Controls on atrazine leaching through a soil-unsaturated fractured limestone sequence at Brévilles, France.
The objective of this study was to identify the main controls on atrazine leaching through luvisols and calcisols overlying fissured limestone using the dual-permeability model MACRO. The model parameterisation was based on a combination of direct measurements (e.g. hydraulic properties, adsorption and degradation), literature data and calibration against bromide leaching experiments in field plots. A Monte Carlo sensitivity analysis was carried out for a typical application pattern, considering two different depths of unsaturated limestone (15 and 30 m). MACRO calibrations to the field experiments demonstrated the occurrence of strong macropore flow in the luvisol, while transport in the calcisol could be described by the advection-dispersion equation. MACRO simulations of tritium and atrazine leaching qualitatively matched tritium concentration profiles measured in the limestone and atrazine concentrations measured in piezometers and in aquifer discharge via a spring. The sensitivity analysis suggested that the thickness of the limestone, as well as the transport properties and processes occurring in the unsaturated rock (e.g. matrix vs. fissure flow) will have little significant long-term effect on atrazine leaching, mainly because degradation is very slow in the limestone. No mineralization of atrazine was detected in one-year incubations and a mean half-life of 10 years was assumed in the simulations. Instead, processes occurring in the soil exerted the main control on predicted atrazine leaching, especially variations in the degradation rate and the strength of sorption and macropore flow. However, fissure flow in unsaturated rock is expected to exert a much more significant control on groundwater contamination for compounds that degrade more readily in the deep vadose zone.
Roulier
Stéphanie
S
Department of Soil Sciences, Box 7014, SLU, Uppsala, Sweden. Stephanie.Roulier@env.ethz.ch
Baran
Nicole
N
Mouvet
Christophe
C
Stenemo
Fredrik
F
Morvan
Xavier
X
Albrechtsen
Hans-Jørgen
HJ
Clausen
Liselotte
L
Jarvis
Nicholas
N
D001280:Atrazine / Q000737:chemistry*; D002119:Calcium Carbonate / Q000737:chemistry*; D004784:Environmental Monitoring; D005602:France; D055593:Geological Phenomena; D005844:Geology; D006207:Half-Life; D006540:Herbicides / Q000737:chemistry*; D010539:Permeability; D012989:Soil Pollutants; D012995:Solubility; D014873:Water Pollutants
D006540:Herbicides; D012989:Soil Pollutants; D014873:Water Pollutants; D002119:Calcium Carbonate; D001280:Atrazine