Â鶹ÊÓƵ

Gabor, Rachel ¹ ; McKnight, Diane ²

¹ University of Colorado-Boulder
² University of Colorado-Boulder

The increasing concentrations of dissolved organic matter observed in many northern latitude regions have potentially significant effects on both ecosystem dynamics and water treatment processes. Many hypotheses for the cause of this change in aquatic concentrations are dependent on changes in catchment processes. Thus, to better understand the dynamics of dissolved organic matter, it is important to elucidate the connection between soluble organic matter in soil and dissolved organic matter in associated streams, with a particular focus on the chemical character of each organic matter pool. In this study, fluorescence spectroscopy has been used to characterize the water-soluble organic matter in the soil of a first-order catchment within the Boulder Creek watershed. Soil samples were collected with an aim to identifying both spatial and temporal patterns in the soil, as well as comparing extraction techniques. Eight soil plots were selected on north-facing and south-facing slopes as well as in the riparian zone and weekly samples were taken from each plot beginning during snowmelt and continuing through mid-summer. Each sample was leached with water and potassium sulfate, as described in Jones and Willet, to compare leaching methods as well as slope location. Samples leached with water showed a generally lower humification index, freshness index, and fluorescence index and a slightly higher redox index and protein content than samples leached with potassium sulfate, indicating the two methods do leach different pools of organic matter. Little variation was found temporally, however, there was a noticeable difference in DOM quality between north- and south-facing slopes and the riparian zone. The moister, more vegetated, north-facing slope has a more advanced weathering profile and longer-lived snowpack, and the organic matter had a younger, more microbially-dominated signal with more reduced character compared to the south-facing slope. By placing these signals into the scope of the larger watershed and comparing them to correlated aquatic samples, it should be possible to develop a clearer picture of the role of terrestrial inputs to dissolved organic matter dynamics and how first order catchments influence larger watersheds.

Monteith D, Stoddard J, Evans C, de Wit H, Forsius M, Hogasen T, Wilander A, Skjelkvale B, Jeffries D, Vuorenmaa J, Keller B, Kopacek J, Vesely J., 2007, Dissolved organic carbon trends resulting from changes in atmospheric deposition chemistry: Nature, v. 450, p. 537-540.

Porcal P, Koprivnjak J, Molot L, Dillon P., 2009, Humic substances—part 7: the biogeochemistry of dissolved organic carbon and its interactions with climate change: Environ. Sci. Pollut. Res, v.16, p.714-726.

Jones DL, Willett VB., 2006, Experimental evaluation of methods to quantify dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) in soil, Soil Biology & Biochemistry, v. 38, p.991-999.