A Terrestrial-Aquatic Model Reveals Cross-Scale Interactions Regulate Lateral Dissolved Organic Carbon Transport From Terrestrial Ecosystems

Abstract

Lateral carbon transport (LCT), the flux of terrestrial C transported to aquatic ecosystems, displaces carbon (C) across the terrestrial-aquatic continuum and is on the same order of magnitude as terrestrial net ecosystem production. However, few continental scale C models include LCT or the C-hydrology linkages necessary for modeling LCT. Those that do exist, borrow processes and conceptual understanding from watershed scale models, assuming that large-scale and small-scale drivers of LCT are the same. We develop a conceptual framework of LCT, which focuses on lateral dissolved organic carbon (DOC) transport (LCT-DOC), and operationalize it with a coupled terrestrial-aquatic C and hydrology model. After comparing our model LCT-DOC to previous estimates derived from a summation of landscape scale fluxes for the Contiguous U.S., we use model experiments to partition the importance of LCT-DOC drivers including total annual precipitation, air temperature, and plant traits, which interact across regional and local scales. We find that climate is the strongest driver of LCT-DOC, where LCT-DOC is positively related to precipitation but inversely related to temperature at continental scales. However, the net effect of climate on LCT-DOC is the product of cross-scale interactions between climate and vegetation. Plant traits also interact strongly with climate and have a measurable influence on LCT-DOC, with water use efficiency as the most influential plant trait because it couples terrestrial water and C cycling. We demonstrate that our conceptual framework and relatively simple linked C-hydrology process model of LCT-DOC can inform hypotheses and predict LCT-DOC.