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1.
Retardation parameters (Rf) for sulfolane and thioalne were estimated using reference values and experimentally as they were mainly observed at an aquifer
underneath a waste disposal site near Brisbane, Australia. Three soil aquifer materials e.g. clay, silty clay and sand were
used as sorbents. At first, Rf was obtained employing Koc–Kow and solubility parameter, respectively, while experimental coefficients were determined from both batch and flow-through
column tests. Additionally, Rf was observed at a single- and bi-solute system through the column test. There was not found any significant difference in
Rf between Koc–Kow and solubility parameters, but the retardation coefficient was significantly dependent on organic carbon content for solubility
parameter. In contrast, using Koc–Kow, the coefficient correspondingly varied with an amount of clay content contained in each soil. In the same manner, the batch-determined
parameters were more subject to clay content. On the other hand, the column-determined parameters can be comparable with the
desk-derived values. In a bi-solute system, they did not influence each other concerning retardation coefficients while they
flew though the column simultaneously. It was concluded that there was a large discrepancy in retardation coefficient of batch-
against both reference-oriented estimation and column-determined values.
Received: 20 August 1998 · Accepted: 17 May 1999 相似文献
2.
《Applied Geochemistry》2001,16(14):1611-1619
Biodegradation of polycyclic aromatic hydrocarbon (PAH) was investigated in the whole matrix and in the different aggregate size fractions of a sandy soil contaminated by a mixture of 8 PAHs and incubated at water holding capacity. The distribution of PAHs and of phenanthrene-degrading bacteria were determined in the bulk soil and in 4 size aggregate fractions corresponding to sand, coarse silt, fine silt and clay. The microbial communities able to degrade phenanthrene were detected at a similar level in the different aggregate fractions of the soil before contamination. After soil contamination and incubation, a significant growth of bacteria was observed and their distribution within aggregates was modified. Bacterial communities of phenanthrene-degraders were present in a higher density in the aggregates corresponding to sand (2000–50 μm) and clay (<2 μm). Chemical analysis show that remaining PAHs (low and high molecular weight) were much more concentrated in the fine soil fractions (fine silt and clay) and were present at a very low content in the larger aggregate size fractions. The interactions of well defined aggregates with PAHs and bacteria were also studied using phenanthrene as PAH model substrate and individual aggregates corresponding to sand and clay size fractions. Incubation of sand and clay aggregate fractions enriched with phenanthrene in the presence of a bacterial isolate NAH1 led to the simultaneous solubilization and biodegradation of phenanthrene. Differences in amounts of solubilized phenanthrene between sand and clay aggregate size fractions would be related to difference in adsorption capacities of phenanthrene by clay and sand aggregates. 相似文献
3.
1IntroductionSoilorganicmatter (SOM)isakeysourceofnutrientsforplantgrowth ,itisessentialforthemaintenanceofsoilstructureanditcontributestotheabilityofsoiltoretainnutrientsandwater.AnimprovedunderstandingofSOMdynamicsiscentraltothedevelopmentofmoreenvironmentallysoundandsustainablepracticesofagriculturalmanagement (Collinsetal.,2 0 0 0 ) .Avarietyofcon ceptualmethodshavebeenusedtodescribetheprocessesofSOMaccumulationandturnover (Jen kinsonandRayner,1 977;Duxburyetal.1 989;Partonetal.,1 99… 相似文献
4.
Toshiyuki Wakatsuki Hisao Furukawa Kazutake Kyuma 《Geochimica et cosmochimica acta》1977,41(7):891-902
Sixteen alluvial and terrace soils from Japan and Thailand were separated into six fractions ; an amorphous sesquioxide and combined organic matter fraction, crystalline sesquioxides, clay, silt, fine sand and coarse sand. Content of ten major and minor elements in these six fractions was analyzed; SiO2, A12O3, Fe2O3, MgO, CaO, K2O, TiO2, Rb2O and SrO were determined by X-ray fluorescence spectrometry, and Na2O was determined by neutron activation analysis. The clay, silt, fine sand and coarse sand mineralogy were estimated semi-quantitatively by X-ray diffraction methods.We propose three indices of geochemical maturity for the soils and test their usefulness as measures of the degree of weathering. Three concomitant factors are proposed to measure the relative resistate, hydrolyzate and oxidate nature of the major elements in the soils. 相似文献
5.
Soil degradation resulted from unreasonable land use and erosion has been a serious problem in the black soil region of northeastern
China. This paper seeks to understand the relationships between topsoil properties and topography and land use for land management
targeting at improving soil quality in this region. A total of 292 soil samples and 81 volumetric rings were taken from a
typical small watershed of the region in June 2005 for examining total carbon (TC), total nitrogen (TN), soil texture (classified
into gravel, sand, silt, and clay), and bulk density (ρ
b), respectively. Spatial variability of these soil properties was evaluated with classical statistics and geostatistics methods.
The results of classical statistics indicated that TC, TN, sand, silt, clay content, and ρ
b were moderate variables while gravel had great variability. Soil properties were mainly correlated to slope position, elevation
and land types. Geostatistical analyses showed that the spatial autocorrelation for TC, TN, and silt was weak, strong for
clay and moderate for and ρ
b sand, respectively. The spatial variations of soil properties are affected comprehensively by topographic factors, land use,
erosion, and erosion control in this watershed. Past erosion, however, is the most important component to induce change of
soil properties. In this small watershed, current soil and water conservation measures play an important role in controlling
soil loss. But the restoration of soil properties was unsatisfactory. Comparing with untilled soil of this region, TC, TN,
silt content are excessively low; whereas ρ
b, sand and clay content are excessively high; gravel appears at most sampling locations. It is necessary for improving soil
properties to protect forest and grassland and change cultivation system of farmlands. 相似文献
6.
Soil hydraulic properties such as soil infiltration rate and hydraulic conductivity are closely linked to runoff generation
and infiltration processes but little is known about them on karst hillslopes. The objectives of this paper were to investigate
the change in soil stable infiltration rate (q
s) and near-saturated hydraulic conductivity (K
ns) in different slope positions and to understand their relationship with rock fragment content and soil texture within the
topsoil in subtropical karst regions of southwest China. Tension infiltrometers (20 cm in diameter) were used to measure q
s and K
ns at pressure head of −20 mm on hillslopes 1 (a disintegrated landslide failure) and 2 (an avalanche slope). The change of
q
s and K
ns was great and they mostly had a moderate variability with coefficient of variations (CV) between 0.1 and 1.0 in the different
slope positions. On average, q
s ranged from 0.43 to 4.25 mm/min and K
ns varied from 0.75 to 11.00 mm/min. These rates exceed those of most natural rainfall events, confirming that overland flow
is rare on karst hillslopes. From bottom to top, q
s and K
ns had a decrease–increase–decrease trend due to the presence of large rock outcrops (>2 m in height) on hillslope 1 but had
an increasing trend on hillslope 2 with less complex landform. They tended to increase with increase in total rock fragment
content (5–250 mm) within the topsoil as well as slope gradient on both hillslopes. Pearson correlation analysis suggested
that higher coarse pebble (20–75 mm), cobble (75–250 mm), and sand (2–0.05 mm) contents as well as total rock fragment content
could significantly facilitate water infiltration into soils, but higher clay (<0.002 mm) content could restrict water movement.
This result indicated that rock fragment, sand, and clay contents may remarkably affect water flow in the topsoil layers,
and should be considered in hydrological modeling on karst hillslopes in subtropical regions. 相似文献
7.
A barrier system based on the hydraulic trap design concept for a landfill was proposed. To study the field scenario in which
a clay liner is underlain by a granular layer functioning as a secondary leachate drain layer, a laboratory advection–diffusion
test was performed to investigate factors controlling the transport of contaminants in a two-layer soil system. The soils
used for this study were Ariake clay and, the underlying layer, Shirasu soil from the Kyushu region of Japan. Potassium (K+) was selected as the target chemical species with an initial concentration of 905 mg L−1. The effective diffusion coefficients (D
e) of K+ for Ariake clay and Shirasu soil were back-calculated using an available computer program, Pollute
V 6.3. Values of D
e derived from this experiment are consistent with previously published ones. The Ariake clay has lower D
e than the Shirasu soil. The hypothesis that mechanical dispersion can be considered negligible is reasonable based on both
the observation that the predicted values well fit the experimental data and the analyses of two dimensionless parameters.
Parametric analyses show that transport of K+ through soils is controlled by advection–diffusion rather than diffusion only, whereas at low Darcy velocity (i.e., ≤10−9 m s−1), transport of K+ will be controlled by diffusion. Applications of the test results and parametric analysis results in practical situations
were reviewed. 相似文献
8.
A total of 87 direct shear tests in a large direct shear-box apparatus have been used to investigate the strength and dilatancy
of sand–gravel mixtures. This paper focuses on the differences in behaviour between a silica sand (yellow Leighton Buzzard
sand) and sand–gravel mixtures obtained by adding fractions of two kinds of gravel to the sand. The purpose is to find a relation
between the grain-size characteristics of the materials and the shearing resistance. Experimental results are analysed in
terms of the frictional and dilatant contributions to the strength of mixtures as a function of their relative density, and
are compared with dilatancy theories and empirical equations. The addition of gravel to the mixtures, even at low fractions
(less than 0.1 by volume), causes an increase in peak friction angle (Φ ′peak) which results both from higher dilatancy at failure (ψmax) and higher constant volume friction angle (Φ ′cv). Use of the minimum voids ratio (emin) of the materials allows the data for the two families of mixtures to be normalized and interpreted in terms of Φ ′cv and the ratio (Φ ′peak − Φ ′cv)/ψmax. The relationships between relative density (Dr), ψmax and Φ ′peak − Φ ′cv are only partly explained on a physical basis, so we develop empirical equations to predict the peak shear resistance of
sand–gravel mixtures (up to gravel contents of 0.5) on the basis of easily measurable quantities. Such equations constitute
a practical tool to overcome the problems arising from the impracticality of testing coarse material in the standard shear-box
apparatus. 相似文献
9.
Characteristics of phenanthrene and pyrene’s sorption and desorption on two local soils in solutions of simulated groundwater, simulated lung fluid, and simulated saliva were studied with batch equilibrium experiments to understand the fate of PAHs in the karst region of southwestern China and to assess the environmental exposure and the health risk of PAHs. The results showed that the sorption and desorption isotherms of phenanthrene and pyrene on two target soils in the three solution systems could be adequately described by the Freundlich model, while the fitted isotherm parameters for the simulated groundwater solution distinguished notably from those for the simulated body fluid solutions. For the sorption experiments, in the simulated groundwater, the n values were 0.722 and 0.672 for phenanthrene and were 0.724 and 0.663 for pyrene, respectively, on the yellow soil and the limestone soil; The log KF values were 3.118 and 3.323 for phenanthrene and were 3.648 and 3.846 for pyrene, respectively, on the yellow soil and the limestone soil. In the simulated body fluids, the n values for phenanthrene and pyrene ranged from 0.622 to 0.836 and from 0.590 to 0.865, respectively, and the log KF values of phenanthrene and pyrene ranged from 2.845 to 3.327 and from 3.344 to 3.779, respectively. For the desorption experiments, in the simulated groundwater, the n values were 0.662 and 0.744 for phenanthrene and were 0.702 and 0.647 for pyrene, respectively, on the yellow soil and the limestone soil. The log KF values were 3.666 and 3.686 for phenanthrene and were 4.128 and 4.225 for pyrene, respectively, on the yellow soil and the limestone soil. In the simulated body fluids, the n values for phenanthrene and pyrene ranged from 0.612 to 0.668 and from 0.631 to 0.819, respectively, and the log KF values of phenanthrene and pyrene ranged from 3.134 to 3.407 and from 3.533 to 3.839, respectively. The limestone soil had relatively higher log KF values but lower KOC values compared to those of the yellow soil, indicated that the nature of sorbent soils played the dominant role in sorption and desorption behaviors of PAHs. The experimental results showed a remarkable differences in sorption and desorption behaviors of PAHs in simulated body fluids and groundwater. The nonlinearities of measured isotherms and the measured sorption capacities of soils in simulated body fluids were significantly lower than corresponding those in the simulated groundwater, and HI values for simulated body fluids systems were significantly smaller than corresponding those for the simulated groundwater systems. The results underscore cautions in assessing environmental exposure and health risks of PAHs based on their sorption–desorption data in simulated groundwater as this is traditionally done.
相似文献10.
Displacement studies on leaching of potassium (K+) were conducted under unsaturated steady state flow conditions in nine undisturbed soil columns (15.5 cm in diameter and
25 cm long). Pulses of K+ applied to columns of undisturbed soil were leached with distilled water or calcium chloride (CaCl2) at a rate of 18 mm h−1. The movement of K+ in gypsum treated soil leached with distilled water was at a similar rate to that of the untreated soil leached with 15 mM
CaCl2. The Ca2+ concentrations in the leachates were about 15 mM, the expected values for the dissolution of the gypsum. When applied K+ was displaced with the distilled water, K+ was retained in the top 10–12.5 cm depth of soil. In the undisturbed soil cores there is possibility of preferential flow
and lack of K+ sorption. The application of gypsum and CaCl2 in the reclamation of sodic soils would be expected to leach K+ from soils. It can also be concluded that the use of sources of water for irrigation which have a high Ca2+ concentration can also lead to leaching of K+ from soil. Average effluent concentration of K+ during leaching period was 30.2 and 28.6 mg l−1 for the gypsum and CaCl2 treated soils, respectively. These concentrations are greater than the recommended guideline of the World Health Organisation
(12 mg K+ l−1). 相似文献
11.
Comparison of numerical simulation of solute transport with observed experimental data in a silt loam subsoil 总被引：1，自引：0，他引：1
Solute transport experiments were conducted on loamy soils of north-eastern Iowa, USA, and the results were compared with
a numerical solution of a classical advection-dispersion transport model developed in this study. Flow experiments in the
laboratory on undisturbed soil columns showed a flow rate of water much higher than was estimated from the soil properties
and grain-size analysis data, suggesting preferential flow regime in the soil. In contrast, the relative concentration peaks
of Cl– and Br– in the effluent were only approximately 70% of those predicted by the classical advection-dispersion equation (ADE). In addition,
the experimental breakthrough curves (BTCs) showed greater tailings of these ions than the model solution. These observations
suggest a loss of solute mass during transport from the dynamic flowing regions to a stagnant, immobile water phase in the
soil matrix. Experiments in small disturbed soil columns showed that movement of Cl– and Br– is in good agreement with predictions of the classical ADE when the tracers are applied as a continuous source. However,
in the case of a pulse source, the BTCs of Cl– and Br– matched the model only in the ascending part of the curves. Such variation indicates greater retardation of these ions than
that of simulation, probably caused by the decrease in soil permeability due to cation exchange reactions in the soil involving
monovalent and divalent cation pairs such as K+–Ca2+ and K+–Mg2+. In addition, retardation occurred as a result of the continuous saturation of soil columns which seemed to have caused an
expansion of clay minerals, thus resulting in decreased soil permeability. In both the continuous and the pulse-source experiments,
K+ was not detected in the effluent samples, which seemed to have been lost in exchange reactions and adsorption.
Received: 20 November 1998 · Accepted: 19 July 1999 相似文献
12.
There is increasing concern about soil enrichment with K+ and subsequent potential losses following long-term application of poor quality water to agricultural land. Different models
are increasingly being used for predicting or analyzing water flow and chemical transport in soils and groundwater. The convective–dispersive
equation (CDE) and the convective log-normal transfer function (CLT) models were fitted to the potassium (K+) leaching data. The CDE and CLT models produced equivalent goodness of fit. Simulated breakthrough curves for a range of
CaCl2 concentration based on parameters of 15 mmol l−1 CaCl2 were characterised by an early peak position associated with higher K+ concentration as the CaCl2 concentration used in leaching experiments decreased. In another method, the parameters estimated from 15 mmol l−1 CaCl2 solution were used for all other CaCl2 concentrations, and the best value of retardation factor (R) was optimised for each data set. A better prediction was found. With decreasing CaCl2 concentration the value of R is required to be more than that measured (except for 10 mmol l−1 CaCl2), if the estimated parameters of 15 mmol l−1 CaCl2 are used. The two models suffer from the fact that they need to be calibrated against a data set, and some of their parameters
are not measurable and cannot be determined independently. 相似文献
13.
Adsorption characteristics of perchloroethylene in natural sandy materials with low organic carbon content 总被引：2，自引：0，他引：2
Laboratory batch tests were conducted to investigate the sorption isotherms and sorption kinetics of the chlorinated hydrocarbon
perchloroethylene (PCE) in five natural sandy materials with an organic carbon content (f
oc) in the range 0.080–0.540%. The amended non-linear dual-mode model can describe the sorption isotherms in materials with
f
oc in the range 0.080–0.090%. For a sample with a much higher f
oc of 0.54%, the absorption isotherm was found to fit a linear model. These results may indicate that organic carbon is not
the main factor influencing the sorption isotherm. The sorption kinetics of PCE in samples with f
oc in the range 0.080–0.090% are not first-order and are different from those observed in the samples with higher f
oc. The sorption process in the materials with lower f
oc involves fast sorption, fast desorption and an equilibrium stage. The results may imply that the factors affecting sorption
kinetics of PCE in low f
oc media are pore filling and capillary condensation rather than organic carbon content. 相似文献
14.
Assessment of natural attenuation of aromatic hydrocarbons in groundwater near a former manufactured-gas plant, South Carolina, USA 总被引：1，自引：0，他引：1
J. E. Landmeyer F. H. Chapelle M. D. Petkewich P. M. Bradley 《Environmental Geology》1998,34(4):279-292
Shallow, anaerobic groundwater near a former manufactured-gas plant (MGP) in Charleston, South Carolina, USA, contains mono-
and polycyclic aromatic hydrocarbons (MAHs and PAHs, respectively). Between 1994 and 1997, a combination of field, laboratory,
and numerical-flow and transport-model investigations were made to assess natural attenuation processes affecting MAH and
PAH distributions. This assessment included determination of adsorption coefficients (K
ad
) and first-order biodegradation rate constants (K
bio
) using aquifer material from the MGP site and adjacent properties. Naphthalene adsorption (K
ad
=1.35×10–7 m3/mg) to aquifer sediments was higher than toluene adsorption (K
ad
=9.34×10–10 m3/mg), suggesting preferential toluene transport relative to naphthalene. However, toluene and benzene distributions measured
in January 1994 were smaller than the naphthalene distribution. This scenario can be explained, in part, by the differences
between biodegradation rates of the compounds. Aerobic first-order rate constants of 14C-toluene, 14C-benzene, and 14C-naphthalene degradation were similar (–0.84, –0.03, and 0.88 day–1, respectively), but anaerobic rate constants were higher for toluene and benzene (–0.002 and –0.00014 day–1, respectively) than for naphthalene (–0.000046 day–1). Both areal and cross-sectional numerical simulations were used to test the hypothesis suggested by these rate differences
that MAH compounds will be contained relative to PAHs. Predictive simulations indicated that the distributions of toluene
and benzene reach steady-state conditions before groundwater flow lines discharge to an adjacent surface-water body, but do
discharge low concentrations of naphthalene. Numerical predictions were "audited" by measuring concentrations of naphthalene,
toluene, and benzene at the site in early 1997. Measured naphthalene and toluene concentrations were substantially reduced
and the areal extent of contamination smaller than was both observed in January 1994 and predicted for 1997. Measured 1997
benzene concentrations and distribution were shown to be relatively unchanged from those measured in 1994, and similar to
predictions for 1997.
Received: 26 June 1997 · Accepted: 25 August 1997 相似文献
15.
L. A. Koroleva N. D. Shikina P. G. Kolodina A. V. Zotov B. R. Tagirov Yu. V. Shvarov V. A. Volchenkova Yu. K. Shazzo 《Geochemistry International》2012,50(10):853-859
The hydrolysis of the Pd2+ ion in HClO4 solutions was examined at 25–70°C, and the thermodynamic constants of equilibrium K (1)0 and K (2)0were determined for the reactions Pd2+ + H2O = PdOH+ + H+ and Pd2+ + 2H2O = Pd(OH)20 + 2H+, respectively. The values of log K (1)0 = −1.66 ± 0.5 (25°C) and −0.65 ± 0.25 (50°C) and log K (2)0 = −4.34 ± 0.3 (25°C) and −3.80 ± 0.3 (50°C) were derived using the solubility technique at 0.95 confidence level. The values of log K (1)0 = −1.9 ± 0.6 (25°C), −1.0 ± 0.4 (50°C), and −0.5 ± 0.3 (70°C) were obtained by spectrophotometric techniques. The palladium ion is significantly hydrolyzed at elevated temperatures (50–70°C) even in strongly acidic solutions (pH 1–1.5), and its hydrolysis is enhanced with increasing temperature. 相似文献
16.
Phosphorus transport in shallow groundwater in peri-urban Kampala, Uganda: results from field and laboratory measurements 总被引：1，自引：0，他引：1
To understand Phosphorus (P) sources and transport processes in the subsurface in Bwaise III Parish, Kampala, P attenuation
and adsorption capacities of soils were studied in situ and from laboratory measurements. Relationships between sorption parameters
and soil matrix properties, rates and mechanism of the adsorption process and soil P fractions were also investigated. P was
generally higher in the wet than the dry season, but for both seasons, the maximum was 5 mgP/l. P transport mechanisms appeared
to be a combination of adsorption, precipitation, leaching from the soil media and by colloids with the latter two playing
an important role in the wet season. The sorption process comprised two phases with the first stage rate constants being about
fourfold those of the second stage. The Langmuir isotherm described the sorption data well (R
2 ≥ 0.95) with the second soil layer exhibiting the highest sorption maximum (C
max) (average value 0.6 ± 0.17 mgP/gDW). The best prediction of C
max had organic carbon, Ca, available P and soil pH. Residual P consisting mostly of organics was the main fraction in all the
layers followed by inorganic HCl-P and NaOH-P in the top and middle layers, respectively. Loosely bound P (NH4Cl-P) was the least fraction (<0.4% of total P) in all layers indicating the high binding capacity of P by the soils. The
study results suggest that P dynamics is related to Ca, Fe and organic carbon content of the soils. 相似文献
17.
Lars Chresten Lund-Hansen Thorbjørn Joest Andersen Morten Holtegaard Nielsen Morten Pejrup 《Estuaries and Coasts》2010,33(6):1442-1451
Optical constituents as suspended particulate matter (SPM), chlorophyll (Chl-a), colored dissolved organic matter (CDOM),
and grain sizes were obtained on a transect in the arctic fjord-type estuary Kangerlussuaq (66°) in August 2007 along with
optical properties. These comprised diffuse attenuation coefficient of downwelling PAR (K
d(PAR)), upwelling PAR (K
u(PAR)), particle beam attenuation coefficient (c
p), and irradiance reflectance R(−0, PAR). PAR is white light between 400 and 700 nm. The estuary receives melt water from the Greenland Inland Ice and stations
covered a transect from the very high turbid melt water outlet to clear marine waters. Results showed a strong spatial variation
with high values as for suspended matter concentrations, CDOM, diffuse attenuation coefficient K
d(PAR), particle beam attenuation coefficients (c
p), and reflectance R(−0, PAR) at the melt water outlet. Values of optical constituents and properties decreased with distance from the melt water
outlet to a more or less constant level in central and outer part of the estuary. There was a strong correlation between inorganic
suspended matter (SPMI) and diffuse attenuation coefficient K
d(PAR) (r
2 = 0.92) and also for particle beam attenuation coefficient (c
p; r
2 = 0.93). The obtained SPMI specific attenuation—K
d*(PAR) = 0.13 m2 g−1 SPMI—and the SPMI specific particle beam attenuation—c
p* = 0.72 m2 g−1—coefficients were about two times higher than average literature values. Irradiance reflectance R(−0, PAR) was comparatively high (0.09−0.20) and showed a high (r
2 = 0.80) correlation with K
u(PAR). Scattering dominated relative to absorption—b(PAR)/a(PAR) = 12.3. Results strongly indicated that the high values in
the optical properties were related to the very fine particle sizes (mean = 2–6 μm) of the suspended sediment. Data and results
are discussed and compared to similar studies from both temperate and tropical estuaries. 相似文献
18.
Identification and characterization of aeolian deposits in arid environments provide information on mechanisms of loess and sand accumulation. The objectives of this study were to (i) identify the distribution of aeolian deposits, (ii) discriminate loess and sand deposits using granulometric data, and (iii) describe the aeolian deposition in Sarakhs area, northeastern Iran. Particle size distributions of 26 surface samples were determined using a laser grain-size analyzer. Fine sand, very fine sand, and very coarse silt were dominant fractions in studied sediments, and the sum of these fractions ranged from 46.9% in loess deposits to 93.8% in sand dunes. The mean grain size (M z ) of sand dunes ranged from 3.31 to 3.54 ?, which gradually changed to 4.09 to 5.50 ? in loess deposits. Sorting, skewness, and kurtosis ranged from 0.84 to 1.94 ?, 0.18 to 0.49, and 0.76 to 2.38, respectively. Aeolian deposits in the area resulted in the incorporation of Hariroud River system and Kopeh Dagh Mountains for aeolian particle production and accumulation. Alluvial comminution in Hariroud River is suggested the main mechanism of sand and silt production and flood plain environment the main reservoir of these particles. The mountains of Kopeh Dagh act as a barrier and play a key role for sand and loess accumulation. 相似文献
19.
Effects of grazing and livestock exclusion on soil physical and chemical properties in desertified sandy grassland,Inner Mongolia,northern China 总被引：3，自引：1，他引：2
Yuqiang Li Halin Zhao Xueyong Zhao Tonghui Zhang Yulin Li Jianyuan Cui 《Environmental Earth Sciences》2011,63(4):771-783
Heavy grazing is recognized as one of the main causes of vegetation and soil degradation and desertification in the semiarid
Horqin sandy grassland of northern China. Soil physical and chemical properties were examined under continuous grazing and
exclusion of livestock for 8 years in a representative desertified sandy grassland. Exclosure increased the mean soil organic
C, total N, fine sand and silt + clay contents, inorganic C (CaCO3), electrical conductivity, and mineral contents (including Al2O3, K2O, Na2O, Fe2O3, CaO, MgO, TiO2, MnO), microelements (Fe, Mn, Zn, B, Cu, Mo), and heavy metals (Pb, Cr, Ni, As, Hg, Cd, Se), and decreased the coarse sand
content, bulk density, and SiO2 in the top 100 cm of the soil. Livestock exclusion also improved available N, P, K, Fe, Mn, and Cu, exchangeable K+, and the cation exchange capacity, but decreased pH, exchangeable Na+, and available S, Zn, and Mo in the top 20 cm of the soil. The greatest change in soil properties was observed in the topsoil.
The results confirm that the desertified grassland is recovering after removal of the livestock disturbance, but that recovery
is a slow process. 相似文献
20.
D. G. Isaak J. D. Carnes O. L. Anderson H. Cynn E. Hake 《Physics and Chemistry of Minerals》1998,26(1):31-43
The ambient pressure elastic properties of single-crystal TiO2 rutile are reported from room temperature (RT) to 1800 K, extending by more than 1200 oK the maximum temperature for which rutile elasticity data are available. The magnitudes
of the temperature derivatives decrease with increasing temperature for five of the six adiabatic elastic moduli (C
ij
). At RT, we find (units, GPa): C
11=268(1); C
33=484(2); C
44=123.8(2); C
66=190.2(5); C
23=147(1); and C
12=175(1). The temperature derivatives (units, GPa K−1) at RT are: (∂C
11/∂T)
P
=−0.042(5); (∂C
33/∂T)
P
=−0.087(6); (∂C
44/∂T)
P
=−0.0187(2); (∂C
66/∂T)
P
=−0.067(2); (∂C
23/∂T)
P
=−0.025; and (∂C
12/∂T)
P
−0.048(5). The values for K
S
(adiabatic bulk modulus) and μ (isotropic shear modulus) and their temperature derivatives are K
S
=212(1) GPa; μ=113(1) GPa; (∂K
S
/∂T)
P
=−0.040(4) GPa K−1; and (∂μ/∂T)
P
=−0.018(1) GPa K−1. We calculate several dimensionless parameters over a large temperature range using our new data. The unusually high values
for the Anderson-Gròneisen parameters at room temperature decrease with increasing temperature. At high T, however, these parameters are still well above those for most other oxides. We also find that for TiO2, anharmonicity, as evidenced by a non-zero value of [∂ln (K
T
)/∂lnV]
T
, is insignificant at high T, implying that for the TiO2 analogue of stishovite, thermal pressure is independent of volume (or pressure). Systematic relations indicate that ∂2
K
S
/∂T∂P is as high as 7×10−4 K−1 for rutile, whereas ∂2μ/∂T∂P is an order of magnitude less.
Received: 19 September 1997 / Revised, accepted: 27 February 1998 相似文献