QUANTIFYING CHARCOAL BUDGETS IN STEEPLAND WATERSHEDS: FIELD MEASUREMENTS AND MODELING OF COUPLED SEDIMENT-CHARCOAL TRANSPORT AND STORAGE IN THE OREGON COAST RANGE

Charcoal storage and transport may play an important role in the carbon cycle in steeplands such as the Oregon Coast Range. Charcoal is stored for 10⁰ -10³ yr in sediment located in various landscape “reservoirs” (e.g., hillslopes, colluvial hollows, valley floor fluvial and debris flow deposits) in steepland watersheds. Surface processes (e.g., soil creep, debris flows, fluvial transport) move this charcoal to downslope reservoirs. The objectives of this research are to: 1) quantify charcoal’s residence time in valley floor deposits (i.e., the lowest reservoirs) and its cumulative residence time in reservoirs upslope of them (the latter time represents an unquantified error when radiocarbon dating charcoal sampled from valley floor deposits); and, 2) constrain residence times in each of these upslope reservoirs. We outline the significant charcoal transport processes and storage reservoirs in the Range. We estimate volumes of wildfire-produced charcoal using previous studies, and measure volumetric concentration of charcoal in sediments in various reservoirs located in uncut forests of the Range. Residence times of charcoal in valley floor deposits and its cumulative residence times in reservoirs upslope of them, are measured via radiocarbon dating ~200 charcoal samples. A coupled sediment-charcoal transport and storage model, using numerous studies that constrain the sediment storage and transport budget in the Range, further constrains volumetric concentrations and residence times of charcoal in the upslope reservoirs. Preliminary results indicate that charcoal remains in valley floor deposits for ~10³ yr on average, about 20% of this charcoal remained in upslope reservoirs for > 10³ yr, and >90% of charcoal passes out of the system in <10² yr.