REU/ROW: Factors Controlling Algal Periphyton Growth and Nitrogen Transformations in a Lowland Tropical Stream

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A transect of rainforest on Costa Rica's eastern slope extends from near sea level on the Atlantic coastal plain to 2,600 m in the volcanic peaks of the Central Cordillera. This land corridor constitutes the last intact tract of primary rainforest spanning such elevational extremes left on Central America's Atlantic Slope, providing an unparalleled site for the investigation of pristine tropical streams. Previous studies suggest that phosphorus-rich streams draining swamp forest at the lower end of this continuum are important sites of nitrogen transformation via microbial denitrification. Micronutrient limitation of algal growth has also been demonstrated. This study focuses on factors controlling algal production and nitrogen transformations in a lowland swamp forest stream. It will advance our understanding of biogeochemical cycles in the Central American tropics and the numerous factors affecting algal primary production. Major objectives are: (1) to measure seasonal variation in nutrient levels and diurnal variations in nutrient flux in selected stream reaches located within, above and below swamp forest; (2) to examine effects of nutrient additions, light and fish grazing on algal growth and primary production under different nutrient regimes above and below swamp forest; and (3) to measure seasonal fluctuations in denitrifying potentials of stream sediments under endogenous and nutrient- enriched conditions, within, above, and below swamp forest.