Hydrologic Controls On Nutrient Processing In A Sub-Arctic Stream
Koch, Joshua 1 ; McKnight, Diane 2 ; Striegl, Robert 3 ; Runkel, Robert 4 ;Wickland, Kimberly 5 ; Ewing, Stephanie 6
1 USGS
2 INSTAAR
3 USGS
4 USGS
5 USGS
6 USGS
The balance between runoff and storage is critical to biogeochemical processing of carbon (C) and nitrogen (N) in boreal ecosystems. Whether C and N are mineralized in soils or flushed from catchments may be related to active layer depths and soil moisture, and has implications for ecosystem productivity and climate change feedbacks. To understand the seasonal dynamics of storage and runoff, we monitored discharge, stream/catchment interactions, and C and N pools and reactivity in a small boreal catchment in the Yukon River Basin, Alaska over the summers of 2008 and 2009. Runoff coefficients were related to soil moisture and active layer depth in the very dry soils. Tracer dilution supports runoff coefficients and suggests that ephemeral tributaries, the saturated soils around these tributaries, and storm runoff are the primary sources of stream recharge. Synoptic sampling, transient storage decay rates, and laboratory incubations suggest that C and N are primarily exported during high flows, with greater C mineralization and nitrate loss at lower flows. These results counter much of the literature and our own hypothesis of a direct relationship between subsurface storage potential and C and N reactivity. This link between hydrologic and biogeochemical activity will likely change given climate change scenarios, which predict that interior Alaska will become warmer and wetter in subsequent years.