The discovery is contained in a thesis of master at Umass Amherst University. To calculate the rate of erosion, a team of researchers quantified the presence of a rare element – Beryllium 10 – in cultivated prairies in 5 US states, comparing them with virgin soils
by Emanuele Isonio
It all starts with a PhD thesis from the Department of Geosciences of the University of Massachusetts Amherst, the largest public university in New England. From his intuitions a study was then developed which involved several researchers from the same institute and which could represent a milestone in the awareness of the speed with which man is degrading the world’s soils.
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Five states involved in the study
The research – financially supported by the government agency National Science Foundation (NSF) and published in the journal Geology – focused on the rate of erosion of agricultural soils in five states of the American Midwest: Iowa, Minnesota, South Dakota, Nebraska and Kansas. Objective: to understand if and to what extent agricultural activity has accelerated the rate of soil erosion compared to the past.
“This research addresses important scientific questions about landscape evolution,” said Justin Lawrence, program director in NSF’s Division of Earth Sciences. “The insights gained could lead to more sustainable agricultural practices.”
Beryllium-10 used as a clue
To succeed in the task, the study exploited Beryllium-10 (10Be). A very rare element, which is formed when the stars of the Milky Way explode and send out high-energy particles, the so-called cosmic rays. These rays, hurling themselves towards the Earth and crashing into the earth’s crust, split the oxygen in the soil, leaving tiny traces of beryllium-10. These residues, once they end up in the upper layer of the soil, can then be used, thanks to their half-life, to accurately determine average erosion rates over thousands or even millions of years.
To measure the quantity of beryllium-10, the researchers identified portions of land that had never been affected by modern agriculture. “We went to 14 small patches of still existing native prairie in each of the five states covered by our survey. Through a hand auger we collected cores of deep soil, a material that dates back to the last ice age,” explains Isaac Larsen, a geoscientist at the University of Massachusetts Amherst and senior author of the publication. “We brought this soil back to our laboratory, l ‘we sieved to isolate individual grains of sand, removed anything that wasn’t quartz, and then ran a chemical purification process to separate the beryllium-10′.
Insufficient federal guidelines
The results amazed the authors of the research themselves: before the arrival of modern agriculture, the average erosion rates in the US prairies were about 0.04 millimeters per year. A fact that goes back in time to the last ice age, about 12,000 years ago. Today the situation has definitely changed. Previous measurements, made in agricultural fields adjacent to the virgin grasslands studied during this survey, show that the cultivated areas are subjected to erosion rates up to a thousand times greater. In about 160 years of modern agriculture, no less than 57.6 billion tons of topsoil has been lost.
But the study by Umass Amherst researchers also clarifies another point: the normal rate of erosion in the pre-modern era is 25 times slower even than the soil loss that the US Department of Agriculture indicates sustainable in its guidelines for soil management. In fact, the USDA considers one millimeter of erosion every year “tolerable”. In a nutshell: even if they were all applied on a large scale, good cultivation practices would not bring erosion rates back to those recorded up to the early nineteenth century.
Billionaire social costs
The rapid deterioration of soils in the US Midwest is not only a worrying environmental threat. It puts precious ecosystems at risk and contributes to an increase in greenhouse gases in the atmosphere. At stake is also American agricultural production. A calculation, carried out a couple of years ago by the Rockefeller Foundation on the “true costs of the food system” in the USA, included the erosion of agricultural land among the consequences of modern agriculture. The cost, for this item alone, is around 67 billion dollars a year: just under 8% of the almost $900 billion of unaccounted environmental costs, caused by the agri-food system on the environment and biodiversity.