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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

Mden Photo 3x2

PROJECT DETAILS

Challenge funding: $230,900

Research duration: January 2017 – December 2018

COLLABORATORS

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What Did We Do?

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?

  • A method was developed to quantify the end product (excess N2) from the denitrification reaction, which can then be used to find the rate of denitrification (by combining with age). With enough data, a 3D map of denitrification could be created.
  • The project team is collaborating with Horizons Regional Council, Environment Southland 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.
  • The method developed by this programme will contribute to the production of an accurate national map of denitrification, which would feed into the Land Use Suitability programme, providing science-based data for land use optimisation to improve water quality.
  • The next step for this research is to get the technique ready for wider adoption on a regional and national level, with improved sensitivity enabling larger catchment studies.

Team Snapshot

Uwe Morgenstern
Research Lead

Uwe Morgenstern

GNS Science
Karyne Rogers

Karyne Rogers

GNS Science
Rob van der Raaij

Rob van der Raaij

GNS Science
Ranvir Singh

Ranvir Singh

Massey University
John Hadfield

John Hadfield

Waikato Regional Council
Heather Martindale

Heather Martindale

Ministry for the Environment

Research Outputs

Papers

Assessment of excess N2 for quantifying actual denitrification in New Zealand groundwater systems

Martindale, H., van der Raaij, R., Daughney, C.J., Morgenstern, U., Singh, R., Jha, N., Hadfield, J
Journal of Hydrology, 2019

Denitrification in groundwaters is a key nitrate (NO3) attenuation process, where leached NO3 can be reduced to gaseous forms of nitrogen (N2). In this study, calculation of the concentration of excess N2 is applied to the New Zealand context to quanitfy the extent of denitrification occurring in groundwater systems under natural flow conditions. The concentration of dissolved atmospheric N2, according to the recharge conditions of the water, can be established by the measurement of two noble gases that are also part of the atmosphere. This enables differntiation of the excess N2 gas produced via denitrification reactions from atmospherically derived N2 gas.

Conference Papers

Quantifying Actual Denitrification in Groundwater Systems

Rogers KM, 1 van der Raaij R, 2 Morgenstern U
NZ Hydrological Society Annual Conference 2019

Measurement of ‘excess N2’ is the most promising method for directly measuring denitrification that has occurred in an aquifer. Current efforts to locate and characterise denitrification zones can also be confirmed by quantifying the extent of denitrification by measuring excess N2 gas changes. Our initial studies show excess N2 gas method is useful to detect denitrification and quantifies the amount that has occurred, even in sites with mixed redox states. This suggests the method will be useful to improve knowledge around denitrification zones and quantify levels for ongoing regulatory monitoring. To consolidate this research, we are now seeking partners to undertake small scale projects and apply the method to further studies.

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 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.

CONFERENCE PRESENTATIONS

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

Quantifying Actual Denitrification in Groundwater Systems

Karyne Rogers, Rob van der Raaij, Heather Martindale, Uwe Morgenstern
New Zealand Hydrological Society Annual Conference, 2019

REPORTS

Quantifying Actual Denitrification in Groundwater Systems

Dr Karyne Rogers
One-page summary, 2019

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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