Water Resources Research Act Program

Details for Project ID VT_2023_Morales1

Influence of artificial aeration on nitrogen fixation and nutrient limitation of phytoplankton in Lake Carmi, VT

Institute: Vermont
Year Established: 2023 Start Date: 2023-09-01 End Date: 2024-08-31
Total Federal Funds: $14,861 Total Non-Federal Funds: $14,861

Principal Investigators: Ana M. Morales-Williams

Project Summary: Oligotrophic lakes Vermont have doubled in total phosphorus (P) over the past 40 years, and cyanobacteria blooms are intensifying or newly emerging across trophic states. Substantial efforts to control P are underway, but nitrogen (N) is less understood. In July 2019 an aeration system was deployed in Lake Carmi, a eutrophic lake in northwestern Vermont, to mitigate cyanobacteria blooms by oxygenating bottom waters and controlling sediment P release. Aeration has not reduced cyanobacteria biomass, has increased biomass of nitrogen-fixing taxa, and displaced late-season diatom blooms. Pre-aeration nutrient limitation bioassays indicated that phytoplankton were N or NP co-limited, indicating the need to understand N-cycling. In 2022, the research team conducted microcosm nutrient limitation experiments to assess changes in nutrient limitation since aeration, and they collected samples to measure N fixation rates using acetylene reduction. This project will support the repeat of these experiments and laboratory analyses. Results will increase understanding of N cycling in eutrophic Lake Carmi and inform future management efforts aimed at mitigating blooms.