A framework for applying interceptive mitigations for diffuse agricultural pollution

ABSTRACTInterceptive mitigation options implemented at the edge of agricultural fields and along run-off and drainage flow-paths can complement preventive in-field management actions to reduce diffuse contaminant losses to surface waters. However, it is often unclear to users which interceptive mitigation option is appropriate for their situation, where it should be located, what contaminant reductions and other benefits can be achieved, and what it would cost to implement, maintain, and operate these practices. We outline a framework for selecting and applying eight interceptive diffuse pollution mitigation practices potentially applicable on New Zealand farms: riparian grass filter, planted and multifunction buffers; constructed wetlands; woodchip bioreactors; filamentous algal nutrient scrubbers; sediment traps; and detainment bunds. The framework provides users with a semi-quantitative evaluation of the relative benefits and costs of the best suited mitigations across a range of farmed landscapes. It highlights where each mitigation has its niche in terms of the landscape fit, flow-path(s) intercepted, contaminant(s) targeted, efficacy, associated co-benefits, relative cost, operation and maintenance requirements, longevity, and consenting requirements. Testing and refinement of this framework is encouraged, using data from field-scale implementation, to better quantify efficacy in practice, and inform empirical models and decision making across farm and catchment scales.KEYWORDS: Diffuse pollutionagricultural run-offdecision support toolnature based solutionsriparian buffersconstructed wetlandsdenitrifying bioreactoralgal nutrient scrubber AcknowledgementsWe thank our colleagues, in particular Lucy McKergow, Fleur Matheson, James Sukias, Rupert Craggs, Erina Watene-Rawhiri, and members of our Iwi Advisory Panel, in particular John Te Maru, for useful discussions and contributions to the development of the framework presented here. We are also grateful to the reviewers for constructive comments that have helped us to improve the manuscript. This study was undertaken as part of the Doubling On-farm Diffuse Pollution Mitigation Endeavour Programme (C01X1818) funded by the New Zealand Ministry of Business, Innovation and Employment.Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingThis work was supported by Ministry of Business, Innovation and Employment [Grant Number C01X1818].