Controls on sediment production in two U.S. deserts Jayne Belnap a,⇑ , Beau J. Walker b , Seth M. Munson a , Richard A. Gill b a United States Geological Survey, Southwest Biological Science Center, Moab, UT 84532, USA b Department of Biology, Brigham Young University, Provo, UT 84602, USA article info Article history: Available online xxxx Keywords: Wind erosion Biological soil crusts Soil protection Disturbance Drylands abstract Much of the world’s airborne sediment originates from dryland regions. Soil surface disturbances in these regions are ever-increasing due to human activities such as energy and mineral exploration and develop- ment, recreation, suburbanization, livestock grazing and cropping. Sediment production can have signif- icant impacts to human health with particles potentially carrying viruses such as Valley Fever or causing asthma or other respiratory diseases. Dust storms can cause decreased visibility at the ground level, resulting in highway accidents, and reduced visual quality in park and wildland airsheds. Sediment pro- duction and deposition is also detrimental to ecosystem health, as production reduces soil fertility at its source and can bury plants and other organisms where it is deposited. Therefore, it is important to under- stand how we can predict what areas are prone to producing sediment emissions both before and after soil surface disturbance. We visited 87 sites in two deserts of the western U.S. that represented a range of soil texture and surface cover types. We used a portable wind tunnel to estimate the threshold friction velocity (TFV) required to initiate sediment transport and the amount of sediment produced by the tun- nel at a set wind speed. Wind tunnel runs were done before and after soil surface disturbance with a four- wheel drive vehicle. Results show that most undisturbed desert soils are very stable, especially if covered by rocks or well-developed biological soil crusts, which make them virtually wind-erosion proof. Particles at disturbed sites, in contrast, moved at relatively low wind speeds and produced high amounts of sed- iment. Silt was an important predictor of TFV and sediment production across all sites, whereas the influ- ence of rock cover and biological soil crusts was site-dependent. Understanding the vulnerability of a site after disturbance is important information for land managers as they plan land use activities and attempt to mitigate the harmful effects that sediment production can have on both human and ecosystem health. Ó 2014 Published by Elsevier B.V. 1. Introduction Researchers have long sought to understand the interacting processes that control the entrainment, transport, and deposition of wind-borne sediments (Bagnold, 1941; Chepil, 1951, 1953; Ravi et al., 2011). Initially, this research was motivated by a desire to understand the geomorphic and erosion processes associated with agriculture (Chepil, 1951, 1953). This research has been rein- vigorated as it has become clear that airborne sediments strongly influence soil fertility, planetary energy balance (Goudie and Middleton, 2001; Goudie, 2008; Ravi et al., 2011), snow surface albedo and thus melt rates on downwind mountain snowpack (Painter et al., 2010, 2012a,b). Human health and safety is of major concern, as airborne sediments can have significant impacts (Kellogg and Griffin, 2006; Griffin, 2007). Particles can carry viruses such as Valley Fever and incidences of this disease are increasing at an alarming rate in the SW United States. Many of the particle sizes can be inhaled and lodge in the lungs, causing asthma, other respi- ratory diseases, or even cancer. Dust storms can also cause decreased visibility, resulting in highway accidents. Airborne parti- cles also compromise resources in areas such as National Parks, where clean air is of great value. However, as the diverse processes that control sediment emission from the micron to planetary scale are synthesized, there are frequent contradictions and uncertain- ties across landforms that span diverse geological and biophysical conditions. An initial understanding of aeolian processes begins with the examination of competing forces. On one hand, aerodynamic forces from wind pick up and entrain sediment. These forces are offset by gravitational forces that inhibit movement of large particles and inter-particle forces that keep finer soil particles bound together. Because of the cohesive forces between fine particles, additional force is necessary to release sediment; sandblasting from saltating particles or compressional disturbances (e.g., vehicles) that disrupt soil aggregates are the most efficient modes of entrainment http://dx.doi.org/10.1016/j.aeolia.2014.03.007 1875-9637/Ó 2014 Published by Elsevier B.V. ⇑ Corresponding author. E-mail address: jbelnap@usgs.gov (J. Belnap). Aeolian Research xxx (2014) xxx–xxx Contents lists available at ScienceDirect Aeolian Research journal homepage: www.elsevier.com/locate/aeolia Please cite this article in press as: Belnap, J., et al. Controls on sediment production in two U.S. deserts. Aeolian Research (2014), http://dx.doi.org/10.1016/ j.aeolia.2014.03.007