the perforated plate can consume sound energy to achieve sound absorption.

An efficient surrogate model-based method for deep-towed seismic system optimization

The towing speed, cable length, towing depth, and hitch position should be optimized to improve the operational safety and efficiency of a deep-towed seismic system. However, the optimization is ineffective due to system nonlinearity and large-scale calculations. Therefore, a surrogate model-based method is proposed to simplify a deep-towed system and promote system optimization. The relationships among the towing speed, viscous drag and pitch angle of the towed vehicle are expressed using a surrogate model generated by using the artificial neural network method. Input variables of the surrogate model are related to the optimization variables through proper design variable selection, which generates an efficient explicit formulation. Additionally, a quasi-static iteration is established to speed up calculating the cable shape of the towing cable, and analytical models simplify the calculations of drag forces acting on the drogue and seismic array. Finally, the best design, such as the towing speed, cable length and hitch position, are obtained with limited cable tension and towing depth in a case study. This research provides an effective method for deep-towed seismic system optimization.

Research on the time-varying mesh stiffness method and dynamic analysis of cracked spur gear system considering the crack position

The occurrence of a crack could change the gear mesh stiffness and consequently influence gear vibration properties. Cracks may occur on the tooth root and tooth surface, but the surface crack type has been seldomly concerned. This study proposes a comprehensive time-varying mesh stiffness (TVMS) calculation method in which the crack position is considered and emphasized. Two tooth crack types (Root crack type: the crack occurs on the root fillet; Surface crack type: the crack occurs on the tooth surface) are modeled and analyzed, and corresponding analytical calculation expressions of TVMS are derived. The finite element method is applied to validate the applicability and accuracy of the proposed analytical method for both root and surface crack types. Besides, by establishing a nonlinear dynamic model for a spur gear system, the influences of the crack depth and crack position on the gear dynamic characteristics are investigated. Several statistic parameters are also applied to evaluate the health conditions for the spur gear system. The method and analysis results reported here may be of interest to researchers and engineers attempting to handle the gear fault analysis analytically and effectively.

Rationality (Online Discussions/Discussion Quality)

Rationality (Online Discussions/Discussion Quality)

Does pin configuration matter in modified tension band wiring for transverse patellar fracture? A biomechanical study

BackgroundModified tension band wiring has been widely used for the treatment of transverse patellar fractures. The optimal position of a Kirschner wire (K-wire) in modified tension band wiring, however, has not yet been determined. The purpose of the present study was to evaluate biomechanically the effect of K-wire position in a modified tension band wiring technique. MethodsForty-two polyurethane foam patellae with a midway transverse fracture were assigned to six different fixation groups regarding different pin configurations in tension band wiring. The depth or sagittal position of the K-wire was divided into anterior and posterior. The coronal position of the K-wire was divided into central, medial and lateral. A specially designed set up simulated a knee with 60° flexion. All specimens were tested under axial traction. Loads at 2 mm and 4 mm fracture displacement and at the failure of the construct were recorded. ResultsAt 2 mm fracture displacement, anterolateral (AL) placement of K-wires revealed significantly less durability when compared with five other groups (P < 0.001). At 4 mm fracture displacement, the AL group also revealed inferior biomechanical strength when compared with other groups. Posteromedial (PM) K-wire placement group revealed more durability when compared with the posterolateral (PL) group (P < 0.05). At failure of the osteosynthesis, anteromedial (AM) and anterocentral (AC) groups revealed superior biomechanical strengths (P < 0.05). ConclusionsThe coronal and sagittal position of K-wire affects the biomechanical characteristics of modified tension band wiring. Anterolateral placement of K-wires revealed inferior strength to all other constructs in modified anterior tension band wiring.

Damage Detection in Cantilever Piping System-Transporting Fluid Using Finite Element Method

Fracture existence in a pipe is considered disruptive as well as detrimental to the pipe systems and equipments. Cracks are the most common mechanism of failure for pipelines of any kind. Therefore, early crack identification may help save the pipe system from catastrophic breakdown. This study focuses on fluid-transporting cantilevered tapered pipes. By using the Bernoulli beam theory, ANSYS is used to simulate the pipe's performance by the finite element method for an incompressible fluid flow through a tapered cantilevered pipe. The effect of a non-propagating open crack on the dynamic and modal behavior of a cantilevered pipe used to convey fluid is investigated. Flow velocity and crack relative location, as well as the crack's depth, will be explored as they relate to the fundamental natural frequency, second, and third natural frequency. Results have showed clearly that crack depth and relative position play a significant role in natural frequency variation. However, fluid inlet velocity is found to have less impact on the natural frequencies considered at a certain relative crack position.

Equipment to tag, track and collect biopsies from whales and dolphins: the ARTS, DFHorten and LKDart systems

Of all animals considered subjects for instrumentation for behavioral or physiological studies, cetaceans probably represent the greatest challenge to the engineer and biologist. The marine environment being harsh to electronics, evasive behavior during tagging approaches and the short time window available to attach instruments, all imply a need for innovative tagging solutions to facilitate better understanding of their life cycle, migration, physiology, behavior, health and genetics. Several animal-attached tag packages holding specific data loggers, e.g., time depth recorders, position, orientation, acoustic and video recorders for short to medium term studies, as well as tags developed for large scale migration telemetry studies are available as off-the-shelf devices, or in many cases as custom made sensor packages. Deployment of those instruments is often the limiting factor for data collection. The Aerial Remote Tag System (ARTS) is a flexible system which can easily be adapted to deploy different tag sensor packages and biopsy collection devices. This paper presents the history and design of the ARTS, and accessories developed for instrumentation and biopsy sampling of cetaceans, such as the recent developed ARTS–LKDart for biopsy sampling. Deployment of archival tags usually requires radio tracking of the instrumented animal, or at least tracking of the tag for recovery. Thus, we also here describe the automatic digital signal processing radio direction finder, the Direction Finder Horten (DFHorten unit).

Eco-evolutionary dynamics of Atlantic cod spatial behavior maintained after the implementation of a marine reserve.

The effects of marine reserves on the life history and demography of the protected populations are well-established, typically increasing population density and body size. However, little is known about how marine reserves may alter the behavior of the populations that are the target of protection. In theory, marine reserves can relax selection on spatial behavioral phenotypes that were previously targeted by the fishery and also drive selection in favor of less mobile individuals. In this study, we used acoustic telemetry to monitor the individual spatial behavior of 566 Atlantic cod (Gadus morhua Linnaeus, 1758) moving within a marine reserve and a control site in southern Norway, starting 1 year before the implementation of the marine reserve and lasting up to 9 years after. Following a before-after-control-impact approach, we investigated changes in (1) survival, (2) selection acting on behavioral traits, and (3)mean behavioral phenotypes, after the implementation of the marine reserve. We focused on three behavioral traits commonly used to describe the mobility of aquatic animals: home range size, depth position, and diel vertical migration range. Survival increased after reserve implementation, but contrary to our expectations, it subsequently decreased to preprotection levels after just 3 years. Further, we found no significance in selection patterns acting on any of the three behavioral traits after reserve implementation. Although some changes related to water column use (the tendency to occupy deeper waters) were observed in the marine reserve after 9 years, they cannot unequivocally be attributed to protection. Our results show that survival and behavioral responses to marine reserves in some cases may be more complex than previously anticipated and highlight the need for appropriately scaled management experiments and more integrated approaches to understand the effects of marine protected areas on harvested aquatic species.

A new approach for the prediction of fatigue life in rolling bearings based on damage accumulation theory considering residual stresses

Today, the service life calculation of rolling bearings is standardized in ISO 281, based on the theory of Lundberg and Palmgren. In the standard calculation method, material properties such as fatigue limit stress were taken into account by introducing the fatigue limit stress proposed by Ioannides and Harris. This standard calculation method provides a reasonable range of fatigue life in good agreement with experimental results under ideal test conditions such as constant external load. However, complex operating conditions of bearings such as varying loads and oscillating motion are not considered. Therefore, there is a need for a new analytical calculation model that can predict the fatigue life of rolling bearings operating under these complex conditions. This makes it possible to advance the application of rolling bearings and optimize their use in machines such as wind turbines. In the proposed approach, the fatigue life is determined based on the Palmgren-Miner linear damage rule, evaluating the subsurface stresses below the rolling contact using the S-N curve according to the fatigue criterion proposed by Lundberg and Palmgren. All rolling contacts that occur in an internal stress cycle due to the internal dynamic behavior during rotating operations are evaluated individually and referred to as partial damage risks. The partial damage risks are accumulated linearly according to the Palmgren-Miner theory to obtain the load cycle to failure. At this time, the loaded volume is assessed along the depth from the contact area to the core of the bearing ring, which makes it possible to indicate the depth position of fatigue occurrence in terms of crack initiation. The material properties such as the fatigue limit stress and the probability of failure are taken from the S-N curve itself. To consider the residual stress, a simple link concept is suggested by using the ratio of the maximum contact pressure to the yield criteria. The proposed approach can be extended to calculate oscillating fatigue life regarding the number of rolling contacts at a given oscillation amplitude. In this study, it can be confirmed that the analytically determined fatigue lifetime according to ISO 281 is still close to the bearing life test result. In addition, it shows that the results obtained using the proposed approach agree well with the calculation results obtained using ISO 281.

High-speed astigmatic dual-beam interferometric particle imaging for direct depth displacement and velocity measurement of metal droplet

High-speed astigmatic dual-beam interferometric particle imaging (HADIPI) is adopted to simultaneously measure the three-dimensional (3D) position, velocity and size of spherical metal droplets. We propose to infer the depth displacement of the droplet directly from the angle shift of the interference fringe. Angular cross power spectral density is used to detect the angular shifts of the interference fringe. The depth displacements and velocities can be further obtained from the obtained angular shifts. Proof-of-concept experiments are conducted on micron-sized gallium droplets, demonstrating that the 3D trajectories of the droplets can be accurately obtained, with depth displacement accuracy of tens of microns, improving accuracy in depth position measurement compared to the traditional Lagrangian framework. Different from traditional imaging methods, HADIPI can directly display the 3D movement of droplets, including in the depth direction. In the combustion measurements of the solid rocket motor, the motion state of metal droplets can be precisely determined, demonstrating the feasibility and practicality.

Measuring Local Atomic Structure Variations through the Depth of Ultrathin (&lt;20 nm) ALD Aluminum Oxide: Implications for Lithium-Ion Batteries

Understanding the atomic structure of ultrathin (<20 nm) atomic layer deposition (ALD) coatings is critical to establish structure–property relationships and accelerate the application of ALD films to stabilize battery interfaces. Previous studies have measured the atomic structure of nanoscale ALD films using cryogenic electron diffraction with a large (∼200 nm) beam diameter. However, for ultrathin ALD coatings, these measurements provide only ensemble average structural information and cannot be used to directly measure differences in atomic structure through the depth of the ALD film. In this study, we localize the electron beam to a small (∼5 nm) spot size using cryogenic scanning transmission electron microscope (STEM), and we collect electron diffraction data at multiple points along the depth of a 12 nm thick ALD AlOx film deposited onto a carbon nanotube (CNT) substrate without a contribution from the substrate. We couple these diffraction measurements with pair distribution function (PDF) analysis and iterative reverse Monte Carlo-molecular statics (RMC-MS) modeling to compare atomic structure metrics at different positions in the film depth. We interpret the modeling results considering the three-dimensional (3D) concentric cylindrical sample geometry of a CNT with uniform AlOx coating. These measurements confirm a two-phase bulk/interface structural model proposed previously for ALD AlOx and indicate that the interfacial layer at the CNT–AlOx interface is 2.5 nm thick─5 times larger than previously reported. This report demonstrates direct measurement of atomic structural variations across nanoscale material interfaces that is of broad interest for electrochemical applications and will help inform the use of ALD coatings to stabilize lithium-ion battery interfaces.

Fanya juu Terraces Improve Maize (Zea mays L.) and Bean (Phaseolus vulgaris L) Grain Yields on Hardsetting Soils of Semi-arid Eastern Kenya

Aims: Fanya juu terraces are constructed by digging a ditch and throwing the soil up-slope with the sole purpose of maintaining an embankment to slow down runoff flow. The effect of the terraces on crop yields along the slope varies with the soil type. The aim of this study was to determine the effect of Fanya juu terraces on maize (Zea mays L.) and bean (Phaseolus vulgaris L.) yields and how these yields differ with slope positions and depth of the ditches.&#x0D; Study Design: Split-split plot design with four replications.&#x0D; Place and Duration of Study: The trial was established on Luvisols in Mua location, Machakos County in Eastern Kenya at 37o15’E 1o29’S and 37o15’E 1o29’S during both long rain (LR) and short rain (SR) seasons of 2014 and 2015 (February 2014 to March 2015).&#x0D; Methodology: Treatments consisted of three ditch depths (60 cm, 30 cm and 0 cm (control)) in the main plots and three cropping systems (maize/bean intercrop, sole maize and sole bean) in the sub plots. Grain yields were compared across the seasons at the upper, middle and lower slope positions of the terraces using analysis of variance and means separated using least significant difference at P≤0.05.&#x0D; Results: There were significant differences in maize grain yields in the interactions of ditch depth and slope position (P=0.004) and ditch depth and season (P&lt;0.001). Higher maize yields were realized when ditches were constructed than in the control. Yields increased from the lower to the upper slope position of the terraces with 30 cm ditch by 49.8% and in the 60 cm by 41.6%. Average yields from treatments with 30 cm ditch were significantly higher than from the control but non-significant from those in the 60 cm ditch. Significant differences (P=0.037) in bean grain yields were observed in interactions of ditch depth and slope position. Higher yields were obtained from the lower position of the 30 cm ditch than the middle and upper positions. Significant differences (P=0.033) were also found in interactions of ditch depths, cropping systems and seasons.&#x0D; Conclusion: The results indicate that Fanya juu terraces had a significant effect on crop yields on hardsetting soils. The study recommends construction of Fanya juu terraces with a ditch depth of 30 cm and intensive management of the lower slope position for improved maize and bean production on hardsetting soils in marginal areas.

Contrasting hydrodynamic regimes of submerged pinnacle and emergent coral reefs

Hydrodynamics on coral reefs vary with depth, reef morphology and seascape position. Differences in hydrodynamic regimes strongly influence the structure and function of coral reef ecosystems. Submerged coral reefs on steep-sided, conical bathymetric features like seamounts experience enhanced water circulation as a result of interactions between currents and the abrupt physical structure. There may also be similar interactions between smaller pinnacles and regional water currents in offshore locations (crests > 10 m), while shallow reefs (crests <10 m) may be more subject to surface currents driven by wind, waves and tide. Here we tested whether coral pinnacles experienced stronger and more variable currents compared to emergent reefs at the same depth in both nearshore and offshore positions. Current speeds and temperature were monitored for 12 months at 11 reefs, representing the three different reef categories: submerged offshore pinnacles, emergent offshore reefs and emergent nearshore reefs. We found different patterns in current speeds and temperature among reef types throughout the year and between seasons. Submerged pinnacles exhibited stronger, more variable current speeds compared to both near and offshore emergent reefs. We found seasonal changes in current speeds for pinnacle and nearshore reefs but no variation in current strength on offshore reefs. Whilst instantaneous current directions did reflect the seascape position of individual sites, there was no difference in the directional variability of current speeds between reef types. Annual daily average temperatures at all reef types were not strongly seasonal, changing by less than 2 °C throughout the year. Daily temperature ranges at specific sites however, exhibited considerable variability (annual range of up to 6.5 °C), particularly amongst offshore emergent reefs which experienced the highest temperatures despite greater exposure to regional-scale circulation patterns. Additionally, we found a consistent mismatch between satellite sea surface temperatures and in-situ temperature data, which was on average 2 °C cooler throughout the annual study period. Our results suggest that distinct hydrodynamic processes occur on smaller submerged structures that are physically analogous to seamounts. Our findings highlight important nuances in environmental processes that occur on morphologically distinct coral reef habitats and these are likely to be important drivers for the community dynamics of organisms that inhabit these reefs.