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Rue, Garrett P ¹ ; McKnight, Diane M ² ; Gabor, Rachel ³ ; Anderson, Suzanne P ⁴

¹ INSTAAR, ENVS; University of Å·ÃÀ¿Ú±¬ÊÓƵ-Boulder
² INSTAAR, CEAE, ENVS; University of Å·ÃÀ¿Ú±¬ÊÓƵ-Boulder
³ Department of Geology and Geophysics, University of Utah
⁴ INSTAAR, GEOG; University of Å·ÃÀ¿Ú±¬ÊÓƵ-Boulder

In September of 2013, upwards of 20 inches of rain fell across Boulder County within one week. It caused mass hillside erosion and landslides throughout the Front Range, as well as streamflow conditions congruent with a 100-year flood. This stochastic event further provided a unique opportunity to study its effect on biogeochemical watershed processes. As part of the continued monitoring of the Gordon Gulch headwater catchment by the Boulder Creek Critical Zone Observatory, the collection of water and soil samples here have allowed for long-term investigations regarding the formation of organic material within the regolith in addition to its fluvial transport. Observations of greater variability in dissolved organic matter (DOM) concentration and quality in Gordon Gulch compared to the higher order receiving stream Boulder Creek, suggests that at times the headwater stream is connected to the drainage from the upper saprolite [Burns 2014]. This coupled relationship can be further demonstrated by the pulse of high dissolved organic carbon (DOC) observed during early Spring snowmelt, which flushes out this near-surface soil organic matter (SOM) sourced from leaf litter breakdown as well as microbially-mediated alteration [Gabor et al 2014]. Given the implicit role of precipitation in connectivity of SOM into streams, with snowmelt providing the first flush of resident, interstitial organic matter, the purpose of this study is to elucidate the additional influence of an extreme hydrologic event on the mobilization DOM to its dynamic equilibrium state [Creed et al. 2015]. From samples collected in Boulder Creek across synoptic and temporal scales, processed through advanced chromatographic techniques and spectroscopic characterization, we seek to identify whether such large inputs of water additionally mobilize accumulated, recalcitrant DOM moieties through enhanced conductivity and deeper flushing of the soil/saprolite boundary. Furthermore, these findings could support the concept that similarly to stream morphology, such events also serve as an effective reset mechanism for terrestrial-aquatic biogeochemical linkages.

Creed, I.R, McKnight, D.M., Pellerin, B.A., Green, M.B., Bergamaschi, B.A.,Aiken, G.R., et al, 2015, The River as a chemosat; fresh perspectives on DOM flowing down the river continuum. Canadian Journal of Fisheries and Aquatic Sciences, v. 72, p. 1272-1285

Gabor,R., Eilers, K., McKnight,D.M., Fierer, N., Anderson, S.,2014, From the litter layer to the saprolite; Chemical changes in water-soluble soil organic matter and their correlation to microbial community composition: Soil Biology and Biochemistry v. 68, p. 166-176

Burns, M., 2014, Hillslope dissolved organic matter transport and transformation in a semi-arid headwater catchment: Masters Thesis, University of Å·ÃÀ¿Ú±¬ÊÓƵ Boulder