Wednesday, November 15, 2006 - 8:30 AM

Analyzing the Spatio-temporal Distribution of Solute Leaching in the Field by Constructing Leaching Surfaces from Measurements with a Variable-Suction Multi-compartment Sampler.

Esther Bloem, Franck A. N. Hogervorst, and Ger H. de Rooij. Wageningen University, Nieuwe Kanaal 11, 6709 PA, Wageningen, Netherlands

Soil heterogeneity, fingered flow and macropore flow cause solutes to spread out in time and space as they move downwards from the soil surface with infiltrating water. Temporal solute spreading is characterized by the breakthrough curve (BTC), which describes the travel time distribution of solutes at a given depth. The spatial solute spreading is characterized by the spatial solute distribution curve (SSDC) that is the spatial equivalent of the BTC. Combining the BTC and the SSDC gives the leaching surface. The leaching surface thus describes both the spatial and the temporal redistribution of uniformly applied solutes at a given depth.  Solute monitoring in the field is often limited to observations of resident concentrations, while flux concentrations govern the movement of solutes in soils. We developed a new multi-compartment sampler, capable of measuring fluxes at a high spatial resolution with minimal disturbance of the local pressure head field. We placed two instruments at 30 cm depth in an agricultural field, leaving the soil above undisturbed. Each sampler contained 100 separate cells of 31 by 31 mm. Water fluxes were measured every 5 minutes for each cell. We monitored leaching of a chloride pulse under natural rainfall by frequently extracting the collected leachate while leaving the samplers buried in situ. We will describe the instruments and present preliminary experimental results, including time series of the percolation fluxes. The chloride leaching will be analyzed by means of leaching surfaces.