Charcoal Production from Agricultural Burning in Central Panama and its Deposition in the Sediments of the Gulf of Panama

Abstract

Widespread agricultural burning during the dry season in the Pacific watershed of Panama is an important ecological phenomenon. During that time over 10% of the land surface (woodlands and savannas) is burned annually, with the resulting production of large amounts of charcoal. The major portion of the charcoal remains on land, but 5% is mobilized by river runoff and winds to the sediments of the Gulf of Panama.The aeolian transport of particulate charcoal by the north-easterly Trade Winds has been monitored by dry-deposition and aerosol paniculate collectors. During the burning-season, atmospheric charcoal concentrations in rural Panama can be similar to urban concentrations in North America or Europe. More than 60% of the charcoal aerosol mass was carried as fine particles (< 2 urn diameter), suggesting that long-range transport is possible.Dry-deposition fluxes, which are positively correlated with the areal extent of land that is burned, are more than an order of magnitude less than the charcoal fluxes to the uppermost near-shore sedimentary deposits in the Gulf of Panama. This implies that aeolian transport is not the principal mechanism of charcoal mobilization to these sediments. The extremely high runoff per unit area in the Gulf of Panama watershed is probably responsible for the predominance of continental runoff as the charcoal transport mechanism in the region.Being relatively indestructible, charcoal can also be used as a tracer for past burning activities. Sediment box-cores have been recovered from the Gulf of Panama, and Pb-210 geochronologies were utilized to determine sedimentation rates. The charcoal particles were isolated by chemical methods and their fluxes, size-distributions, and morphologies, were analysed. The relative uniformity of these measurements in the marine sediment geochronologies indicates stability of burning patterns in central Panama during the last two centuries.