Land users and managers require decision support tools (DSTs) that enable them to estimate losses of contaminants from land to freshwater. MitAgator is a DST that estimates losses of nitrogen (N), phosphorus (P), 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 the least cost. Some of the algorithms present within Overseer (a standard DST used in New Zealand for N and P management) have been modified and appended to include spatial analysis in MitAgator. Outputs from MitAgator showed good (R 2 > 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. 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 inputs, if better local data are available, then they should be used. Furthermore, while MitAgator is easy to use by a novice, MitAgator outputs should only be interpreted in collaboration with an experienced user so that limitations concerning cost-effectiveness estimates and spatial and temporal scales are not exceeded.

No abstract