Quantifying atmospheric dust deposition to the Colorado Front Range

Over recent decades, atmospheric dust deposition to the Colorado Rocky Mountains has been increasing, likely due to land use change and increasing aridity. Because dust is often enriched in organic carbon, phosphorus, and trace metals, increased rates of dust deposition can alter nutrient fluxes to aquatic and terrestrial ecosystems, which in turn can shift ecosystem productivity, structure, and function. In the alpine and subalpine zones of the Colorado Front Range (>3000 m), most of the dust deposited is likely derived from the Colorado Plateau. Ecosystems at lower elevations (1650-3000 m) are more proximal to anthropogenic sources of dust from agricultural and urban activity. Along this steep elevation gradient, differences in dust source may lead to variations in dust flux and composition that have the potential to modify the impact of dust deposition to different ecosystems. To quantify dust deposition and measure dust-derived nutrient inputs across all elevations of the Colorado Front Range, we have established an elevation transect of nine dust collection sites extending from the plains up through the foothill, montane, subalpine, and alpine ecosystems. At each site, we collect monthly precipitation and atmospheric dust samples using passive aeolian collectors. Monthly dust fluxes ranged from 2-30 g m^-2 yr^-1, with the highest fluxes recorded during the spring season at all sites along the elevation transect. Spatially, the foothills, montane, and subalpine ecosystems received higher dust fluxes than the alpine and plains ecosystems. Preliminary results suggest that dry deposition in the Colorado Front Range is enriched in phosphorus relative to average continental crust concentrations and contributes roughly 5 mg m^-2 yr^-1 of this limiting nutrient to the region. The foothills, montane, and subalpine ecosystems, where dust flux may be highest, could be subjected to disproportionate increases in nutrient and trace metal inputs due to dust deposition.