Daniel J. Brogan

Redistribution of pyrogenic carbon from hillslopes to stream corridors following a large montane wildfire

Pyrogenic carbon (PyC) constitutes a significant fraction of organic carbon in most soils. However PyC soil stocks are generally smaller than what is expected from estimates of PyC produced from fire and decomposition losses, implying that other processes cause PyC loss from soils. Surface erosion has been previously suggested as one such process. To address this, following a large wildfire in the Rocky Mountains (CO, USA), we tracked PyC from the litter layer and soil, through eroded, suspended, and dissolved solids to alluvial deposits along river sides. We separated deposited sediment into high- and low-density fractions to identify preferential forms of PyC transport, and quantified PyC in all samples and density fractions using benzene polycarboxylic acid markers. A few months after the fire, PyC had yet to move vertically into the mineral soil and remained in the organic layer or had been transported off site by rainfall driven overland flow. During major storm events PyC was associated with suspended sediments in river water, and later identified in low-density riverbank deposits. Flows from an unusually long-duration and high magnitude rain storm either removed or buried the riverbank sediments approximately one year after their deposition. We conclude that PyC redistributes after wildfire in patterns that are consistent with erosion and deposition of low-density sediments. A more complete understanding of PyC dynamics requires attention to the interaction of post-fire precipitation patterns and geomorphological features that control surface erosion and deposition throughout the watershed. Index Terms: Carbon Cycling, Soils, Biogeochemistry.

Spatio-temporal variability of snowpack properties: Comparing operational, field, and ICESat remote sensing data over Northern Colorado, United States

Snowpack properties vary spatially and temporally. Three snow depth datasets are evaluated to assess this variability across different scales: operational station data, auxiliary field measurements and remotely sensed estimates from the Geoscience Laser Altimeter System (GLAS) lidar instrument that was aboard the Ice, Cloud and land Elevation Satellite (ICESat). The variability is best illustrated by the field measurements; spatially concurrent snow-off and snow-on ICESat overpassed are rare so the satellite estimates are more approximate while integrating over much larger support or footprint. The operational data cover the least area; even the snowcourse transects measured over 100s of metres show limited variability.