The heating and partial combustion of organic matter produces a diverse suite of organic compounds that range from sugar-like molecules to graphite. Charcoal formed at high temperatures, here termed “black carbon”, tends to be less biolabile (i.e. less degradable by microbes) than charcoal formed at low temperatures. Consider how you make and enjoy a piece of toast: Lightly singed bread is quite tasty (or “biolabile”), whereas bread burnt to a crisp is bitter and unpalatable. When charred material interacts with water, some of it dissolves and is carried away by rivers to the ocean. Therefore, understanding the relative biolability (or “tastiness”) of dissolved black carbon is important for understanding whether or not it is degraded in rivers before entering ocean waters.
A gradient of toast.
Isolating and tracking different molecular components of charcoal and black carbon in the environment is very challenging from an analytical perspective - Different methods measure different fractions of charcoal along the “combustion continuum”. Therefore, charcoal and black carbon are operationally defined by the method used to quantify and characterize it. Questions still remain about exactly how, or to what degree, the analytical windows of these methods overlap … if they overlap at all.
Sasha Wagner and colleagues recently published a Matters Arising in Nature Communications entitled “Questions remain about the biolability of dissolved black carbon along the combustion continuum” that dives into discussion about the comparison of black carbon analytical windows, biolabile charcoal fractions, and the terminology used to describe this important yet enigmatic compound class.
