Simulation of movement of pesticides towards drains with a preferential flow version of PEARL

Abstract

After calibration, PEARL could simulate well the observed rapid movement towards drains of two pesticides with contrasting sorption and degradation rate properties. The calibrated value for the fraction of the internal catchment domain was high (90%). This means that a large fraction of water entering the macropores infiltrates into the soil matrix, thus reducing the fraction of rapid flow.

A spatially distributed model of pesticide movement in Dutch macroporous soils

“…This process is called internal catchment (Bouma and Dekker, 1978) and is explicitly simulated in SWAP. The following subsections describe those parts of the model that are essential for understanding this paper; a more detailed description, including mathematical equations, can be found in Tiktak et al (2012b).…”

“…The exchange of water between the soil matrix and the macropores is determined to a large extend by the soil polygon diameter (Larsbo et al, 2005) and hence by the horizontal spacing of the (Tiktak et al, 2012b). Z Ah (m) is the depth of the plough layer, Z ica (m) is the bottom depth of the internal catchment domain, Z sta (m) is the bottom depth of the static macropores, V sta,0,byp (m 3 m À3 ) is the volume fraction of macropores in the bypass domain at soil surface, and V sta,0,ica (m 3 m À3 ) is the volume fraction of macropores in the internal catchment domain at soil surface.…”

“…The new preferential flow component of PEARL (Tiktak et al, 2012b) simulates the transport of pesticides through the soil Fig. 1.…”

“…For the assessment of ecotoxicological effects on aquatic organisms, the peak concentration is considered the most important exposure endpoint (Brock et al, 2009). In ditches adjacent to macroporous soils, the peak concentration is primarily affected by rapid drainage (Hendriks et al, 1999;Scorza Júnior and Boesten, 2005;Tiktak et al, 2012b), so a macropore version of GeoPEARL is needed for the exposure part of the aquatic risk assessment.…”

“…Macropores in the internal catchment domain end at various depths in the soil, forcing macropore water to infiltrate into the soil matrix at these depths. The concept was tested at a number of field sites (Hendriks et al, 1999;Van Schaik et al, 2010;Tiktak et al, 2012b).…”