Quantifying interactive photochemical and microbial removal of terrestrial dissolved organic carbon: From experiments to modeling

Abstract The biogeochemical fate of terrestrial dissolved organic carbon (tDOC) in aquatic environments is a poorly understood part of the carbon cycle. In nature, tDOC undergoes photochemical and microbial degradation simultaneously. However, photochemical and microbial degradation are generally quantified separately, and nonlinear interactions between these processes remain poorly constrained. We describe a novel experimental method to quantify simultaneous photochemical–microbial degradation, and show that interactive photochemical–microbial degradation can account for around half of tDOC and of colored dissolved organic matter degradation. The degradation rates depend asymptotically on the absorbed light dose rate. Our method yields a simple equation that relates the interactive tDOC degradation rate to the absorbed light dose rate, which can be adapted to represent tDOC degradation in biogeochemical ocean models. Our method offers a straightforward and transferable approach to quantify interactive tDOC degradation rates in different ecosystems and to better represent tDOC degradation in biogeochemical ocean models.