Incorporating macropore flow into focus PEC models

Abstract

This paper describes efforts to incorporate descriptions of macropore flow into the exposure assessment models PEARL and PELMO, recommended for use in pesticide registration in the EU. We also outline improvements made to an existing macropore flow model (MACRO), including upgraded numerical routines, new processes (e.g. tillage, kinetic sorption), and an inbuilt inverse modelling capability (SUFI) to help parameterization.

Simulations made with the macropore flow version of PELMO and the existing FOCUS version of the model were compared with measurements of pesticide leaching made in two clay soils (Lanna, Andelst). Results showed that the functional description of macropore flow included in PELMO appears promising, and should be further tested on additional high-quality datasets. Use of SUFI to estimate parameters in MACRO 4.3 and 5.0 for the Lanna dataset, showed that the effects of differences in parameter optimization methods were overshadowed by differences between models in process descriptions and numerical methods. Despite the comprehensive nature of the dataset, one important parameter regulating the strength of macropore flow could only be identified with a large uncertainty.