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 is critical to understanding how dry deposition influences biogeochemical cycling in high-elevation environments. In this 2 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 similar to 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 Clean Air Status and Trends Network site indicate that seasonal dry deposition patterns are regional phenomena with important implications for the larger Rocky Mountain region. Plain Language Summary High-elevation environments are considered to be our pristine reference sites; however, these environments are rapidly changing due to climatic and other anthropogenic influences. In the Colorado Rocky Mountains, dust transport and transport of particulate pollutants from urban and agricultural areas may provide substantial inputs of carbon (C) and nutrients to alpine and other high-elevation environments. Although these inputs may have implications for water quality and ecosystem and human health, they have not been well documented. Our 2 year study of both dry and wet deposition inputs to a high-elevation site in the Colorado Rocky Mountains demonstrated that dry inputs were comparable to those in wet deposition, with highest values measured in the summer. The annual organic C input to the study site from the atmosphere was very high and was related to nutrient deposition from adjacent urban and agricultural areas. Spring dust transport with sources in the arid west and Four Corners, USA, also had a measurable influence on the deposition of C, nutrients, and calcium, and magnesium. Similar seasonal deposition patterns at our site and another distant Rocky Mountain site indicate that dry deposition is a regional phenomenon with important implications for the larger Rocky Mountain region.