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

哥斯达黎加东部斜坡上的热带雨林从大西洋沿岸平原的近海平面延伸到中部科迪勒拉火山峰的2600米。这片陆地走廊构成了中美洲大西洋斜坡上最后一片完整的原始雨林，为原始热带溪流的研究提供了一个无与伦比的场所。先前的研究表明，在这个连续体的低端，排水于沼泽森林的富磷溪流是通过微生物反硝化作用进行氮转化的重要场所。微量元素对藻类生长的限制也已得到证实。本文研究了低地沼泽森林溪流中藻类生产和氮转化的控制因素。它将促进我们对中美洲热带生物地球化学循环和影响藻类初级生产的众多因素的理解。主要目标是：(1)测量位于沼泽森林内部、上方和下方的选定溪流的养分水平的季节变化和养分通量的日变化；(2)研究不同营养条件下，添加营养物、光照和放鱼对沼泽森林上下藻类生长和初级生产的影响；(3)测量内源和富营养化条件下，沼泽森林内部、上面和下面水系沉积物反硝化势的季节波动。

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.