Achieving good water quality through output controls is difficult. The New Zealand Government recently proposed enforceable bottom lines to protect ecosystem health of 1mgL–1 dissolved inorganic nitrogen (DIN) and 0.018mgL–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.

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水质政策对土地利用的影响：新西兰方法的案例研究

通过输出控制实现良好的水质是很困难的。新西兰政府最近提出了可强制执行的底线，以保护 1mgL-1 溶解无机氮 (DIN) 和 0.018mgL-1 溶解活性磷 (DRP) 的生态系统健康，但现在已推迟考虑。在研究是否可以通过减轻现有土地用途的 DIN 和 DRP 损失来满足这些底线时，我们发现，如果到 2035 年实施所有已知的减少 N 和 P 损失的策略，预计超过这些底线的流域比例将DIN 为 4%，DRP 为 9%。如果执行底线，土地使用可能会发生变化，但要成功改变，需要良好的建议和有效的多层次治理。建议应扩大和标准化农场环境计划的要素，这些要素在空间上隔离 N 和 P 损失的关键源区，并应用具有成本效益的缓解措施。治理应侧重于将这些计划与国家底线和技术支持相结合，将农场规模的实践和土地利用与流域规模的水质底线联系起来。