28 June 2024

How climate and human activities have eroded the US soil

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Climate and land-use change have promoted erosion in the United States over the past 70 years. The Central Great Plains has experienced the most significant loss

by Matteo Cavallito

 

Climate plays a key role in shaping soil dynamics and soil erosion. This was revealed by a recent research conducted by a group of researchers from several countries that focused on a time horizon of almost seventy years. “Understanding spatio-temporal changes in soil thickness and their natural and anthropogenic driving factors are essential for earth system modeling and natural resource conservation,” the authors explain.

The study, which involved the Universities of Wisconsin and Oregon, in the USA, the University of Córdoba, in Spain, and the University of Minas-Gerais, in Brazil, processed data collected between 1950 and 2018 in the 48 contiguous US states, i.e. the entire US territory with the exception of Hawaii and Alaska.

The study

The authors, says a statement from the University of Córdoba, analysed the spatial variability of soil using various statistical methods and Big Data techniques. They also drew on a huge database of the depth of the so-called ‘A horizon’, the top soil layer, and the total soil depth in 37,712 and 22,409 locations in the United States, respectively. Depth, the authors say, is crucial because it determines agricultural fertility and controls the hydrological cycle and biodiversity. Knowing its variation, therefore, becomes essential for planning crop management and soil conservation.

Another unique aspect of the study, published in the journal Nature, is the breadth of its time dimension, which spans 69 years, from 1950 to 2018.

By analysing such a broad horizon, the researchers were thus able to observe particularly relevant yet often ignored changes. Traditional erosion studies are limited to observing a period of no more than two years, the note notes. This analysis, on the other hand, extended over a sufficiently long period of time to allow, for example, the detection of a significant loss of the top soil layer in the Great Plains, where Mollisol, a particularly productive soil, is predominant, as well as in sloping areas and cultivated areas in general.

The climate effect

The analysis found a correlation between climate and “the spatial distribution of soil thickness, and land use and erosion associated with its temporal variation,” the study states. Moreover, “, “The A horizon and solum (i.e. the surface and subsurface layers, ed.) thickness displayed strong longitudinal patterns, correlated with soil moisture and temperature, respectively. Temporal changes in the thickness varied across land resource regions, affected by topography, land use, and erosion”.

According to the authors, the most significant loss of the A horizon occurred mainly in soils of the Central Great Plains, on steep slopes and in cultivated soils. “These findings – they explain, – enhanced our fundamental understanding of soil formation and biogeochemical cycles during the Anthropocene across scales and identified regions for conservation practices to reduce further topsoil loss.”

The human factor behind erosion

The study once again highlights the weight of human activities resulting in land-use change. A topic that has long attracted the attention of scientists. Last year,  a study sponsored by the National Science Foundation  (NSF) and published in the journal Geology found that agricultural activity had produced an astonishing acceleration in the rate of erosion of agricultural soils in five states of the American Midwest: Iowa, Minnesota, South Dakota, Nebraska and Kansas.

Before the arrival of modern agriculture, the authors explained, average erosion rates in the US prairies were about 0.04 millimetres per year. This figure dates back to the last ice age, some 12,000 years ago. Since the advent of modern agriculture to the present, i.e. over the past 160 years, prairie farmland has been subjected to erosion rates up to a thousand times greater. With a total loss of no less than 57.6 billion tonnes of topsoil.