Dissolved Organic Carbon in High Arctic Soil Water: The Influence of Periglacial Features and Ecology on Chemical Structure

The Arctic contains one of Earth's largest reservoirs of soil carbon and has received much attention due to its vulnerability to climate change. Rates of carbon turnover in soils are likely mediated by the concentration and chemical speciation of dissolved organic carbon (DOC), which in turn influences its microbial degradability. This study investigates DOC variability in High Arctic ecosystems and reveals that two different pools of soil water DOC occur across a series of non-sorted stripes; a prevalent periglacial feature in the High Arctic. Soil water was collected using tension lysimeters installed under vascular plant cover and in soils that are colonized primarily by cryptogams. Soil water collected under vascular plants are darker in color, have higher molecular weight DOC (as determined by ultrafiltration), and have more complexed Fe and Al relative to soil water collected under areas that are dominated by cryptogamic crust. UV-Vis absorbance measurements reveal that DOC in these samples are mostly aromatic, supporting the assertion that the DOC is most likely derived from the degradation of lignin. Soil water collected under cryptogam cover has DOC concentrations up to 50ppm C of which approximately 60% is low-molecular weight (passes a 500 Dalton ultrafiltration membrane). A lack of complexed Fe and Al in these samples supports the notion that the DOC is not comprised of low-molecular weight organic acids, and could be derived from polysaccharides and amino sugars commonly associated with cryptogamic crust. Preliminary work suggests that DOC in the clear soil solutions is more labile. Polysaccharide content is being determined by mass spectrometry to source compounds typical of cryptogams. Understanding the structure and lability of DOC will provide insights into mineralization rates for soil DOC and its contribution to High Arctic carbon fluxes.