PARENT SESSION
Oral Session # 96: Disturbance Ecology: Wind and Water.
Presiding: L Battaglia
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 202.
Hillslope and streamwater nutrient dynamics following upland riparian canopy tree windthrow in the southern Appalachians.
Yeakley, J.*,1, Coleman, D.2, Haines, B.3, Kloeppel, B.2, Meyer, J.2, Swank, W.4, Steiner, S.2, 1 Environmental Science, Portland, OR, USA2 Institute of Ecology, Athens, GA, USA3 Department of Plant Biology, Athens, GA, USA4 Coweeta Hydrologic Laboratory, Otto, NC, USA
ABSTRACT- We investigated effects of natural blowdown of canopy trees on nutrient export to streams in the southern Appalachians. Transects were instrumented on adjacent hillslopes in a first order watershed at the Coweeta Hydrologic Laboratory (35o03' N, 83o 25' W). Dissolved organic carbon (DOC), K+, Na+, Ca2+, Mg2+, NO3--N, NH4+-N, PO43--P, and SO42- were measured for two years prior to disturbance. In October 1995, Hurricane Opal uprooted nine canopy trees on one of the hillslopes, downing 81% of total woody biomass. During three years following disturbance, soilwater NO3--N on the storm-affected hillslope showed persistent 500-fold increases, groundwater NO3--N increased by fourfold, and streamwater NO3--N doubled. Significant changes also occurred in soilwater pH, DOC, SO42-, Ca2+ and Mg2+. By the end of the sixth year following disturbance, streamwater levels of NO3--N had returned to pre-disturbance levels, although soilwater NO3--N concentrations remained slightly elevated. Our results suggest nutrient uptake by canopy trees is a key control on NO3--N export in upland riparian zones, and that streamwater nutrient responses to localized riparian canopy tree windthrow in upland forested watersheds may last as long as half a decade.
Key words: disturbance, watershed, biogeochemistry, nutrient cycling