Seasonal Patterns of Dry Deposition at a High‐Elevation Site in the Colorado Rocky Mountains

In the Colorado Rocky Mountains, high elevation barren soils are deficient in carbon (C) and phosphorus (P) and enriched in nitrogen (N). The seasonal variability of dry deposition and its contributions to alpine elemental budgets are critical to understanding how dry deposition influences biogeochemical cycling in high elevation environments. In this two-year study, we evaluated dry and wet deposition inputs to the Niwot Ridge Long Term Ecological Research (NWT-LTER) site in the Colorado Rocky Mountains. The total organic C flux in wet + dry (including soluble and particulate C) deposition was >30 kg C ha-1 yr-1 and represents a substantial input for this C-limited environment. Our side-by-side comparison of dry deposition collectors with and without marble insert indicated that the insert improved retention of dry deposition by ~28%. Annual average dry deposition fluxes of water soluble organic carbon (4.25 kg C ha-1 yr-1) and other water soluble constituents, including ammonium (0.16 kg NH4+ha-1 yr-1), nitrate (1.99 kg NO3- ha-1 yr-1), phosphate (0.08 kg PO43- ha-1 yr-1), and sulfate (1.20 kg SO42- ha-1 yr-1), were comparable to those in wet deposition, with highest values measured in the summer. Backward trajectory analyses implicate air masses passing through the arid west and Four Corners, USA as dominant source areas for dry deposition, especially in spring months. Synchronous temporal patterns of deposition observed at the NWT-LTER site and a distant Rocky Mountain National Park CASTNET site indicate that seasonal dry deposition patterns are regional phenomena with important implications for the larger Rocky Mountain region.