Calibration and Temperature Correction of Heat Dissipation Matric Potential Sensors
01 Sep 2002-Soil Science Society of America Journal (John Wiley & Sons, Ltd)-Vol. 66, Iss: 5, pp 1439-1445
TL;DR: In this paper, heat dissipation sensors, used to measure soil water matric potential, were analyzed to develop a normalized calibration equation and a temperature correction method, which resulted in a mean absolute error of 23% over a matric possible range of -0.01 to -35 MPa.
Abstract: This paper describes how heat dissipation sensors, used to measure soil water matric potential, were analyzed to develop a normalized calibration equation and a temperature correction method. Inference of soil matric potential depends on a correlation between the variable thermal conductance of the sensor's porous ceramic and matric potential. Although this correlation varies among sensors, we demonstrate a normalizing procedure that produces a single calibration relationship. Using sensors from three sources and different calibration methods, the normalized calibration resulted in a mean absolute error of 23% over a matric potential range of -0.01 to -35 MPa. Because the thermal conductivity of variably saturated porous media is temperature dependent, a temperature correction is required for application of heat dissipation sensors in field soils. A temperature correction procedure is outlined that reduces temperature dependent errors by 10 times, which reduces the matric potential measurement errors by more than 30%. The temperature dependence is well described by a thermal conductivity model that allows for the correction of measurements at any temperature to measurements at the calibration temperature.
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TL;DR: In this paper, the authors examined the effects of land use/land cover changes on groundwater recharge and solute transport in the Amargosa Desert (AD) in Nevada and in the High Plains (HP) in Texas, US.
Abstract: Humans have exerted large-scale changes on the terrestrial biosphere, primarily through agriculture; however, the impacts of such changes on the hydrologic cycle are poorly understood. The purpose of this study was to test the hypothesis that the conversion of natural rangeland ecosystems to agricultural ecosystems impacts the subsurface portion of the hydrologic cycle by changing groundwater recharge and flushing salts to underlying aquifers. The hypothesis was examined through point and areal studies investigating the effects of land use/land cover (LU/LC) changes on groundwater recharge and solute transport in the Amargosa Desert (AD) in Nevada and in the High Plains (HP) in Texas, US. Studies use the fact that matric (pore-water-pressure) potential and environmental-tracer profiles in thick unsaturated zones archive past changes in recharging fluxes. Results show that recharge is related to LU/LC as follows: discharge through evapotranspiration (i.e., no recharge; upward fluxes o0.1mmyr � 1 ) in natural rangeland ecosystems (low matric potentials; high chloride and nitrate concentrations); moderate-to-high recharge in irrigated agricultural ecosystems (high matric potentials; lowto-moderate chloride and nitrate concentrations) (AD recharge: � 130‐640mmyr � 1 ); and moderate recharge in nonirrigated (dryland) agricultural ecosystems (high matric potentials; low chloride and nitrate concentrations, and increasing groundwater levels) (HP recharge: � 9‐32mmyr � 1 ). Replacement of rangeland with agriculture changed flow directions from upward (discharge) to downward (recharge). Recent replacement of rangeland with irrigated ecosystems was documented through downward displacement of chloride and nitrate fronts. Thick unsaturated zones contain a reservoir of salts that are readily mobilized under increased recharge related to LU/LC changes, potentially degrading groundwater quality. Sustainable land use requires quantitative knowledge of the linkages between ecosystem change, recharge, and groundwater quality.
553 citations
Cites background from "Calibration and Temperature Correct..."
..., Logan, UT, USA) measure matric potential via thermal properties of a calibrated porous element that is in hydraulic equilibrium with the surrounding soil (Flint et al., 2002; Scanlon & Andraski, 2002)....
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...HDS (Model 229, Campbell Scientific Inc., Logan, UT, USA) measure matric potential via thermal properties of a calibrated porous element that is in hydraulic equilibrium with the surrounding soil (Flint et al., 2002; Scanlon & Andraski, 2002)....
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TL;DR: In this paper, the impact of water content, pore water pressure and hydrological hysteresis on safety factor reconstruction was analyzed by applying two different models (Lu and Godt's and SLIP models) to a monitored slope located in Oltrepo Pavese (Northern Italy).
160 citations
TL;DR: In this article, the role of interannual to multidecadal climate variability on groundwater levels, deep infiltration (3 − 23 m) events, and downward displacement of chloride and nitrate reservoirs in thick vadose zones across the regionally extensive High Plains aquifer was systematically examined.
Abstract: Responses in the vadose zone and groundwater to interannual, interdecadal, and multidecadal climate variability have important implications for groundwater resource sustainability, yet they are poorly documented and not well understood in most aquifers of the USA. This investigation systematically examines the role of interannual to multidecadal climate variability on groundwater levels, deep infiltration (3–23 m) events, and downward displacement (>1 m) of chloride and nitrate reservoirs in thick (15–50 m) vadose zones across the regionally extensive High Plains aquifer. Such vadose zone responses are unexpected across much of the aquifer given a priori that unsaturated total-potential profiles indicate upward water movement from the water table toward the root zone, mean annual potential evapotranspiration exceeds mean annual precipitation, and millennia-scale evapoconcentration results in substantial vadose zone chloride and nitrate reservoirs. Using singular spectrum analysis (SSA) to reconstruct precipitation and groundwater level time-series components, variability was identified in all time series as partially coincident with known climate cycles, such as the Pacific Decadal Oscillation (PDO) (10–25 yr) and the El Nino/Southern Oscillation (ENSO) (2–6 yr). Using these lag-correlated hydrologic time series, a new method is demonstrated to estimate climate-varying unsaturated water flux. The results suggest the importance of interannual to interdecadal climate variability on water-flux estimation in thick vadose zones and provide better understanding of the climate-induced transients responsible for the observed deep infiltration and chemical-mobilization events. Based on these results, we discuss implications for climate-related sustainability of the High Plains aquifer.
156 citations
Cites background from "Calibration and Temperature Correct..."
...The HDPs are capable of measuring the matric potential from approximately −0.01 to −100 MPa with a sensitivity that is proportional to the matric potential (Flint et al., 2002)....
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...01 to −100 MPa with a sensitivity that is proportional to the matric potential (Flint et al., 2002)....
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TL;DR: In this paper, the authors assess the potential of updating soil moisture states of a distributed hydrologic model by assimilating streamflow and in situ soil moisture data for high-resolution analysis and prediction of stream flow and soil moisture.
134 citations
Cites methods from "Calibration and Temperature Correct..."
...The measured temperature difference, DT, is used to estimate the matric potential of the soil via the van Genuchten equation [64,65], which is then converted to soil moisture, h, via the van Genuchten equation [63,65]....
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TL;DR: The results highlight the importance of precise root activity measurements, as root mass was a poor indicator of root activity, and trees and grasses partitioned soil resources, but this partitioning did not reflect the ability of trees to access deep soil water that was unavailable to grasses.
Abstract: Summary
•As described in the two-layer hypothesis, woody plants are often assumed to use deep soils to avoid competition with grasses. Yet the direct measurements of root activity needed to test this hypothesis are rare.
•Here, we injected deuterated water into four soil depths, at four times of year, to measure the vertical and horizontal location of water uptake by trees and grasses in a mesic savanna in Kruger National Park, South Africa.
•Trees absorbed 24, 59, 14 and 4% of tracer from the 5, 20, 50, and 120 cm depths, respectively, while grasses absorbed 61, 29, 9 and 0.3% of tracer from the same depths. Only 44% of root mass was in the top 20 cm. Trees absorbed tracer under and beyond their crowns, while 98% of tracer absorbed by grasses came from directly under the stem.
•Trees and grasses partitioned soil resources (20 vs 5 cm), but this partitioning did not reflect, as suggested by the two-layer hypothesis, the ability of trees to access deep soil water that was unavailable to grasses. Because root mass was a poor indicator of root activity, our results highlight the importance of precise root activity measurements.
133 citations
References
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TL;DR: Van Genuchten et al. as mentioned in this paper proposed a closed-form analytical expression for predicting the hydraulic conductivity of unsaturated soils based on the Mualem theory, which can be used to predict the unsaturated hydraulic flow and mass transport in unsaturated zone.
Abstract: A new and relatively simple equation for the soil-water content-pressure head curve, 8(h), is described in this paper. The particular form of the equation enables one to derive closedform analytical expressions for the relative hydraulic conductivity, Kr, when substituted in the predictive conductivity models of N.T. Burdine or Y. Mualem. The resulting expressions for Kr(h) contain three independent parameters which may be obtained by fitting the proposed soil-water retention model to experimental data. Results obtained with the closed-form analytical expressions based on the Mualem theory are compared with observed hydraulic conductivity data for five soils with a wide range of hydraulic properties. The unsaturated hydraulic conductivity is predicted well in four out of five cases. It is found that a reasonable description of the soil-water retention curve at low water contents is important for an accurate prediction of the unsaturated hydraulic conductivity. Additional Index Words: soil-water diffusivity, soil-water retention curve. van Genuchten, M. Th. 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44:892-898. T USE OF NUMERICAL MODELS for simulating fluid flow and mass transport in the unsaturated zone has become increasingly popular the last few years. Recent literature indeed demonstrates that much effort is put into the development of such models (Reeves and Duguid, 1975; Segol, 1976; Vauclin et al., 1979). Unfortunately, it appears that the ability to fully characterize the simulated system has not kept pace with the numerical and modeling expertise. Probably the single most important factor limiting the successful application of unsaturated flow theory to actual field problems is the lack of information regarding the parameters entering the governing transfer equations. Reliable estimates of the unsaturated hydraulic conductivity are especially difficult to obtain, partly because of its extensive variability in the field, and partly because measuring this parameter is time-consuming and expensive. Several investigators have, for these reasons, used models for calculating the unsaturated conductivity from the more easily measured soil-water retention curve. Very popular among these models has been the Millington-Quirk method (Millington and Quirk, 1961), various forms of which have been applied with some success in a number of studies (cf. Jackson et al., 1965; Jackson, 1972; Green and Corey, 1971; Bruce, 1972). Unfortunately, this method has the disadvantage of producing tabular results which, for example when applied to nonhomogeneous soils in multidimensional unsaturated flow models, are quite tedious to use. Closed-form analytical expressions for predicting 1 Contribution from the U. S. Salinity Laboratory, AR-SEA, USDA, Riverside, CA 92501. Received 29 June 1979. Approved 19 May I960. 'Soil Scientist, Dep. of Soil and Environmental Sciences, University of California, Riverside, CA 92521. The author is located at the U. S. Salinity Lab., 4500 Glenwood Dr., Riverside, CA 92502. the unsaturated hydraulic conductivity have also been developed. For example, Brooks and Corey (1964) and Jeppson (1974) each used an analytical expression for the conductivity based on the Burdine theory (Burdine, 1953). Brooks and Corey (1964, 1966) obtained fairly accurate predictions with their equations, even though a discontinuity is present in the slope of both the soil-water retention curve and the unsaturated hydraulic conductivity curve at some negative value of the pressure head (this point is often referred to as the bubbling pressure). Such a discontinuity sometimes prevents rapid convergence in numerical saturated-unsaturated flow problems. It also appears that predictions based on the Brooks and Corey equations are somewhat less accurate than those obtained with various forms of the (modified) Millington-Quirk method. Recently Mualem (1976a) derived a new model for predicting the hydraulic conductivity from knowledge of the soil-water retention curve and the conductivity at saturation. Mualem's derivation leads to a simple integral formula for the unsaturated hydraulic conductivity which enables one to derive closed-form analytical expressions, provided suitable equations for the soil-water retention curves are available. It is the purpose of this paper to derive such expressions using an equation for the soil-water retention curve which is both continuous and has a continuous slope. The resulting conductivity models generally contain three independent parameters which may be obtained by matching the proposed soil-water retention curve to experimental data. Results obtained with the closedform equations based on the Mualem theory will be compared with observed data for a few soils having widely varying hydraulic properties. THEORETICAL Equations Based on Mualem's Model The following equation was derived by Mualem (1976a) for predicting the relative hydraulic conductivity (Kr) from knowledge of the soil-water retention curve
22,781 citations
TL;DR: In this article, the authors 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.
Abstract: 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.
305 citations
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TL;DR: In this paper, various thermal properties of soils accessible through simple measurements are described, such as the insulating effect of soil, the existence of the soil temperature wave, and the propagation of this wave through the soil.
Abstract: Various thermal properties of soils accessible through fairly simple measurements are described. These properties include the insulating effect of soil, the existence of the soil temperature wave, and the propagation of this wave through the soil.
154 citations
01 Jan 1990
TL;DR: In this article, the authors present an instrumentation for studying vegetation canopies for remote sensing in optical and thermal infrared regions, pp. 301-310, with a focus on soil thermal conductivity.
Abstract: (1990). Soil thermal conductivity. Remote Sensing Reviews: Vol. 5, Instrumentation for studying vegetation canopies for remote sensing in optical and thermal infrared regions, pp. 301-310.
117 citations