Quantifying contaminant losses to water from pastoral landuses in New Zealand II. The effects of some farm mitigation actions over the past two decades

ABSTRACT

In New Zealand the primary sector together with central and local government agencies have been promoting measures to mitigate the adverse effect of farming practices on water quality over the last few decades. We assessed the effectiveness of some key measures such as stock exclusion, riparian protection, and nutrient and effluent management on reducing losses of nitrogen (N), phosphorus (P) and sediment to water. Our aim was to determine how much progress has been made in decreasing contaminant discharges between 1995 and 2015 and to determine what the loads would have been if no mitigation had occurred. To do this we estimated losses from 37 dairy and non-dairy/sheep/beef farm typologies that captured the main attributes of production and contaminant loss pathways, nationally. We also accounted for the rate of uptake of measures. Our findings indicated that while the implementation of these measures has helped to reduce P losses (an estimated 20%–25% reduction) to water, they have not been sufficient to off-set estimated increases in N losses (25%) due to expansion of dairy land over the same period. National sediment load is estimated to have decreased (29%) because of afforestation and other soil conservation works.

KEYWORDS:

• Water quality
• grazed pastures
• dairy
• sheep
• beef
• mitigation
• nitrogen
• phosphorus
• sediment
• typology

Acknowledgements

The authors wish to thank the many expert individuals and industry representatives who provided helpful guidance on the modelling approaches undertaken in this study. We particularly thank staff from regional councils and MPI who provided soil conservation data and DairyNZ who provided DairyBase records. Pike Brown provided the riparian management results from the Survey of Rural Decision Makers. This work was funded as an output from the Sources & Flows programme of the Our Land and Water National Science Challenge (New Zealand Ministry of Business, Innovation and Employment contract C10X1507). Thanks are also expressed to the reviewers who provided helpful advice on the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by DairyNZ; Ministry for Business Innovation and Employment [grant number contract C10X1507].