Miller, Matthew听1听;听McKnight, Diane听2听;听Borgnis, Evyan听3
1听INSTAAR, University of Colorado
2听INSTAAR, University of Colorado
3听University of San Francisco
The pulse of dissolved organic matter (DOM) that occurs during snowmelt in mountain catchments is associated with the flushing of DOM from soils and plant leachates. This flushing may be attenuated and/or the chemical character of the DOM may be altered by the presence of wetlands in the catchment. As summer progresses, the DOM in alpine lakes is also derived from autochthonous algal production. We studied the impact of an unusual 3-day mid-summer rainstorm on the biogeochemistry of DOM in an alpine lake in the Green Lakes Valley in the Colorado Front Range. The July 7th-9th, 2006 rain event produced 9 cm of precipitation and increased discharge from the lake 2.5 fold compared to peak snowmelt. Characterization of DOM by fluorescence spectroscopy, PARAFAC, and other methods shows that immediately following the rain event, the DOM fluorescence characteristics were reset to values similar to those observed during snowmelt. Then, in response to increased primary productivity, the DOM fluorescence indicated an increasing microbial contribution and a progressively more oxidized state of the fulvic acid quinones. Analyses of samples collected from an upstream wetland indicate that the wetland acts as a source of terrestrially derived reduced DOM throughout the season. Lake modeling results provide a quantitative measure of the relative contribution of in-lake and watershed derived DOM over the course of the growing season and attribute these sources to hydrologic and biological changes in the catchment.