Aeolian Sand Sorting and Soil Moisture in Arid Namibian Fairy Circles

Hezi Yizhaq (), Constantin Rein, Lior Saban, Noa Cohen, Klaus Kroy and Itzhak Katra
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Hezi Yizhaq: Department of Solar Energy and Environmental Physics, Blaustein Institutes for Desert Research, Sede Boqer Campus, Ben Gurion University of the Negev, Beersheba 8499000, Israel
Constantin Rein: Institute for Theoretical Physics, Leipzig University, Brüderstr. 16, 04103 Leipzig, Germany
Lior Saban: Department of Environmental, Geoinformatics, and Urban Planning Sciences, Ben Gurion University of the Negev, Beersheba 8410501, Israel
Noa Cohen: Department of Environmental, Geoinformatics, and Urban Planning Sciences, Ben Gurion University of the Negev, Beersheba 8410501, Israel
Klaus Kroy: Institute for Theoretical Physics, Leipzig University, Brüderstr. 16, 04103 Leipzig, Germany
Itzhak Katra: Department of Environmental, Geoinformatics, and Urban Planning Sciences, Ben Gurion University of the Negev, Beersheba 8410501, Israel

Land, 2024, vol. 13, issue 2, 1-14

Abstract: We studied fairy circles 20 km west of Sesriem at one of the driest locations of fairy circles in Namibia, at the foot of the popular Sossusvlei dunes. These fairy circles lack the typical hexagonal order of the Namibian fairy circles. After years of drought, their pattern is more similar to that of vegetation rings, due to the sparse vegetation in the area between the circles. Cross-section measurements of the soil water content (SWC) show that the upper layer (12 cm) is very dry (~1%) and much below the wilting point of Stipagrostis ciliata grasses, whereas the deeper soil layer is wetter (4%). The grain size distribution of soil samples taken from inside and outside the fairy circles reveals considerable heterogeneity in the size fractions due to aeolian (wind-driven) sand sorting. The bare soil inside the fairy circles contains coarser grains, and the ground surface is covered by sand megaripples. There is a linear trend between the vertical soil moisture gradient and the median grain diameter. Fine particles trapped on the vegetated edges of the fairy circle result in small nebkhas that increase the soil water retention at the surface. The dry and loose coarser topsoil inside the fairy circles may prevent the recolonization of new seedlings with short root lengths inside the fairy circles. Our results highlight the role of aeolian sand transport and deposition in desert vegetation environments and seem to support the notion that fairy circle formation may be affected by the interplay between sand sorting and soil moisture gradients.

Keywords: fairy circles; grain size distribution; megaripples; hydraulic conductivity; soil water content; droughts; nebkhas (search for similar items in EconPapers)
JEL-codes: Q15 Q2 Q24 Q28 Q5 R14 R52 (search for similar items in EconPapers)
Date: 2024
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