Phytoplankton group-specific and community responses to co-limiting nutrients in a managed reservoir: Lake Murray, South Carolina.

This article focuses on the effects of nitrate (N as NO₃⁻) and phosphate (P as PO₄³⁻) additions on phytoplankton community composition in Lake Murray, a temperate reservoir in South Carolina. Using high-performance liquid chromatography and ChemTax analysis from 2021 to 2023, the study found that green algae, diatoms, and cryptophytes dominated the phytoplankton community, with cyanobacteria comprising a smaller portion. Monthly bioassays in 2023 revealed that all phytoplankton groups except cyanobacteria were co-limited by nitrogen and phosphorus, with nitrogen as the primary limiting nutrient, while cyanobacteria were primarily phosphorus-limited. Nutrient additions of both N and P together caused significant shifts in community structure, notably promoting green algae growth, suggesting that simultaneous increases in nitrogen and phosphorus loading may drive major changes in lake phytoplankton composition, whereas increased phosphorus relative to nitrogen may favor cyanobacterial growth. These findings highlight the importance of managing both nitrogen and phosphorus inputs to mitigate harmful algal blooms and maintain water quality in freshwater lake systems.