Online Conference Proceedings

< Return to abstract list

Translating Science into Policy: setting nutrient limits for agricultural land use

IWRA World Water Congress 2017 - Cancun Mexico
A. Bridging science and policy
Author(s): Bryan Jenkins
Bryan Jenkins

Keyword(s): diffuse source management, policy for nutrient limits, linking science and policy
Article: Oral:


The paper addresses the translation of science into policy prescriptions for managing impacts of nutrients from agricultural intensification on water quality. Developing policy prescriptions to manage cumulative effects of diffuse source pollution with the expansion of the dairy industry has been a significant challenge in New Zealand.

The legislation is based on managing the effects of activities within environmental limits. While effective in managing point source discharges, it is not well suited to managing the cumulative impacts of diffuse sources from land use intensification.

Four case studies highlight the challenges.

The Central Plains Project involved irrigation of 60,000 hectare. Nitrate criteria for groundwater, surface water and a lake were already exceeded. While increased nitrate concentrations from the project were acknowledged, hearing commissioners argued on the basis of the legislation that effects were minor and could be mitigated by requiring best management practices.

For water management of Lake Taupo, a market was established for nitrogen discharge allowances from farms. A nitrogen cap was set. However scientific studies showed that insufficient allowance was made for the time lag associated with groundwater contaminated by recent land use intensification in the catchment. Thus greater reductions in nitrogen load (and greater cost) are needed to meet the water quality target.

Nutrients in the Hurunui River were causing algal blooms in the lower reaches. Nutrient caps were put in place and a policy rule limiting nutrient increase from land use change on existing farms to 10% was imposed. This was considered inequitable by dryland farmers with low emissions because it provided greater constraints on their operations while giving greater flexibility to inefficient dairy farmers with high emissions.

Wainono Lagoon is classed as hypertrophic. Nutrient caps were set based on modelling of loads and water quality. However updated models of the impacts of the loads for defining limits have affected the basis of the negotiated agreement on load allocation and reignited debate about the appropriate nitrogen allocation methodology.

However, approaches have been developed in other jurisdictions that provide better policy approaches for these issues. The Sydney Catchment Authority has developed an approach for catchments at water quality limits. Applicants seeking approval for discharges have to demonstrate a neutral or beneficial effect of their proposal on water quality rather than argue adverse effects are minor.

Arizona has an approach to groundwater management in “active management areas” where groundwater overdraft is most severe. Developers have to demonstrate that water of sufficient quantity and quality is available to sustain proposed developments for 100 years.

The Murray-Darling Basin approach to salinity is more effective than cap-and-trade approaches to facilitate water quality improvement by economic means. New actions need to pay the marginal cost of salinity mitigation projects to offset effects of their actions.

For dealing with equity issues and allocation constraints, the South African Water Act has provision for responsible authorities to undertake reallocation processes that can incorporate equity issues and other factors.

The paper provides a comparative analysis of these approaches and their potential transferability to different contexts.

IWRA Proceedings -