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Measuring Denitrification

The development of a method for measuring denitrification is a first for New Zealand, providing vital data for understanding natural denitrification processes

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Challenge funding: $230,900

Research duration: January 2017 – December 2018

What Are We Doing?

Nitrate is the most pervasive groundwater contaminant. Around 40% of long-term groundwater monitoring sites in New Zealand show above-natural concentrations. Understanding and better managing nitrogen loads through New Zealand’s aquifers is vital for maintaining freshwater quality.

Denitrification is a natural process involving microorganisms that reduce dissolved nitrate to nitrogen gas. This has potential to significantly reduce nitrate loads in groundwater systems, and as a result, reduce the nitrogen entering water bodies such as streams, springs and lakes.

No quantitative and direct technique for measuring the extent of this denitrification process has been available in New Zealand.

This research project has developed and proven a methodology for measuring dissolved neon which, in combination with argon and nitrogen measurements, can be used to quantify excess nitrogen in groundwater. This enables the amount of nitrate that has undergone complete denitrification to be calculated.

How Can The Research Be Used?

  • The project team is collaborating with Horizons Regional Council and Waikato Regional Council to ensure that the measurement tools will be used by the councils. For example, the method has been used in the Waikato Regional Council’s test wells.
  • Testing in the Lake Taupō catchment, which is under threat from excess nitrogen contaminants, aims to understand denitrification for better protection of this nationally significant environment.

Team Snapshot

Research Outputs

Conference Papers

Measuring actual denitrification to understand nitrogen loads through aquifers

Martindale, H.; van der Raaij, R.W.; Morgenstern, U.
Fertiliser and Lime Research Centre workshop 31, February 2018

Ne is an inert, soluble, gas which is present in air and has been used in international studies to understand recharge conditions. The aim of establishing a sampling and analysis technique for Ne is two-fold: (i) enable the quantification of excess nitrogen in the groundwater and thus, denitrification, and (ii) improve groundwater dating via gas tracers by providing the correct recharge temperature and excess air to obtain more robust age tracer concentrations.

Measuring actual denitrification to understand nitrogen loads through aquifers

Martindale, H.; van der Raaij, R.W.; Morgenstern, U.; Hadfield, J.
New Zealand Hydrological Society Annual Conference, December 2018

Measurement of ‘excess N2’ is the most promising method for directly measuring denitrification that has occurred in an aquifer. The aim of this study was to validate a method for identification of denitrification in an aquifer and quantification of the extent of any denitrification that actually has taken place. Of the 27 sites sampled, 19 had N2 in excess above the range of uncertainty. 12 were highly anoxic. 5 of the sites had dissolved oxygen between 2.5 mg L-1 and 5.79 mg L-1, indicating that complex flow pathways between the oxic and anoxic zones in the aquifer or in the well exist.


Measuring actual denitrification to understand nitrogen attenuation

Heather Martindale, Rob van der Raaij, Dr Uwe Morgenstern, John Hadfield
New Zealand Freshwater Sciences Society Conference, December 2018


Measurement of neon in groundwaters for quantification of denitrification in aquifers

Martindale, H.; van der Raaij, R.W.; Daughney, C.J.; Hadfield, J.; Morgenstern, U.
GNS Science report 2018/34, October 2018

Measurement of neon in groundwaters – analysis and validation

Martindale H, van der Raaij RW, Daughney CJ, Morgenstern U, Hadfield J
GNS Science report, December 2017

Have a Question?

We are happy to answer any questions about this research and how it can be used.

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