摘要:

Simulation of soil temperatures under forest and range fires requires reliable estimates of soil thermal properties over a range of temperatures from ambient to about 600°C. We measured thermal conductivity of soil samples differing in texture, bulk density, water content, and temperature and then fit the results with a modification of the de Vries equation. Thermal conductivity increases dramatically with temperature in moist soil, reaching values 3 to 5 times the ambient value at 90°C. The modified de Vries theory agreed well with data at low temperature, and provided an upper boundary for measurements at higher temperatures. Only four parameters are required to specify thermal conductivity as a function of bulk density, temperature, and water content: thermal conductivity of the mineral fraction, water content at which liquid flow becomes limiting, a power for the liquid flow function, and a shape factor. Adequate estimates of the conductivity of the mineral fraction can be obtained from handbooks if the soil mineralogy is known, and the water content for liquid return flow can be predicted from soil texture. The other two parameters show a fairly narrow range of variation and can probably be estimated with sufficient accuracy for most simulation purposes.

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

This study focused on the chemistry of soil water samples (SWS) obtained by tension-free lysimetry from serpentinitic, i.e., Cr- and Ni-rich, Dystric Eutrochrepts. Soil water samples from undisturbed soil profiles had total elemental concentrations (μnmol/L) of O.1–3.2 Cr, O.2–3.1 Ni, 3–154 Fe, and 55–401 Mg; however, dialysis revealed that on average, only 72% of total Mg, 39% Ni, 28% Cr and 15% Fe were present in dissolved form. Thus, in serpentinitic soils, colloids can be an important means of element translocation. Among metallic cations, Mg contributed generally more than 50% to the positive charge of SWS; also, there was a high linear correlation between dissolved (dialyzable) Mg

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

It is hypothesized that soil adsorption properties can be estimated from contents and adsorption properties of individual soil components (additivity principle), if the data are consistent. Therefore, adsorption of molybdenum(VI) by synthetic aluminum oxide, ferrihydrite, goethite, extracted humic acid and a sandy soil sample was determined as a function of Mo concentration (0–1.2 mmol/L) and pH (3.5–8). For each pH and adsorbent, the Langmuir adsorption maximum (adsorption capacity) was calculated. For the oxides, plots of these capacities against pH resulted in adsorption envelopes exhibiting maxima at pH 4–5, i.e., near the pKa1and pKa2for molybdenum acid. At this pH, adsorption corresponded to 1.8 μmole/m2(aluminum oxide), 2.4 μmole/m2(ferrihydrite), and 3.6 μmole/m2(goethite), suggesting formation of binuclear surface complexes involving monomeric Mo. The corresponding plot for humic acid differed in shape by rapidly decreasing adsorption from its maximum at pH 3.5, indicating a different mechanism, probably complex formation between carboxyl and phenol groups on humic acid and Mo in octahedral coordination. Good agreement between measured Mo adsorption by the soil and the amount calculated from the adsorption capacities of the pure oxides and humic acid and the contents of oxalate- and dithionite-ex-tractable Al and Fe and total carbon in the soil for the entire pH range emphasizes the importance of the Al and Fe oxides and organic matter for soil Mo adsorption but also indicates that adsorption properties of various constituents in soil are additive.

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The aim of this work was to study the influence of low molecular weight organic acid concentration (0 to 1600 μmol C L−1) and type (oxalic, citric (CI), salicylic) and of solution pH (3.2 to 4.7) on the kinetics of SO4sorption by the B horizon of two Spodosols (HER and CON) from the Lower Laurentians, Quebec. Using a miscible displacement technique, the soil materials were leached at a flow rate of 0.2 ml min−1for 6 h at 25°C. The slope parameter (1/β) of the Elovich equation was used as an apparent SO4sorption rate. The presence of organic ligands in solution reduced SO4sorption by the HER B and the CON B horizons from 543 to 365 μmol SO4kg−1and from 1053 to 642 μmol SO4kg−1, respectively. For both soils, 1/β values were always higher (97 to 51 μmol kg−1In min−1(HER) and 256 to 135 μmol kg−1In min−1(CON)) in systems that were free of organic acids; however, the relationships between the properties of the acids and their relative SO4sorption inhibition capacity was not clear. The extent of SO4sorption inhibition increased considerably as CI concentration was augmented from 100 to 1600 μmol C L−1. The efficiency of CI in reducing SO4sorption by the HER B horizon was pH dependent, with SO4sorption during the experiment decreasing by 23% at pH 3.2 and by 355% (desorption) at pH 4.7. The presence of CI led to the desorption of native exchangeable SO4when the pH was above 4.2 or when the total C concentration was high (1600 μnol C L−1). The data thus reveal that temporal changes in C cycling can affect SO4mobility in acidic forest soils with potential implications on the transport of nutrient cations if the total anionic equivalent charge of the soil solution is increased.

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Alachlor persistence was studied in three corn fields from two regions of Spain. The effect of soil temperature and soil moisture content on the rates of alachlor degradation was measured under controlled conditions in soil samples from the same fields. Laboratory data in conjunction with meteorological records were used in two computer models to predict alachlor persistence in the fields. The Walker model was used with a correction on the Linacre equation to take into account the Spanish field conditions. The degradation predicted with this model was faster than the data measured in the fields. The LEACHP v.3 model was used, with a modification in the subroutine that simulates the influence of temperature and moisture content on the degradation component. There was an acceptable agreement between measured and predicted residue levels with the LEACHP model in the three fields. Alachlor persistence and model prediction were discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The ability to accurately predict the mobility of a soil-applied herbicide is important to product registration and recommendations for environmentally safe use. Commonly, mobility is affected by time-dependent sorption processes. Parameters for such nonequilibrium sorption may be conveniently determined from batch kinetic studies; however, applicability of these parameters for subsequent use in transport modeling must be verified. The objective of this study, therefore, was to determine whether batch kinetic data were appropriate for predicting nonequilibrium sorption during alachlor [2-chIoro-N-(2,6-diethylphenyl)-N-(methoxymethyl)-acetamide] transport in Dundee silt loam soil. Batch (solution and extraction) data previously generated in this laboratory were used to determine sorption parameters for two- or three-site equilibrium/kinetic sorption models. Predictions of alachlor mobility generated from the corresponding transport models were then compared with miscible displacement data. Use of sorption parameters determined from batch solution data alone resulted in only qualitative predictions of alachlor movement. However, more accurate predictions were obtained if sorption parameters were based on both soil extraction and soil solution data.

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The emission of N2O and CH4from a calcareous soil was studied, in the laboratory, with the addition of inorganic N at different soil water levels. On the whole, the addition of NH+4led to significantly higher N2O emissions than the addition of NO−3. At 2/3 and 1.5 times field capacity, the N2O production was caused mainly by nitrification. At 3 and 6 times field capacity, nitrification and denitrification produced N2O simultaneously, in spite of low nitrification rates. The highest N2O emission was obtained at the more intermediate soil water levels (1.5 and 3 times field capacity) at which marginal oxygen conditions are likely to occur rather than at the soil water levels that had the highest nitrification (2/3 field capacity) or denitrification (6 times field capacity) process rates. This indicates that the effect of O2on the relative N2O production was more important in determining the N2O emission than the process rate. The C2H2inhibition of the reduction of N2O to N2failed at 6 times field capacity, probably because of insufficient C2H2diffusion into the soil.

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Peatland ecosystems may contribute about 65% of all natural methane emission to the atmosphere. During May—June 1988, CH4and CO2fluxes were measured with the static chamber method at the surface of a basin swamp and at three depths. The daily average fluxes of CH4and CO2at the surface of the swamp ranged from 1.146 to 2.178 mmol m−2d−1and from 1.966 to 7.242 mmol m+2d−1respectively. These amounts of CH4and CO2corresponded to 0.02–0.03% of what was released from the 45 to 60-cm depth when exposed to atmospheric pressure. Statistically significant correlations between physical and botanical peat properties and trapped CH4and CO2and water flow suggest that outgassing of trapped CH4and CO2are closely associated with the peat matrix, peat properties, hydraulic potential, temperature, and concentration gradients.

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Weathered granitic rock is a material with properties intermediate between soil and hard rock. It retains structural features of the hard rock, including joint fractures, but also has porosity generated as a result of weathering of primary minerals, clay formation, and root invasion. This study evaluated the physical and hydraulic properties of moderately and highly weathered granitic rock (class 5 and 6, respectively, of the classification scheme of Clayton and Arnold (1972)) in the San Jacinto Mountains of southern California. Class 5 and 6 samples exhibited comparable bulk densities (approximately 1.94 g cm−3), porosities (27%), and particle size distributions. Saturated hydraulic conductivities were also similar for both weathering classes (approximately 5.5 cm h−1). Water retention data indicate that about 50% of the water held at saturation is drained at −100 cm head. Effective pore size distributions calculated from water retention data indicate that 25% of the total porosity was associated with pores >100 μm in diameter.

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID