Anthropogenic increases of catchment nitrogen and phosphorus loads in New Zealand

Spatial regression models were used to predict yields of nitrogen (N) and phosphorus (P) discharged from catchments throughout New Zealand. The models were derived using loads (kg yr‚àí1) of TN, NO3-N, TP and DRP calculated for 592 river water quality monitoring sites. Anthropogenic increases in loads of TN, NO3-N, TP and DRP exported to the ocean were 74%, 159%, 48% and 18%, respectively. Increases in loads varied considerably at smaller scales, between 4- and 26-fold for N and 6- to 9-fold for P. Predictions of yields and loads have utility in the development of strategies to manage nutrients.