This project examined the organic matter (carbon) remaining after the combustion of biomass, an important component of the carbon cycle that has received relatively little prior research attention. In particular, we examined the formation and transformation of dissolved pyrogenic carbon (pyC), which is the form of carbon which might be exported from the terrestrial to the aquatic environment.

To examine these processes in a systemic way, we; 1) analyzed the chemistry of dissolved pyrogenic C leached from a series of charcoal solids, and 2) analyzed the chemistry of these dissolved pyrogenic C samples that had been exposed to light over a 5 days, and that was incubated it with soil microbes over 96 days. The pyrogenic C lost by solid charcoals during leaching ranged from 0.3 to 16.9%, decreasing with the temperature at which the char was made. The chemistry of the leachates was dissimilar from their parent chars, being much more enriched in O-containing functional groups and only contained about 9?23% condensed aromatic C, as opposed to 24?57% of the pyrogenic solids. This is important since condensed aromatic C is often used to estimate the amount of pyrogenic C in aquatic systems.

When exposed to light, about 10?20% of oak char leachate organic C was lost over five days, with greater proportions lost from leachates of higher temperature parent chars. Most of the lost C was aromatic and benzenepolycarboxylic acid (BPCAs) analysis indicated that 75?94% of condensed aromatic C was lost, with half-lived on the order of about a day. A less photoreactive fraction was lost with half-lives of 1-2 years. In contrast, microbial decomposition resulted in 37 - 45% loss of over 96 days (greater proportions from low temperature-derived C), and mainly attacked the low molecular weight constituents (i.e., simple alcohols and acids) of dissolved pyrogenic C. These findings are summarized in the accompanying figure.

This research provided the first comprehensive understanding of the processes likely to control the amount and type of py-DOM produced and exported from terrestrial environments. It also critically evaluated the molecular markers currently used to quantify py-DOM in environmental samples, and was among the first to combine advanced analytical methods to understand cycling of OM of any environmental setting.

Given the current and future predicted increase in wildfires, it is important to better understand the fate of dissolved carbon released from soil charcoal. Results of this research will be of interest to soil scientists, aquatic ecologists, marine chemists, climate scientists, and those studying pollutant fate and transport. It may also have a strong impact on our understanding of marine chemistry, long-term C cycling and associated climate changes and pollutant transport.

This project brought together organic geochemists with a range of expertise and backgrounds and provided opportunity for 1 undergraduate and 1 graduate student (at University of Florida), and others at collaborating institutions, to be trained in multiple state of the art analytical techniques to conduct highly collaborative multi-disciplinary research. Funding for this project almost wholly supported the PhD of a Kyle Bostick at UF and another student at ODU. Five peer-reviewed publications have resulted from this project and six others are nearing submission stage. In addition, 20 presentations have been made at international science conferences.

Another important broader impact of the project was the development and installation of an exhibit and activity on biochar and other pyrogenic materials and at the North Carolina Museum of Natural Sciences (http://naturalsciences.org/) in Raleigh, NC. It was incorporated into the Museum?s Investigator Labs (I-Labs), and was successful in exposing an educating a large number people on the importance of fire in the environment.

Last Modified: 07/24/2020
Modified by: Andrew R Zimmerman