An initial assessment of Mitagator; a farm scale tool to estimate and manage the loss of contaminants from land to water

Land users and managers require decision support tools (DST) that enable them to estimate losses of contaminants from land to freshwater. The MitAgator™ is a DST that estimates losses of nitrogen, phosphorus, sediment, and fecal indicator bacteria (E. coli) and the cost-effectiveness of different strategies to mitigate losses so that a water quality target can be met at least cost. Some of the algorithms present within the DST Overseer® (a standard DST used in New Zealand for N and P management) have been modified and appended to include spatial analysis in the MitAgatorTM. Outputs from MitAgatorTM showed good (R2 > 0.77; p < 0.001) prediction of measured N and P losses across a range of land uses, but accuracy decreased at larger (catchment) scales. An analysis for P outputs indicated that the most sensitive inputs were hydrological characteristics, followed by soil characteristics and P inputs. Although national databases are used for many of these, if better local data are available, then they should be used. Furthermore, while easy to use by a novice, outputs of the MitAgatorTM should only be interpreted in collaboration with an experienced user so that limitations around cost-effectiveness estimates and spatial and temporal scales are not exceeded.