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 | 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.
  • 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.

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

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

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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Academic outputs He whakaputanga ngaio

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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Journal Article

Assessing the leaching of cadmium in an irrigated and grazed pasture soil

To decrease topsoil cadmium (Cd) concentrations we need to make inputs < outputs. Phosphorus fertiliser is the main input of Cd and leaching the main…
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Journal Article

Do soil cadmium concentrations decline after phosphate fertilizer application is stopped: A comparison of long-term pasture trials in NZ

Stopping phosphorus (P) fertiliser can decrease topsoil cadmium (Cd) concentrations. Stopping P fertiliser applications reduced soil Cd concentrations after 21 and 26 years. Reductions only…
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Journal Article

The implications of lag times between nitrate leaching losses and riverine loads for water quality policy

Understanding the lag time between land management and impacts on riverine nitrate–nitrogen (N) loads is critical to understand when action to mitigate nitrate–N leaching losses…
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Journal Article

Reductive dissolution of phosphorus associated with iron oxides during saturation in an agricultural soil profile

In soils with a fragipan or poor permeability, water may remain in a soil profile long enough to make it anoxic and reductive. The reductive…
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