Elevated Rangeland Dust Emissions Threaten Ecosystem Services with Continued Grazing and Vehicle Disturbance and Increasing Drought.

Measured dust fluxes between 2004 and 2015 in rangelands and adjacent to unsurfaced roads in a dryland region of the southwestern US highlight unsustainable wind erosion rates. Empirical spatial modeling of road and rangeland emissions revealed that rangelands are producing at least 92-93% of regional dust and roads only 7-8%. Measured ‘hot spots’ in rangeland flux rival the highest ever recorded including 7,460 gm^-2day^-1 (spring 2009) in an off-highway vehicle (OHV) area, but were more commonly 50-2,000 gm^-2day^-1  in areas with heavy grazing or OHV use throughout the period of record. During average flux years, the overall mean rangeland flux was 5.71 gm^-2day^-1, which is considerably lower than heavily grazed areas (~8-20 gm^-2day^-1) and OHV areas (414 gm^-2day^-1), but still corresponds to an unsustainably high estimated soil loss rate (1.2 mm yr^-1 under assumption that horizontal flux at 1m height represents emissions). In contrast, an area monitored with minimal disturbance averaged 1.60 gm^-2day^-1 (0.34 mm yr^-1). Annual dust flux values on all rangeland land use types (light/no grazing, heavily grazed, and OHV) were associated with climate variables with flux generally rising with increased annual temperature, increased winds, and decreasing precipitation. Road sites averaged 30.7 gm^-2day^-1 with a maximum observed seasonal flux of 299.5 gm^-2day^-1 along a producing oil well access road. Four of the five highest road flux values (n=33 total) measured were adjacent to roads primarily used to access oil or gas well-pads, while one was a popular recreational road that also provides access to oil and gas developments. These findings suggest that predicted future regional mega-droughts may increase dust emissions already elevated due to land management, potentially further compromising air quality, hydrologic cycles, and other ecological services effected by dust.