Long‐Term Solute Transport under Semi‐Arid Conditions: Pedon to Field Scale

Abstract

Knowledge of factors controlling the spatial and temporal variability of transport in the vadose zone is limited. The objective of this study was to quantify the transport of a tracer at the field scale after 34 yr of low transient flow under semiarid conditions. A Cl− tracer was surface applied to plots (a Chernozemic soil) near Saskatoon, Canada. Thirty‐four years later, soil cores (6‐m depth) were taken along a 90‐m transect (1‐m spacing) and two embedded 10‐m transects (0.2‐m spacing) along one of the plots. The cores were sectioned (0.1‐m intervals) and analyzed for Cl−, bulk density, and soil water content. Although the site is level, slight differences in surface slope had a great effect on surface water redistribution, soil profile development, and the movement of water and solute. After 34 yr, the mean travel depth of the Cl− on a slight knoll was 1.70 m below the surface, compared with 2.76 m in a very slight depression 20 m away. The grade between knoll and depression was 1.8%. After a 19‐mo fallow period, considerably more redistributed surface water was stored in the soil in the slight depression than on the nearby level area. The spatial pattern of the increase in soil water storage (19 mo) was significantly correlated to Cl− transport (34 yr) suggesting that the measured pattern of increase in soil water storage was typical of long‐term patterns. The measurements suggested that 10% of redistributed water ended up as increased deep drainage.