A review of the policies and implementation of practices to decrease water quality impairment by phosphorus in New Zealand, the UK, and the US

The improper use of phosphorus (P) on agricultural land in developed countries is related to P losses that impair surface water quality. We outline policy in New Zealand, the UK, and the US who have imposed limits for P measured as ecological status, but in some cases, also as chemical concentrations or loads. We contrast the strategies used in each country and discuss their likelihood of being able to decrease P losses and improve surface water quality. All three countries have focused on understanding pathways and catchment processes so that cause and effect can be traced across spatial and temporal scales. A poor understanding of catchment processes and critical source areas of P loss has resulted in some areas where regulation has had minimal effect on P discharges. Furthermore, while biophysical science can inform policy, we give several examples where social and economic challenges are of equal if not greater relevance to P discharges (e.g. subsidies). Some evidence shows that these challenges can be overcome at the farm to small catchment scale with a mix of mandatory and voluntary rules in targeted areas. Other policy instruments (e.g. trading schemes) may be needed at larger scales, but should be flexible and encourage innovation over a culture of dependence. There is increasing recognition among all three countries that while targeting good management practices can substantially decrease P losses from existing land use, to achieve 'good' water quality in catchment, policy may have to consider land use change.