Soil erosion rates "jump" at political borders: Study

The rate at which soils erode strongly depends on which side of a national border, and in which country the soil lies, according to a study which may lead to better strategies in conserving soil.

The researchers, including those from ETH Zurich in Switzerland, employed satellite imagery and numerous other data sources to investigate the socio-economic causes of soil erosion around the world.

"Governments around the world are trying to address the issue of soil erosion. However, we do not know whether countries have much actual control over their soil erosion," the researchers wrote in the study.

The findings of their study, published in the journal Nature Sustainability, revealed that the erosion rate is generally changing continuously through space but "jumps" abruptly at country borders.

According to the researchers, such abrupt "jumps" at political borders reveal the influence of the countries that are left and right of the borders.

Using the high-resolution remote sensing data, and numerous other data sources, the researchers created an erosion map of the world.

As an example, the scientists used the island of Hispaniola, home to Haiti and the Dominican Republic.

They said, in its natural form Hispaniola is uniformly covered with a dense tropical forest with low erosion since this vegetation can protect the soil from rain.

However, they said, along the border, Haiti's soils lose 50 tonnes more per year and per hectare than those of the Dominican Republic.

The scientists explained that if Hispaniola had not been subject to human intervention and were still in its natural state, there would be no sharp increase in soil erosion along the border.

"But the presence of such a rise points to political entities, not natural borders," said study co-author David Wuepper from ETH Zurich.

He said the differential erosion along the border of the two Caribbean states was extremely high -- 30 times higher than the global average.

According to the researchers' calculations, the erosion seen in these states stands at 1.4 tonnes per year and hectare of arable land.

In comparison, they said, the rate of erosion in Germany was 0.2 tonnes lower than that of its neighbouring countries.

This suggests that erosion is also fairly low in the countries that border Germany, they explained.

"Our findings illustrate how inconsistent the pattern observed around the world is," Wuepper said.

The study noted that a country's strongest influence on soil erosion was its agriculture, and the way its farmers cultivated the soil.

According to the researchers, there is a potential for countries to improve their soil protection and how they go about it.

Until now, they said soil erosion had been seen as a predominantly local problem.

"Now we've shown that larger-scale factors also strongly influence erosion in a given country," Robert Finger study co-author, also from ETH Zurich said.

The method used in the current study can also be used to determine whether measures that countries take to improve soil protection are effective or not, the researchers said.

One measure, for example, is introducing economic incentives to encourage greater soil cover or reduced tillage, they explained.

However, according to the researchers, measures to protect against erosion can also result in new conflicts of interest.

As an example, they said, reduced tillage may lead to increased use of pesticides for weed control.

"The basis for good policy-making in this respect is to identify and quantify these conflicting goals," Finger said.