Scientists from the Australian Nuclear Science and Technology Organisation (ANSTO) and Macquarie University have combined their respective backgrounds in nuclear science and geomorphology to determine rates of soil erosion across catchments in Asia and the Pacific.
The study, using fallout radionuclides, is part of a technical cooperation project under the Regional Cooperative Agreement for Asia and the Pacific, funded by the International Atomic Energy Agency.
Soil erosion reduces land productivity and degrades soil, and can be caused by poor agricultural practices. Understanding the causes and rates of soil erosion is essential for maintaining productive agricultural landscapes, food security and the surrounding environment.
“Nuclear techniques give us an opportunity to look at the longer term patterns of soil erosion and deposition through strategic sampling and analysis,” says Dr Tim Ralph, senior lecturer at Macquarie University’s Department of Environmental Sciences. “Instead of monitoring soil erosion for many years, selective samples can be used to interpret the pattern of erosion over the past 10 or 20 years, or longer.”
The soil samples were analysed by ANSTO scientists for radioactive isotopes, such as naturally occurring Lead 210 (210Pb). “Within your soil profile, you can also see high levels of 210Pb in the top of your profile, and then the deeper you go, the more it has decayed away,” says Professor Henk Heijnis, senior principal research scientist and leader of environmental research within the Nuclear Science and Technology cluster at ANSTO.
“If you have soil erosion, you don’t see that decay of 210Pb with the profile. You might see very low values right at the top; that means the top has disappeared and nothing is accumulating at that time,” explains Heijnis.
Samples were also analysed for compound specific stable isotopes of carbon, oxygen and nitrogen, which are produced by various crops in different amounts. These elements accumulate in deposition sites at the bottom of a catchment and can help determine, particularly across larger catchment areas, which crops are contributing to erosion.
“The analysis at the deposition site for compound-specific stable isotopes will give you a list of crops and land uses,” Heijnis says. “The relative abundance of these compounds will tell you the contribution of each of the types of land use and crops.”
Understanding the causes and rates of erosion and which agricultural practices are contributing to erosion will inform steps to mitigate the effects of these practices, such as terracing slopes or planting crops that can assist in soil stability.
“One of the big things this project did was to build a regional database of soil erosion based on these radionuclide techniques, so that we can now get a picture of the extent of erosion throughout Asia and the Pacific,” Ralph explains.
Scientists are continuing to construct the database of natural and unnatural erosion rates across different catchments. Ralph says the data to date shows that erosion rates were hugely variable between countries and even between different land uses within a single catchment.
There are plans for a future project to look at soil and water quality and soil structure, which would further add to the erosion database.