Spatial variability of solute leaching: Experimental validation of a quantitative parameterization

Soil heterogeneity, soil structure, and fingered now affect solute leaching from the vadose zone to the ground water, Recently, the spatial variation of cumulative solute fluxes at a given depth was characterized by fitting t he two-parameter beta distribution to sorted amounts of solute leaching at different sampling points. We tested this parameterization on data front a chloride tracer experiment performed on a monolith lysimeter, below which d rainage was collected from 300 compartments with a combined area of 0.75 m( 2). The effect of total sampling area, sample size, and the number of sampl es and their spatial distribution (random locations vs, clustered) on the f itted parameters was examined. Sixteen or more sampling locations of 25 cm( 2) each (5% of the total area) resulted in adequate representation of param eter values. Increasing the sample size underestimated the degree of hetero geneity. We therefore recommend that the fitted parameter values of the bet a distribution be reported together with the sample size. In solute-transpo rt experiments, collecting many small samples will give more accurate resul ts than taking fewer but larger samples.