Internal loading of nitrogen and phosphorus supports non-N-fixing cyanobacteria in Honeoye Lake

Session: Finger Lakes Water Quality (2)

Justin Myers, Wright State University, justin.myers@wright.edu
Silvia Newell, Wright State University, silvia.newell@wright.edu
Roxanne Razavi, SUNY College of Environmental Science and Forestry, razavi@esf.edu
Lisa Cleckner, Finger Lakes Institute, Hobart and William Smith Colleges, cleckner@hws.edu
Mark McCarthy, Wright State University, mark.mccarthy@wright.edu

Abstract

Honeoye Lake is a small, shallow lake within the Finger Lakes (New York, USA) characterized by an increasing frequency of harmful cyanobacterial blooms. Nitrogen (N) and phosphorus (P), sourced from external (e.g., runoff) and internal loading (e.g., remineralization, N fixation), often control algal growth in lakes. Microbial processes contribute to both nutrient removal (e.g., denitrification) and internal loading. To investigate sediment nutrient dynamics in Honeoye Lake, intact sediment cores were collected five times (May–October) from two sites and incubated using bottom water with no amendments (control) or ¹⁵N stable isotope additions. Sediment cores were sampled daily for nutrients (phosphate, ammonium, nitrate, nitrite, urea) and dissolved gases (O₂, N₂). Sediments were a net source of ammonium (201 ± 66 µmol N m^-2 h^-1) and ortho-phosphate (1.9 ± 0.8 µmol P m^-2 h^-1). Reduced N forms dominated the N pool, and nitrate limited N removal via denitrification. N and P loading from sediments is periodically mixed to the surface layer by meteorological events, promoting algal blooms and a community shift from N-fixing (e.g., Gloeotrichia) to non-N-fixing (e.g., Microcystis) cyanobacterial taxa. Effectively reducing internal and, especially, external loads of N and P is necessary to reduce occurrences and toxicity of these blooms.