B43B-0237:
Connections Among Terrestrial Sources of Organic and Inorganic Carbon and Surface Waters in a Permafrost- and Wildfire-Impacted Headwater Catchment, Alaska
Thursday, 18 December 2014
Kimberly Wickland1, Joshua C Koch2, John T Crawford3,4, Mark Dornblaser4, Kathy Kelsey5 and Robert G Striegl4, (1)USGS, National Research Program, Baltimore, MD, United States, (2)USGS Alaska Science Center, Anchorage, AK, United States, (3)University of Wisconsin Madison, Center for Limnology, Madison, WI, United States, (4)USGS, National Research Program, Boulder, CO, United States, (5)University of Colorado, Boulder, CO, United States
Abstract:
High-latitude headwater catchments commonly contain permafrost soils and are subject to disturbance by wildfire. Processes governing transport of organic and inorganic carbon from headwater catchments to surface waters, and the influence of permafrost and disturbance on those processes, remain poorly characterized. We conducted a two-year field study of a headwater catchment in interior Alaska to better understand terrestrial-aquatic linkages of carbon (C) in these systems. The 4.1 km2 catchment is underlain by permafrost, and is drained by a first-order stream. Portions of the catchment burned in 2003, resulting in localized removal of organic soils and subsequent permafrost thaw. During May – September of 2010 and 2011, we sampled stream and soil pore waters throughout the catchment on a weekly to bi-weekly basis for dissolved organic carbon (DOC), specific UV absorbance (SUVA), dissolved inorganic carbon (DIC), and dissolved carbon dioxide (CO2) and methane (CH4). Stream discharge and water chemistry were measured at two locations, reflecting drainage from the upper catchment (2.6 km2) and the entire catchment. Soil pore water sampling sites located between the two stream sampling stations included unburned hillslopes with permafrost depths ranging from 0.6 m to 0.75 m, burned hillslopes with permafrost depths to 1m, and riparian wetland with permafrost > 1m depth. Seasonal, interannual, and spatial differences in delivery of C constituents to the stream were evident over the two study years. Mean seasonal C loads and flow-weighted mean C concentrations (FWMC) for each stream reach showed that DOC and CH4 increased, and DIC and CO2 decreased in the downstream direction. Comparing stream FWMC to mean concentrations in soil pore waters, we determined that stream DOC, SUVA, and CH4 at the downstream location matched closely with values measured in the riparian wetland and burned hillslope locations, whereas DIC concentration was most similar to unburned hillslopes. This suggests a decoupling of organic and inorganic C sources, perhaps mediated by reactivity. We use an end-member mixing model, soil hydrologic properties, and measures of DOC biodegradation to explore sources of water and C from the distinct catchment landcover types to the stream and the role of permafrost and wildfire in C delivery to streams.
