Testa, Charles, Biology, Bucknell University, 580 South 7th Street, Lewisburg, Pa, 17837, charlie_t06@icloud.com; Matthew, McTammany, R, Biology Department, Bucknell University, 1 Dent Drive, Lewisburg, PA, 17837, mmctamma@bucknell.edu.
Many previous studies have measured chlorophyll concentrations at varying depths in lake water columns, finding a near-linear decrease in chlorophyll levels with increasing depth (Demidov & Mosharov, 2015). While these studies provide valuable insights into algal productivity, they primarily focus on lentic systems and neglect benthic algae and flowing water environments. The goal of this research was to determine whether algae in flowing water systems are similarly influenced by light and nutrient limitations. To address this, we conducted two experiments: a nutrient-diffusing substrate (NDS) experiment in Stony Run, Cowan, Pennsylvania, and a controlled in-tank experiment at Bucknell University. In both experiments, we varied light intensity and nutrient availability to evaluate how resource availability affects algal growth. In the NDS (field) experiment, nutrient supplementation was the primary driver of algal growth, with nitrogen and phosphorus treatments producing the highest chlorophyll concentrations, followed by phosphorus alone. In contrast, the in-tank experiment showed that light was the most influential factor overall, while combined nitrogen and phosphorus supplementation had the strongest nutrient effect, followed by nitrogen alone. Previous literature suggests that algal growth in freshwater systems is typically nitrogen-limited (Tank et al., 2017), and our in-tank results support this pattern. However, our field results differed, indicating that further investigation of nutrient dynamics in Stony Run is warranted.