Variability of Solute Transport In Large Lysimeters.

The large variability in contaminant transport that has been regularly observed in field soils is generally attributed to variations in soil properties, topography, and other factors.  Variability in transport depends on the scale of the domain of interest and the scale of observation.  In agricultural applications, the domain of interest is frequently the “field”, whereas the observation scale is often a volume of soil having a surface area on the order of 1 m² and a depth that encompasses the root zone.  One problem encountered in assessing the accuracy of field-scale contaminant transport models is that it may be difficult to distinguish transport variability due to field-scale parameter variations, and that which may be due to random fluctuations (i.e. uncertainty) in local transport measurements.  Due to the impossibility of repeated field trials, very little is known about what sort of confidence bounds should be placed on local transport measurements.  A possible approach to obtaining information about local uncertainty is replicated transport experiments conducted on observation-scale soil volumes.  In this presentation, we report four years of transport data from twelve large lysimeters having identical (repacked) 1.75 m layered soil profiles.  The variability in transport observed across the replicated lysimeters for both sorbing and nonsorbing solute will be demonstrated.  The effects of irrigation water chemistry on observed transport variability will also be characterized.