Applications of stable isotope data
The continuous monitoring of water quality will be vital in global efforts to tackle nitrogen pollution. Stable isotope analysis should be a key part of this, and with wider access to a new method of sample preparation, this is now much easier to achieve than it has ever been. Carol’s dual isotope plot will play a significant role in this effort.
Carol told us that the US is leading the way in this respect, with authorities making good use of the isotope data that are available thanks to routine continuous monitoring. “They’re interested in our data, because it answers their questions. They might need to know whether there's any possibility that the high nitrate content in a sample might be from manure rather than fertiliser, and we can show them the results. For example, in one stretch of the river, it may look like manure is a larger component, but at another point, manure is the lesser component and fertiliser is the bigger source. They can use that to start developing tailored solutions, and the fact that [the US Geological Survey and others] continue to fund such projects over many years shows that they have value.”
Thanks to the ongoing monitoring and data collection programmes in the USA, there are many opportunities for researchers to piggyback on these data and plot stable isotope data, in order to generate more insights into the environmental mechanisms at play. The insights that US agencies are able to gain by collecting longitudinal data could act as a useful example and incentive for governments, researchers and environmental stakeholders around the world to expand their capacity and use of stable isotope analysis.
Another factor that could expedite this uptake is the development of a new method for stable isotope analysis by Drs Mark Altabet and Leonard Wassenaar. Older methods often had significant downsides - they were offered by only a few laboratories around the world because they required complicated sample preparation, and as a result, it could be slow and expensive to obtain results. The new method, which uses titanium (III) chloride, has removed almost all of the barriers to entry and means that data can be collected much more quickly and cost-effectively. We expect to see more labs take up this kind of analysis over the next few years as a direct result of this innovation, and this could mean much greater access to stable isotope data. Using Carol’s plot, this could offer researchers a much more detailed understanding of the causes of pollution in natural waterways.
For Carol, the strength of her plot is the way that it clearly communicates the results of a study. With data visualisation, scientists can make more persuasive arguments, she says. “To be able to show a simple plot that identifies where hotspots of nitrogen were, and what the sources are, is a great way to hold people accountable.” This gives researchers a key tool with which to communicate the problems of nitrate pollution to politicians and decision makers. By presenting the data visually and with the clarity that Carol’s plot affords, environmental researchers can show the anthropogenic sources of nitrate in water samples in a way that is easy for stakeholders to understand. This allows them to emphasise the urgency of the nitrogen problem and empowers decision-makers to take action. This visual clarity is another reason that the dual isotope plot has enjoyed enduring appeal.
After 25 years, Carol’s plot is still being used to make a difference in environmental research, at a time when this is more important than ever.
Carol Kendall is a hydrologist, who is known for her research in nutrient tracking in aquatic ecosystems, using combinations of stable isotopes. She spent much of her career with the US Geological Survey, as a research hydrologist and later as a project lead for the National Research Program's Isotope Tracers Project. Undertaking her PhD with the University of Maryland while working full-time at USGS, her thesis focused on isotopes in shallow water systems. Carol has since retired and now spends her time caring for rare species of butterflies.
We'd like to thank Carol for taking the time to speak with us.