Natural Resources, School of


Date of this Version

Spring 4-23-2010


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Natural Resources Sciences, Under the Supervision of Professor Steven A. Thomas. Lincoln, Nebraska: May, 2010
Copyright (c) 2010 Tyler J. Kohler


Light and nutrient availability are strong factors determining the nutrient composition of epilithon in temperate stream ecosystems. However, little work has been performed regarding this association in tropical streams. In our study, we investigated 1) how gradients of canopy cover and nutrients and 2) wet/dry seasonality influence epilithon standing stocks and nutrient quality. We surveyed 18 stream locations within six watersheds that varied in nutrient and light conditions during both the wet and dry seasons on the island of Trinidad to test these questions. Additionally, we sampled four stream reaches bimonthly for three years, thinning the canopy of two of the streams to create high light conditions. All epilithon was analyzed for nutrient composition (C:N:P) and biomass, and linear mixed-effects models were used to explain variation within each parameter. We found nutrient ratios to be influenced by nutrient concentration and open canopy, though the magnitude differed by system and approach. Furthermore, we found that seasonality has a large influence on the standing stock and % carbon of epilithon, suggesting nutritional differences by season and watershed. These finding contribute to the growing number of studies investigating the Light : Nutrient hypothesis, as well as the nutrient quality of base resources in the tropics.