Part III Biogeochemical Processes

Water, Air, and Soil Pollution

, Volume 77, Issue 3, pp 229-246

First online:

Hillslope nutrient flux during near-stream vegetation removal

I. A multi-scaled modeling design
  • J. A. YeakleyAffiliated withInstitute of Ecology, University of Georgia
  • , J. L. MeyerAffiliated withInstitute of Ecology, University of Georgia
  • , W. T. SwankAffiliated withCoweeta Hydrologie Laboratory, Southeastern Forest Experiment Station, USDA-Forest Service

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At the Coweeta Hydrologie Laboratory in the southern Appalachians of western North Carolina, a near-stream vegetation manipulation experiment is being conducted to determine the effect of removal of streamside Rhododendron maximum L. on the export of hillslope nutrients (K, Na, Ca, Mg, N, P, S) and organic matter. Experimental hillslope transects that span topographical flowpaths from a local highpoint to the stream have been instrumented with lysimeters and TDR rods at two depths, as well as with streambed and streambank piezometers. We present a review of studies of nutrient flux in the riparian zone of forested watersheds. In the southern Appalachians, we hypothesize that R. maximum is a keystone species at the interface between terrestrial and aquatic systems, with extensive near-stream thickets having a possible impact on carbon and nutrient transport into streams. We present the conceptual basis and initial implementation of a model-based experimental design to test the effect of R. maximum removal on hillslope nutrient and organic matter export in upland watersheds. The model is terrain-based and will be used to extrapolate elemental flux measurements both spatially from the hillslope to watershed scale and temporally for various climate regimes. The model consists of three modules: (1) objective terrain analysis (TAPES-C); (2) a dynamic interception canopy module; (3) a hillslope hydrology module (IHDM4) with a 2-D Richard's equation of subsurface moisture dynamics. Calibration and validation of the model will occur at two scales: at the hillslope scale, using well, lysimeter, and TDR data; at the watershed scale, using streamflow measurements across a variety of storm types. We show watershed terrain analysis for the experimental watershed (WS56) and discuss use of the model for understanding effects of watershed management of riparian zone processes.