Silting also hits natural paradises

Researchers study sediments in the Kruger National Park

A two meter thick, clayey and well mixed sediment layer was in a stowage position. © Jussi Baade
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A Jena scientist has now confirmed in a recent study that it can also lead to soil erosion in areas close to nature without human intervention. The researcher examined the sediments of 20 dried-up reservoirs in the Kruger National Park in South Africa.

110 years ago, Paul Kruger, then President of the Transvaal Republic, protected an area of ​​about 2, 500 square kilometers in southern Africa - in 1926 the extended area was declared a nature reserve. Today, the approximately 20, 000 square kilometers Kruger National Park home to countless animal and plant species.

Untouched nature

"The area has been protected from settlements and agriculture for 100 years and thus an almost natural ecosystem, " explains Jussi Baade from the University of Jena. This almost untouched nature was needed by the Jena geologist for his investigations. He has been a member of the park's Science Team since May 2008, a group of international scientists working in the Kruger National Park. With the support of the Federal Ministry of Education and Research, Baade is investigating soil erosion in the national park in a pilot project.

The scientist found an astonishing find in sedimentological investigations of deposits on the ground of 20 dry reservoirs in the southern part of the park: "At the deepest point of a water reservoir, we found a surprisingly thick layer of sediment two meters thick, " reports Baade.

Low removal rates

If the amount of sediment in the 5.5-hectare Siloweni Reservoir is extrapolated to its catchment area, the researcher continues, then it turns out that relatively low removal rates are responsible for the silting up of the water reservoir. About 28, 000 cubic meters of material were in the reservoir. The sediment was on average 0.5 meters thick, resulting in an average erosion of two millimeters. "It is possible to determine an annual removal rate of 0.1 to 0.2 millimeters, which corresponds to a very low removal rate of about 1.5 to three tons per hectare per year, " explains Baade. display

The studies also provided information about the distribution of nutrients in the sediment layer. "The upper layers contained about five times more phosphate and were therefore much more nutrient-rich than the layers at the base, " says Baade. Unfortunately, the sediment layer, which mainly consisted of clay, had been thoroughly mixed so that interchangeable deposits were not recognizable and therefore no conclusions could be drawn about individual natural phenomena.

60 reservoirs and hundreds of pumps

"Around 60 water reservoirs created by the accumulation of rivers and hundreds of pumps that bring groundwater to the surface of the earth exist throughout the national park, " notes the Jena scientist. As part of his fieldwork, he conducted test drilling in dry reservoirs to analyze the sequence of soil layers.

With the help of further sedimentological methods, Baade scientists determined the grain size, composition and chemical parameters of the deposits. The data are the preliminary work for further investigations, in which the sediments are to be determined volumetrically and qualitatively. The goal is to establish soil erosion rates.

"The sediments are archives that document the soil erosion events of the last 60 to 70 years, " explains Baade. To be able to do this in an area that has been largely left to its natural state for more than 100 years is a rare blessing.

(idw - University of Jena, 16.12.2008 - DLO)