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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Periphyton
NUTRIENT LIMITATION ACROSS A GEOLOGICALLY DIVERSE LANDSCAPE.
L.A. Panayotoff and J.W. Feminella. Department of Biological Sciences, Auburn University, Auburn, Alabama
We assessed the influence of nutrient limitation on algal biomass accrual and species composition in 6 streams in NW Alabama that differ in geology, 3 flowing through sandstone bedrock and 3 flowing through limestone bedrock. In situ bioassays were conducted in winter and summer using nutrient diffusing substrata (NDS) enriched with N, P, both, or unenriched. We predicted that effects of nutrient enrichment would be distinct with respect to geologic type in terms of 1) nutrient(s) limiting biomass accrual, 2) degree of limitation, and 3) algal taxa most affected by enrichment. Nutrient limitation status varied widely across streams in winter, as indicated by algal biomass accrual (as chlorophyll-a) on enriched versus control NDS. Where nutrients were limiting, there was a 2- to 3-fold increase in biomass with enrichment, mainly due to increase in stalked or erect diatom taxa. In summer, N was primarily limiting in limestone streams, with P secondarily limiting. Enrichment caused a 3- to 8-fold increase in biomass above controls, mainly due to increase in Achnanthidium minutissimum. N and P were not limiting in sandstone streams. These results demonstrate that geology can contribute to spatial and temporal variability in nutrient limitation in streams within a small geographic region.
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