WOOD AND CARBON EXPORT VIA LANDSLIDES AND FLOODS ON THE UPPER RIO CHAGRES, PANAMA (Invited Presentation)

Recent attempts to quantify the different components of the global carbon cycle highlight the role of rivers, and our relative ignorance of the details of this role. Relatively small, mountainous rivers are closely coupled to terrestrial carbon sources. Carbon export by these rivers is particularly responsive to extreme events such as storms that create landslides and floods. Our work on the 414 km² Upper Rio Chagres catchment in central Panama since 2002 has facilitated observation of how wood and carbon exports vary through time in response to extreme storms. Widespread intense rainfall over the Upper Chagres during Dec. 2010 triggered extensive landslides and a large flux of wood to Lake Alhajuela, a reservoir formed by construction of Madden Dam in 1934. We took continuous videos during helicopter flights along the Upper Chagres in February and June 2011, and used these to tally wood stored along the lakeshore and within the channel, and landslides reaching the channel. We then used these tallies, in connection with ground-calibrated values of average wood piece size and landslide surface area, and assumptions regarding wood density, carbon content, and aboveground biomass, to develop a first-order estimate of wood and carbon export during the 2010 storm. Based on the wood tallies, we estimate carbon export of 34 + 8.5 Mg C/km². Based on the landslide tallies, we estimate carbon export of 24-32.5 Mg C/km². These are conservative estimates that are an order of magnitude smaller than estimates for background carbon export from small, non-mountainous catchments in the southern Amazon and Puerto Rico, and two orders of magnitude smaller than event-based estimates for carbon export from catchments in Taiwan during Typhoon Morakot.