Cm Of Clay Research Articles

Dynamics of grass stand formation in poplar plantations on different types of reclamations of disturbed lands of Western Donbass

The purpose of our research was to study the long-term dynamics of the herbage cover at different stages of growth and development of poplar plantations on the types of artificial soils of the forest reclamation area. The object of research is flora phytotoxic dumps of «Blagodatna» coal mine, where imported substrates such as sand-clay, clay loam, red-brown earth and humic soil in various combination were applied to create reclamations layer on the surface of the mine dumps (Dnipropetrovsk region, Pavlograd region). Type 1: 30 cm of soil mass of typical chernozem (SMTC), 50 cm of red-brown earth, 80 cm of alluvial sand-clay and sand, and deeper there is the coal mine solid; type 2: 30 cm of SMTC, 80 cm of sand, and mine solid deeper; type 3: 30 cm of SMTC, 60 cm of alluvial sand-clay, 60 cm of clay, and deeper there is mine solid; type 4: 40 cm of SMTC, 30 cm of red-brown earth, 40 cm of sand and mine solid deeper; type 5: 55 cm of alluvial sand-clay, deeper there is mine solid. Stationary observations were carried out in poplar plantations of 8-, 16-, 27- and 34-year-old age on permanent trial plots. They were presented with a black poplar and seven hybrid poplars. The research has established that climatic conditions, influence of surrounding phytocenoses of undisturbed lands, inheritance by pedozems of seed material of grass plants with a fertile layer of the soil set the direction of succession on the way of formation of zonal herbal group. The long-term growth of the role of the arid element indicates the formation of a structure close to the zonal flora. The formation of the flora of technical soils in poplar plantations occurs in four stages: the first is pioneer plant communities, which begins with the completion of the technical phase of reclamation and confined to the stages of forest formation; the second is a simple grouping that is associated with the development of the stand until the closure of canopy and inter-row soil cultivation; the third is a complex grouping that is fraught with pole wood stage of stand development and partial getting sparse; the fourth in our studies, is partially closed when gradually tree plants disappear and their influence disappears. In addition to the influence of tree vegetation, its age and stage of development, the formation of lower layers of biogeocenoses is significantly influenced by the conditions stipulated by the stratigraphy and the power of artificial substrates, as well as the elements of the landscape, both created initially and formed as a result of the fragmentary subsidence of the dump territory. These factors, depending on their dynamic changes, regulate correlation between various groups of biomorphs, climamorphs, trofomorphs, hygromorphs, heliomorph and zenomorphs in the grass cover. Created forest vegetation conditions on the plateau and the upper third of the dump do not meet the needs of hybrid poplars under conditions of acute shortage of moisture, which are characteristic of the steppe zone. Fast-growing poplar hybrids can be used as a pioneer culture up to 15–20 years of age.

Interactive influence of water level, sediment heterogeneity, and plant density on the growth performance and root characteristics of Carex brevicuspis

Water level, sediment heterogeneity, and plant density are important factors that determine plant growth, distribution, and community structure. In the present study, we investigated the effects of these factors on the growth and root characteristics of Carex brevicuspis . We conducted an outdoor experiment to monitor biomass accumulation and allocation, relative root distribution mass ratio, longest root length, and total N and P contents of C. brevicuspis plants. We used a factorial design with two water levels (0 cm and −15 cm relative to the soil surface, named high and low water level treatments, respectively), three sediment types (sand/clay sediment with 0–15 cm of sand and 15–30 cm of clay; mixed sediment with 0–30 cm mixture of sand and clay with 1:1 volumw ratio; and clay/sand sediment with 0–15 cm of clay and 15–30 cm of sand), and three plant densities (88 plants per m 2 , 354 plants per m 2 , and 708 plants per m 2 ). Biomass accumulation decreased with increasing plant density and was significantly higher in the low water level and the clay/sand sediment than in the high water level and the other two sediment types. The shoot:root ratio was markedly higher in the high water level than in the low water level and decreased with increasing plant density; further, in the high water level, it was significantly lower in the sand/clay sediment than in the other two sediment types. The relative root distribution mass ratio was markedly higher in the high water level treatments than in the low water level treatments. Further, in the high water level treatments, the relative root distribution mass ratio increased with increasing plant density in the clay/sand sediment and was lower in the sand/clay sediment than in the other two sediment types. The longest root length was significantly lower in the high water level than in the low water level and increased with increasing plant density in the sand/clay sediment in the high water level. Total N content in the plants was influenced only by sediment type; on the other hand, total P content was markedly higher in the high water level than in the low water level. Our data indicate that growth of C. brevicuspis was limited by higher water level, higher density and sand/clay sediment. Plants can increase shoot:root ratio and develop shallow root system to acclimate to high water level and thus could adjust shoot:root ratio and root characteristics, e.g. decrease their shoot:root ratio and allocating more root and increasing root length to the nutrient rich layer to acclimate to conditions of higher density and sediment heterogeneity.

Extent of oxidation in Boom Clay as a result of excavation and ventilation of the HADES URF: Experimental and modelling assessments

For the construction and operation of a geological repository, the excavation and ventilation of galleries is necessary. Oxidation of the anaerobic host rock is unavoidable, and the favourable host rock properties may be affected. In this study, the extent of oxidation as a result of excavation and ventilation of galleries in Boom Clay was studied by experimental and modelling assessments. In situ experiments in the HADES URF aimed at comparing the oxidation around the Test Drift (excavated in 1987) and the Connecting Gallery (excavated in 2002). Pore water sampling and analyses were done from two identical piezometers installed in both galleries. Clay cores were used for detailed mineralogical and pore water analyses close to the gallery. The most striking result is the similarity between both galleries. Only within the first meter of clay around the galleries, the pore water chemistry is affected by oxidation, as indicated by the increased concentrations of sulphate and most cations. The trend of increasing sulphate concentrations towards the gallery, as observed in the piezometer-waters, is further continued in the pore waters obtained from the leaching of the clay cores. The effect of oxidation on the mineralogy is less pronounced and less extended. Gypsum is present within the first 4.5 cm of clay around the galleries. The experimental data and scoping calculations enabled to work out a conceptual model for oxidation around the HADES URF in Boom Clay. The main idea is that oxidation is related to fracturing. After sealing of the fractures, oxidation products are redistributed in the clay matrix by a combined diffusion–advection transport. In addition, a continuous oxygen diffusion from the gallery into the clay is maintained. Both processes seem to have minor effects on the further extent of oxidation, as indicated by the experimental data and modelling assessments. In the case of the Boom Clay, the extent of the oxidised zone is about 1 m, even after 20 years of ventilation.

Growth and root distribution of Vallisneria natans in heterogeneous sediment environments

Plant growth, biomass allocation and root distribution were investigated in the submerged macrophyte Vallisneria natans growing in heterogeneous sediments. Experimentally heterogeneous sediment environments were constructed by randomly placing 4 cm of clay or sandy loam into the top (0–4 cm) or bottom (4–8 cm) layer within an experimental tray, providing two homogeneous and two heterogeneous treatments. Biomass accumulation was significantly affected by the experimental treatments: higher in the homogeneous sediment of clay (32 mg per plant) and the two heterogeneous treatments (about 27 mg per plant), but lower in the homogeneous sediment of sandy loam (15 mg per plant). Root: shoot ratio was also different among the four treatments. Compared with the treatments of clay in the top layer, plants allocated more biomass to roots at the treatments of sandy loam in the top layer. Heterogeneous sediments significantly affected root distribution pattern. Compared with the treatments of sandy loam in the bottom layer, root number (7–8 versus 13–14) and total root length (3.6–4.0 cm versus 29.5–40.0 cm) in the bottom layer were significantly higher in the treatments with clay in the bottom layer. These results indicate that both sediment structure and nutrient availability influence growth and root system distribution of V. natans.

Twenty years of salt marsh succession on a Dutch coastal barrier island

After a formerly grazed salt marsh was released from cattle grazing, changes in plant species composition were monitored for 20 yr, using vegetation maps and permanent plots. Three areas, differing in age and nutrient status were compared. The number of plant species and plant communities decreased.Elymus athericus (Elytrigia pungens) became dominant in most plant communities after 5–20 yr on the oldest and most productive salt marsh. In younger areas it took more time forE. athericus to become dominant. At least 7 cm of clay seemed to be a prerequisite for this plant species to increase in dominance. The results from monitoring over decades are discussed in view of the knowledge on succession over centuries as derived from a chronosequence.

Woody plant roots fail to penetrate a clay-lined landfill: Managment implications

In many locations, regulatory agencies do not permit tree planting above landfills that are sealed with a capping clay, because roots might penetrate the clay barrier and expose landfill contents to leaching. We find, however, no empirical or theoretical basis for this restriction, and instead hypothesize that plant roots of any kind are incapable of penetrating the dense clays used to seal landfills. As a test, we excavated 30 trees and shrubs, of 12 species, growing over a clay-lined municipal sanitary landfill on Staten Island, New York. The landfill had been closed for seven years, and featured a very shallow (10 to 30-cm) soil layer over a 45-cm layer of compacted grey marl (Woodbury series) clay. The test plants had invaded naturally from nearby forests. All plants examined—including trees as tall as 6 m—had extremely shallow root plates, with deformed tap roots that grew entirely above and parallel to the clay layer. Only occasional stubby feeder roots were found in the top 1 cm of clay, and in clay cracks at depths to 6 cm, indicating that the primary impediment to root growth was physical, although both clay and the overlying soil were highly acidic. These results, if confirmed by experimental research should lead to increased options for the end use of many closed sanitary landfills.

Electroosomotic Removal of Gasoline Hydrocarbons and TCE From Clay

This laboratory study examines the application of electroosmosis (EO) for removal of hydrocarbons from clay. EO mobilization is conducted in 7.62‐cm inside diameter (id) glass columns containing 30.48 cm of clay and tap water electrolyte. Iron electrodes are used to impress a 0.4‐volt/cm DC electrical gradient. Destructive sampling of columns following various periods of EO treatment results in breakthrough curves describing relative hydrocarbon contaminant mobilization. EO flushing of dissolved organic chemicals in fine‐grained soils can be predicted using traditional contaminant‐transport equations, which incorporate advection, dispersion, and adsorption. Chemicals with relatively high water solubilities and low distribution coefficients (i.e., benzene, toluene, trichloroethylene (TCE), and m‐xylene) are easily removed from Kaolin by EO. Chemicals with a low water solubility and high distribution coefficient (i.e., hexane and isooctane) are transported from the clay at a slower rate. EO has the potentia...

Sonar attenuation modeling for classification of marine sediments

An attenuation-based model for classification of marine sediments is developed for the chirp sonar operating in the frequency range of 2–10 kHz. A relaxation-time model is proposed that combines the various dissipative energy loss mechanisms of sound in marine sediments into a single parameter. Historical data were analyzed by converting attenuation values reported in ‘‘dB/m@kHz’’ to a single relaxation time value. Analysis of these previous attenuation measurements supports the use of a relaxation-time model. Based on this large collection of data, an empirical equation is developed that relates relaxation time to grain size (in phi units). Using this model, very little phase dispersion is observed for a correlated chirp pulse traveling through 40 m of sand, silt, or clay. Yet, this is not so for a pulse in the ultrasonic frequency range (0.2–1.0 MHz) traveling through only 10 cm of clay. Here, significant dispersion is noted. Because of the unique Gaussian-like shape of the correlated chirp pulse power spectrum, pulse elongation due to attenuation is minimized. Using the center frequency shift in the pulse spectrum, a new ‘‘instantaneous frequency’’ method of attenuation estimation is proposed that overcomes the problems associated with interfering reflections. Based on the relaxation-time model, the correlated chirp pulse was synthetically attenuated to establish a relation between the relaxation time and the center frequency shift. In situ sediment-type predictions from chirp sonar data using the instantaneous frequency method and analyses of core samples taken in the Narragansett Bay, Rhode Island are in good agreement.

Effects of vegetation, a clay cap and environmental variables on 222Rn fluence rate from reclaimed U mill tailings.

We measured 222Rn fluence rate and several environmental variables on two plots with U mill tailings buried beneath 30 cm of overburden and 20 cm of topsoil. An additional 30 cm of clay covered the tailings on one plot and each plot was subdivided into bare soil and vegetated subplots. We used linear correlation, two-way ANOVA and stepwise multiple regression to analyze the effects of the plot characteristics and the environmental variables on 222Rn fluence rate. The most important effect on 222Rn fluence rates from these plots was the combination of a clay cap and a vegetated surface. The mean annual fluence rate from the plot having both of these characteristics (520 +/- 370 mBq m-2 s-1) was over three times that of the vegetated plot without a clay cap (170 +/- 130 mBq m-2 s-1) and 18 times that of the bare plot with a clay cap (29 +/- 13 mBq m-2 s-1). The interaction effect may have been due to the growth of roots in the moist clay and active transport of dissolved 222Rn to the surface in water. This speculation is supported by the observation that on vegetated plots with a clay cap, moisture in the clay enhanced the fluence rate.

Hydraulic conductivity of contaminated natural clay directly below a domestic landfill

The hydraulic conductivity of natural clays in the 1.5 m contamination zone below a 15 year old domestic waste landfill has been determined.Water-soluble contaminants such as chloride, sodium, and dissolved organic carbon have migrated about 1.0 m compared with only 15 cm for copper, zinc, iron, lead, and manganese. The migration, primarily by diffusion, has rendered the clay perfect for assessment of clay–leachate compatibility with respect to hydraulic conductivity, k.Oedometer tests on tube samples of the clay yielded k values of 1.4 × 10−8 cm/s with a slight decrease to about 1 × 10−8 cm/s in the upper 20 cm of clay at the waste–clay interface. Direct measurement of k on "undisturbed" tube samples, reconsolidated to their field stress state and permeated with pore fluid squeezed from adjacent contaminated samples, yielded values of 1.5 × 10−8 cm/s at 1 m depth decreasing to 0.75 × 10−8 cm/s at the interface.The decrease in k near the interface seems to correlate directly with increased pollutant concentration of soluble species, total heavy metal concentration, and a slight decrease in void ratio. The changes in k are so small, however, that for the test leachates and undisturbed test soils at this domestic waste site, it is concluded that the hydraulic conductivity has not changed significantly as a result of contamination. Key words: domestic waste, leachate, hydraulic conductivity, clay barriers, compatibility.

Solute Movement in a Field Soil

AbstractSolute and water movement was studied under steady‐state flow conditions in a field soil consisting of 70 cm of clay to silty clay over a medium sand. A steady‐state water flow condition was maintained by applying irrigation water at a constant flux of 2 cm per day. During the steady‐state condition some of the water leached into the plot was labelled with chloride and tritium. The positions of the chloride and tritium as functions of soil depth and time were measured by extracting samples of the soil solution with soil suction probes. Extremes in solute displacement occurred at equal and different depths within the plot. An analysis of these measurements indicated that observations of the pore‐water velocity and the apparent diffusion coefficient were log normally distributed. Twenty‐four soil suction probes, used to identify the rate at which a solute was displaced in the soil, will yield an estimate of the mean pore‐water velocity of this soil within a range of approximately ±25% of its true value providing the effects of potential solute‐soil interactions are taken into account.