Sand Site Research Articles

Soil organic carbon stocks in topsoil and subsoil controlled by parent material, carbon input in the rhizosphere, and microbial-derived compounds

Despite a large body of studies investigating soil organic carbon (SOC) stocks and potential influencing factors, the impact of contrasting parent material, particularly in the subsoil, has received little attention. To reveal potential effects varying parent materials exert on SOC stocks, we investigated chemical (14C content and overall chemical composition via 13C NMR spectroscopy) and plant/microbial related parameters (root mass, amino sugars) of bulk soil and soil organic matter fractions from topsoil, subsoil, and rhizosphere soil at three European beech stands (Fagus sylvatica L.) only differing in parent material (Tertiary sand, Quaternary loess, and Tertiary basalt).The results suggest that the clay fraction, its amount being largely dependent on the respective parent material, took a central role in shaping differences in SOC stocks among the investigated sites by affecting soil organic matter stabilization via organo-mineral association and aggregation. This fraction was particularly relevant in the subsoil, where it accounted for up to 80% of the bulk soil SOC stocks that decreased with decreasing amounts of the clay fraction (basalt > loess > sand site). Determining the soil's nutrient composition, parent material likely also indirectly affected SOC stocks by changing rhizosphere traits (such as fine root density or mortality) and by attracting root growth (and thus organic matter inputs) to subsoil with higher nutrient contents, where in situ root inputs in the form of rhizodeposits were likely the prime source of plant-derived SOC. However, root inputs also contributed in large part to topsoil SOC stocks and were associated with higher abundance of microbial compounds (amino sugars), whose relative importance increased with increasing soil depth.Independent of soil depth and site, amino sugars and the amount of the clay fraction, combined with parameters related to the input of organic matter (root mass and amount of the particulate organic matter fraction) explained more than 90% of the variability in SOC stocks, indicating a key role of these measures in impacting SOC stocks. Because parent material directly or indirectly influenced these parameters, we demonstrate the necessity to consider differences in parent material when estimating and predicting SOC stocks.

Selection of representative shear modulus reduction and damping curves for rock, gravel and sand sites from the KiK-Net downhole array

Representative computation of ground response parameters requires accurate information about nonlinear dynamic behavior of the soil column, commonly incorporated in site response analysis through shear modulus reduction and damping curves which are functions of the strain level. Most site response studies are carried out by considering a set of existing shear modulus and damping curves, without knowing its suitability for the in situ soil type. In this study, an attempt has been made to identify suitable shear modulus and damping curves for soil grouped into different classes viz. sand, gravel and rock. Soil profiles of sites having surface and bedrock motion recordings are selected from the KiK-Net downhole array database and equivalent linear and total stress nonlinear site response analysis has been carried out by varying the shear modulus and damping curves for different sites. Estimated surface response spectra for each set of shear modulus and damping curves are compared with the observed response spectra at each site, and a detailed analysis is made to find out which set of curves gives a best match with the recorded data. Based on this study, representative property curves for rock, gravel and sand are suggested, which could be used for further site response studies in the region. This study shows that only a set of shear modulus and damping curves ensure a compatible spectrum with the recorded data from the KiK-Net downhole array sites, among the many available shear modulus and damping curves in the literature.

Weed control increases nitrogen retranslocation and growth of white spruce seedlings on a reclaimed oil sands soil

Early establishment of seedlings in reclaimed oil sand areas is often limited by low nutrient and water availability due to factors such as strong understory vegetation competition. Management practices such as nursery fertilization and field weed control could help early establishment of planted seedlings and reclamation success. We investigated the effect of nursery nutrient loading and field weed control on the growth, nitrogen (N) retranslocation within seedling components, and plant N uptake from the soil for white spruce (Picea glauca [Moench] Voss) seedlings planted on a highly competitive reclaimed oil sands site for two years. Exponential fertilization during nursery production increased the root biomass but not the nutrient reserve in the seedling. In the field experiment, on average across the treatments, 78 and 49% of the total N demand of new tissue growth in the first and second year were met by N retranslocation, respectively. Though exponential fertilization did not affect N retranslocation, it increased the percent height and root collar diameter growth. Weed control increased not only the growth of seedlings by increasing soil N availability, but also N retranslocation within the seedlings in the second year after outplanting. We conclude that vegetation management by weed control is feasible in improving the early growth of white spruce seedlings planted on reclaimed soils and facilitate tree establishment in the oil sands region. Optimization of the nursery exponential N fertilization regime for white spruce may further help with early revegetation of reclaimed oil sands sites.

Growth and nitrogen uptake of jack pine seedlings in response to exponential fertilization and weed control in reclaimed soil

We evaluated the impact of exponential fertilization in nursery and weed removal in the field on growth and nitrogen (N) retranslocation and uptake from the soil of jack pine (Pinus banksiana Lamb.) seedlings planted on an oil sands reclaimed soil. Exponential fertilization is a method of supplying nutrients at an exponential rate to achieve constant internal nutrient concentrations in seedlings without changing their size during their growth in the nursery. The N retranslocation in seedlings was traced using 15N isotope labeling. Exponential fertilization increased nutrient reserve in the seedling in nursery production, and increased height (P = 0.003), root collar diameter (P < 0.001), total biomass (P < 0.001), and N content (P < 0.001) of seedlings at the end of first growing season in the field growth. Conventionally fertilized seedlings allocated a greater percent of biomass to roots than to current-year needles. The 15N isotope analysis showed that 59 to 82% of total N demand of new growth was met by retranslocation from old tissues. Exponential fertilization increased N retranslocation by 147% (P < 0.001) and N uptake from the soil by 175% (P = 0.012). Weed removal marginally increased (P = 0.077) N uptake from the soil but decreased (P = 0.046) N retranslocation with no net effect on total N content in new tissues. We conclude that exponential fertilization improves the early growth of jack pine and can help improve revegetation in reclaiming disturbed oil sands sites.

Soil type more than precipitation determines fine-root abundance in savannas of Kruger National Park, South Africa

Our aim was to examine how soil type and precipitation affect fine-root abundance in savanna ecosystems across Kruger National Park (KNP), South Africa. Fine-root distributions were measured in four sites that represent the natural factorial combination of soil types (basalt-derived clay or granite-derived sand) and precipitation regimes [wet (~750 mm mean annual precipitation) or dry (~500 mm mean annual precipitation)] that occur in KNP. Root area and biomass (at soil depths of 0–75 cm) were estimated from measurements of root number, length and width in images from minirhizotron tubes at each site. Measurements were made during one mid-season sampling during three subsequent years. Fine-root area was more than twice as large in clay (2.3 ± 0.0 mm2 cm−2) than sand (0.8 ± 0.3 mm2 cm−2) sites but did not differ between wet and dry sites. Root number, length and width, used to derive area, showed similar patterns to fine-root area. Fine-root biomass estimated from these values was 5.5 ± 0.6 Mg ha−1 in clay sites and 2.2 ± 0.9 Mg ha−1 in sand sites. Across the four sites, a change from sand to clay soils had a greater effect on fine-root abundance and distributions than a 50% increase in precipitation from dry to wet sites. Results highlight the importance of soil properties on root dynamics and carbon pools in the region.

Before-After analysis of the trophic network of an experimental dumping site in the eastern part of the Bay of Seine (English Channel)

An experimental study was conducted to assess the physical and biological impacts of muddy fine sand dredged material dumped on a medium sand site Machu offshore the Seine Estuary. Complementary trophic web modelling tools were applied to the Machu ecosystem to analyse the effects of dumping operations. Results show that, after the dumping operations, the biomass of fish increased while invertebrate biomass remained relatively stable through time. Nevertheless, the biomasses of benthic invertebrates, omnivores/scavengers and predators showed some increases, while non-selective deposit feeders and filter feeders decreased. At the ecosystem level, results show that the total ecosystem activity, the ascendency and the overall omnivorous character of the food-web structure increased after dumping operations, whereas recycling subsequently decreased. Finally, the fine and medium sand habitat offshore from the Seine estuary, which undergoes regular natural physical perturbations, shows a high resilience after a short dumping phase.

Effects of Supplemental Feeding on Northern Bobwhite Populations in South Texas

During 1985–87, the effects of supplemental feeding on northern bobwhite (Colinus virginianus) populations were studied on 4 paired sites, representing a cross-section of soils, vegetation, and hunting pressure in south Texas. Whole milo was provided from late fall–March. Feeding increased winter survival of birds on deep sand sites (225–245%), but not on red sandy loam or clay sites. Feeding did not improve reproductive success on any of the study sites. Most birds collected had milo in their crops and there was a tendency to find birds close to feeders more often than at random points. The study demonstrated that supplemental feeding can increase survival if food is limiting, however, data suggested feeding was not effective when habitat structure was inappropriate, or when food was not limiting.

CHD pile performance: part II – numerical modelling

A set of simple finite-element modelling procedures that can be used to estimate the load–settlement behaviour of continuous helical displacement (CHD) piles in sand is presented. The approach makes use of a stress- and strain-dependent non-linear soil model that can be parameterised using basic soil data that can be determined through routine site investigation. The procedures are validated against a database of physical model tests (reported in a companion paper), where they are shown to be suitable for estimating the load–settlement behaviour of CHD piles within the serviceability range. In this way they are complementary to the analytical method reported in the companion paper for estimating the ultimate capacity of a CHD pile. In this paper, the finite-element method and analytical model are applied to four historical load tests on CHD piles conducted at three different sand sites. The modelling is further validated and used to discuss potential savings in pile material and therefore cost due to additional confidence in performance determination at both ultimate and serviceability limit states.

Field experiments on instrumented winged monopiles

This paper presents the results of field tests performed to investigate the field behaviour of winged-monopile foundations. The principle of the winged monopile is that steel plates are attached to a standard monopile (in the area near the ground or seabed surface) to increase the foundation stiffness and lateral resistance. The experimental tests described in this paper consisted of load tested driven instrumented prototype scale standard (reference) monopiles and piles with varying wing geometries at two sand sites. The overall load–displacement performance and mobilised bending moment profiles were examined to assess the potential benefits of adding wings to monopiles. Experimental p–y curves were developed for the piles to analyse how the presence of wings influenced the soil–structure interaction of the foundation system. The use of simplified p–y methods for predicting the winged-pile response was assessed. The experiments proved that the addition of wings greatly improved the lateral resistance and stiffness of the piles; however, the results suggest that conventional p–y curve methods are limited as they cannot account for the effect that the enhanced stresses mobilised by the wings have on the strength and stiffness response of the pile below the wing location.

Shaft resistance of driven cast-in-situ piles in sand

Driven cast-in-situ (DCIS) piles are classified as a large displacement pile, despite sharing certain aspects of their construction with replacement pile types. However, there are relatively few case histories of load tests on DCIS piles in the literature to verify the assumption that they behave as large displacement piles. In particular, the shaft resistance of DCIS piles in sand is uncertain due to the complex interaction between the freshly cast concrete and surrounding displaced soil after extraction of the steel installation tube. This paper describes the installation, curing, and maintained compression load testing of three temporary-cased DCIS test piles at a uniform sand site near Coventry, United Kingdom. The piles were instrumented with vibrating wire strain gauges to enable accurate measurement of the local shear stress generated on the pile shaft during maintained compression loading. The tests showed that the peak average and local shear stresses tended to mobilize at greater shaft displacements than traditional preformed displacement piles during loading. A clear reduction in normalized local shear stresses (and hence radial effective stress) at failure with distance from the pile base, i.e., friction fatigue, was evident for all piles, implying that radial stresses generated during driven installation of the steel tube are not erased upon concreting and tube withdrawal. Furthermore, the inferred normalized radial effective stresses at failure were remarkably similar to those reported for traditional preformed displacement piles in the literature.

Features of revegetation of drift sand sites in the northern taiga subzone of Western Siberia

Features of revegetation of drift sand sites in the northern taiga subzone of Western Siberia

Fine root dynamics in lodgepole pine and white spruce stands along productivity gradients in reclaimed oil sands sites.

Open-pit mining activities in the oil sands region of Alberta, Canada, create disturbed lands that, by law, must be reclaimed to a land capability equivalent to that existed before the disturbance. Re-establishment of forest cover will be affected by the production and turnover rate of fine roots. However, the relationship between fine root dynamics and tree growth has not been studied in reclaimed oil sands sites. Fine root properties (root length density, mean surface area, total root biomass, and rates of root production, turnover, and decomposition) were assessed from May to October 2011 and 2012 using sequential coring and ingrowth core methods in lodgepole pine (Pinus contorta Dougl.) and white spruce (Picea glauca (Moench.) Voss) stands. The pine and spruce stands were planted on peat mineral soil mix placed over tailings sand and overburden substrates, respectively, in reclaimed oil sands sites in Alberta. We selected stands that form a productivity gradient (low, medium, and high productivities) of each tree species based on differences in tree height and diameter at breast height (DBH) increments. In lodgepole pine stands, fine root length density and fine root production, and turnover rates were in the order of high > medium > low productivity sites and were positively correlated with tree height and DBH and negatively correlated with soil salinity (P<0.05). In white spruce stands, fine root surface area was the only parameter that increased along the productivity gradient and was negatively correlated with soil compaction. In conclusion, fine root dynamics along the stand productivity gradients were closely linked to stand productivity and were affected by limiting soil properties related to the specific substrate used for reconstructing the reclaimed soil. Understanding the impact of soil properties on fine root dynamics and overall stand productivity will help improve land reclamation outcomes.

Estimation of groundwater recharge via deuterium labelling in the semi-arid Cuvelai-Etosha Basin, Namibia

The stable water isotope deuterium (2H) was applied as an artificial tracer (2H2O) in order to estimate groundwater recharge through the unsaturated zone and describe soil water movement in a semi-arid region of northern central Namibia. A particular focus of this study was to assess the spatiotemporal persistence of the tracer when applied in the field on a small scale under extreme climatic conditions and to propose a method to obtain estimates of recharge in data-scarce regions. At two natural sites that differ in vegetation cover, soil and geology, 500 ml of a 70 % 2H2O solution was irrigated onto water saturated plots. The displacement of the 2H peak was analyzed 1 and 10 days after an artificial rain event of 20 mm as well as after the rainy season. Results show that it is possible to apply the peak displacement method for the estimation of groundwater recharge rates in semi-arid environments via deuterium labelling. Potential recharge for the rainy season 2013/2014 was calculated as 45 mm a−1 at 5.6 m depth and 40 mm a−1 at 0.9 m depth at the two studied sites, respectively. Under saturated conditions, the artificial rain events moved 2.1 and 0.5 m downwards, respectively. The tracer at the deep sand site (site 1) was found after the rainy season at 5.6 m depth, corresponding to a displacement of 3.2 m. This equals in an average travel velocity of 2.8 cm d−1 during the rainy season at the first site. At the second location, the tracer peak was discovered at 0.9 m depth; displacement was found to be only 0.4 m equalling an average movement of 0.2 cm d−1 through the unsaturated zone due to an underlying calcrete formation. Tracer recovery after one rainy season was found to be as low as 3.6 % at site 1 and 1.9 % at site 2. With an in situ measuring technique, a three-dimensional distribution of 2H after the rainy season could be measured and visualized. This study comprises the first application of the peak displacement method using a deuterium labelling technique for the estimation of groundwater recharge in semi-arid regions. Deuterium proved to be a suitable tracer for studies within the soil–vegetation–atmosphere interface. The results of this study are relevant for the design of labelling experiments in the unsaturated zone of dry areas using 2H2O as a tracer and obtaining estimations of groundwater recharge on a local scale. The presented methodology is particularly beneficial in data-scarce environments, where recharge pathways and mechanisms are poorly understood.

Benthic oxygen exchange in a live coralline algal bed and an adjacent sandy habitat: an eddy covariance study

Coralline algal (maerl) beds are widespread, slow-growing, structurally complex perennial habitats that support high biodiversity, yet are significantly understudied compared to seagrass beds or kelp forests. We present the first eddy covariance (EC) study on a live maerl bed, assessing the community benthic gross primary productivity (GPP), respiration (R), and net ecosys- tem metabolism (NEM) derived from diel EC time series collected during 5 seasonal measurement campaigns in temperate Loch Sween, Scotland. Measurements were also carried out at an adja- cent (~20 m distant) permeable sandy habitat. The O2 exchange rate was highly dynamic, driven by light availability and the ambient tidally-driven flow velocity. Linear relationships between the EC O2 fluxes and available light indicate that the benthic phototrophic communities were light - limited. Compensation irradiance (Ec) varied seasonally and was typically ~1.8-fold lower at the maerl bed compared to the sand. Substantial GPP was evident at both sites; however, the maerl bed and the sand habitat were net heterotrophic during each sampling campaign. Additional inputs of ~4 and ~7 mol m −2 yr −1 of carbon at the maerl bed and sand site, respectively, were required to sustain the benthic O2 demand. Thus, the 2 benthic habitats efficiently entrap organic carbon and are sinks of organic material in the coastal zone. Parallel deployment of 0.1 m 2 benthic chambers during nighttime revealed O2 uptake rates that varied by up to ~8-fold between repli- cate chambers (from −0.4 to −3.0 mmol O2 m −2 h −1 ; n = 4). However, despite extensive O2 flux vari- ability on meter horizontal scales, mean rates of O2 uptake as resolved in parallel by chambers and EC were typically within 20% of one another.

Quantification of prior knowledge in geotechnical site characterization

Geotechnical characterization of a project site often starts with desk-study and site reconnaissance, which provide site information available prior to the project (e.g., existing data in literature, engineering experience, and engineers' expertise). Such information can be used as “prior knowledge” under a Bayesian framework and be quantitatively reflected by a prior distribution in Bayesian methods. However, it is not a trivial task for engineering practitioners to properly quantify prior knowledge as a prior distribution. This paper develops two different methods to quantify prior knowledge during geotechnical characterization of a project site. Where there is no prevailing prior knowledge on the site, a non-informative prior distribution (e.g., uniform prior distribution) is used to reflect quantitatively the engineering common sense and judgment. As prior knowledge improves and becomes much more informative, a subjective probability assessment framework (SPAF) is proposed to estimate the prior distribution from prior knowledge. The proposed SPAF framework assists geotechnical engineers in formulating and expressing their engineering judgments in a quantifiable and transparent manner. These two different methods are illustrated using information from a sand site of the US National Geotechnical Experimentation Sites (NGES) at Texas A&M University (TAMU).

Reconciling Harvest Intensity and Plant Diversity in Boreal Ecosystems: Does Intensification Influence Understory Plant Diversity?

Overall demand for forest products in the boreal forest is increasing to supply growing bio-energy demands in addition to traditional forest products. As a result, there is a need to refine current forest policies to reconcile production and ecosystem function within the context of ecologically sustainable management. This study assessed understory plants' richness, evenness, and diversity in six harvested boreal black spruce-dominated stands situated on loam, sand, and peat site types 15years after the application of four harvest treatments of increasing biomass removals. Treatments included uncut, stem-only harvest, full-tree harvest, and full-tree harvest+blading of O horizon. Following canopy removal, species richness and diversity (Shannon's and Simpson's indices) increased on all soil types. The more than doubling of slash loading on the stem-only treatment plots compared to the full-tree plots led to significantly lower species diversity on loam sites; however, the reverse was observed on peat sites where the slash provided warmer, drier microsites facilitating the establishment of a broader array of species. Preexisting ericaceous shrub and sphagnum components continued to dominate on the peat sites. Compositional shifts were most evident for the full-tree+bladed treatment on all soil types, with increases in herbaceous cover including ruderal species. The results suggest that the intensification of harvesting on plant diversity varies with soil type, and these differential results should be considered in the refinement of forest biomass-harvesting guidelines to ensure ecological sustainability and biodiversity conservation over a broad suite of soil types.

Shearing resistance during pile installation in sand

This paper examines the detailed stress changes recorded by surface stress transducers equipped on model piles during jacked installation of various piles at sand sites with different groundwater regimes and sand characteristics. Three separate types of shear stress–displacement characteristics are observed and these are explained using findings from existing laboratory and field-based studies on soil-pile–penetrometer interface friction. The findings advance understanding of factors influencing the shearing resistance developed during displacement pile installation in sand, which is an important consideration for pile driveability assessments.

Maximizing Natural Trembling Aspen Seedling Establishment on a Reclaimed Boreal Oil Sands Site

Actively facilitating the natural establishment of trees on reclamation sites is seen as an important step in ecosystem recovery after oil sands mining. We examined the effect of different reclamation prescriptions, including two soil types (peat-mineral mix and forest floor-mineral mix) and two fertilizer levels (200 kg N ha–1 and no fertilizer), on naturally established trembling aspen ( Populus tremuloides ) seedlings and other deciduous trees. Aspen has a tiny, windblown seed which is very sensitive to moisture stress during establishment. Seedling establishment was greatest on peat-mineral mix soil with no fertilizer application and was related to the increased surface roughness and soil moisture and lack of vegetation competition with this soil prescription. Surprisingly, seedling establishment was not related to microsite characteristics such as concavity. Once established, average seedling height was not significantly different among soil types or fertilization treatments. Overall, using peat-mineral mix soil and increasing surface roughness offer a starting point for developing best management practices for facilitating natural deciduous tree seedling establishment in this region.

Liquefaction Potential of Recent Fills versus Natural Sands Located in High-Seismicity Regions Using Shear-Wave Velocity

The liquefaction potential of clean and silty sands is examined on the basis of the field measurement of the shear-wave velocity, Vs. The starting point is the database of 225 case histories supporting the Andrus-Stokoe Vs-based liquefaction chart for sands, silts, and gravels. Only clean and silty sands with nonplastic fines are considered, resulting in a reduced database of 110 case histories, which are plotted separately by type of deposit. A line of constant cyclic shear strain, γcl≈0.03%, is recommended for liquefaction evaluation of recent uncompacted clean and silty sand fills and earthquake magnitude, Mw=7.5. The geologically recent natural silty sand sites in the Imperial Valley of southern California have significantly higher liquefaction resistance as a result of preshaking caused by the high seismic activity in the valley. A line of constant cyclic shear strain, γcl≈0.1–0.2%, is recommended for practical use in the Imperial Valley. Additional research including revisiting available Vs-based and penetration-based databases is proposed to generalize the results of the paper and develop liquefaction charts that account more realistically for deposit type, seismic history, and geologic age.

First-Order Assessment of the Influence of Three EPS and Calcite-Producing Microbes Isolated from a Cemented Sand Site on Soil Shear Strength

Subsurface geotechnical data from a cemented tailings sand site in eastern India indicated that the cementation was at least partially biogenic. Three strains of aerobic soil-residing bacteria from this site exhibited capabilities of producing extracellular polymeric substance, calcite and struvite when grown in minimal mineral salt media. These strains grew easily under a variety of physical, chemical and nutritional conditions. Drained triaxial testing of loose sand samples indicated that they became stronger upon hosting these strains. No details on EPS and calcite production of these isolates and the effects of these products on soil behavior were found in the literature.