Oral Presentation Society for Freshwater Science 2025 Annual Meeting

Examining environmental drivers of Gloeotrichia density over space and time (118785)

Emily R Arsenault 1 , Holly A Ewing 2 , Kathy L Cottingham 3 , B G Steele 4 , Danielle J Wain 5 , Ben L Peierls 6 , Linda C Bacon 7 , Denise A Bruesewitz 8 , Cayelan C Carey 9 , Shana L Ederer 2 , Meredith L Greer 2 , Colin Holme 6 , Amanda Pratt 10 , Kathleen C Weathers 11 , Maggie Welch 6
  1. State University of New York College of Environmental Science and Forestry, Syracuse, NY, United States
  2. Bates College, Lewiston, ME, USA
  3. Dartmouth College, Hanover, NH, USA
  4. Colorado State University, Fort Collins, CO, USA
  5. 7 Lakes Alliance, Belgrade, ME, USA
  6. Lakes Environmental Association, Bridgton, ME, USA
  7. Maine Department of Environmental Protection, Augusta, ME, USA
  8. Colby College, Waterville, ME, USA
  9. Virginia Tech University, Blacksburg, VA, USA
  10. Portland Water District, Portland, ME, USA
  11. Cary Institute of Ecosystem Studies, Millbrook, NY, USA

While both climate change and nutrient additions have been implicated in freshwater cyanobacterial blooms, the drivers of such blooms in low-nutrient lakes are not well understood. Gloeotrichia spp. are colonial, nitrogen-fixing cyanobacteria that may be present in low- as well as high-nutrient systems. Though paleorecords document Gloeotrichia in low-nutrient systems over hundreds of years, their presence has been increasingly reported in northeastern North America over the last few decades. Because Gloeotrichia density seems to be controlled by interacting factors working across temporal and spatial scales, the specific interannual drivers of cross-lake differences in Gloeotrichia density are unclear. Here, we describe a collaborative effort to identify potential environmental drivers of Gloeotrichia density (colonies/L) using a 15-year dataset collected across 52 lakes by researchers and community scientists associated with academic, governmental, and non-profit institutions in New Hampshire and Maine (USA). While Gloeotrichia were observed at levels of at least 1 colony/L in 13 lakes and levels of at least 10 colonies/L in 11 lakes over the period of study, peak density did not correspond across lakes within a year. The general absence of cross-lake temporal coherence in bloom timing and magnitude suggests that any climatic driver must be modified by lake-specific characteristics. Rarefaction analysis indicated that the unpredictability of the timing of peak Gloeotrichia density necessitates sampling at weekly or sub-weekly scales—timing that may be particularly well-suited to observations from community scientists who may live near or recreate frequently on lakes. While laboratory counts of Gloeotrichia provide specific numerical values for density, we found that visual scale data collected by community scientists capture many of the same major patterns in Gloeotrichia dynamics over time. Our collaborative, long-term dataset highlights the occurrence of Gloeotrichia across lakes and the highly dynamic nature of its density over space and time.