Implications of water quality policy on land use: A case study of the approach in NZ

Achieving good water quality through output controls is difficult. The New Zealand Government recently proposed enforceable bottom lines to protect ecosystem health of 1 mg L–1 dissolved inorganic nitrogen (DIN) and 0.018 mg L–1 dissolved reactive phosphorus (DRP), but has now delayed considering them. In examining whether these bottom lines could be met through mitigating DIN and DRP losses from existing land uses, we found that if all known strategies to mitigate N and P loss were implemented by 2035, the proportion of catchments exceeding these bottom lines would be predicted to be 4% for DIN and 9% for DRP. If bottom lines were enforced, land use would likely change, but to change successfully good advice and effective multilevel governance are required. Advice should expand and standardise elements of farm environment plans that spatially isolate critical source areas of N and P loss and apply cost-effective mitigations. Governance should focus on combining these plans with the national bottom lines and technical support to connect practices and land use at the farm scale to meeting water quality bottom line at the catchment scale.