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Monday, June 4, 2007 - 4:00 PM
58
Towards More Accurate Assessment of Food Resource Quality: Correcting for Abiotic Sediment Sorbtion to Assess the P-Content in Algal Periphyton Across a Natural Gradient in SRP
Gaston E. Small and Catherine M. Pringle. Institute of Ecology, University of Georgia, Athens, GA 30602-2202
Our ability to accurately estimate food resource quality in ecological studies is constrained by the resolution at which nutrient content is measured. Standard procedures for sampling periphyton lead to the collection of abiotic sediment as well as algae, microbes, and nonliving organic matter. Periphyton nutrient content has been observed to increase with stream nutrient enrichment, but it is unclear how much of this increase is due to abiotic nutrient sorbtion versus biotic uptake. We measured the P-content of periphyton across natural and experimental SRP gradients (2-250 μg/L) at La Selva Biological Station, Costa Rica. In order to isolate the P-content of organic and inorganic fractions, we used both physical separation (centrifugation in colloidal silica) and a mixing model. Both separation techniques indicated that the inorganic component showed slight P-enrichment with increasing SRP, while the organic component underwent extensive P-enrichment. The degree of periphyton P-enrichment was positively related to chlorophyll a concentration in the organic fraction, suggesting that algal P uptake is responsible for most of the observed nutrient enrichment. Because the organic component of periphyton was enriched in P relative to bulk periphyton samples, failing to correct for abiotic sediment will lead to underestimating the food resource P content.