95th ESA Annual Meeting (August 1 -- 6, 2010)

COS 20-7 - CANCELLED - Are N Immobilization-Mineralization Dynamics in Foliar Litter related to patterns of stream nitrate exports? A Study in an Appalachian Forest

Tuesday, August 3, 2010: 10:10 AM
334, David L Lawrence Convention Center
Kathryn B. Piatek, West Virginia University, Morgantown, WV and Mary Beth Adams, Northern Research Station, USDA Forest Service, Morgantown, WV

The central hardwood forest receives some of the highest rates of atmospheric nitrogen (N) deposition, which results in nitrate leaching to surface waters threatening aquatic habitat. Immobilization of N in foliar litter during litter decomposition represents a potential mechanism for temporal N retention of atmospherically-deposited N in forest ecosystems. Recent work in a central Appalachian hardwood forest shows that 6 to 11 kg N ha-1 yr-1 may be immobilized in fresh litter depending on the mass of litter. This represents a potential retention of 50 to 100% of the amount of N in throughfall. The strength of this potential retention mechanism is likely to decrease and then possibly subside when new litter layer (Oi) is yet to form at the end of the summer/ early fall.  We tested a hypothesis that these N dynamics in litter are reflected in the relative rates of nitrate exports in stream water, with low exports in summer and late fall, and high exports in late winter and late summer/ early fall. We performed a simple regression analysis of litter N dynamics and monthly N exports to test this hypothesis. We used stream N export data for 2002 -2006 in two watersheds, one reference, and one impacted by 3x ambient rates of atmospheric N deposition.

Results/Conclusions Linear regression of monthly stream nitrate export values with litter N flux revealed no relationship in either watershed. We conclude that while foliar litter immobilizes N, and the amount of immobilized N is of similar magnitude as that arriving with deposition, this N retention mechanism does not translate into lowered nitrate exports in stream. Similarly, N mineralization from the litter layer is apparently not related to high stream nitrate exports.