Rivers and streams draining active mountain terrains are known to transport an amount of sediment and chemical weathering products that is disproportionately large compared to the amount of land area occupied by active mountain terrains on the earth’s surface. SuchThese high rates of material transport are attributed to the high rates of physical erosion that accompany active mountain building events. Physical erosion mobilizes particulate material, including organic carbon, and can expose un-weathered bedrock to atmospheric weathering. Chemical weathering in active mountain terrains plays a significant role in the global carbon cycle and thus plays a role in global climate change over geologic time scales by removing CO2 from the atmosphere. The relationship between CO2 and climate has been illustrated, as has the theory that current atmospheric CO2 concentrations will result in global climate change. It is critical that carbon fluxes from the atmosphere be quantified in order to better understand the mechanisms controlling atmospheric CO2 concentrations.
Natural mechanisms controlling atmospheric CO2 concentrations vary regionally, and so it is important that CO2 yields from watersheds in previously unstudied actively uplifting regions be quantified and controls on these yields elucidated. Here, CO2 yields from watersheds draining the Sierra de las Minas in Guatemala are quantified. These yields are similar to the high yields observed in other active mountain regions worldwide and underscore the importance of these areas in the global carbon cycle and global climate forcing. In addition, this study also supports the positive relationship between annual precipitation and chemical yields that has been observed elsewhere. This relationship may be influenced by mountain uplift causing local orographic increases in precipitation.
Extreme storm events such as typhoons and hurricanes have been shown to transport a large percentage of annual particulate organic carbon yields. This transport of particulate organic carbon can be a sink of atmospheric CO2 if it can be buried and removed from the atmosphere before it is consumed and oxidized. In 1998, Hurricane Mitch triggered widespread landslide activity throughout the Sierra de las Minas that mobilized material, including particulate organic carbon. Here, relationships among carbon and nitrogen concentrations and δ13C in streambed sediments and shale were used to speculate on the fate of material mobilized by landslides during Hurricane Mitch. These speculations are supported by satellite observations made immediately following Hurricane Mitch that map the extent of landslide scours. It is speculated herein that much of the landslide transported organic carbon was efficiently removed from the fluvial-hillslope interface and buried. These speculations are supported by the noted importance of event controlled carbon export in regional organic carbon yields.