Permafrost natural organic matter (NOM) chemical composition and reactivity is poorly understood in sub-Arctic Alaska. This poor understanding does not allow for adequate interpretation of how permafrost organic matter will affect the surface water chemistry and photoreactivity upon thaw in the warming climate of sub-Arctic Alaska. This study assessed two questions:
The investigation of question 1 determined that aliphatic chemical compounds do not leach out of soil into surface waters and that the chemical composition and photoreactivity of permafrost are heterogeneous down the depth of the core as well as within the same watershed.A few trends were observed in chemical characterization as the carbon age increased: carbohydrates decreased with age and aromatics increased with age. The decrease in carbohydrates is indicative that older material could have been more processed prior to freezing. The increase in aromatics with depth differs from the few previous studies elsewhere that observed permafrost has decreased aromaticity compared to the active layer.
The primary findings thus far for Question 2 concern photoreactivity and seasonality. First, the chemical composition and photoreactivity of the sampled boreal forest sub-Arctic NOM is different than that of the reference material of microbial derived or terrestrial derived organic matter. As for seasonality, winter NOM has minimal natural •OH production in the presence of light.
Finally, addition of dissolved iron to NOM solutions did not increase rates of photochemical •OH promotion. This indicates that either iron complexation was not increased in lake NOM to increase the lake’s NOM reactivity to •OH production, or that other interactions with iron were preventing •OH enhancement.
