Controls on Charcoal Distribution in Lake Sediments: Case Studies from Yellow-stone National Park and Northwestern Minnesota

Summary

The identification of past fires from sedimentary charcoal requires information on the processes that transport and deposit charcoal into lakes. Two case studies are presented that describe the taphonomy of lake-sediment charcoal. In Yellowstone National Park, charcoal accumulation was measured in eight lakes during the five years following large fires in 1988. Lakes in burned and unburned watersheds received charcoal as airborne fall-out during the fire, and secondary charcoal was transported from the littoral zone in subsequent years. In the fifth year, sites within burned watersheds accrued more charcoal in deep water than those within unburned watersheds. The lag before clear registration of a fire signal suggests that charcoal peaks in the stratigraphie record represent several years of sediment accumulation. At Elk Lake, Minnesota, sediment-trap studies and a transect of surface samples revealed that charcoal deposition in deep water occurred during times of strong spring circulation, when charcoal and other allochthonous material were moved from the littoral to the profundal zone. The transport mechanisms within the lake were not related to the fires that produced the charcoal. A record of sedimentary charcoal from Elk Lake showed that intervals with abundant charcoal generally coincided with decades of regional drought and burning. Both case studies demonstrate the importance of understanding charcoal depositional processes as an important step in fire history investigations.