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CARBON AND NITROGEN POOLS IN OREGON CASCADES FORESTS OVER A SUCCESSIONAL GRADIENT
Citation:
Cairns, M A. AND K. J. Lajtha. CARBON AND NITROGEN POOLS IN OREGON CASCADES FORESTS OVER A SUCCESSIONAL GRADIENT. Presented at American Geophysical Union fall meeting, San Francisco, CA, December 10, 2003.
Description:
In a study to examine impacts of successional and disturbance history on N export from 20 headwater stream systems in the west central Cascades of Oregon, a region of low anthropogenic N inputs, watersheds of differing ages showed a number of significant difference in nutrient export. In order to determine the mechanistic factors driving these differences, we measured soil solution and mineral soil C and N, forest floor and coarse woody detritus biomass, C and N in 12 plots categorized into 4 different classes of successional development.
In streamwater, DON ranged from 24\% to 51\% of TDN in the youngest and oldest watersheds, respectively. In soil solution, \%DON did not vary with succession, and was 40-75\% of TDN. Although ammonium concentrations were very low in streamwater, ammonium was 25-59\% of TDN in lysimeter samples and also did not vary with time since disturbance.
The C content and C:N ratio of the forest floor was significantly higher in the youngest plots, most likely due to post-harvest residue and slash. Although there were 2-fold differences in the C content of the mineral soil, these differences were not related to disturbance history. Even with these sharp differences in both forest floor and mineral soil C contents as well as C:N ratios among plots, no measure of N export -- not soil solution, not stream flow -- was significantly related to forest floor, down wood, or mineral soil characteristics. This is most likely because forest floor C:N ratios (54-126:1) all greatly exceed the C:N ratios reported to allow significant leakage.