Assessing Contaminants with Stream Order

Determining whether excluding livestock from large streams in flat catchments would substantially decrease the contaminant load

Project Details Ngā taipitopito

Project Status:
Challenge funding:
Research duration:
January 2017 – December 2017

Collaborators Ngā haumi

AgResearch | Land Water People

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What are we doing?E aha ana mātou?

The New Zealand dairy industry’s Water Accord requires farmers to exclude livestock from all large fourth-order streams – “wider than a stride and deeper than a Red Band gumboot” – by committing to a riparian planting plan (due by 31 May 2020, with 50% of planting complete). Government is considering implementing this as national policy.

Our research looked at whether excluding livestock from large streams (over 1 metre wide, over 30cm deep) would substantially decrease the load of contaminants (nitrogen, phosphorus, sediment and E.coli) entering waterways.

The researchers found that loads from large streams in flat catchments dominated by pasture accounted for, on average, 23% of the national load of all contaminants. This research suggests additional mitigations should be implemented to reduce the 77% of contaminants that enter waterways from smaller streams in rolling to steep land.

Further Our Land and Water research is now developing a simple tool for farmers to identify mitigations that are more cost-effective than fencing.

How can the research be used? Ka pēhea e whai take ai te rangahau?

  • We discovered that fencing only large streams to exclude stock would have less effect on freshwater quality than originally thought. Small, steeply sloping streams contribute, on average, 77% of the load of freshwater contaminants. This work was covered in all major newspapers, and radio and TV stations.
  • Farm environment plans and tools such as MitAgator can help farmers target strategies to mitigate contaminant losses from critical source areas. This means that cheaper strategies than fencing can be used to keep livestock out of smaller streams, for better effect.
  • The results challenge proposed government stock exclusion regulations.
  • This research is now being used by regional government to determine policy to improve the quality of freshwater. For example, Taranaki Regional Council has committed to fencing more streams than those covered by central government’s proposed stock exclusion regulations.
  • This research is being used internationally. The paper Assessing the Yield and Load of Contaminants by Stream Order was awarded JEQ Best Paper 2019, for the best paper produced in the prior three years, as awarded by the editors of the American Tri-Societies, whose members number over 20,000 North American scientists covering the primary and environmental sectors.

Research team Te hunga i whai wāhi mai

Research Lean
Richard McDowell
Ton Snelder
Land Water People
Neil Cox

Tools & resources Ngā utauta me ngā rauemi

Journal Article

The longevity of fencing out livestock as a method of decreasing contaminant concentrations in a headwater stream

Water quality can be improved by fencing off streams from livestock. However, the remedial effect of fencing can fail as livestock trample near stream areas.…
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Academic outputs He whakaputanga ngaio

Journal Article

Anthropogenic increases of catchment nitrogen and phosphorus loads in New Zealand

Spatial regression models were used to predict yields of nitrogen (N) and phosphorus (P) discharged from catchments throughout New Zealand. The models were derived using…
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Journal Article

Assessing the Yield and Load of Contaminants with Stream Order: Would Policy Requiring Livestock to Be Fenced Out of High-Order Streams Decrease Catchment Contaminant Loads?

This paper won the JEQ Best Paper Award 2019. Concentration and flow data for 1998 to 2009 were used to calculate catchment load and yields…
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Journal Article

Estimation of Catchment Nutrient Loads in New Zealand Using Monthly Water Quality Monitoring Data

Causes of variation between nutrient loads estimated using alternative calculation methods and their repeatability were investigated using 20 years of daily flow and monthly concentration…
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Journal Article

Estimation of nutrient loads from monthly water quality data

Causes of variation between loads estimated using alternative calculation methods and their repeatability were investigated using 20 years of daily flow and monthly concentration samples…
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