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scales, it is important that the various coupled transport processes are measured simultaneously.Water, solute, and heat transport processes in soils are mutually In addition to being variable in time, soil transport interdependent as each includes convective water flow and each transproperties and processes are known to be highly variable port mechanism is partly controlled by fluid saturation, pore geometry, in space. Because of the inherent soil spatial heterogenetemperature, and other soil environmental conditions. Therefore, their measurement in approximately identical measurement locations and ity, the outcome of a soil measurement is dependent on volume is essential for understanding transport phenomena in soils. measurement volume. The scale dependency of soil prop-We introduce a 2.7-cm-diameter multi-functional heat pulse probe erties and their relation to vadose zone flow and trans-(MFHPP), which consists of a single central heater, four thermistors, port processes have precluded a unifying concept of and four electrodes (Wenner array) that together are incorporated in water flow and chemical transport across spatial scales, six 1.27-mm-o.d. stainless-steel tubes. The bulk soil thermal properties from the microscopic pore scale to the macroscopic local and volumetric water content of Tottori Dune sand were determined scale (Hopmans et al., 2002b). Therefore, it is essential from the measurement of the temperature response of all four thermisto estimate soil properties at the same location, using tor sensors after application of an 8-s heat pulse by the heater sensor. approximately equal measurement volumes. Hence, the Simultaneously with the temperature measurements, the bulk soil justification of the proposed MFHPP is to ensure that electrical conductivity (EC b ) was measured using the Wenner array, from which soil solution concentration (EC w ) can be obtained after the different measurement types are conducted within calibration. All measurements were taken during multistep outflow identical soil volumes, minimizing soil heterogeneity efexperiments, which also allowed estimation of the soil's hydraulic fects and providing more accurate measurements of soil properties. We demonstrated that the MFHPP can effectively measure physical properties for environmental monitoring. volumetric water content, thermal properties, and EC b , and can be The proposed MFHPP originates from the dual-probe used to indirectly estimate soil water fluxes at rates larger than 0.7 heat-pulse (DPHP) method introduced by Campbell et m d Ϫ1 in the sand.

cluding empirical and tracer methods, were presented by Tyler et al. (1999) and Flint et al. (2002). A major A small multi-functional heat pulse probe (MFHPP) was applied advantage of the MFHPP technique is that the water to further develop measurement methodologies to improve on water flux estimations for unsaturated soils. The temperature responses of flux can be estimated indirectly from heat transport by four thermistors surrounding a central heater in a 2.7-cm diam. probe convection, without the need for either soil water matric were analyzed by the heat transport equation to estimate thermal head or hydraulic conductivity measurements. properties and convective heat flow. Volumetric heat capacity, water Temperature measurements have been used to meacontent, and thermal diffusivity were estimated from the horizontally sure water fluxes in other fields. For example, steady placed thermistors, neglecting the convective flow effects in the transstate measured temperature gradients in bore holes were verse direction, whereas the water flux density was estimated from used to estimate vertical water flow rates in groundwater, the temperature responses to the vertically placed thermistors. A using the analytical solution of Bredehoeft and Papadoparameter optimization technique was employed to fit the most likely pulos (1965), with minimum flow rates of about 30 cm parameters to the relevant analytical solutions. Falling head and multiyr Ϫ1 using thermistors with a practical precision of about step outflow experiments yielded independently obtained water flux measurements. Results showed that the estimated volumetric water 0.01ЊC (Sorey, 1971). Using time-series measurements, content corresponded well with independent gravimetric measure-thermal signatures in shallow estuarine sediments have ments with a RMSE of 0.0056 m 3 m Ϫ3 , across a wide range of water been successfully used to estimate changes in nutrientfluxes smaller than 0.5 m d Ϫ1. Thermal diffusivity values as obtained contaminated ground water recharge rates toward coastal with the MFHHP also agreed well with independently measured therwaters (Land and Paull, 2001) and to estimate percolamal diffusivity values, for water flux density values smaller than 2 m tion rates in deep vadose zone environments (Constantz d Ϫ1. For saturated conditions, the estimated water fluxes from the et al., 2003). Early application of the heat pulse tech-MFHPP measurements were accurate in the range between 0.056 and nique to estimate water flow originates in the plant 27.0 m d Ϫ1 , with a R of 0.995 and RSME of 0.0952 log(m d Ϫ1) (0.52 m science literature, where advective transport of heat by d Ϫ1). For unsaturated flow, MFHHP estimations significantly overestiwater was used to indirectly estimate sap flow rates in mated water flux density for flux values smaller than 0.10 m d Ϫ1. Within these limitations, we conclude that MFHPP methodologies trees (Marshall, 1958), mostly measuring flow magnitudes are now available, making possible simultaneous estimation of thermal of 1 ...

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Water, solute, and heat transport processes in soils are mutually interdependent as each includes convective water flow and each transport mechanism is partly controlled by fluid saturation, pore geometry, temperature, and other soil environmental conditions. Therefore, their measurement in approximately identical measurement locations and volume is essential for understanding transport phenomena in soils. We introduce a 2.7‐cm‐diameter multi‐functional heat pulse probe (MFHPP), which consists of a single central heater, four thermistors, and four electrodes (Wenner array) that together are incorporated in six 1.27‐mm‐o.d. stainless‐steel tubes. The bulk soil thermal properties and volumetric water content of Tottori Dune sand were determined from the measurement of the temperature response of all four thermistor sensors after application of an 8‐s heat pulse by the heater sensor. Simultaneously with the temperature measurements, the bulk soil electrical conductivity (ECb) was measured using the Wenner array, from which soil solution concentration (ECw) can be obtained after calibration. All measurements were taken during multistep outflow experiments, which also allowed estimation of the soil's hydraulic properties. We demonstrated that the MFHPP can effectively measure volumetric water content, thermal properties, and ECb, and can be used to indirectly estimate soil water fluxes at rates larger than 0.7 m d−1 in the sand.