HR: 1330h
AN: C42A-1013    [PDF]
TI: Use of fluorescence spectroscopy to detect the seasonal change in the redox state of dissolved organic matter in Nymph Lake, Rocky Mountain National Park, CO
AU: * Cory, R M
EM: rose.cory@colorado.edu
AF: Institute of Arctic and Alpine Research at the University of Colorado, Boulder, 1560 30th St, Boulder, CO 80309 United States
AU: McKnight, D
EM: diane.mcknight@colorado.edu
AF: Institute of Arctic and Alpine Research at the University of Colorado, Boulder, 1560 30th St, Boulder, CO 80309 United States
AB: Fluorescence spectroscopy was used to examine the redox state and chemical character of dissolved organic matter (DOM) in Nymph Lake, a seasonally ice-covered lake in Rocky Mountain National Park, CO. Water samples were collected monthly beneath the ice from December through April during the 2002/2003 winter and spring seasons. A sample was also collected in June when the lake was ice free and well mixed. Excitation-Emission Matrices (EEMs) of filtered, whole water samples shifted in a manner consistent with laboratory reduced fulvic acid (Klapper et al. 2002) as the winter season progressed. The EEMs from December through March showed a pattern of decreasing intensity and disappearance of the two peaks in region A and C (peaks labeled according to Coble et al. 1990). The April EEM showed an increase in intensity and reappearance of the two peaks, suggesting some oxidation had occurred. The two peaks in region A and C had the highest intensities in the June EEM, suggesting further oxidation and/or input of oxidized DOM during snowmelt. Titration with ferric citrate of the reduced March and partially reduced April samples resulted in an increase of ferrous iron concentration proportional to the amount of ferric iron added. Furthermore, titration with ferric citrate caused a shift in the March and April EEMs; peaks in regions A and C reappeared in the March sample and the intensities of those peaks were increased in the April sample. An increase in ferrous iron concentration with a simultaneous shift in the EEMs upon addition of ferric iron provide compelling evidence that redox-active moieties of DOM serve as electron shuttles for microbially mediated ferric iron reduction under the ice in Nymph Lake. Trends in dissolved oxygen, ferrous and ferric iron concentration, and Eh potential under the ice provided additional evidence for microbially mediated reduction of Nymph Lake DOM. Lastly, the EEMs from this study clearly show that the redox-active moieties of DOM, quinones (Scott et al. 1998), are largely responsible for the fluorescent character of Nymph Lake DOM, and likely contribute to the fluorescence of DOM from many environments.
DE: 0330 Geochemical cycles
DE: 0400 Biogeosciences
SC: Cryosphere [C]
MN: 2003 Fall Meeting