Biogeomorphology of mega nebkha in the Fahraj Plain, Iran: Sensitive indicators of human activity and climate change

Abstract

The biogeomorphology of nebkha dunes, was investigated in the Fahraj Plain, which is located in southern part of the Lut Plain in southeastern Iran. Field investigations were performed to determine nature of nebkha dunes, whose genesis and growth involves the trapping of aeolian sand within the body of a plant. This study demonstrated that Tamarix , a shrub/tree in the Tamaricaceae family, has played a major role in reducing dust and sand storms in the region by trapping aeolian sediments and accumulating them in the form of nebkhas. In contrast, another tree/shrub that grows in the area, Prosopis cineraria (a variety of mesquite in the Fabaceae family), due to its structure seems not to have played an important role in aeolian sediment accumulation or in shaping any nebkha dunes in the area. Whereas previous investigations indicated that the highest nebkhas, which are located at the western margin of the Lut basin on the Takab plain, were no more than 12 m in height, our field investigations and measurements revealed that on the Fahraj plain there are nebkhas greater than 20 m in height. This would suggest that some of these nebkhas are among the largest and highest that have been reported in the world. Some were connected by rows of Tamarix and formed very long ridges more than 200 m in length. It seems that their form may be due to human activity. During our survey of nebkhas in the region we observed ongoing and increasing degradation in the nebkha field that we were examining. This seemed to be due to current climate variability and human impact. Investigation of the past climate of this region reveals that the Indian monsoon is and has been a major factor. Examination of this history also reveals the relationship between climate and sand movement in the region, and the inferred past history of nebkha dunes. Past analogue conditions from that history can provide a scenario of future nebkha evolution, and reveal if their current, ongoing degradation is a long-term trend or simply a short-term cycle.