Hillslope Nutrient Dynamics Following Upland Riparian Vegetation Disturbance |
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Authors: | J Alan Yeakley David C Coleman Bruce L Haines Brian D Kloeppel Judy L Meyer Wayne T Swank Barry W Argo James M Deal Sharon F Taylor |
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Institution: | (1) Environmental Sciences and Resources, Portland State University, Portland, Oregon 97207-0751, USA, US;(2) Institute of Ecology, University of Georgia, Athens, Georgia 30602, USA, US;(3) Department of Plant Biology, University of Georgia, Athens, Georgia 30602 USA, US;(4) Coweeta Hydrologic Laboratory, USDA–Forest Service, Otto, North Carolina 28763, USA, US |
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Abstract: | We investigated the effects of removing near-stream Rhododendron and of the 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 2 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 the total woody biomass. Over the 3 years following the disturbance, soilwater concentrations
of NO3
−-N tripled on the cut hillslope. There were also small changes in soilwater DOC, SO4
2−, Ca2+, and Mg2+. However, no significant changes occurred in groundwater nutrient concentrations following Rhododendron removal. In contrast, soilwater NO3
−-N on the storm-affected hillslope showed persistent 500-fold increases, groundwater NO3
−-N increased four fold, and streamwater NO3
−-N doubled. Significant changes also occurred in soilwater pH, DOC, SO4
2−, Ca2+, and Mg2+. There were no significant changes in microbial immobilization of soil nutrients or water outflow on the storm-affected hillslope.
Our results suggest that Rhododendron thickets play a relatively minor role in controlling nutrient export to headwater streams. They further suggest that nutrient
uptake by canopy trees is a key control on NO3
−-N export in upland riparian zones, and that disruption of the root–soil connection in canopy trees via uprooting promotes
significant nutrient loss to streams.
Received 30 January 2001; accepted 25 July 2002. |
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Keywords: | : biogeochemistry dissolved organic carbon hillslope hydrology nutrient uptake soilwater chemistry southern Appalachian mountains streamwater quality vegetation removal watershed management windthrow |
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