L. Guo et al., NONEQUILIBRIUM TRANSPORT OF REACTIVE SOLUTES THROUGH LAYERED SOIL PROFILES WITH DEPTH-DEPENDENT ADSORPTION, Environmental science & technology, 31(8), 1997, pp. 2331-2338
The pesticide atrazine was used as a reactive tracer in a series of mi
scible displacement experiments that were conducted with soil columns
containing the same amount of sludge or manure, but distributed either
as a layer or uniformly in depth. Travel time probability density fun
ction (pdf) of Cl- and atrazine measured from both types of columns wa
s analyzed based upon a transfer function model that assumes a two-sit
e nonequilibrium advection-dispersion equation (ADE). Sorption sites c
ontributed by both organic materials were primarily rate-limited. Trav
el time of atrazine, estimated by temporal moment analysis on the meas
ured travel time pdf, was consistently increased in organic material-a
mended columns for both distributions. When flux concentration of atra
zine was fitted to the nonequilibrium ADE, either a higher overall dis
tribution coefficient (Kd) or a higher fraction of instantaneous adsor
ption sites (f) or both were found for layered columns, indicating an
enhanced accessibility to sorption sites of organic amendments probabl
y due to less shielding by soil minerals.