To meet water quality goals, losses of nitrogen (N), phosphorus (P) and sediment from dairy and sheep and beef farms must be reduced. We modelled losses of N, P and sediment for the years 1995 and 2015 using farm typologies. The ~130 typologies considered landscape vulnerability attributes (e.g. topography and climate factors) and land use pressures (e.g. such as farm inputs and feed and stock management practices) as variables known to influence the inherent risk of contaminant transport to water. Losses were estimated for:
In 1995 and 2015 typologies covered 89% and 92% of total dairy and sheep and beef land, respectively. We validated 2015 yields (i.e. kg ha-1 yr-1) against observed data. Loads (tonnes) in 2015 of N, P and sediment from pastoral land use across New Zealand were dominated by sheep and beef (57, 79 and 91%, respectively) owing to a much larger area of sheep and beef farming. If better management hadn’t been adopted, loads of N and P from dairy farmed load would be 45 and 98% greater than measured in 2015. About half of this increase was due to land use change. Loads of N and P from sheep and beef farmed land were estimated to have changed little due to land use change. However, sediment would have been 30% greater.
If all known mitigation measures were implemented, 2015 N and P loads would have decreased by 19 and 24%, respectively. Potential decreases were greater under dairying (40% N and 28% P), because of its greater per hectare yield and number of mitigation measures available before land use change. If all known and developing mitigation measures were implemented by 2035, the potential load of N, P and sediment was 34, 36 and 66% less than the load in 2015.
These data can inform investment and planning by the rural sector and policy as part of an assessment of the potential for measures to mitigate losses from existing land use, and achieve catchment water quality objectives, or whether a change in land use or land use intensity is required.