Biomass combustion as a source of terrigenous organic matter to the coastal ocean

Abstract

Natural and anthropogenic combustion processes are major sources of organic carbon into the environment. Biomarkers of biomass combustion can be used to monitor the impact of combustion on carbon cycling at multiple scales, particularly in natural systems. Biomarkers of biomass combustion (lignin-oxidized phenols and anhydrosugars) were selectively extracted from standard solutions and natural solutions using both a liquid-phase extraction (LPE) and a solid-phase extraction (SPE). The LPE was found to be both highly accurate and highly reproducible with an average recovery from standard solutions of 100±9% and 91±7% for lignin phenols and anhydrosugars, respectively. The quantities of lignin phenols and anhydrosugars extracted from dissolved organic matter derived from a honey mesquite charcoal were similar than values previously produced in the lab demonstrating the reproducibility of this method over time. The SPE extracted measurable but variable quantities of lignin phenols but demonstrated no recovery of anhydrosugars, showing that the SPE disks selected were not efficient for extracting the compounds of interest from natural waters. Further tests will be required to identify a method of extraction for such highly polar molecules from aqueous solutions. We applied the LPE protocol to extract free lignin phenols from a series of natural waters along a seasonal gradient in an Arctic river and compared these to previously measured polymeric lignin phenol concentrations. The temporal trend in free phenol concentrations matches that of the polymeric lignin with a maximum during the spring freshet peak flow event. The proportion of total lignin phenols that occur as free phenol ranges 2-9% with a maximum prior to the spring freshet peak flow event and a minimum during the spring freshet. Molecular signatures of the free phenols show that the dissolved lignin during the spring freshet contains high proportions of acid groups, which suggests a more degraded state of the dissolved terrigenous organic matter.