The principal aim of this approach is to identify areas where the use of pesticides applied to the land represents a pollution risk due to an elevated likelihood that they will be mobilised and transported through or over the soil and into a watercourse.
A number of proprietary tools and modelling approaches have been developed to assess the spatial risk of pesticide pollution. These include the Cranfield University CatchIS tool, the ADAS Pesticide Risk Assessment Model and the GfK Kynetec i-MAP Water system, but all are essentially based on similar conceptual models.
We used the i-MAP Water system to model pesticide application rates across the sub-catchments of the Tamar catchment. It is generally accepted that, while the i-MAP dataset is robust at catchment or sub-catchment scale, its aggregation to a finer scale than the sub-catchment level would result in significant inaccuracy in the final model.
To achieve our modelling aim we developed a spatial mapping protocol (summarised right), which is essentially based on the application rate of the pesticide (derived from the i-MAP system), the landuse for which it is used, the propensity of the soil to release pesticides by leaching or run-off, and the hydrological connectivity of the land.
Using this method we have developed risk models for all of the active ingredients
detected in the Crownhill water treatment works catchment. Risk maps derived for two acid herbicides; Mecoprop and MCPA, and one neutral herbicide; Chlorotoluron are shown below.