Characterization And Spatial Distribution Of Particulate And Soluble Carbon And Nitrogen From Wildfire Impacted Sediments
Cawley, Kaelin M 1 ; Hohner, Amanda K 2 ; McKee, Georgina A 3 ; Borch, Thomas 4 ; Omur-Ozbek, Pinar 5 ; Oropeza, Jill 6 ; Rosario-Ortiz, Fernando 7
1 National Ecoloogical Observatory Network (NEON)
2 University of Colorado at Boulder
3 Colorado State University
4 Colorado State University
5 Colorado State University
6 City of Fort Collins
7 University of Colorado at Boulder
The heavily forested Cache la Poudre (CLP) watershed in northern Colorado (USA) was impacted by the High Park wildfire in 2012. The wildfire burned land and vegetation immediately adjacent to the CLP River. Along the CLP River, blackened, ashy sediment samples were collected from five sites upstream of the City of Fort Collins drinking water intake to evaluate the spatial distribution and heterogeneity of burned sediments. At each site samples were collected from three locations: 1) the edge of the bank adjacent to the water edge; 2) 1 meter upslope of location 1; and 3) 2 meters upslope of location 1. All solid sediment samples were analyzed for elemental composition and a subset of solid sediment samples were analyzed with 13C solid state nuclear magnetic resonance (NMR) spectroscopy. Sediments were mixed with CLP River water collected from upstream of the wildfire (site PBR) and allowed to leach for 6 and 24 hours to determine the quantity and quality of water soluble organic matter. Filtered samples were analyzed for dissolved organic carbon (DOC), iron, manganese, and inorganic nutrient concentrations. In addition, dissolved organic matter (DOM) was characterized by optical properties (absorbance and fluorescence) and for disinfection byproduct (DBP) formation. Percent carbon and nitrogen content of the solid sediments were good predictors of leachate DOC concentration. The mean fluorescence index was higher for wildfire impacted sediment leachates (1.50) compared to background CLP River water (1.37) which may be due to changes in DOM molecular weight and oxidation of organic matter. All sediment leachates showed consistently higher haloacetonitrile and chloropicrin yields (DBP concentration/DOC concentration) compared to background CLP River water, whereas carbonaceous DBPs did not. Results suggest hydrology is an important factor in the spatial distribution of burned sediments and that wildfire induced changes to nitrogen species, including dissolved organic nitrogen concentration and characteristics, which may be important for the formation of DBPs.