Linking Legacies to Wai

Accounting for lag times and natural concentrations of contaminants in groundwater

The Duke of Edinburgh (third from left) observes border dyke irrigation at the Winchmore Research Station Irrigation Scheme, 23 January 1954. Image published with permission of Archives New Zealand, Alexander Turnbull Library 1/2-04226F (AAQT 6538/1)

Project Details Ngā taipitopito

Project Status:
Challenge funding:
Research duration:
January 2022 – March 2023

Collaborators Ngā haumi

AgResearch | Aqualinc | DairyNZ | Environment Canterbury | Lincoln University | Ministry for the Environment

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What are we doing?E aha ana mātou?

The decisions farmers make today on land can take many years to be reflected in the health of water in our rivers and groundwater. In the past, this ‘lag time’ contributed to a lack of understanding of the intrinsic connection between wai and whenua.

This research will demonstrate the effects of agriculture on our freshwater over the past 170 years and will predict how quickly future land-use decisions will restore the health of degraded water. The project aims to use this knowledge to grow understanding among land stewards of the connection between whenua and wai.

This project will have a focus on groundwater. It will find out how long it takes for changes in land use or intensity to be reflected in nitrate concentrations in groundwater.

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

  • The lag time between land-use changes (largely intensification) and the increase in the load of nitrate in streams and rivers has been quantified as 4.5 years on average for 77 catchments that capture about 50% of Aotearoa’s agricultural activity.
  • A key finding of this research was that without human activity such as farming, nitrate concentrations in groundwater in Aotearoa would likely be around 1.65mg/L. This has given MfE and StatsNZ justifiable reference conditions for nitrate concentrations in groundwater, and advice that the appropriate national-scale threshold ought to be 1.65 mg/L. This finding is also important for considering a nitrogen bottom-line for rivers, because most baseflow in rivers is fed by groundwater.
  • This research will help set realistic timeframes to decrease nitrate concentrations in groundwater, and streams and rivers. If nitrate is not decreasing quickly enough, Councils will have evidence to take further action.

Participation & engagement Te hunga i whai wāhi mai

  • Māori, government (central and local) and peak industry bodies were asked to prioritise land uses, land practices and past and future years to be examined.
  • DairyNZ’s environmental science team revisited dairy farms in five catchments to assess whether on-farm actions have helped improve water quality over time. The five catchments – Waiokura (South Taranaki), Toenepi (Waikato), Waikakahi (Canterbury), Bog Burn (Southland) and Inchbonnie (West Coast) – are dairy-dominated and were part of the 2001-2010 Best Practice Dairy Catchments project, which monitored water quality and environmental work on-farm.

Research team Te hunga i whai wāhi mai

Science Lead
Richard McDowell
John Bright
Alasdair Noble
Kohji Muraoka
Ministry for the Enironment
Ognjen Mojsilovic

Tools & resources Ngā utauta me ngā rauemi

Journal Article

Determining the likelihood and cost of detecting reductions of nitrate nitrogen concentrations in groundwater across New Zealand

Nitrate‑nitrogen (NO3-N) is a contaminant of concern in groundwater worldwide. Stakeholders need information on the ability to detect changes in NO3-N concentrations to prove that…
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Journal Article

In recognition of Mike Hedley: fate of fertiliser in soil and mobilisation of recalcitrant nutrients

This special issue brings together papers that examine topics studied during the career of Professor Mike Hedley, a soil scientist now retired and living on…
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Journal Article

The Our Phosphorus Future Report

Unsustainable phosphorus use is at the heart of many societal challenges. Unsustainable phosphorus use affects food and water security, freshwater biodiversity and human health. Increasing…
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Journal Article

Nitrogen fertilization effects on soil phosphorus dynamics under a grass-pasture system

Nitrogen (N) and phosphorus (P) are critical to pasture productivity; however, limited information is available on how the single and combined additions of N and…
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Academic outputs He whakaputanga ngaio

Journal Article

Linking the uptake of best management practices on dairy farms to catchment water quality improvement over a 20-year period

Intensive land use, such as dairying, can impair water quality. Although many guidelines exist on how to mitigate the loss of dairy-associated contaminants from land…
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Journal Article

Reference conditions and threshold values for nitrate-nitrogen in New Zealand groundwaters

Management of groundwater quality is assisted by an understanding of reference conditions, which describe the concentration ranges expected for key substances in the absence of…
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Journal Article

The longevity of cultivation in decreasing the potential for phosphorus loss in runoff

Phosphorus (P) loss from highly fertilised grazed pastures can impair surface water quality. High P concentrations in grazed pastures are maintained to boost legume production,…
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Journal Article

Phosphorus and iron-oxide transport from a hydrologically isolated grassland hillslope

Losses of N, P and Fe in drainage responded differently to waterlogging. Moderate nitrate concentration prevented Fe–P dissolution and loss in drainage. Low nitrate concentrations…
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Journal Article

Sediment and water-column phosphorus chemistry in streams at baseflow across varying catchment geologies

Streams can attenuate inputs of phosphorus (P) and therefore dampen the likelihood of ecosystem eutrophication. This P attenuation derives from many processes and remains poorly…
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Journal Article

Reflecting on the journey of environmental farm planning in NZ

Environmental farm planning in New Zealand dates to the 1950s when soil conversation plans were first undertaken. Since then the extent and complexity of whole…
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This project has produced
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