Influence of Soil Erosion and Landslide Occurrence on Soil Organic Carbon Storage and Loss in the Luquillo Critical Zone Observatory, Puerto Rico

Abstract:

Tropical rainforests play a significant role in the global carbon (C) cycle. The Luquillo Critical Zone Observatory (LCZO) in Puerto Rico is characterized by intense erosion and landslide occurrence, which have been historically influenced by human activity and land use change, and drive the redistribution and burial of soil organic C (SOC) across the landscape. Estimates of regional C budgets do not systematically account for linkages between hydrological, geomorphological, and biogeochemical processes, which control the fate of eroded SOC. We quantify the impacts of erosion and rainfall-triggered landslides on SOC oxidation and accumulation at the Mameyes and Icacos watersheds. We developed and calibrated a spatially-explicit model of SOC dynamics, i.e. tRIBS-ECO (Triangulated Irregular Network-based Real-time Integrated Basin Simulator-Erosion and Carbon Oxidation), based on a coupled physically-based hydro-geomorphic model. The model inputs we used include measurements of SOC content at different horizons, and SOC oxidation and production rates derived from SOC turnover characteristics. We demonstrate the extent to which depth-dependent SOC oxidation and production are altered at eroding hillslopes and at landslide locations, and how this is being moderated by management practices. We estimated the SOC deposition rates at the floodplains of Mameyes and Icacos rivers, part of which is fluvially transported out of the system. The contrasting lithology of the two watersheds leads to different hydro-geomorphological behavior which controls the redistribution and storage of SOC. Results showed that topography and heterogeneity of tropical vegetation lead to significant spatial variability of the erosion-induced soil CO₂ flux to the atmosphere. We highlight the importance of the representation of SOC redistribution driven by local variation in lithological and geomorphological characteristics and hydroclimatic conditions in attempts to quantify watershed-scale soil C dynamics.