Monday, September 19, 2011, 12:00PM - 1:00PM
ARC room 620
Alpine environments are often thought of as remote areas unaffected by direct human influence. However, there is much evidence that atmospheric deposition of pollutants, dust, nutrients, and other aerosols, both inorganic and organic, influences alpine areas. For example, aeolian transport delivers P, Ca, and other nutrients to oligotrophic alpine lakes and has been shown to have a fertilizing effect on phytoplankton in these systems. More recently, atmospheric deposition of organic carbon was found to have an important influence on dissolved organic matter (DOM) concentrations and optical properties in clear, alpine lakes globally. The potential for atmospheric deposition of nutrients and DOM to also influence terrestrial biogeochemical processes is a central question for our research in the barren alpine regions of Green Lake Valley, Niwot Ridge, CO. To assess this influence, we evaluated concentrations and loadings of organic and inorganic species in snow and in National Atmospheric Deposition Program (NADP) and NWT-LTER deposition collectors at Niwot Ridge.
Wet deposition was found to be a seasonally variable source of dissolved organic carbon (DOC), depositing roughly 1500 kg C to the Green Lake 4 (GL4) watershed. This input of DOC was equivalent to over 80% of the carbon yield from the watershed. Wet deposition loadings of nitrogen and phosphorus were also substantial compared to the yield of these constituents. Dry deposition represents another extremely important input of DOC, nitrogen, and phosphorus and appears to be the main input of calcium to the GL4 watershed.
Given that atmospheric DOM inputs are substantial, a key question now is whether this C source is labile and involved in microbial and biogeochemical processes in these barren soils. Characterization of DOM quality in wet and dry deposition by fluorescence and absorbance spectroscopy showed that in summer months, high concentrations of amino acid-like fluorescence were associated with large numbers of pollen and other bioaerosols. Further, the optical properties of DOM in atmospheric deposition reflect intense photobleaching of DOM, which may enhance its bioavailability.