Effects of Nutrient Enrichment on the Growth of the Green Alga Spirogyra

Abstract- Spirogyra is a lamentous green alga that inhabits the streams and lakes of North America, including Conesus Lake, NY. Two separate experiments were designed to determine if nutrient enhancement had an effect on Spirogyra growth. In one experiment, known quantities of Spirogyra were placed in 12 containers provided with mesh screens. The containers were separated into three groups and held in racks that were placed at increasing distances from a stream with a known efuent nutrient load. The average percent change in biomass calculated after two weeks for near, middle and far distances were 35.38, 16.62, and 4.12 (respectively). The growth rates of algae incubated near the stream were signicantly higher than algae living farther away from the stream. In a second experiment, Spirogyra was incubated in 12 closed one-liter containers. Each set of jars contained different concentrations of enhanced nitrogen and phosphorous; amounts of lake water and Spirogyra remained constant. Two sets of jars had enhanced concentrations of N and P, while a third contained ambient lake water. The average percent change in increased biomass determined after two weeks in the lake was 19.8 (high nutrient concentration), 10.8 (low nutrient concentration) and 7.5 (no nutrient addition). There was a statistically signicant difference in the growth rates of algae living in high concentration and control environments. The results obtained from these two experiments support our hypotheses that Spirogyra living in an environment with enhanced nutrient levels will have an accelerated growth rate compared to algae living in waters with ambient levels of N and P. Since the greatest Spirogyra growth was observed with increasing distance from stream outlets into the lake, articial nutrient addition should be a concern to the Conesus Lake community. ___________________________________________________________________________________________________________