Kimberly P. Wickland — Page 3

USGS2007

Carbon export and cycling by the Yukon, Tanana, and Porcupine rivers, Alaska, 2001-2005

Loads and yields of dissolved and particulate organic and inorganic carbon (DOC, POC, DIC, PIC) were measured and modeled at three locations on the Yukon River (YR) and on the Tanana and Porcupine rivers (TR, PR) in Alaska during 2001–2005. Total YR carbon export averaged 7.8 Tg C yr −1 , 30% as OC and 70% as IC. Total C yields (0.39–1.03 mol C m −2 yr −1 ) were proportional to water yields (139–356 mm yr −1 ; r 2 = 0.84) at all locations. Summer DOC had an aged component (fraction modern (FM) = 0.94–0.97), except in the permafrost wetland‐dominated PR, where DOC was modern. POC had FM = 0.63–0.70. DOC had high concentration, high aromaticity, and high hydrophobic content in spring and low concentration, low aromaticity, and high hydrophilic content in winter. About half of annual DOC export occurred during spring. DIC concentration and isotopic composition were strongly affected by dissolution of suspended carbonates in glacial meltwater during summer.

Water Resources Research↗

USGS1998

Winter fluxes of CO 2 and CH 4 from subalpine soils in Rocky Mountain National Park, Colorado

Fluxes of CO 2 and CH 4 through a seasonal snowpack were measured in and adjacent to a subalpine wetland in Rocky Mountain National Park, Colorado. Gas diffusion through the snow was controlled by gas production or consumption in the soil and by physical snowpack properties. The snowpack insulated soils from cold midwinter air temperatures allowing microbial activity to continue through the winter. All soil types studied were net sources of CO 2 to the atmosphere through the winter, whereas saturated soils in the wetland center were net emitters of CH 4 and soils adjacent to the wetland were net CH 4 consumers. Most sites showed similar temporal patterns in winter gas fluxes; the lowest fluxes occurred in early winter, and maximum fluxes occurred at the onset of snowmelt. Temporal changes in fluxes probably were related to changes in soil-moisture conditions and hydrology because soil temperatures were relatively constant under the snowpack. Average winter CO 2 fluxes were 42.3, 31.2, and 14.6 mmol m −2 d −1 over dry, moist, and saturated soils, respectively, which accounted for 8 to 23% of the gross annual CO 2 emissions from these soils. Average winter CH 4 fluxes were −0.016, 0.274, and 2.87 mmol m −2 d −1 over dry, moist, and saturated soils, respectively. Microbial activity under snow cover accounted for 12% of the annual CH 4 consumption in dry soils and 58 and 12% of the annual CH 4 emitted from moist and saturated soils, respectively. The observed ranges in CO 2 and CH 4 flux through snow indicated that winter fluxes are an important part of the annual carbon budget in seasonally snow-covered terrains.

Global Biogeochemical Cycles↗