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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Periphyton
PERIPHYTON RESPONSE TO NUTRIENT ENRICHMENT IN AN APPALACHIAN HEADWATER STREAM.
J.L. Greenwood and A.D. Rosemond. Institute of Ecology, University of Georgia, Athens, Georgia 30602
The response of periphyton to nutrient enrichment was examined in two forested headwater streams at Coweeta Hydrologic Laboratory. These streams have low ambient nutrient concentrations and are heavily shaded with a "double canopy" of evergreen Rhododendron maximum and deciduous trees. Light levels reaching the stream are typically 20 μmol/m2/sec year-round. Bimonthly periphyton samples were taken one year prior to treatment in July 2000 and for the following year of continuous enrichment from the treatment and control streams. Treatment nutrient concentrations were approximatley 150 μg/L NO3- + NH4+ and 35 μg/L SRP. Chlorophyll a values averaged 5-15 mg/m2 in both control and treatment streams from July 1999-January 2001. From March 2001-May 2001, chlorophyll a in the treatment stream increased by 10-20mg/m2 relative to the control. However, by July 2001, chlorophyll a levels were again similar between treatment and control streams. Increased chlorophyll a in the treatment stream occurred when light levels were at their maximum, but were not sustained under full canopy leaf out. No differences between streams or seasonal patterns were apparent with AFDM data. These results indicate that small variations in light can affect periphyton response to nutrients, but that periphyton biomass responded little to continuous nutrient enrichment in these shaded, headwater streams.
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