Multiple responses of fine root resource uptake strategies to gravel content in a subtropical plantation

Most forest soils contain substantial amounts of gravel. However, unlike the more widely known root resource uptake behaviors which respond to resource patches in substrate without gravels, how roots respond to substrate containing different gravel levels is poorly understood. We grew roots in substrates with five gravel levels (0, 10, 20, 30, and 40% of volume) in a subtropical Schima superba plantation, determined fine root dynamics and turnover rate with minirhizotrons, measured fine root morphological, architectural, mycorrhizal colonization, chemistry, and mass allocation. The presence of gravel in the substrate delayed the timing of peak root growth. In the substrate with higher gravel content, plants produced more in roots in autumn, but there were fewer roots in summer and the roots tended to exhibit lower fine root turnover rate and mycorrhizal colonization, but higher root biomass allocation. The higher root biomass in the substrate with higher gravel content was associated with higher root carbon/nitrogen ratio. Our findings emphasize the complexity of root resource uptake behavior in response to gravel content and suggest that incorporating substrate gravel content into root studies may help to improve the prediction of patch exploitation and nutrient acquisition in stony soils.

Investigation of distinctive physico-chemical soil correlations for Kirkuk city using spatial analysis technique incorporated with statistical modeling

In the sense of challenging economic situation, it is difficult to perform laboratory tests in a whole intended area to define the soil characteristics for whatever task or situation within an entire city. Hence, this study has used the spatial analysis through applying the inverse distance weighted (IDW) technique to integrate with the available data for 56 different soil samples collected from various depths of Kirkuk city. The studied characteristics were mainly classified to physical soil properties included gravel, sand, silt, and clay contents with chemical soil properties included organic and gypsum contents, pH content, sulfur trioxide, and total dissolved solids (TDS) content. Moreover, statistical investigations such as physico-chemical correlation, linear single and linear multi regression models have been applied. The results of this study have focused on constructing thematic digital maps for visualizing different physical and chemical characteristics of Kirkuk soil. In statistical analysis, negative linear correlations are obtained from the relation between the values of the pH, gypsum, organic, and SO3 contents with the increase of the gravel content, whereas a positive linear correlation is attained for the values of TDS content with the increase of the gravel content. Furthermore, the proposed linear multi regression model predicts the pH values reasonably where most of the values were close to the equality line. The obtained digital maps accompanied with the statistical models will provide comprehensive spatial, agricultural, chemical and mechanical visualizations of the nature and morphology of the soils in Kirkuk city.

Numerical simulation study on the crack propagation of conglomerate

The conglomerate reservoir is rich in oil and gas reserves; however, the gravel's mechanical properties and laws are difficult to gain through laboratory experiments, which furthermore constrain the hydraulic fracturing design. To analyse the failure law of conglomerate, we simulated the uniaxial compression test based on discrete element software PFC2D and analysed the effect of different cementation strength, gravel content and gravel geometry on the rock deformation and failure characteristics. Results show that (i) as the cementation strength decreases, the compressive strength and elasticity modulus both reduce clearly, while the crack shapes get more complex and the critical value is 0.3; (ii) as the gravel content increases, the conglomerate strength first decreases then increases under the influences of cracks bypassing gravels; cementation strength and gravel content of the conglomerate both contribute to the increase in local additional stress, which leads to a series of changes in crack shapes and mechanical properties of the conglomerate. Based on the above research, the conglomerate strength and crack shapes after failure are relatively complex due to the common influence of cementation strength and gravel content. The gravel edge crack caused by stress concentration is the micro-mechanism that affects the conglomerate mechanical properties.

Laboratory Model Tests on Flow Erosion Failure Mechanism of a Slope Consisting of Anqing Group Clay Gravel Layer

The Anqing group clay gravel layer is a special geological body composed of gravel and clay. In excavation projects, involving this soil, such a gravel layer, is prone to slope collapse and instability under the influence of rainfall. To clearly understand the failure mechanism and influencing factors of clay gravel slopes, an indoor artificial rainfall erosion model testing was carried out to analyse the effect of various slope ratios, gravel contents, and rainfall intensities. The slope erosion damage form, runoff rate, infiltration rate, scoured material, and slope stability of the clay gravel slope were studied. The test results show that sloping surfaces of the gentle slope were mainly damaged by erosion, and the degree of damage gradually increased from the top to the bottom of the sloping surface; however, the stability of the surface was good. In the case of the sloping surface layer of the steep slope, large-scale landslides occurred, and the stability of the surface was poor. When the gravel content was small, the surface failure was manifested as a gully failure. When the gravel content was large, it was manifested as a “layer-by-layer sliding” failure. The degree of influence of different conditions on the stable runoff rate was as follows: rainfall intensity>slope ratio>gravel content. The degree of influence of the parameters on the stable infiltration rate was as follows: slope ratio>rainfall intensity>gravel content. On gentle slopes, the total mass of the scoured material was inversely proportional to the gravel content and directly proportional to the rainfall intensity; on a steep slope, the total mass of the scoured material increased with an increase in the rainfall intensity and gravel content. Moreover, the slope ratio was the key influencing factor to decide whether there was gravel in the scoured material.

Bender Element Test and Numerical Simulation of Sliding Zone Soil with Gravels of Huangtupo Landslide

<p>In order to study the effect of the different consolidation pressure, loading-unloading path and gravel content on the shear modulus of the small strain of sliding zone soil, a set of consolidation bender element test device was developed. The device consists of three parts: a consolidation system, a deformation measuring system, and a shear wave testing system. The consolidation system is composed of a traditional consolidation instrument and the plexiglass cylinder box. The sample is cylindrical in shape and has a size of 50 mm×50 mm. The consolidation displacement is measured by a digital display micrometer. Shear wave testing system is a wave velocity measurement system made of piezoelectric ceramic. The experimental results show that the device can control the consolidation pressure and measure the vertical deformation, measure the shear wave velocity of the sliding zone soil in real-time, and then study the variation rule of the small strain shear modulus of the sliding zone soil with gravels. The shear modulus of the sliding zone soil increases with an increase in the consolidation pressure. The shear modulus of the unloading of sliding zone soil is larger than that of loading. Under the loading pressure of 200 kPa and 400 kPa, the shear modulus of the sliding zone soil first decreases and then increases with an increase in the gravel content. In the process of unloading, the shear modulus of the sliding zone soil increases with an increase in the gravel content. </p>

The late Pleistocene and Holocene glaciation history of sub-Antarctic South Georgia

<p>The ice cap of the sub-Antarctic island South Georgia is influenced by the Antarctic Circumpolar Current and is hence more sensitive to changing climate than the significantly larger and more isolated Antarctic ice sheets. Furthermore, the sediment deposits in fjords and glacially eroded troughs around the island have superbly archived glacier behavior, environmental and climatic changes since the late Pleistocene. This makes South Georgia an attractive target to study past climate variability in the Southern Hemisphere. Nevertheless, the ice sheet’s extents and dynamics during the Last Glacial Maximum (LGM), the Antarctic Cold Reversal (ACR), and the Holocene deglaciation phase are still poorly understood. Although several studies on land and in marine near-shore areas of South Georgia have addressed this, only few studies are based on marine sediment cores from the continental shelf. In this study, we use ten gravity cores from three different troughs on the southern and northwestern shelf to further investigate the climatic and glaciological evolution of South Georgia during and since the LGM.</p><p>Multi-proxy sedimentological analyses carried out in this study include core logging, XRF geochemical profiling, XRD analyses on bulk sediment and clay fraction, measurements of physical properties, magnetic susceptibility, grain size distribution and shear strength. For the Drygalski Trough on the southern shelf, lithofacies description reveals the deposition of stratified, predominantly sandy diamicton and greenish-grey massive to laminated, sometimes bioturbated mud with variable amounts of clasts. First radiocarbon ages from benthic foraminifera constrain the deposition of the diamicton, interpreted as waterlain till, on the outer shelf to the LGM. Inferred linear sedimentation rates attest to low sediment input on the outer shelf during the LGM (34 cm/ka) and the Holocene (23-32 cm/ka). In contrast, a higher sedimentation rate (114 cm/ka) between 14.7 and 13.7 cal ka BP is likely associated with enhanced erosion due to a possible re-advance of South Georgia’s glaciers during the ACR’s colder and wetter climate. For island-proximal cores, sedimentation rates are generally higher than on the outer shelf with rates of 80-2300 cm/ka during the Mid- to Late Holocene. This stronger fluctuation of sedimentation rates is due to higher temporal resolution of the dated sediments compared to the outer shelf. Grain-size distribution on the outer shelf shows a gravel content of 1-28 wt% in the diamicton facies from the LGM and 1-5 wt% in a sediment interval dated to 16.8 cal ka BP. This sediment interval is also characterized by a high content of pebbles, likely reflecting an increased input of IRD. The overlying ACR and Holocene show a low gravel content of 0-0.7 wt%. The diamicton suggests that ice-proximal conditions prevailed on the outer shelf during the LGM and therefore supports the theory of a shelf-wide glaciation. The combination of a low-resolution sediment core from the outer shelf and island-proximal high-resolution sediment cores has the potential to give new insights into South Georgia’s climate history from the Late Pleistocene to the Late Holocene.</p>

The Gravel Parameterization Schemes on Tibetan Plateau and Its Assessment Using RegCM4

<p>In this paper, the impact of gravel is taken into account in regional simulations on the Tibetan Plateau (TP). The differences of ground surface and soil hydrological processes in the TP are compared when the gravel parameterization schemes and the original soil hydrothermal parameterization schemes are respectively adopted in the regional climate model version 4.7 (RegCM4.7), which is driven by the EIN15. Moreover, the performances in simulating the liquid soil moisture (LSM) by using the two schemes are also assessed. When the impact of gravel is considered, the changes of ground hydrological processes are consistent with those of liquid precipitation and snow meltwater except the infiltration, indicating the dominance of liquid precipitation and snow meltwater in ground hydrological processes. The lower gravel content will facilitate the downward transportation of LSM. However, in the case of high gravel content, the roles of gravel content are completely opposite in the western and central TP. The most obvious change is that the simulated LSM by the gravel schemes is lower at most soil depths compared with that by the original schemes, which is beneficial in most cases. For instance, the mean absolute errors of the reference data with the simulations by the gravel schemes and original schemes at the soil depth of 0.1 m in the southeastern TP are 0.026 and 0.101, respectively. Besides the southeastern TP, the performance in simulating the temporal variation of the LSM below the middle soil layers still needs to be improved.</p>