摘要:

Temperature-by-time data obtained using a dual-probe heat-pulse device can be analyzed using two different approaches to determine the soil thermal diffusivity, volumetric heat capacity and thermal conductivity. One approach, referred to as the single-point method, is based on accurate identification of the peak in the temperature-by-time measurements. The second approach involves a nonlinear model fit of the appropriate temperature model to the temperature-by-time data. In this paper, we analyze dual-probe heat-pulse data and show how the soil thermal properties determined using these two approaches compare. The single-point method is easy to apply, but results are sensitive to choice of the peak value, which can be difficult to identify if the data are sparse and contain noise. The nonlinear model fit (Marquardt method) copes better with broad, flat peaks and sparse, noisy data. Soil thermal properties obtained using either approach should be checked by comparing the fitted model with the measured temperature-by-time data. By doing so, one can quickly determine the validity of the results.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

An approximation to an implicit infiltration formula presented earlier in this series is developed. At worst, the relative error of the approximation is always less than 1%, and it is much better than that for most cases. The approximation becomes more accurate in both the short- and long-term limits as it becomes exact in each case. Application of the new formula is demonstrated using both laboratory and numerical experiments.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

The convection-dispersion equation (CDE) is the most commonly used process representation for describing solute movement through soils. A transfer function is a model for studying complex soil systems in a simple way by characterizing the output flux as a function of the input flux. Extensive solute transport data from a laboratory experiment conducted through long soil columns were used to validate the intrinsic assumptions of the CDE and the transfer function. Analyses of the experimental data showed that the observed dispersion coefficient increased with the travel distance for both homogeneous and heterogeneous soils. The dispersion coefficients had a two-order change within the 1250-cm soil columns and were described using a linear function of the solute travel distance. At the same travel distance, the dispersion coefficients in the heterogeneous soil column were about 50 times higher than those in the homogeneous soil. The experimental data better supported the assumptions of the transfer function than those of the CDE. An excellent linear relationship was found between the mean of log of the travel time and log of the travel distance. In turn, the relationship well described the scale-dependent dispersion coefficients of the homogeneous and heterogeneous soil columns. The convection-dispersion equation and the transfer equation were utilized to predict solute transport in homogeneous and heterogeneous porous media. Compared with the experimental data, the transfer function predicted solute transport in the porous media much more accurately than did the CDE for these examples. In addition, the soil spatial variability had a less profound effect on the transfer function predictions than on the CDE predictions.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Dual-energy gamma radiation systems are currently used to simultaneously determine either the dry bulk density of a porous medium and the volumetric content of one fluid, the volumetric fluid contents of two fluids, or the salt concentration and volumetric water content. In this paper an error analysis based on the well-known error propagation formula is presented for all three types of measurements. For each application, formulae are derived that calculate the variance of a measured variable as a function of the observed count rates, attenuation coefficients, and path length. These formulae can be implemented in data acquisition or postprocessing programs. In addition, formulae are presented that relate the variance to the values of the measured variables, measurement counting time, calibration counting time, path lengths, source intensities, and attenuation coefficients. The latter formulae benefit experimental design. The effect of counting and calibration time, attenuation coefficients, source strengths, and path lengths on the probable error are demonstrated. For each type of measurement, experiments are conducted to test the validity of the presented theory. It was shown that, in general, the difference between the measured value and the true value of a variable is less than 1 standard deviation.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Fractionation techniques have been applied widely to assess the behavior of various geological trace elements. However, relatively few studies have been conducted on solid-phase speciation and geochemical assessment of selenium (Se) through fractional partitioning. Soils collected from contrasting range and mine environments of Wyoming were partitioned fractionally to investigate the significance of different Se fractions in assessing solid-phase speciation and geochemical transformations. The Se fractions extracted by the partitioning technique were aqueous (0.25MKCI), exchangeable (1MKH2PO4), acid-extractable (4MHCI), sulfide and humic bound (KCIO3+ 12MHCI), and siliceous (15.8MHNO3+ 11.7MHCIO4+ 28.9MHF); each fraction was also speciated for selenite (Se+4) and selenate (Se+6). In addition, the soil samples were analyzed for total soil Se after a strong mixed-acid digestion (15.8MHNO3+ 11.7MHCIO4+ 28.9MHF). High percent recovery (85–104%) was observed between total Se and sum of the partitioned fractions, which were also significantly correlated (r= 0.99). With increasing exchangeable Se, there was a corresponding increase in the aqueous fraction (r= 0.72). A similar increasing trend was found between the exchangeable and acid-extractable fractions (r= 0.51). For the aqueous fraction, Se+6was found to be the potential species, whereas in the exchangeable fraction, Se+4predominated. Both Se+4and Se+6were distributed almost evenly in the acid-extractable fraction. Speciation data for sulfide and humic bound, and siliceous fractions, however, were not conclusive. Selenium in the available and conditionally available fractions increased as the weatherable fraction decreased (for bothr= −0.83). Total soil Se increased with increasing clay content (r= 0.81), and a reverse trend was observed with sand content (r= −0.69), suggesting Se is associated with the clay-sized soil fraction. Siliceous Se was linearly related to total soil Se (r= 0.91), suggesting the presence of Se in soil minerals. This fraction was again found to increase with increasing clay content (r= 0.74). Average distributions of the five Se fractions indicated the soils were dominated by the siliceous Se, with aqueous fraction comprising the least abundant Se level. Statistical analysis indicated all of the above mentioned correlations were significant at theP< 0.01 or 0.001 level.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Nine podzolic soil profiles (n= 67 horizons) were sampled in southern Quebec to evaluate the effects of drying on soil pH measurements in H2O (pHw) and in 0.01MCaCI2(pHCA) and to identify the existence of relationships between pH changes on drying and soil properties. The precision of pH measurements (global precision of ± 0.035 pH unit) varied, with the poorest precision value (0.10) being recorded for pHwin field-moist samples of organic horizons (O). For any soil horizon group (O, E, B, C), the pH change attributable to drying was always larger in H2O (up to 0.50 pH unit or 130 μmol H+L-1) than in CaCI2(up to 0.25 pH unit or 520 μmol H+L-1). When expressed in terms of H+concentration, the trend is inverted because pHCAvalues are often one pH unit more acidic than pHwvalues for the same horizon. Drying generally resulted in soil acidification for all horizon types although both acidification and alkalinization could occur in a given profile. We found positive and significant relationships between pH changes attributable to drying expressed as |Δ H+I and organic C and exchangeable Al for both electrolytes. The relationships were stronger when soil materials were grouped on a profile basis (averagervalue = 0.78 and 0.62 for organic C and exchangeable Al, respectively) than when grouped by horizon type (averagervalue = 0.39 and 0.49 for organic C and exchangeable Al, respectively). The DOC concentrations in both electrolytes and for any given horizon were always higher in dry than in moist soil samples. Absolute changes in DOC concentrations were correlated to the absolute magnitude of pH changes upon drying (0.67 <r< 0.96; α ≤ 0.05). However, the relationships between the magnitude of DOC changes and the polarity of pH changes upon drying (Δ H+) varied with the electrolyte used. In H2O, the decrease in soil pH is mostly associated with the acidifying effect of an increase in organic matter solubility after drying. In CaCI2, it is suggested that the potential reduction of Al availability after soil drying and the flocculation of organic substances by Ca3+ions could contribute to the increase in pH. Characterizing the suite of organic substances present in individual horizons could also prove very helpful in elucidating the response of soil pH to drying.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

We investigated the competitive and mutualistic interactions between common colonizers of low productivity sites in southern New Jersey's Pinelands National Reserve. These included pitch pine (Pinus rigida), the N2-fixing bayberry (Myrica pensylvanica), and their respective symbionts Pisolithus tinctorius and the actinomyceteFrankia.We initiated a 2-year greenhouse study to examine the effects of intra- and interspecific plantings of these woody perennials, with and without the endobiontsP. tinctoriusandFrankia.Biomass accumulation and partitioning, leaf nutrient concentrations, and a15N-dilution technique were used to evaluate the success of the different planting combinations.After two growing seasons, symbionts increased the development of their hosts. Pines in interspecific plantings with bayberry exhibited similar levels of total production to those grown with conspecifics, whereas biomass partitioning to the shoots was increased in the mixed-species plantings. Bayberry exhibited trends toward higher production whenFrankiarapidly colonized its roots or when the associated pine lackedP. tinctorius.There was no evidence that nitrogen fixed by bayberry seedlings reached companion pines after 2 years. Timing of endobiont colonization was a dominant factor influencing plant growth and the capacity to mitigate competition for limiting resources.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID