McKnight, D. M., University of Colorado, Boulder, USA,
Miller, M. ., University of Colorado, Boulder, USA,
Chapra, S. ., Tufts University, Somerville, USA,
Williams, M. ., University of Colorado, Boulder, USA,
Borgnis, E. ., San Francisco State University, San francisco, USA,


The chemical character of dissolved organic matter (DOM) in alpine lakes changes seasonally. In Green Lake 4, an alpine lake in the Rocky Mountains, DOM from shallow soils and wetlands is flushed into the lake during snowmelt. During summer, phytoplankton growth is an in-lake DOM source with distinct chemical characteristics. Further, photochemical transformation may change the chemical quality of lake DOM. An unusual sustained mid-summer rainstorm in 2006 flushed wetland DOM into Green Lake 4 and provided an opportunity to study photochemical transformation of DOM. In the nearby wetland, the DOC concentrations in lysimeter samples were ~20 mg/L, much greater than in the lake. Characterization of DOM by fluorescence spectroscopy, PARAFAC, and fractionation methods provided measures of DOM source and redox state. We found that reduced fulvic acid quinones were produced in the wetland and transported downstream. We used a lake mixing model based on 18O as a conservative tracer to evaluate the in-lake change in humic DOM following snowmelt and the mid-summer rainstorm. Comparison of predicted humic DOM with measured concentrations showed that substantial degradation occurred. The humic DOM remaining in the lake became progressively more oxidized, suggesting photochemical transformation as an important process. The loss of humic DOM in the lake influences the light regime and potentailly the structure and function of the alpine lake ecosystem.

Oral presentation

Presentation is given by student: No
Session #:SS01
Date: Friday, June 13, 2008
Time: 3:00 PM

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