Southern Appalachian Forest Soils Show a Pattern of Long-Term Carbon Loss.

Globally soil represents a large carbon pool and may play an important role in carbon sequestration. We examined soil C data collected from 1970 to 2012 in five watersheds within the Coweeta Hydrologic Laboratory, in the southern Appalachian mountains of southwestern NC.  The watersheds examined included a high elevation and two low elevation reference watersheds, a watershed clearcut in 1977, and a watershed converted from native hardwood to white pine in 1956.  All five watersheds show similar patterns of declining soil C in both surface (0–10 cm) and subsurface (10–30 cm) soil. The rate of C loss was greatest in subsurface soils during the earliest years of collection, 1970 until 1994. Surface C loss was greatest between 1970 and 1990.  Since the 1990s soil C has shown little change in both soil layers. We used existing long-term data to estimate potential C loss mechanisms. Dissolved organic C loss from the watersheds was reconstructed using stream inorganic chemistry.  We parameterized a soil respiration model by synthesizing results from various soil CO2 efflux measurement campaigns within the basin and historic soil temperature data.   Irrespective of the fate, the relationship between soil C and other long-term data at Coweeta suggest that increasing temperature along with changes in overstory species composition and biomass aggradation are important factors in long-term changes in soil carbon.