Soil Water Residence Time Research Articles

Principles of evaluation of soil water residence time using queueing disciplines with water budget data (theoretical background-I)

Principles of evaluation of soil water residence time using queueing disciplines with water budget data (theoretical background-I)

Evaluation of soil water residence time in a monolith lysimeter from the application of queueing disciplines to water budget data (demonstration-II)

Evaluation of soil water residence time in a monolith lysimeter from the application of queueing disciplines to water budget data (demonstration-II)

Lysimeter and Centrifuge Soil Solutions: Seasonal Differences between Methods

AbstractLysimetry and centrifugation were compared as variable‐tension (centrifugation) and low‐tension (lysimetry) soil‐solution collection methods. Low‐tension lysimetry and low‐ and high‐speed centrifugation with double‐bottom cups were used to collect soil solutions from each major horizon of a subalpine Spodosol. Solution samples were collected monthly and compared throughout a 1‐yr period. Few seasonal changes were observed in the cation, anion, pH, or C concentrations of the lysimetry solutions. Both low‐ and high‐speed centrifuge solutions showed a strong seasonal cycle for major cations, anions, and C; peaks occurred in winter and summer and were especially evident in the upper horizons. Centrifuge solution concentrations were frequently greater than those of the lysimeter solutions. Aluminum and Si were exceptions, with lysimetry solution concentrations equal to or greater than those of the centrifuge solutions. Centrifuge solution concentrations of Al and Si also showed increases in concentration during summer months only. Seasonal variations may be due to differences in soil water residence time or biological processes. Results suggest that both the methodology used for obtaining soil solutions and the time of sampling can influence solution composition.

Principles of evaluation of soil water residence time using queueing disciplines with water budget data (Theoretical background—I)

Soil water residence time is an important aspect of soil hydrology. It is an important factor affecting the chemical composition of water in the soil. Water that makes up recharge and discharge to and from a hydrologic reservoir can be considered to consist of individual increments of water called fluid elements. Queueing disciplines can be used to describe the order in which the fluid elements move through the reservoir. Possible queueing disciplines that can be related to soil water movement are last-in-first-out (LIFO), first-in-first-out (FIFO), and a combination of LIFO and FIFO. When water budget records are available, the queueing disciplines can be used as models to allow the calculation of residence time estimates. Computer algorithms have been written for the purpose of making estimates of soil water residence times in a weighable monolith lysimeter.

Evaluation of soil water residence time in a monolith lysimeter from the application of queueing disciplines to water budget data (Demonstration — II)

Soil water residence time in a monolith lysimeter at the North Appalachian Experimental Watershed was estimated by applying queueing disciplines to the lysimeter water budget data. The lysimeter contains an undisturbed soil block measuring approximately 6 ft wide, 14 ft long and 8 ft deep, and a permanent grass cover is maintained on the soil. The lysimeter water budget data used consist of monthly totals of precipitation, evapotranspiration, runoff and percolation for the period of January, 1947–December, 1985. The three following queueing discipline models were applied to the water budget data: (a) all of the water in the lysimeter follows first-in-first-out (FIFO) queueing discipline; (b) all of the water in the lysimeter follows last-in-first-out (LIFO) queueing discipline; (c) discharge by evapotranspiration follows LIFO queueing discipline and discharge by percolation follows FIFO queueing discipline. The FIFO model generated minimum residence times of three months and maximum residence times of eleven months with approximately half the assigned values being six months or less. The LIFO model generated minimum residence times of less than one month and a maximum of 140 months. More than half of the values were less than one month. The combined LIFO-FIFO model generated minimum residence time of less than one month and a maximum residence time of 63 months with half of the values being less than six months. The FIFO model tended to assign the higher residence time values to water that entered the lysimeter in the summer months, while the LIFO and LIFO-FIFO models tended to assign the high residence time values to water that entered the soil in the winter months.

Soil-water residence time and solute uptake

Results are presented for miscible displacement experiments in undisturbed soil cores using tritiated water (3H2O). Measured breakthrough curves were well described by an analytical solution incorporating mobile and stagnant regions with sideward exchange. Resulting transport parameters were observed to be dependent upon the input flux rate, reflecting a pattern of increasing breakthrough curve asymmetry with increasing flux. This was attributed to the combined influences of pedal by-passing and increasing non-equilibrium for diffusion-controlled solute transfer between the mobile and stagnant regions.

Soil-water residence time and solute uptake: 2. Dye tracing and preferential flow predictions

The occurrence of preferential flow, by-passing soil peds, is predicted from the occurrence of rainfall intensities in excess of pedal sorption; depth of preferential tracer penetration is estimated from the displacement of this excess through a small operational volume of preferential flow, θ f. θ f-values estimated from column drainage experiments to lie between 0.01 and 0.03 cm 3 cm −3 for rainfall intensities from 1 to 10 mm hr. −1, increasing to ∼ 0.1 cm 3 cm −3 at saturation. Observed tracer penetration is compared with predicted tracer penetration and mean profile θ f-values are calculated. The preferential flow calculations discussed provide a useful approximation for characterising field tracer behaviour.

Soil-water residence time and solute uptake: 1. Dye tracing and rainfall events

Fluorescent dyes have been used to label rainfall infiltrating into a well-structured calcareous woodland soil in situ. Soil-water outflow was monitored using throughflow troughs. The occurrence of dye output from the soil could not be totally predicted by the use of a simple storage model but was related to the occurrence of intense-rainfall events equal to or greater than 3 mm hr. −1 lasting for at least 2 hr.

Soil water residence times and solute uptake on a dolomite bedrock—preliminary results

AbstractCalcium and magnesium levels have been monitored in slope foot drainage waters on a dolomite bedrock. Both calcium and magnesium rich pulses occur. Short term dissolution experiments demonstrate high calcium levels in solution while other authors have suggested that long residence time groundwater has relatively high levels of magnesium due to calcite precipitation. Patterns of field fluctuations in Ca: Mg ratios can thus be tentatively interpreted in terms of short residence time water of high calcium content mixing with long residence time water of high magnesium content. Fluorometric dye tracing has been used to indicate the orders of magnitude of soil water residence times, suggesting that quickflow components are resident in the system for a few hours to a few days. Further work is in progress.