Dissolved organic matter characterization in soils and streams in a small coastal low-Arctic catchment

• Published in: Biogeosciences
• Main Authors: Speetjens, Niek Jesse, Tanski, George, Martin, Victoria, Wagner, Julia, Richter, Andreas, Hugelius, Gustaf, Boucher, Chris, Lodi, Rachele, Knoblauch, Christian, Koch, Boris P., Wünsch, Urban, Lantuit, Hugues, Vonk, Jorien E.
• Format: Text
• Language: English
• Published: 2022
• Subjects: Arctic; Canada; Yukon; Ice; permafrost; wedge*
• Online Access: https://doi.org/10.5194/bg-19-3073-2022; https://bg.copernicus.org/articles/19/3073/2022/

Ongoing climate warming in the western Canadian Arctic is leading to thawing of permafrost soils and subsequent mobilization of its organic matter pool. Part of this mobilized terrestrial organic matter enters the aquatic system as dissolved organic matter (DOM) and is laterally transported from land to sea. Mobilized organic matter is an important source of nutrients for ecosystems, as it is available for microbial breakdown, and thus a source of greenhouse gases. We are beginning to understand spatial controls on the release of DOM as well as the quantities and fate of this material in large Arctic rivers. Yet, these processes remain systematically understudied in small, high-Arctic watersheds, despite the fact that these watersheds experience the strongest warming rates in comparison. Here, we sampled soil (active layer and permafrost) and water (porewater and stream water) from a small ice wedge polygon (IWP) catchment along the Yukon coast, Canada, during the summer of 2018. We assessed the organic carbon (OC) quantity (using dissolved (DOC) and particulate OC (POC) concentrations and soil OC content), quality ( δ 13 C DOC, optical properties and source apportionment) and bioavailability (incubations; optical indices such as slope ratio, S r and humification index, HIX) along with stream water properties (temperature, T pH; electrical conductivity, EC; and water isotopes). We classify and compare different landscape units and their soil horizons that differ in microtopography and hydrological connectivity, giving rise to differences in drainage capacity. Our results show that porewater DOC concentrations and yield reflect drainage patterns and waterlogged conditions in the watershed. DOC yield (in mg DOC g −1 soil OC ) generally increases with depth but shows a large variability near the transition zone (around the permafrost table). Active-layer porewater DOC generally is more labile than permafrost DOC, due to various reasons (heterogeneity, presence of a paleo-active-layer and sampling strategies). ...