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Reconciling Change in Oi-Horizon Carbon-14 with Mass Loss for an Oak Forest

^a Environmental Sciences Division, Oak Ridge National Lab., Oak Ridge, TN 37831-6422
^b Center for Accelerator Mass Spectrometry, Lawrence Livermore National Lab., Livermore, CA 94550
^c Univ. of California, Irvine, CA 92697

View larger version (67K): [in a new window]   Fig. 1. Map of the Oak Ridge Reservation near Oak Ridge, TN showing the location of the EBIS study sites. The Walker Branch (WB) and TVA sites are on Chestnut Ridge and have Ultisol soils. The Haw Ridge (HR) and Pine Ridge (PR) have Inceptisol soils.

View larger version (61K): [in a new window]   Fig. 2. Mean monthly air temperature and cumulative monthly rainfall for previous litterbag decomposition studies conducted on the Oak Ridge Reservation plotted against the long-term (54-yr) climate record.

View larger version (37K): [in a new window]   Fig. 3. Published data for litter mass loss from mixed and species-specific litterbag studies conducted on the Oak Ridge Reservation (upper graph), and the fitted response (solid line) to the full data set with the data for Nyssa removed (lower graph). Dashed lines in the lower graph are the 95% confidence interval around the regression line. Error estimates associated with k and p are ±95% confidence intervals.

View larger version (27K): [in a new window]   Fig. 4. Mean ±95% confidence intervals for litter mass remaining after 9 mo measured by litterbag mass loss studies (MRLB), or calculated from 14C litter-enrichment or 14C litter-dilution. The dashed line for comparison is the mean mass remaining based on MRLB. The "?" placed on the right-hand column indicates the uncertainty of this result (see Discussion) even though the calculated value of litter mass remaining was an acceptable result from the two-compartment model (Eq. [1a]).

View larger version (41K): [in a new window]   Fig. 5. Diagram of the hypothetical path of 14C-isotopes through a well-mixed Oi-horizon with stable 14C-signatures (A. Walker Branch site), and through a manipulated Oi-horizon having distinct 14C signatures in all measurable litter cohorts (B. TVA site). Values contained within bold boxes are measured data from Tables 1 and 2. All other data are estimates of cohort-specific components of the time-zero and 9-mo litter Oi-horizons used to estimate one year's worth of change. Mass estimates (g dry matter m–2) and decomposition losses (g dry matter m–2 y–1) were derived from the fitted litterbag relationship in Fig. 3. The carbon content of newly added Oi-cohorts and older Oi litter was similar (46–47%).