Predicting input of pesticides to surface water via drains - comparing post registration monitoring data with MACRO model predictions

Sub-surface drain concentrations of pesticides modelled in the D4 loamy soil scenario (Skousbo, Denmark) by MACRO (Ver. 4.3) has been compared with measured concentration of pesticides in drains from three sandy loam test fields in the Danish Pesticide Leaching Assessment Programme (PLAP).

MACRO is a physically-based one-dimensional numerical model of water flow and reactive solute transport in field soils (Jarvis et al., 1994) providing drain contributions to the FOCUS surface water model (FOCUS_TOXWA), which is used to estimate surface water concentrations as part of the European framework for environmental risk assessment of pesticides (FOCUS, 2001).

PLAP is an intensive monitoring programme aimed at evaluating the leaching risk of pesticides under field conditions. It analyses whether pesticides applied in accordance with granted uses enter the aquatic environment in unacceptable concentrations.

One year of modelling and monitoring data (weekly concentrations) are provided for similar usage (crop, dose, time of application) of the three pesticides pirimicarb, bentazone and glyphosate having different physio-chemical properties.