The transfer of modern organic carbon by landslide activity in tropical montane ecosystems

Abstract

Geomorphic processes play an important role in the transfer and storage of carbon within steep mountainous terrain. Among these, mass wasting stands out because of its impact on above-and below-ground carbon pools and its potential for releasing or sequestering carbon. A combined remote-sensing and GIS modeling approach was used to quantify the amount and spatial redistribution of modern organic carbon mobilized by mass wasting activity in a tropical mountain setting. The study focused on a population of hundreds of shallow, translational landslides triggered by Hurricane Mitch (1998) on seven watersheds draining the southern flank of the Sierra de Las Minas mountain range (SLM) in central-eastern Guatemala. Results illustrate that mass wasting contributed to the transfer of 43 × 10 4 MgC, or 3%, of the pre-event C in above-ground vegetation and soils for an equivalent carbon flux rate of 0.08-0.33 MgC ha -1 y -1, depending on whether we consider Hurricane Mitch to be a landslide-triggering event with a 20-year or an 80-year recurrence interval. While 30% of this carbon was delivered to hillslopes or first-order streams with a presumed high potential for long-term sequestration, the remaining 70% was delivered to higher-order streams with unknown carbon retention capabilities. Therefore, the ultimate fate of the carbon released by landsliding is very uncertain, but depending on the proportion sequestered by colluvial deposits, the recurrence interval of landslide-triggering events, and the rate of ecosystem recuperation at the landslide failure sites, mass wasting could be either a net source or sink of carbon. In a simulated setting based on the SLM study results in which all carbon transferred by landslides from all tropical mountains of the globe is released to the atmosphere, it would represent an amount equivalent to 1%-11% of the global carbon currently being released by the burning of fossil fuels. Meanwhile, in a projected scenario where a significant proportion of the carbon transferred by landslides is retained within sedimentary deposits, sequestration rates would equal 2%-19% of the residual land sink. © 2012. American Geophysical Union. All Rights Reserved.