Wildfires are known to chemically transform soil and plant material.  However, few, if any, studies have focused on the concentration and character of dissolved and particulate organic matter (DOM/POM) derived from this heated soil and biomass that is mobilized into water bodies following wildfires.  The main objective of this study was to evaluate the concentration and character of DOM and POM in a river upstream and downstream of a burned area. Samples were collected from three sites within the watershed: a control site located upstream of the burned area and two sites which were categorized as fire-impacted. Samples were collected bi-weekly during spring snowmelt and summer (April through August, 2013), monthly for the fall of 2013 and during select storm events (PNF site only). POM was extracted from glass fiber filters with NaOH.  Samples were analyzed for general water quality parameters and DOM/POM character, including fluorescence, UV-visible absorbance, and size exclusion chromatography (SEC).  Minimal differences in DOC concentrations were observed between the control and impacted sites, suggesting that wildfire did not significantly alter DOC concentration. However, POM concentrations were much higher at the impacted sites than the control site during snowmelt.  A measure of DOM character, the fluorescence index (FI), was higher for burned versus unburned sites.  Though, the seasonal variability in FI was greater than the variability between the control and wildfire impacted sites. SEC showed little difference between the control and impacted sites for a given sampling date, but showed clear seasonal trends with average molecular weight increasing at the onset of spring snowmelt (indicated by a shift to shorter retention times) and then decreasing as the spring progressed.  During storm events DOC concentration increased relative to baseflow or snowmelt.  Overall, our findings suggest a decoupling of DOM and POM sources in the watershed.

Concentration and character of particulate and dissolved organic matter mobilized following a wildfire

248th National Meeting (2014)

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