Demystifying the particulate black carbon conundrum in aquatic systems

Particulate black carbon (PBC) constitutes a notable fraction of riverine particulate carbon (C), and is considered to be a potent sink of C due to its refractory nature in the environment. However, its potential to regulate global climate has been challenged with recent arguments of transformation of BC in the environment. In this study, we explore the transport and transformation of PBC along the continuum of six river basins in western India. Using the CTO-375 method and measuring the concentration and stable isotopic composition of the soot fraction of the BC spectrum, we examined the reasons for its variation in the river continuum. Our investigation suggested that changes in concentration and isotopic composition were due to allochthonous inputs and degradation, implying that BC may not be as recalcitrant as previously thought. We also estimated riverine export fluxes of PBC to the Arabian Sea, which was a minor fraction of the current global flux estimates.