STRONG SEASONALITY OF BIOGEOCHEMICAL CHARACTERISTICS AND SOURCE REGIONS IN PERMAFROST WATERSHEDS

Abstract:

High latitude watersheds experience a dramatic seasonality of up to nine months of cold, snow covered winter and a warm, bright, summer. Spring melt runoff is a dramatic two to three week period when up to 75% of the yearly precipitation runs off. Identifying sources and measuring fluxes of compounds out of Arctic rivers is difficult in large rivers because they represent the combined effect of innumerable plot-scale melt water sources, each coming from different soil and vegetation types, each experiencing a slightly different melt timing and evolution. Numerous studies have shown spring melt is characterized by an ionic pulse of solutes, dissolved organic carbon and other nutrients (ammonium, phosphate and nitrate) leached by snow melt water from surface vegetation and soils. Summer and fall flows are comprised largely of shallow to deepening sources from a downwardly expanding seasonally thawed (“active”) layer. In late summer flowpaths deepen and the biogeochemical composition of surface waters may be sourced from an increasing mineral weathering zone representing landscape scale soil processes. The watershed biogeochemical response to precipitation may also yield insight into subsurface permafrost geomorphological characteristics and flowpaths through water tracks or other small depressions. Winter processes are the least studied or understood but overflow ice (“aufeis”) provides access to deep, old waters. The deeper snow pack in depressions can provide protection against winter cold and feed back to deeper summer season thaw. This presentation will focus on using water stable isotopes, major ion concentrations, trace metals, nutrients, and permafrost delineation to identify biogeochemical sources in watersheds draining continuous and discontinuous permafrost in Alaska. Biogeochemical processes associated with scaling, meteorology, and climate warming will be discussed.