Influence of Linked Hydrologic and Geomorphic Processes on the Terrestrial Carbon Cycle

Abstract

Soil erosion driven by hydro-climatic factors and anthropogenic activity is closely linked to the global carbon (C) cycle. Elucidating complex interrelations between climate, vegetation, soils, and human impacts is critical for advancing our understanding on how diverse ecosystems respond to global environmental change. This work introduces a spatially-explicit process-based model of soil organic C dynamics (Triangulated Irregular Network-based Real-time Integrated Basin Simulator-Erosion and Carbon Oxidation), developed within with an existing coupled physically-based hydro-geomorphic model, to quantify the influence of linked hydrologic and geomorphic processes on the C cycle in a range of ecosystems. Two sites are studied: the Calhoun Critical Zone Observatory (CZO) in South Carolina, USA, which has experienced some of the most serious agricultural soil erosion in North America, and the Luquillo CZO (Puerto Rico), a tropical site of particular hydro-geomorphological interest. This study uses multiple observations of hydrologic and geomorphic processes and soil biogeochemical properties. The substantial topographic variability in the redistribution of soil organic C in agricultural landscapes as soil erosion and deposition proceed is highlighted. The uncertainty characterizing estimates of the hydrologically driven CO2 exchange with the atmosphere in intensively managed landscapes is significant. In the Luquillo CZO, the capacity of contrasting tropical landscapes to act as a net atmospheric C source or a C sink in response to hydro-climatic perturbations is demonstrated. This work highlights that the natural spatial variation of soil hydrological and geotechnical properties greatly influences slope instability in tropical watersheds. Also, as shown, hillslope erosion and landslide occurrence in the Luquillo CZO are expected to remain significant in the 21st century, despite a projected precipitation decline in south Caribbean. It is recommended that future studies assessing the contribution of erosion on atmospheric CO2, and the response of diverse landscapes to natural and anthropogenic perturbations systematically account for the fine spatio-temporal variability of linked hydro-climatic, geomorphological, and biogeochemical processes at a range of settings.