Water-saturated Soil Research Articles

Role of soil pore structure in water infiltration and CO2 exchange between the atmosphere and underground air in the vadose zone: A combined laboratory and field approach

The soils above caves represent a membrane that regulates the connection between the underground environment and the outside atmosphere. In this study, soils from two different field sites (Cueva de Altamira and Cueva del Rull in Spain) are investigated. Field results are analysed and linked to laboratory tests. Several laboratory experiments are performed to quantify CO2 diffusion coefficients and water infiltration rates in these soils under different degrees of soil water saturation and compaction.Tests confirm that the grain size distribution, organic matter content, mineral composition and water content of soils affect gas transport through the soil pore network. Both field and lab results reveal that Altamira soil has a coarser texture and therefore has higher CO2 diffusion coefficients, infiltration rates and hydraulic conductivity values than Rull soil. Rull soil contains a higher proportion of fine particles and organic matter, which explains the lower fluid transport coefficients.When soils are near saturation, fluid transport does not depend on the physical properties of soil but depends on the soil water content. In this state, liquid transport regulates the available space within the soil pores, which leads to a reduction in the gaseous diffusion coefficient of the soil. After rainfall episodes, the connection between the exterior atmosphere and underground cavities is hindered due to a rise in the soil water content, which is responsible for the closure of the overlying membrane. This study demonstrates that soil-produced CO2 reaches the underground atmosphere through diffusion processes that are controlled by the intrinsic properties of soil (porosity, grain size distribution, texture, mineralogy and organic matter content) and soil water content.

Modelling of deformation of underground tunnel lining, interacting with water-saturated soil

Built finite element method of calculating the deformation of underground tunnel lining, interacting with dry and water-saturated soils. To simulate the interaction between the lining and soils environments, including physical and non-linear, a special "contact" finite element, which allows to consider all cases of interaction between the contacting surfaces. It solved a number of problems of deformation with the ground subway tunnel lining rings.

Effects of different management practices on vertical soil water flow patterns in the Loess Plateau

Different management practices are adopted to ensure sustainable development in agriculture and to maintain ecological environment security. However, the soil water infiltration types under different management practices were still unclear. This study was designed to assess the effect of different management practices on the water flow behavior of soil. Four management practices were carefully selected. Plot 1 was uncultivated field, Plot 2 contained alfalfa (Medicago sativa L.) and was untilled for two years (alfalfa field), Plot 3 contained maize (Zea mays L.) with conventional tillage from 2008 to 2015 (conventional tillage field), and Plot 4 contained maize with conservation tillage from 2008 to 2015 (conservation tillage field). Soil physical properties (e.g., gravimetric water content, soil bulk density, total porosity, and saturated water content) in the top 50cm layer were measured following conventional methods A dye tracer was introduced to these plots, and the different types of water flows were visualized using classified dye-stained patterns. In the uncultivated field, preferential flow was triggered by wetting front instabilities and generally confined to the upper 15cm of the soil profile. The presence of preferential paths (alfalfa taproot) in the alfalfa field resulted in high and continuous preferential flow. The macropore flow bypassed the compacted soil and was confined into two isolated patches, making it the dominant flow behavior in the conventional tillage field. Conservation tillage systems enhanced the continuity and connectivity of the macropore system and converted the shape of the preferential flow to an inverted triangular distribution. The order of continuity and connectivity degree for the macropore system from highest to lowest was alfalfa field, conservation tillage field, uncultivated field, and conventional tillage field. Above mentioned results that were newly achieved from this study highlighted a significant change in soil water storage and flow behaviors with different management practices compared with those of uncultivated land. The present study suggests that local governments and farmers would prefer alfalfa field and conservation tillage field to other management measures.

Electrodeposition of self-assembled poly(3,4-ethylenedioxythiophene) @gold nanoparticles on stainless steel wires for the headspace solid-phase microextraction and gas chromatographic determination of several polycyclic aromatic hydrocarbons

In this work, a novel poly(3,4-ethylenedioxythiophene)@Au nanoparticles (PEDOT@AuNPs) hybrid coating was prepared and characterized. Firstly, the monomer 3,4-ethylenedioxythiophene was self-assembled on AuNPs, and then electropolymerization was performed on a stainless steel wire by cyclic voltammetry. The obtained PEDOT@AuNPs coating was rough and showed cauliflower-like micro-structure with thickness of ∼40μm. It displayed high thermal stability (up to 330°C) and mechanical stability and could be used for at least 160 times of solid phase microextraction (SPME) without decrease of extraction performance. The coating exhibited high extraction capacity for some environmental pollutants (e.g. naphthalene, 2-methylnaphthalene, acenaphthene, fluorene and phenathrene) due to the hydrophobic interaction between the analytes and PEDOT and the additional physicochemical affinity between polycyclic aromatic hydrocarbons and AuNPs. Through coupling with GC detection, good linearity (correlation coefficients higher than 0.9894), wide linear range (0.01–100μgL−1), low limits of detection (2.5–25ngL−1) were achieved for these analytes. The reproducibility (defined as RSD) was 1.1–4.0% and 5.8–9.9% for single fiber (n=5) and fiber-to-fiber (n=5), respectively. The SPME-GC method was successfully applied for the determination of three real samples, and the recoveries for standards added were 89.9–106% for lake water, 95.7–112% for rain water and 93.2–109% for soil saturated water, respectively.

Estimation of soil hydraulic parameters for different land-uses

Water retention capacity and saturated hydraulic conductivity are important soil hydraulic properties that affect soil productivity and the environment. The knowledge of soil water properties and land-use effects on these properties are important for efficient soil and water management. The aim of this work was to evaluate the effect of cultivation of rangelands on soil water retention. Furthermore, the use of the van Genuchten equation to estimate soil saturated water content (θ s ) and water content (θ h ) was assessed. The comparison of the parameters of this equation [water release parameters (α and n) and residual water content (θ r )] obtained in cultivated and rangelands was also evaluated. Moreover, a comparison between measured and estimated soil saturated hydraulic conductivity (K s ) by several selected pedotransfer functions (PTFs) was performed. The study showed that the land-use effect on soil water retention was significant only at water potentials of −33 and 0 kPa in the top 15 cm of the soil. At the −1500 kPa pressure head, water content was not affected by the land-use type at soil depths of 0–15 cm and 15–30 cm. In this study, α, n, and θ r values were not significantly different between the two land-use types. The fit of the van Genuchten model to water retention data resulted in a low sum of squared errors and high coefficient determination values. Overall, the van Genuchten equation can be used as a physically based model for soil water retention characterization in the studied area. However, this model was not able to accurately estimate K s . No distinct trend for estimated K s by the selected PTFs in the studied area was observed. Thus, it is essential to evaluate the model applicability for different soils at various sites.

The responses of Scots pine seedlings to waterlogging in a fine-textured till soil

Growth decline of Scots pine (Pinus sylvestris L.) on reforestation sites with fine-textured soils are suggested to be due to periodic soil wetness. In this study, Scots pine seedlings were exposed to waterlogging in fine-textured till soil in growth chambers. The treatments started 5 weeks after germination and lasted either for 3 or 8.5 weeks. Three weeks in water-saturated soil affected negatively the root length, root surface area, root volume, the number of root tips, the length of the longest root, root dry mass, the root to shoot ratio, needle water and nitrogen content, and the apoplastic electrical resistance of the stem. The changes by 3 weeks exposure were recoverable since most of the attributes returned to the level of controls when the oxygen content returned to a normoxic level. In contrast, detrimental, but not lethal, effects of water saturation were observed after exposure for 8.5 weeks. Additional effects of prolonged exposure were a decrease in the potential efficiency of photosystem II, the distribution of absorbed light energy between light reactions and the release as heat by chlorophyll fluorescence, and the chlorophyll content index of the needles. We conclude that prolonged water saturation of fine-textured soil is detrimental to the development of Scots pine seedlings which should be considered in practical forest regeneration.

An Advanced Technology for Stabilizing Dust Producing Surfaces of Built-Up Technogenic Massifs During Their Operation

The goal of this research was to develop an advanced technology for stabilizing exposed shore fronts and sides of embankments of built-up technogenic massifs using a binding reagent (mainly a bitumen emulsion) through the development of a hovercraft-based fast-response mobile dust-suppression complex that exhibits good terrain-crossing capability over water-saturated soil with low load-bearing capability. The article presents a description and specific design features for a fast-response mobile dust-suppression complex, and describes its principle of operation.

Soil properties and plant community relationship in a saltmarsh of the Grado and Marano lagoon (northern Italy)

The relationship between soil properties and plant communities was investigated in a saltmarsh of the Grado and Marano lagoon (northern Italy), where hydrology and micromorphology strongly influence the features of the ecosystem. A multidisciplinary approach was used to assess the change of soil properties and plant communities in relation to the submergence of soil. The plant community and soil profile surveys were both carried out along a transect in six sampling sites of the Gran Chiusa saltmarsh (Grado and Marano lagoon). The morphological and physicochemical parameters of soil profiles were investigated, and soils were classified according to Soil Taxonomy. The concentration of macronutrients in both soils and plants was analysed by inductively coupled plasma-optical emission spectrometry. Cluster and linear discriminant analysis were used to assist the interpretation of the data of plant communities and soil properties, respectively. The bioconcentration factor explored the macronutrient relationship between plant community and soil. A high, middle and low zone were identified by clustering the different plant communities along the studied transect. Discriminant analysis showed how the increase in soil submergence supported the accumulation of S and Ca content and depletion of Fe and Na. The development of different plant communities was linked to both soil water saturation and to the capacity of halophytes to tolerate anoxic conditions or salinity, by extrusion or bioconcentration strategies. This study demonstrates that tide level plays an important role in the pedological development and chemical transformations along a soil hydrosequence. The micromosaic vegetation pattern may therefore represent a useful index of the hydrological and nutritional status of the underlying soils and could be used to predict changes in coastal ecosystems.

Methyl Mercury Formation in Hillslope Soils of Boreal Forests: The Role of Forest Harvest and Anaerobic Microbes.

Final harvest (clear-cutting) of coniferous boreal forests has been shown to increase streamwater concentrations and export of the neurotoxin methyl mercury (MeHg) to freshwater ecosystems. Here, the spatial distribution of inorganic Hg and MeHg in soil as a consequence of clear-cutting is reported. A comparison of soils at similar positions along hillslopes in four 80 years old Norway spruce (Picea abies) stands (REFs) with those in four similar stands subjected to clear-cutting (CCs) revealed significantly (p < 0.05) enhanced MeHg concentrations (ng g(-1)), MeHg areal masses (g ha(-1)), and percent MeHg of HgTOT in O horizons of CCs located between 1 and 41 m from streams. Inorganic Hg measures did not differ between REFs and CCs at any position. The O horizon thickness did not differ between CCs and REFs, but the groundwater table and soil water content were significantly higher at CCs than at REFs. The largest difference in percent MeHg of HgTOT (12 times higher at CCs compared to REFs, p = 0.003) was observed in concert with a significant enhancement in soil water content (p = 0.0003) at intermediate hillslope positions (20-38 m from stream), outside the stream riparian zone. Incubation experiments demonstrated that soils having significantly enhanced soil pools of MeHg after clear-cutting also showed significantly enhanced methylation potential as compared with similarly positioned soils in mature reference stands. The addition of inhibitors demonstrated that sulfate-reducing bacteria (SRB) and methanogens were key methylators. Rates of demethylation did not differ between CCs and REFs. Our results suggest that enhanced water saturation of organic soils providing readily available electron donors stimulate Hg-methylating microbes to net formation and buildup of MeHg in O horizons after forest harvest.

Soil structure amelioration with quicklime and irrigation experiments in earth graves

Air supply and soil moisture have significant impact on the decay time necessary for complete decomposition of an interred body. Concerning the general structure and hydraulic as well as pneumatic conditions, in many cases, a permeable refilled soil material surrounded by the undisturbed and less permeable soil outside the grave results in water ponding, less aerated conditions, and lower redox potential values within the grave. This reduces the decomposition speed or even leads to preservation of the entire body. In order to ascertain soil structural processes and hydraulic properties in an earth grave within the first year after burial, a monitoring of soil redox and matric potentials was realized in newly refilled artificial (empty) graves. We surveyed four variations: undisturbed reference soil, soil backfill in artificial grave, soil backfill in artificial grave amended with 20 kg CaO m−3, and grave base and walls strewed with CaO. In the fourth artificial grave (soil backfill only), irrigation experiments were conducted in order to simulate the effects of grave maintenance on soil water budget. Pore size distribution, air conductivity, and saturated hydraulic conductivity were measured on soil core samples from the variations. The monitoring was realized with redox sensors and tensiometers in 50- and 130-cm depth in all four variations. Soil structure disruption increased soil porosity but also favored saturation of the soil in context with precipitation events. Compared with the graves without amendment, the addition of quicklime resulted in higher air capacity and air permeability, saturated hydraulic conductivity, and a better-aerated (higher redox potentials) and less water-saturated soil. Non-recurring irrigation with 2.2, 4.4, and 8.9 mm did not affect the soil moisture in the 50- and 130-cm depth. Repeated irrigation with 8.9 mm on consecutive days led to persistent water saturation in the soil, especially in the 130-cm depth. The disturbed soil structure in the cover layer of an earth grave is sensitive to settlement and, together with a tendency to the development of stagnic conditions, this can have negative impact on soil aeration in the grave. Addition of quicklime to the soil enhances crack development in the base and walls of the grave, stabilizes the soil fragments in the backfill, and prevents intensive settlement processes. This reduces water ponding and leads to a better aeration of the soil. Irrigation of earth graves should be reduced to a minimum.

Rare Carboniferous and Permian glacial and non-glacial bryophytes and associated lycophyte megaspores of the Paraná Basin, Brazil: A new occurrence and paleoenvironmental considerations

Fossil bryophytes are rare because their preservation is compromised by the presence of a thin cuticle (if any) and a lack of lignin. Except for the occurrence of one bryophyte in the glacial Dwyka Group of the Karoo Basin, the other rare Late Paleozoic records in Gondwana are notably from the Paraná Basin in Southeast/South Brazil. Four bryophyte sites (including a newly discovered one) were found in the lower part of the thick Permo-Carboniferous glacial succession of the Itararé Group, and one was found in the Guadalupian Teresina Formation, which was roughly assigned to an epeiric sea (or “lake”) dominated by a warm, semi-arid climate. This study describes the fossils from the new occurrence from the Itararé Group and discusses the context in which the bryophyte beds originated in the basin. The new samples confirm that all of the bryophytes of the Itararé Group can be classified as Dwykea araroii Ricardi-Branco et al. (a possible pleurocarp) and are associated with the lycophyte megaspore Sublagenicula brasiliensis (Dijkstra) Dybová-Jachowicz. In the much younger Teresina Formation, the bryophytes are Yguajemanus yucapirus Cristiano-de-Souza et al. and Capimirinus riopretensis Cristiano-de-Souza et al., and abundant charophytes and rare dwarf lycophyte stems and bracts are present in the same layers. Although the two stratigraphic units represent distinct paleoenvironments and climates, they seem to share some characteristics: a) the bryophyte assemblages were transported very little; b) they were deposited in very calm environments; c) they were the main components (along with some lycophytes) of local or poorly diversified regional vegetation. The low number of species, which is characteristic of opportunistic communities, can be explained by local or regional conditions that would have been stressful for the vascular plants in other areas. During the deposition of the Itararé Group, the main control was probably the cold climate in addition to a relative (liquid) water deficit because the bryophyte vegetation may have belonged to a tundra biome in areas of retreating glaciers. For the Teresina Formation, it is possible that the control was scarce freshwater, an unstable environment and water-saturated soil in a scenario of bryophyte vegetation living around temporary ponds in a wide marginal area of the epeiric sea.

The chloroform fumigation efficiency in water-saturated soils increases by mixing sand and decreasing packing thickness

The chloroform fumigation efficiency for measuring microbial biomass in water-saturated soils is low due to limited diffusion of chloroform. To suggest modifications for the improvement of the fumigation efficiency, the effects of sand mixing and soil packing thickness on the fumigation efficiency in water-saturated soils were investigated through four experiments. Two soils with contrasting organic carbon content were used to examine if the modifications are applicable regardless of microbial biomass level. The soils were waterlogged to mimic rice paddy soils, and sand was mixed to decrease water content by either adding an increasing amount of sand to a decreasing amount of soil (Exp-1) or an increasing amount of sand to a constant amount of soil (Exp-2). Soil packing thickness was decreased by packing a decreasing amount of soil into same-sized containers (Exp-3) or by placing the same amount of soil into progressively wider containers (Exp-4). Overall, the effects of sand mixing and packing thickness on the fumigation efficiency did not differ with soil microbial biomass level. In both soils which were originally saturated with water, increasing the amount of sand mixing decreased (P < 0.001) soil water content and increased (P < 0.001) the concentration of extracted organic carbon by fumigation (EOCf) by up to 303% in Exp-1 but decreased (P < 0.001) EOCf by up to 80% in Exp-2, likely due to the concomitant increase in soil packing thickness. Decreasing soil packing thickness increased (P < 0.001) EOCf by up to 128% (Exp-3) and 298% (Exp-4). It was also found that the amount of soil packed affected the fumigation efficiency (Exp-2 and 3). We suggest using the same amount of sample and same-sized beakers for fumigation is more practical to minimize the confounding effect of soil amount and packing thickness on the fumigation efficiency of water saturated soils and thus to help the comparison of microbial biomass between soils.

Explaining anisotropic macroseismic fields in terms of fault zone attenuation—A simple model

In this work, we present a simple model of anisotropic macroseismic field based on the assumption that local and regional geological structures change the shape of the isotropic macroseismic field (as expected in 1D media). Local geological structures, like water saturated stratified media, may increase intensity level by multiple reflections, constructive interference and resonant effects, but inelastic attenuation, significantly stronger in water-saturated soils, as well as destructive interference, may decrease intensities. On the other hand, large geological structures like seismotectonically active fault zones decrease intensities due to energy redistribution and inelastic attenuation. This model has been developed for the Karst region of the Outer Dinarides where site effects may be neglected because of specific building construction. Neglecting of site effects simplifies the model, so we just need a map of seismically active faults acting as modulator of macroseismic field. In order to demonstrate how the model works, we have calculated the standard error for 10 earthquakes and the macroseismic fields for three of them with epicenters in the Outer Dinarides and compared the model to empiric isoseismals.

Using pedotransfer functions to estimate soil hydraulic conductivity in the Loess Plateau of China

Soil hydraulic conductivity (Ks) is a crucial soil physical property that not only influences soil hydrological processes, but also the planning for vegetation recovery, irrigation practice and drainage design. However, Ks data are often lacking at large-scale soil database due to difficulties in direct measurement that is often labour intensive, time consuming and cost inefficient. The objective of this study was to compare the performance of different emerging methods [Multiple linear regression (MLR) and artificial neural network (ANN)] of Ks prediction. The pedotransfer function (PTF) is one such method that is based on selected factors closely correlated with Ks at regional scale. We collected disturbed and undisturbed soil samples in the 0–40cm soil layer at 243 sites across the entire typical Loess Plateau of China (430,000km2) and then measured Ks and the potentially related factors. The results showed that Ks was normally distributed with moderate a spatial variation (CV=67%). Correlation analysis indicated that bulk density (BD), saturated soil water content (SSWC), clay content (Clay), silt content (Silt) and latitude were closely correlated (p<0.05) with Ks. Although the accuracies of MLR and ANN were equal in terms of estimating Ks, the stability of PTF developed via ANN was not as good as that of MLR. Thus PTF developed via MLR, which included BD, Silt and Clay, was considered as the best model for estimating Ks. There is a need to closely monitor the stability and repeatability of PTF during comparison and determination of PTF.

Could alluvial knickpoint retreat rather than fire drive the loss of alluvial wet monsoon forest, tropical northern Australia?

AbstractDrainage rejuvenation through headward migration of alluvial knickpoints is common in ephemeral semi‐arid streams, but has not yet been described for tropical rivers. In the Australian monsoon tropics (AMT), wet monsoon forests have an important ecological function, and are present along many alluvial valleys and springs within a eucalypt‐savanna dominated landscape. Using a combination of LiDAR, remote sensing and field evidence, we observe the ongoing destruction of wet monsoon forest through hydro‐geomorphic feedbacks, along with the headward retreat of an alluvial knickpoint at Wangi Creek in Litchfield National Park, Northern Territory. Due to the highly transmissive shallow aquifer along the lower Wangi Creek, this knickpoint retreat leads to a downstream drop in in‐channel water level, which in turn drives a decrease in the local groundwater table. The lowered groundwater level causes the shallow anabranches and formerly water saturated peaty floodplain soil to desiccate, which results in a reduction of vegetation density. The resulting dry surface conditions allow annual to bi‐annual high frequency low‐intensity fires to affect the monsoon forest, while wet rainforest upstream of the knickpoint remains intact. In this paper, we argue that such hydro‐geomorphic feedbacks may cause the initial destabilization of the forest, which then provides the necessary conditions for the impact of fire. This scenario thus challenges the prevalent view that fire is a first‐order control on the spatial extent of wet monsoonal rainforest in the study area, and provides a new and testable hypothesis for further studies in the AMT. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Swimming performance of Bradyrhizobium diazoefficiens is an emergent property of its two flagellar systems.

Many bacterial species use flagella for self-propulsion in aqueous media. In the soil, which is a complex and structured environment, water is found in microscopic channels where viscosity and water potential depend on the composition of the soil solution and the degree of soil water saturation. Therefore, the motility of soil bacteria might have special requirements. An important soil bacterial genus is Bradyrhizobium, with species that possess one flagellar system and others with two different flagellar systems. Among the latter is B. diazoefficiens, which may express its subpolar and lateral flagella simultaneously in liquid medium, although its swimming behaviour was not described yet. These two flagellar systems were observed here as functionally integrated in a swimming performance that emerged as an epistatic interaction between those appendages. In addition, each flagellum seemed engaged in a particular task that might be required for swimming oriented toward chemoattractants near the soil inner surfaces at viscosities that may occur after the loss of soil gravitational water. Because the possession of two flagellar systems is not general in Bradyrhizobium or in related genera that coexist in the same environment, there may be an adaptive tradeoff between energetic costs and ecological benefits among these different species.

The impact of sieving on heterotrophic respiration response to water content in loamy and sandy topsoils

Understanding the relation between soil heterotrophic respiration and water content is important for the prediction of climate change effects on soil CO2 emissions. In order to quantify the influence of air-drying and sieving with 2mm meshes on the heterotrophic respiration response to soil water content we incubated intact cores and sieved samples of two loamy and two sandy soils for six levels of effective soil water saturation. We further determined soil textural properties and the soil water retention curves of the soils with the intent to identify links between soil physical characteristics and moisture sensitivity functions of heterotrophic respiration. The incubation of sieved and intact soils revealed distinct differences in the response of heterotrophic respiration to soil water content. The sieved soils exposed a threshold-type behaviour, whereas the undisturbed soils exposed a quadratic increase of heterotrophic respiration with increasing effective soil water saturation. Further, we detected significant correlations between the moisture response functions of the undisturbed soils and soil texture. From the comparison of sieved and intact soil incubations we conclude that the destruction of soil structure by sieving hampers the transferability of measured soil moisture response of heterotrophic respiration to real-world conditions. For modelling purposes we suggest the use of a quadratic function between relative respiration and effective saturation for soils with a clay fraction<20%.

One-dimensional consolidation in unsaturated soils under cyclic loading

The one-dimensional consolidation model of poroelasticity of Lo et al. (2014) for an unsaturated soil under constant loading is generalized to include an arbitrary time-dependent loading. A closed-form solution for the pore water and air pressures along with the total settlement is derived by employing a Fourier series representation in the spatial domain and a Laplace transformation in the time domain. This solution is illustrated for the important example of a fully-permeable soil cylinder with an undrained initial condition acted upon by a periodic stress. Our results indicate that, in terms of a dimensionless time scale, the transient solution decays to zero most slowly in a water-saturated soil, whereas for an unsaturated soil, the time for the transient solution to die out is inversely proportional to the initial water saturation. The generalization presented here shows that the diffusion time scale for pore water in an unsaturated soil is orders of magnitude greater than that in a water-saturated soil, mainly because of the much smaller hydraulic conductivity of the former.

Effects of soil type and water saturation on growth, nutrient and mineral content of the perennial forage shrub Sesbania sesban

Sesbania sesban (L.) Merr is a perennial N2-fixing tree with high potential for use in agricultural production systems as a green manure and livestock forage. We studied the interactive effects of soil type and water level on the growth, biomass allocation, nutrient and mineral content of S. sesban. Four-week old seedlings of S. sesban were grown for 49 days (n = 5) in a factorial mesocosm set-up with six soil types (sediment, sand, alluvial, acid-sulfate, saline and clay) and three water levels (drained, water-saturated and flooded). The soils tested represent the predominant alluvial soil types of the Mekong delta, Vietnam. Sesbania sesban grew well with relative growth rates (RGR) around 0.08 g g−1 d−1 in all studied soil types, except the saline soil where plants died. In the low-pH (3.9) acid sulfate soil, that constitute more than 40 % of the Mekong delta, the RGR of the plants was slightly lower (0.07 g g−1 d−1), foliar concentration of calcium was 3–6 times lower, and concentrations of iron and sodium up to five times higher, than in other soils. The nutrient and mineral contents of the plant tissues differed between the soils and were also affected by the flooding levels. Foliar concentrations of nitrogen (50–74 mg N g−1 dry mass) and phosphorus (5–9 mg P g−1 dry mass) were, however, generally high and only slightly affected by water level. The results show that S. sesban can grow well and with high growth rates on most wet soils in the Mekong delta, except saline soils where the high salt content prevents establishment and growth. The nutrient and mineral contents of the plants, and hence the nutritional value of the plants as e.g. fodder or compost crops, is high. However, soil type and water level interactively affect growth and tissue composition. Hence, optimal growth conditions for S. sesban differ in the different regions of the Mekong delta.

Development of a permanent geological environment model of Kazan city aimed to solve various engineering-geological problems (Russia)

The article discusses the composition, structure and operation principles of a digital geological environment model for the urban area located in the valley of a large lowland river (the Volga). The model is implemented in ESRI (ArcView and ArcGis) and MapInfo software environments. The basis of the model is the data on the composition and physical and mechanical properties of soils, the information about ground waters and industrial loads. The model has been used to conduct zoning of soil conditions, groundwater aggressivity to the materials of underground structures. Also, the areas of existing and possible exogenous geological processes (flooding, karst, suffusion, erosion, landslides) have been identified. According to the model, it is offered to evaluate the stability of geological environment to human impact using typification on the soil conditions based on the pre-zoning of water content and the degree of drainage. A new monitoring system of dangerous exogenous geological processes has been developed, the impact of exogenous processes on the residential buildings has been estimated, and, also, the analysis and evaluation of geological risks have been performed. According to the data on the composition, density and water saturation of soils, the stability of the ground bases to a dynamic impact has been estimated.