Freshwater reforms may have minimal impact on greenhouse gas emissions

05/05/2017

Two separate independent studies have found that the incidental impact of freshwater reforms on greenhouse gas emissions will not be large unless they lead to a lot more trees being planted.

The National Policy Statement for Freshwater Management directs regional councils to establish objectives and set catchment-by-catchment limits for freshwater in their regional plans.

Independent studies led by Motu Economic and Public Policy Research and AgResearch estimated that land-based gross greenhouse gas (GHG) emissions would be reduced by 2-4 percent after the freshwater reforms.

“Across New Zealand, planned reductions in contaminants varies widely from catchment to catchment  but the average reduction in contaminants expected is less than 10 percent from current levels,” said Suzi Kerr, Senior Fellow at Motu and co-author of the report synthesising the research. “Nitrogen will be reduced between 4-6 percent, phosphorous by 5 percent, sediment by 18 percent and E.coli by 10 percent.”

“The small scale of the GHG reductions are because reductions in contaminants are targeted at a relatively small areas of need, the required reductions in contaminants are not likely to be large overall, and the likely low cost mitigation options outside of reforestation may have only small effects on gross GHGs,” said Dr Kerr.

The studies found that in many cases, it is possible to achieve the nitrogen mitigation targets without changes in animal numbers.

“This consequently limits effects on GHG emissions, because it is animal numbers that really matter when it comes to GHGs.” said Dr Kerr.

For each 1 percent of nitrogen reduced, gross GHG emissions are on average reduced by about 0.3-0.7 percent. Adding trees as a part of the mitigation mix increases this to closer to 1:1.

Both studies primarily focused on options that maintained land use and productivity.

“However, we did some additional analysis that found if farmers were willing to afforest some of their less productive bits of land, a high proportion of the mitigation could be achieved in that way,” said Dr Kerr.

No single measure will substantially mitigate the impacts of farming activities on the environment: Improvements in freshwater quality will instead be achieved by the implementation of a range of measures. These include:

  • stock exclusion from streams and wetlands (via fencing – possibly with riparian planting),
  • controlling hill-country erosion (e.g., via spaced pole planting and afforestation),
  • improved stock, effluent and fertiliser management, and,
  • where deemed necessary, the introduction of farm infrastructure that allows for soil protection and the capture of animal excreta during periods when the risk of runoff is relatively high.

The greatest GHG emission benefits from the freshwater reforms are likely to come from activities on sheep and beef farms, especially those located in hill country.

“On land used for sheep and beef farming, afforestation would provide the greatest reductions in sediments and phosphorous and the greatest GHG co-benefits,” said Dr Kerr.

“There’s also a good alternative if farmers don’t want to plant forest. Spaced pole planting on land prone to erosion allows landowners to maintain stock production, although the added benefit of carbon sequestration would be lower,” said Dr Kerr.

This was the first national level research assessing the indirect impacts of the water quality component of the freshwater reforms on New Zealand’s greenhouse gas emissions. The independent teams, included one led by AgResearch with assistance from Scion and Plant and Food; and the other led by Motu Economic Public Policy Research with Landcare Research and assistance from NIWA and AgResearch. The two teams took quite different approaches, but some of their results are directly comparable.

A synthesis of the research outlines this issue in more depth: “New Zealand’s freshwater reforms: What are the potential impacts on greenhouse gas emissions?” is now available. The underlying reports from the Motu-led team are also available and the AgResearch paper will be available shortly. This research was commissioned by the Ministry for Primary Industries.