Vegetation Scenarios to Improve the Conditions at the Desiccated Aral Seabed and to Reduce the Impacts of Sand and Dust Storms

Abstract

Although Central Asia has been exposed to sand and dust storms (SDS) due to the Kyzylkum and Karakum deserts, it is also the place of a most tragic environmental disaster of the 20th century: the drying out of the Aral Sea created the Aralkum desert that is considered a relatively new addition to the global hotspot SDS sources. The loss of Aral Sea transformed the surrounding environment into a vast area of bare land dominated by solonchak soils prone to further degradation and desertification. Consequently, the exposed saline sediments have become SDS sources across the region, causing negative impacts on multiple socio-ecological aspects. Recently, the government of Uzbekistan launched and further investigated various campaigns on planting adapted shrub and tree species to establish a robust rangeland ecosystem. This study aims to determine the effects of the vegetation-based options on protecting the erodible sediments from wind-induced movement and improving the local ecological conditions. Wind erosion depends on soil erodibility, selected plant species for out-planting, and vegetation cover succession that might develop. This study developed six vegetation cover scenarios to represent a broad spectrum of potential vegetation cover and stages, ranging from a bare surface (newly dried seabed) to dense vegetation cover conditions. Local 3-hourly wind speed data of the past 20 years was analyzed to define erosive wind events. Each vegetation cover scenario was used in the wind erosion simulation model to assess the impact of different covers on soil erosion. The simulation of the physical-based erosion model revealed critical wind speed thresholds of erosion initiation that most likely occur when wind velocities exceed 10-15 m/s. The erosion ranges linked to the exceedance of three hourly wind speeds of >= 15 m/s (class 1), >= 20 m/s (class 2), and >= 25 m/s (class 3), respectively, were investigated for the six clearly defined vegetation scenarios. The simulation unveils that dense vegetation covers of assorted trees, shrubs, and grasses could ultimately stop erosion, as locally verified through observations in scattered and well protected well-vegetated areas. A more likely and large coverage of a lower-density vegetation could reduce erosion by around 40%. Combining shrubs and potentially emerging grasses would reduce wind erosion by up to 70%. The study indicates that plantation and increasing vegetation cover could remarkably enhance SDS prevention. In addition, it would improve the local ecosystem services such as e.g. storing carbon and serving as potential feed sources for livestock, while preventing contaminated and saline dust from being transported to vulnerable off-site areas.