Dissolved Organic Matter and Iron Redox Reactions in an Alpine Wetland

The source and chemical character of dissolved organic matter (DOM) in mountain catchments is in part determined by the timing and extent of snowmelt. Another important factor controlling DOM chemistry in mountain catchments is the presence of landscape features such as lakes or wetlands. We studied the impact of a small alpine wetland on the biogeochemistry of DOM and iron in surface waters in the Green Lakes Valley in the Colorado Front Range. Dissolved organic carbon concentrations collected from soil lysimeters (~20 mg/L) in the wetland were 10-20 times greater than DOC concentrations in the surface waters entering and draining the wetland. Characterization of DOM by fluorescence spectroscopy, PARAFAC, and other methods shows that fulvic acid quinones with a microbial contribution (FI~1.5) were processed in the wetland before reaching the outlet; and that the reduced quinones produced in the wetland were transported to the downstream surface waters. Furthermore, high concentrations of dissolved iron in the wetland (1.82 mg/L) resulted in an increase in downstream surface water iron concentrations. However, the iron in the wetland, a more reducing environment, was mostly present as ferric iron; whereas the iron in the surface water samples was predominantly ferrous iron. This trend highlights the potential importance of the role of iron-DOM complexation in the wetland as well as photoreduction of iron in surface waters. These results indicate that the presence of small wetlands in alpine ecosystems can act as biogeochemical hotspots and have a disproportionately large impact on the biogeochemistry of downstream surface waters.