Nuclear techniques to measure soil erosion

Every year 75 billion tonnes of fertile soil are lost to erosion. It is expensive and labour-intensive to monitor this invaluable resource using conventional methods, which is why the Joint FAO/ International Atomic Energy Agency (IAEA) Programme on Nuclear Techniques in Food and Agriculture has been looking into other options. Recently published by FAO and the IAEA, Use of 137Cs for soil erosion assessment describes a promising technique that uses traces of nuclear activity to measure soil loss.

Measurable amounts of the radionuclide 137Cs were released into the atmosphere during nuclear weapons testing in the 1950s and 1960s as well as more recently during accidents in Chernobyl and Fukushima. When 137Cs comes into contact with soil, it sticks to the soil particles and tends not to wash away or be taken up by plants. This means that changes in 137Cs inventories are good indicators of erosion.

Scientists analyse the 137Cs content using a method known as gamma spectroscopy, which determines levels of radioactivity. Providing that undisturbed reference sites are available, the technique can provide useful information on erosion rates and soil/sediment dynamics and redistribution. This publication sets out the practical steps involved in data collection as well as data processing and interpretation.

With a dedicated research programme launched in the 1990s, the joint FAO/IAEA division has become the international reference regarding 137Cs use to measure soil erosion.

Soil erosion by water, wind and tillage are among the most common and important land degradation processes, with both on-site and off-site impacts. They affect more land than all other degradation processes put together. A total of 75 billion tons of fertile soil is removed every year from global soilscape by erosion. As a result, precious soil resources, which should be preserved for next generations, are continuously reduced. Every year approximately 12 million ha of land is lost. It is therefore important that erosion research is conducted to assess the soil redistribution rates, their spatial distribution and temporal dynamics in order to counteract this process.
The measurement of soil redistribution is not an easy task because soil erosion is caused by a number of processes running at different temporal and spatial scales. Conventional erosion measurement methods, such as volumetric, erosion plots, hydrological method and geodetic methods, are used for different erosion processes and they cover different spatial and temporal scales. Most conventional methods have severe limitations. They are associated with point data (measurement profiles) and do not provide information on spatial distribution of erosion. However the major disadvantage is that they are labour-intensive and require long monitoring periods. These disadvantages can be overcome by using 137Cs as an erosion tracer.
The basic principle of the 137Cs method for soil erosion assessment is based on the chemical characteristics of Caesium. The 137Cs is a human-induced environmental radionuclide, released into the atmosphere by nuclear weapons testing in the 1950s and 1960s, whereby the radionuclide spread to the stratosphere and gradually descended to the land surface.