Investigating Atmospheric Inputs of Dissolved Black Carbon to the Santa Barbara Channel During the Thomas Fire (California, USA)

Abstract

Southern California (USA) has a long history of wildfire, with major burn events generally occurring every 20-40 years according to sedimentary charcoal records (

Of Sea and Smoke: Evidence of Marine Dissolved Organic Matter Deposition from 2020 Western United States Wildfires

“…The challenge in tracing pyOM across global biogeochemical cycles is due in part to the molecular heterogeneity of burn-derived compounds, influenced by source material, burn temperature, and biomediated and photomediated transformations. − This diversity of molecular species limits the efficacy of traditional methodology to identify pyOM, such as quantitation of benzene polycarboxylic acids (BPCAs), recalcitrant condensed aromatic structures. − While condensed aromatic structures comprise a substantial component of pyOM, a combustion “continuum” of structural complexity has been proposed amid growing characterization of both (i) aliphatic contributions to pyOM ,− and (ii) the reactivity of even thermodynamically stable condensed aromatic structures via ozonolysis, photooxidation, ,− and microbial mineralization. − Nonpyrogenic materials (oak biomass, grass biomass, and compost) and their leachates can also produce BPCAs, confounding their predictive efficacy. , Characterizing and quantifying the composition of pyOM is a complex yet important endeavor …”

“…In the United States, warmer climates, accumulation of fuel from a legacy of fire suppression, and higher fuel aridity have resulted in a quadrupling of burned area in the last four decades. , As the frequencies, durations, and intensities of these fires are expected to increase, particularly in coastal western states, so are contributions of pyOM to marine systems . PyOM can reach the surface ocean via a diversity of mechanisms, including atmospheric deposition of aerosol and terrestrial runoff, , and may be further transformed during transport.…”

“…While strides have been made to characterize the molecular composition of pyOM in soil and watershed systems where reactive mineral matrices and leachate transport dynamics govern persistence, ,, contributions to marine dissolved organic matter (DOM) remain poorly understood. Indeed, historic sedimentary records indicate a significant amount of wildfire-derived material is ultimately delivered to marine sediments, − yet the input and fate of C during active fires have only been studied recently (e.g., The Thomas Fire in the Santa Barbara Channel). , …”

Measuring dissolved black carbon in water via aqueous, inorganic, high-performance liquid chromatography of benzenepolycarboxylic acid (BPCA) molecular markers

“…Using the described protocol, we have measured and published DBC data for diverse aquatic systems, including major and minor rivers, along oceanic depth profiles, throughfall and stemflow, petroleum-contaminated groundwater, and coastal environments [ 13 , 18 , 29 – 32 ]. Although DOC analysis is not explicitly described in the current protocol, we strongly recommend that users of this method measure and share bulk DOC concentrations alongside BPCA and DBC concentrations.…”

“…The mobilization of DBC serves as a link between terrestrial and marine reservoirs and DBC concentrations are usually higher in rivers (1.5 to 140 uM-C) than in the ocean (0.08 to 2.5 uM-C; [ 3 ]). Leaching experiments indicate a high degree of variability in terms of the amount and composition of DBC leached from soils, charcoal, and pyrogenic aerosols [ 9 – 13 ]. Due to the heterogeneous nature of DBC compounds, which exist in an even more complex dissolved organic matter matrix, the direct quantification of these condensed aromatic molecules is analytically challenging.…”