Dust Emission from Wet and Dry Playas in the Mojave Desert, USA 1811 Published in 2007 by John Wiley & Sons, Ltd. Earth Surf. Process. Landforms 32, 1811–1827 (2007) DOI: 10.1002/esp Earth Surface Processes and Landforms Earth Surf. Process. Landforms 32, 1811–1827 (2007) Published online 19 April 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/esp.1515 Dust Emission from Wet and Dry Playas in the Mojave Desert, USA † Richard L. Reynolds, 1 * James C. Yount, 1 Marith Reheis, 1 Harland Goldstein, 1 Pat Chavez, Jr., 2 Robert Fulton, 3 John Whitney, 1 Christopher Fuller 4 and Richard M. Forester 1 1 U.S. Geological Survey, Denver, CO, USA 2 U.S. Geological Survey, Flagstaff, AZ, USA 3 California Desert Studies Consortium, California State University Fullerton, Baker, CA, USA 4 U.S. Geological Survey, Menlo Park, CA, USA Abstract The interactions between playa hydrology and playa-surface sediments are important fac- tors 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. Published in 2007 by John Wiley & Sons, Ltd. Keywords: dust; playa; evaporite minerals; Mojave Desert; wind erosion *Correspondence to: Richard L. Reynolds, U.S. Geological Survey, Box 25046, MS 980, Denver, CO 80225, USA. E-mail: rreynolds@usgs.gov † This article is a U.S. Government work and is in the public domain in the U.S.A. Received 14 July 2006; Revised 30 January 2007; Accepted 19 February 2007 Introduction The growing recognition of the importance of dust for global climate, air quality with respect to visibility and human health, the fertilization of marine and terrestrial ecosystems, transportation and indications of desertification has spawned many recent efforts to locate sources of dust (e.g. Prospero et al., 1981; Goudie and Middleton, 2001; Middleton and Goudie, 2001; Prospero et al., 2002; Ginoux and Torres, 2003; Mahowald et al., 2003; Washington et al., 2003). Continued advances in understanding dust emissions and the ability to forecast locations and amounts of dust emission depend on better understanding of the geologic and hydrologic processes that promote or suppress emission from source areas. As one type of source, playas (also known as dry lakes) have been associated with dust emission (see, e.g., Blackwelder, 1931; Young and Evans, 1986; Pye, 1987; Rosen, 1994; Wood and Sanford, 1995; Gill, 1996; Goudie and Middleton, 2001; Yechieli and Wood, 2002; Prospero et al., 2002; Bryant, 2003; Washington et al., 2006). The aim of this paper is to show that different processes control fundamentally different amounts and compositions of dust emitted from two distinct types of playa – the wet playa and the dry playa. The Mojave Desert in southern California (USA) offers the opportunity to examine both types of playa under conditions of minimal to extensive human disturbance. Repeated ground-based and satellite observations of wet and dry playas in the Mojave Desert between 2000 and 2005, along with previous hydrologic studies (Czarnecki, 1997), provide the basis for this report. These observations reveal that surface sediments at three wet playas (Franklin Lake, Soda Lake and West Cronese