Logging effects on sediment flux observed in a pollen-based record of overbank deposition in a northern California catchment

摘要

A palynological approach was used to estimate overbank deposition rates in a forested catchment affected by logging. The palynological approach uses downcore variations in total fossil pollen and fossil pollen assemblage to calculate rates of overbank deposition and has a distinct advantage over radioisotopic approaches in that it is not limited by radioactive decay. Using this approach, we determined that overbank deposition rates increased over 400 per cent within years or logging events and that the increased rates persisted for less than 4 years. After logging-induced deposition peaked, overbank deposition decreased over 60 per cent relative to the pre-logging background values. The decreased deposition rates persisted for over 40 years. The immediate effect of logging in this catchment was to induce mass-wasting events in hollows that produced rapidly travelling sediment pulses. In the subsequent recovery period, reduced sediment loading occurred as a result of a reduction in the volume of sediment available for transport. The reduction in sediment load led to a reduction in overbank deposition rates until subsequent logging disturbances destabilized and emptied other hollows. Copyright (C) 2005 John Wiley & Sons, Ltd.