Dust emission from wet and dry playas in the Mojave Desert, USA

Abstract

The interactions between playa hydrology and playa-surface sediments are important factors that control the type and amount of dust emitted from playas as a result of wind erosion. The production of evaporite minerals during evaporative loss of near-surface ground water results in both the creation and maintenance of several centimeters or more of loose sediment on and near the surfaces of wet playas. Observations that characterize the texture, mineralogic composition and hardness of playa surfaces at Franklin Lake, Soda Lake and West Cronese Lake playas in the Mojave Desert (California), along with imaging of dust emission using automated digital photography, indicate that these kinds of surface sediment are highly susceptible to dust emission. The surfaces of wet playas are dynamic -surface texture and sediment availability to wind erosion change rapidly, primarily in response to fluctuations in water-table depth, rainfall and rates of evaporation. In contrast, dry playas are characterized by ground water at depth. Consequently, dry playas commonly have hard surfaces that produce little or no dust if undisturbed except for transient silt and clay deposited on surfaces by wind and water. Although not the dominant type of global dust, salt-rich dusts from wet playas may be important with respect to radiative properties of dust plumes, atmospheric chemistry, windborne nutrients and human health. Lake playas) in the Mojave Desert are dynamic and at times are vulnerable to wind erosion and dust emission when sufficiently soft and (or) loose. Surface sediments at dry playas, on the other hand, are typically stable and hard and thus generally do not emit large amounts of dust when undisturbed by human activities. The emphasis of this report is on the hydrologic and sedimentologic interactions that may sustain dust production from wet playas. Wet and Dry Playas -Definitions and CharacteristicsPlayas vary greatly in their geologic and hydrologic settings, leading to several classification schemes that group playas by sedimentologic or hydrologic characteristics (summarized by Smoot and Lowenstein, 1991;Rosen, 1994;Gill, 1996). With respect to dust emission from playas, we find useful the distinction between 'wet ' and 'dry' playas (see Rosen, 1994). In a wet playa, ground water is near (typically <5 m) or at the playa surface, through which it is lost by evaporation or fluid outflow (Figure 1(a)). In a dry playa, ground water does not interact with the surface because the water table lies far below the surface (typically >5 m; Figure 1(b)). Both wet and dry playas may receive surface-water runoff.The different hydrological and hydrochemical processes operating at wet and dry playas produce very different surfaces and surficial sediments (see, e.g., Thompson

Analyses of Recent Sediment Surface Dynamic of a Namibian Kalahari Salt Pan Based on Multitemporal Landsat and Hyperspectral Hyperion Data

“…The mineralogical data published by [27] were sampled in 1991 and 1992. During this >20 year time frame the surface alteration, e.g., by redistribution of surface particles due to surface flooding [15] and or wind erosion [9] are possible scenarios. The formation of fresh halite crust after significant rainfall and flooding events may superimpose underlying less soluble (e.g., clastic) minerals [110] and hide these (minor) components from surface observations, especially in the central halite dominated, dynamic part of the salt pan.…”

“…Although the area of individual salt pans is small, mostly less than a few square kilometers, except for prominent examples such as Salar de Uyuni (Bolivia) or Etosha pan (Namibia), the study of salt pan is important because of increasing population, agricultural demand and the hydrology of these dry regions becoming greatly stressed [4]. Salt pans are also one of the biggest sources of mineral dust emission in arid regions [5,6] especially in the southern Africa Kalahari desert (Botswana, Namibia, and Republic of South Africa) [7] and the specific salt pan mineralogy influences the susceptibility for dust emission [8][9][10]. For continued advances in understanding dust sources a spatially and temporally detailed assessment of their surface sediments is necessary [11].…”

Anthropogenic dust emissions due to livestock trampling in a Mongolian temperate grassland

“…The higher diversity of dust fluxes presents morphological disparity and sedimentological diversification in test areas. That dust emissions are highly variable with space and between distinct landforms, even within individual landforms, may be caused as a result of aeolian processes (Gill, 1996;Reynolds et al, 2007). It may also be related to dust fluxes not coming from a similar saturation from a field site (Gillette and Passi, 1988).…”

Dust: Small‐scale processes with global consequences

“…Though many dry and drying lakes, whether natural (e.g., Australia's Lake Eyre, Chad's Bodélé Depression) or manmade (e.g., California's Owens Dry Lake, central Asia's Aral Sea), are significant sources of dust, research has shown that not all dry lakes are dust sources or, at least, not all the time [Reynolds et al, 2007]. One consequence of this generalization is the notion that nonlake sources are not significant.…”