ICMGP - Conference Presentation

Abstract Information :

Soil organic matter (SOM) has fundamental roles in terrestrial processes influencing carbon storage, microbial growth, and metal biogeochemistry. The most labile and reactive fraction of SOM is water extractable organic matter (WEOM) and understanding the chemical composition of WEOM is particularly important due to the abundance of oxygen and sulfur heteroatoms that can participate in the comobilization of both mercury and methylmercury (MeHg). In this study, we used Fourier transform ion cyclotron resonance mass spectrometry to characterize the chemical composition of WEOM in relation to water extractable total mercury (THg) and MeHg concentrations across different layers of upland forest soils, wetland soils, and stream sediments in Canada?s central boreal forests. Water extractable THg concentrations were significantly higher in the O and A horizons of upland forest soils, ranging from 8.21-42.3 ng g-1, and were significantly positively (p < 0.05; ? > 0.75) correlated with the relative abundance of WEOM molecules within polyphenolic compound classes. Conversely, water extractable MeHg concentrations ranged from 0.06-0.46 ng g-1, peaking in near-surface wetland soil and stream sediment layers. Compared to soils, we found that stream sediments were comprised of a significantly (p < 0.001) higher content of unsaturated aliphatic WEOM, where 75 % of the total WEOM pool is likely biologically labile. Moreover, the relative abundance of unsaturated aliphatic molecules in WEOM significantly correlated to MeHg concentrations. Our findings highlight possible comobilization mechanisms of phenolic plant-based biomolecules for THg transport in upland soils whereas unsaturated aliphatic WEOM in stream sediments may be involved in MeHg comobilization. Together, our findings begin to shine new light on how the chemical composition of WEOM may be related to THg and MeHg comobilization across terrestrial and aquatic systems.