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Water quality in New Zealand: Land use and nutrient pollution

21 November 2013

I still think of Canterbury as home. For a hundred years, farmers grew crops and ran sheep on the patchwork plains. But over the last twenty years, water has transformed much of this long-familiar landscape into bright green pasture grazed by dairy cows. Often the first sign of such change has been the felling of macrocarpa shelter belts to make way for irrigators up to a kilometre long travelling across paddocks. In parts of the North Island too, large-scale and rapid land use change has been taking place. For instance, north of Taupō, tens of thousands of hectares of pine forests have been felled and replaced by dairy farms. 

These land use changes reflect the changing economics of farming. In 1982, the number of sheep in New Zealand peaked at 70 million; now there is less than half that number. Beef cattle numbers have also fallen. Changing how we use land in response to market signals is not new. 

However we use our land, the quality of the water in our rivers and streams, lakes, estuaries and aquifers is affected. This report is focused on how current changes in land use are affecting the amounts of nitrogen and phosphorus that end up in fresh water. As explained in my 2012 report, Water quality in New Zealand: understanding the science, too much nitrogen and phosphorus in water lower its quality by causing excessive growth of weeds, slime and algae, affecting populations of insects, fish and waterbirds. On land, nitrogen and phosphorus are valuable nutrients; above certain concentrations in water, they are pollutants.

There are a number of regional land use maps accompanying this report.

  • Resources

    Water quality in New Zealand: Land use and nutrient pollution (PDF 4.7 MB)
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  • Related resources

    Update report – Water quality in New Zealand: Land use and nutrient pollution (PDF 950 KB)
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    Water quality in New Zealand: Understanding the science (PDF 3.2 MB)
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  • Consultant reports

    Motu – Land use and farming intensity: For 1996, 2008 and 2020 (PDF 2.47 MB)
    Motu – Mitigation of nutrient loss from New Zealand agriculture (PDF 475 KB)
    Motu – Understanding the practice of land use modelling (PDF 295 KB)
    Motu – Understanding the practice of water quality modelling (PDF 486 KB)
    NIWA – National nutrient mapping using the CLUES model (PDF 4.8 MB)