Carbon in Soils of Boreal Beaver Ponds.

Several studies of trace gas fluxes in boreal regions have shown beaver ponds to be hot spots of methane emission, but have not explained the source of carbon for methanogenesis. Soils that are flooded by beaver dams are often hydric prior to inundation by beaver, and may contain substantial stores of carbon. Soil profiles associated with active and drained beaver ponds at Voyageurs National Park were described and sampled for sources of carbon that could fuel methanogenesis. Organic carbon deposits were close to the surface in a glaciofluvial hydrosequence, whereas organic and inorganic carbon deposits were distributed deeper in the profiles of glaciolacustrine soils. Carbon rich soils included Haplosaprists and Endoaquolls, in which organic carbon was incorporated to a depth of 30 cm or more. Other carbon rich layers included histic epipedons, buried organic layers, poorly decomposed sedges killed by flooding, and other sources of thick surface plant litter. On a per volume basis, organic horizons contained 33 to 110 kg C m^-3, whereas A horizons contained 18 to 34 kg C m^-3. The lower B horizons of Glossudalf soils adjacent to beaver ponds contained free carbonates, and one of the soils sampled contained 52 kg C m^-3 at about 65 cm depth. The implications of these carbon stores to gaseous carbon fluxes are discussed.