Addressing Arctic Aufeis As Unique And Critical Ecological Habitats
Hendrickson, Patrick J 1 ; Gooseff, Michael N 2 ; Huryn, Alexander D 3
1 University of Colorado-Boulder
2 University of Colorado-Boulder
3 University of Alabama
Aufeis (icings or naleds) are seasonal arctic and sub-arctic features that form through repeated overflow and freeze events of river or spring discharge. Aufeis fields, defined as the substrate on which aufeis form and the overlaying ice, have been studied to mitigate impacts on engineering structures; however, ecological characteristics and functions of aufeis fields are poorly understood. Melting ice maintains flow downstream of aufeis during summer months, while an insulating ice layer maintains a wet base beneath aufeis during winter months. Consequently, the perennial springs supplying warm water to aufeis fields create unique fluvial habitats that act as winter and summer oases for biota. To investigate ecosystem function, we measured seasonal freeze-thaw patterns, water table elevations, and whole-stream metabolism at the Kuparuk River Aufeis (North Slope, AK), a large (~5 km 2 ) field composed of cobble substrate. An Onset meteorological station, Onset stage and temperature loggers, and PME miniDOT dissolved oxygen loggers were installed in August 2016, and data downloaded Summer 2017. The single-station open channel diel oxygen method was utilized at several dissolved oxygen (DO) stations located within and downstream of the aufeis field. Daily ecosystem respiration (ER), gross primary production (GPP) and reaeration rates were modeled using BASE. Results show that freezing initially occurs at the downstream boundary of the field, and upstream aufeis development does not begin until late in the season. Modeled stream metabolic rates indicate net heterotrophy in the fall season when minimum ice extent is observed. GPP, ER, and net metabolism show the highest magnitudes at the upstream reach near the spring source, and decrease downstream. As flow exits the aufeis field, the stream system becomes dependent on autochthonous processes, suggesting a shift in stream metabolic dynamics between arctic tundra and aufeis habitat.