Tracking nitrate and ammonium in the environment
Newly developed methodologies are improving our understanding of nitrogen cycling.
20/10/2022
At BGS’s Stable Isotope Facility, we are developing a suite of laboratory methodologies to analyse the key nitrogen-bearing species nitrate and ammonium. These methods will allow much lower concentration samples to analysed, helping improve our understanding of nitrogen cycling within the environment.
The nitrogen cycle
Alongside carbon and phosphorus, nitrogen is one of the key micronutrients critical to all life on Earth. It is a core component in amino acids, which, in turn, form the building blocks of all genetic material: DNA and RNA.
Nitrogen is the most abundant gas on Earth, making up 78 per cent of the air we breathe. Atmospheric nitrogen is converted by bacteria in the soil to ammonium (NH4+), in a process called nitrogen fixation. From here it is converted to nitrite (NO2–) and nitrate (NO3–), which can be taken up by plants, thus entering the food chain.
In addition to natural nitrogen fixation, humans apply nitrogen-rich fertilisers to soils to reduce natural nitrogen limitation and promote crop productivity.

The nitrogen cycle, showing nitrogen fixation from nitrogen in the atmosphere to ammonium and the conversion of ammonium to nitrate before it is taken up into plants. Denitrification is the main process by which nitrogen is then lost back into the atmosphere. BGS © UKRI.
This application of fertilisers can have negative consequences. When nutrient-rich water runs off arable land and enters surface waters, for example lakes or rivers, it can promote uncontrollable algal growth. This can drastically decrease water quality, reducing the water’s oxygen content and leading to the death of aquatic species. Additionally, high concentrations of nitrogen can enter groundwater, from which it is almost impossible to remove, polluting aquifers that are traditionally used for water extraction and human consumption.
It is therefore critical that we understand how nitrogen enters our most precious environments, how it is cycled, transformed between different nitrogen species and released back into the atmosphere. To understand these processes, we need effective ‘tracers’. One of these is the stable isotope composition of nitrogen within different key molecules, including nitrate and ammonium.
New methods
The Stable Isotope Facility has carried out stable isotope analysis of nitrate and ammonium for many years. Traditional methods convert dissolved nitrate or ammonium to a solid, for example silver nitrate, allowing for the combustion of this solid within an elemental analyser coupled to a mass spectrometer. However, these methods required large volumes of sample water (more than 1 l) and high concentrations of either nitrate or ammonium. This used to limit the types and numbers of samples we could realistically analyse.
Recently, we have been working to improve in line with recent published methods. These new methods are up to a thousand times more sensitive than our old procedures, meaning we can analyse much smaller volumes of samples (1 to 4 ml) and at much lower concentrations (less than 1 mg-l). Unlike our old methods, these new techniques convert the dissolved nitrate or ammonium to nitrous oxide gas, which is then analysed by our trace gas and mass spectrometer system (Sercon Cryogas HS2022). This new mode of analysis has needed a lot of setting up and testing over the past year, but we are now getting great data for low concentration nitrogen species.

The Sercon and BGS team, who developed the Cryogas system currently used for N2O and other trace gas stable isotope analysis at BGS. BGS © UKRI.
The hope is that this faster, cheaper and more sensitive analysis will promote more wide-ranging nitrogen cycling studies using stable isotopes, helping to answer some of the key questions surrounding nitrogen pollution and sustainable fertilisation.
Acknowledgment
Thanks goes to the BGS Innovation Fund and Sercon for supporting this work.

Dr Andrew Smith
Isotope geochemist
Relative topics
Latest blogs

Hemsby coastal erosion: the scale of the transformational challenge around the coastlines of England and Wales
24/03/2023
The recent closure of Hemsby beach in Norfolk provides key information on the transformational challenge of coasts around England and evidence of historical change along the coastlines of England and Wales.

Six ways we’re improving recycling at BGS Keyworth
24/03/2023
Sustainability at the BGS site in Keyworth, Nottingham, is being improved by recycling, managing our waste, making our labs more efficient and more…

A tale of two groundwaters
21/03/2023
Why the United Nations 2023 Water Conference needs to know more about groundwater.

Below the bonnie banks: mapping Loch Lomond’s underwater landslides
07/03/2023
Using high-resolution, multibeam bathymetry and shallow seismic imaging, BGS’s marine geoscience and landslides teams are mapping historic landslides under the waters of Loch Lomond.

When did the cows come home?
23/02/2023
PhD student David Osborne is exploring Bronze Age animal husbandry using isotopes and X-rays.
Property subsidence assessment: helping to mitigate shrink–swell hazard risk
25/01/2023
The BGS Property Subsidence Assessment dataset provides insurers and homeowners with tools to better understand shrink–swell and the risk it poses to homes and businesses.

MYRIAD-EU: shifting the paradigm in disaster risk management
17/01/2023
How changing our approach to disaster risk reduction practices can create a more resilient future.

Five places in Yorkshire to assess key geological hazards
21/12/2022
A field trip to Yorkshire has helped our data products team improve their output.

IODP Expedition 386: hosting a sampling party in Japan
19/12/2022
BGS help lead the final phase of IODP Expedition 386 in Japan, coordinating science colleagues from around the globe to extract samples from sediment cores aboard DV Chikyu.

Mushroom spotting at BGS Keyworth
09/12/2022
Colleagues at BGS are mapping mushrooms as part of efforts to enhance biodiversity on the Keyworth site.

Building underneath the Colosseum: the importance of urban geology
21/11/2022
Tim Kearsey reports on his underground excursion around Rome.

Introducing the BGS Debris Flow Susceptibility Model for Great Britain
21/11/2022
Debris flows are a landslide hazard of particular concern to transport infrastructure managers and local authorities.