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FOREST, RANGE & WILDLAND SOILS

Soil Carbon and Nitrogen Changes in Forests of Walker Branch Watershed, 1972 to 2004

^a Natural Resources and Environmental Science, Fleischmann Agriculture Bldg. 370, Univ. of Nevada, Reno, NV 89557
^b Environmental Sciences Division, Oak Ridge National Lab., P.O. Box 2008, Building 1059, Oak Ridge, TN 37831-6422
^c USDA Forest Service, 2730 Savannah Hwy., Charleston, SC 29141
^d Natural Resources and Environmental Science, 1000 Valley Rd., Univ. of Nevada, Reno, NV 89512

^* Corresponding author (dwj{at}cabnr.unr.edu).

Changes in soil C and N concentrations and contents in four samplings during a 32-yr period on Walker Branch watershed in Tennessee were determined and compared with previously measured C and N fluxes and with changes in ecosystem C and N pools during this period. Soils showed significant increases in C and N concentrations in surface horizons from 1972 to 2004, and most of this increase occurred between 1972 and 1982. A previously observed decline in soil C and N contents between 1982 and 1993 was reversed in 2004 such that the latter increased to near 1982 values. The changes in soil C content could be approximately accounted for by previously measured litterfall and soil CO₂–C fluxes. Changes in soil N could not be accounted for by leaching, increments in vegetation, or by laboratory bias, changes during sample storage, or reasonable estimates of field sampling errors. We conclude that, although vegetation C and N pools increased steadily during the sampling period in most cases, changes in soil C and N pools on Walker Branch watershed are highly variable in both space and time, and there has been no unidirectional trend during the time period of this study.