Regulating agricultural land use to manage water quality: The challenges for science and policy in enforcing limits on non-point source pollution in New Zealand

Non-point source pollution from agricultural land use is a complex issue for the management of freshwater worldwide. This paper presents a case study from New Zealand to examine how predictive modelling and land use rules are being used to regulate diffuse pollution to manage water quality. Drawing on a science studies conceptual framework, the research evaluates the deployment of a numeric regime to enforce compliance with resource limits. It shows that in contrast to claims that a quantitative modelled 'outputs-based' approach would provide certainty and clarity and remove ambiguity in the implementation of resource limits at the farm scale, the opposite is unfolding. It is argued from the case study that in the development of land use policy greater recognition and understanding is needed of the social and political dimensions of numbers and predictive models. This research highlights epistemological, institutional and practical challenges for the workability and enforceability of policy regimes seeking to regulate diffuse pollution that tightly link numbers derived from predictive models to compliance and enforcement mechanisms.