Search for: All records

Abstract The Thomas Fire ignited on December 4, 2017 and burned for over one month. As the Thomas Fire burned, Santa Ana winds carried a thick plume of smoke and ash over the Santa Barbara Channel. We sought to determine whether the deposition of Thomas Fire ash to the Santa Barbara Channel had a measurable effect on the concentration and stable carbon isotopic composition (δ¹³C) of dissolved black carbon (DBC) in coastal waters. DBC is the condensed aromatic fraction of thermally altered organic carbon quantified using the benzenepolycarboxylic acid (BPCA) method. DBC δ¹³C signatures were determined via BPCA‐specific stable carbon isotopic analysis. Surface water DBC concentrations beneath the smoke plume were up to 13% higher than other sampling stations. Via controlled leaching experiments, we found that Thomas Fire ash released a considerable amount of DBC in seawater (1.4 g‐DBC per kg of ash organic carbon), which was further enhanced by photodissolution. By combining in situ and experimental data, we constructed an isotopic mixing model to estimate inputs of ash‐derived DBC to marine surface waters. Although we were able to detect slight elevations in DBC concentrations beneath the smoke plume, the ash‐derived contributions were too small to meaningfully shift the δ¹³C signature, which resulted in an observed mismatch between modeled and measured DBC δ¹³C values. Few studies have investigated the immediate impacts of wildfire on coastal biogeochemistry. Therefore, our work provides an important foundation for understanding atmospheric contributions of fire‐derived DBC to coastal margins. 

Dissolved black carbon (DBC) is the condensed aromatic portion of dissolved organic matter produced from the incomplete combustion of biomass and other thermogenic processes. DBC quantification facilitates the examination of the production, accumulation, cycling, transformation, and effects of biologically recalcitrant condensed aromatic carbon in aquatic environments. Due to the heterogeneous nature of DBC molecules, concentrations are difficult to measure directly. Here, the method for DBC quantification consists of oxidizing condensed aromatic carbon to benzenepolycarboxylic acids (BPCAs), which are used as proxies for the assessment of DBC in the original sample. The concentrations of oxidation products (BPCAs) are quantified using high-performance liquid chromatography. DBC concentrations are determined from the concentration of BPCAs using a previously established conversion factor. Details and full descriptions of the preparative and analytical procedures and techniques of the BPCA method are usually omitted for brevity in published method sections and method-specific papers. With this step-by-step protocol, we aim to clarify the steps of DBC analysis, especially for those adopting or conducting the BPCA method for the first time. 

Abstract Central African tropical forests face increasing anthropogenic pressures, particularly in the form of deforestation and land-use conversion to agriculture. The long-term effects of this transformation of pristine forests to fallow-based agroecosystems and secondary forests on biogeochemical cycles that drive forest functioning are poorly understood. Here, we show that biomass burning on the African continent results in high phosphorus (P) deposition on an equatorial forest via fire-derived atmospheric emissions. Furthermore, we show that deposition loads increase with forest regrowth age, likely due to increasing canopy complexity, ranging from 0.4 kg P ha −1  yr −1 on agricultural fields to 3.1 kg P ha −1  yr −1 on old secondary forests. In forest systems, canopy wash-off of dry P deposition increases with rainfall amount, highlighting how tropical forest canopies act as dynamic reservoirs for enhanced addition of this essential plant nutrient. Overall, the observed P deposition load at the study site is substantial and demonstrates the importance of canopy trapping as a pathway for nutrient input into forest ecosystems.