J. Alan Yeakley, David C. Coleman, Bruce L. Haines, Brian D. Kloeppel, Judy L. Meyer, Wayne T. Swank, Barry W. Argo, James M. Deal, and Sharon F. Taylor.  2003.  Hillslope nutrient dynamics following upland riparian vegetation disturbance.  Ecosystems 6: 154-167.

Abstract

We investigated effects of removing near-stream Rhododendron and 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 (35 03 N, 83 25 W).  Dissolved organic carbon (DOC), K⁺, Na⁺, Ca²⁺, Mg²⁺, NO₃^--N, NH₄⁺-N, PO₄^3--P, and SO₄^2- were measured for two years prior to disturbance.  In August 1995, riparian Rhododendron on one hillslope was cut, removing 30% of total woody biomass.  In October 1995, Hurricane Opal uprooted nine canopy trees on the other hillslope, downing 81% of total woody biomass.  During three years following disturbance, soilwater concentrations of NO₃^--N tripled on the cut hillslope.  There were also small changes in soilwater DOC, SO₄^2-, Ca²⁺ and Mg²⁺.  No significant changes occurred, however, in groundwater nutrient concentrations following Rhododendron removal.  In contrast, soilwater NO₃^--N on the storm-affected hillslope showed persistent 500X increases, groundwater NO₃^--N increased by 4X, and streamwater NO₃^--N doubled.  Significant changes also occurred in soilwater pH, DOC, SO₄^2-, Ca²⁺ and Mg²⁺.  No significant changes occurred in microbial immobilization of soil nutrients or water outflow on the storm-affected hillslope.  Our results suggest Rhododendron thickets play a relatively minor role in controlling nutrient export to headwater streams.  Our results further suggest nutrient uptake by canopy trees is a key control on NO₃^--N export in upland riparian zones, and disruption of the root-soil connection in canopy trees via uprooting promotes significant nutrient loss to streams.