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Fig. 12. Effect of measurement type and transport distance class on the ratio v/vp, which is a measure for preferential solute transport (v/vp > 1) or solute retardation (v/vp < 1), derived from tracer experiments with (a) saturated conditions at the soil surface or a flow rate >10 cm d–1 and (b) unsaturated conditions and a flow rate <10 cm d–1. The boxes span the 25 and 75% percentiles, the thick black line is the median. The numbers correspond with the number of observations in the class.
