title: Seasonal and decadal patterns in Discostella (Bacillariophyceae) species from bi-weekly records of two boreal lakes (Experimental Lakes Area, Ontario, Canada).
abstract: A recent rise in the relative abundance of Discostella species (D. stelligera and D. pseudostelligera) has been well documented from sedimentary diatom assemblages across the Northern Hemisphere. This unprecedented change over the last ~150 years has been linked to rises in atmospheric temperatures, changes in ice cover, and/or increases in thermal stability, among other factors. The bi-weekly monitoring data from two boreal lakes at the Experimental Lakes Area (ELA) in northwestern Ontario were analyzed across seasons (spring, summer, and fall) and decades (1970s-2000s). We found that Discostella species are primarily spring/early summer bloomers (i.e., late April to June) in these lakes and changes in concentrations of Discostella over time were most pronounced in the spring or early summer months. Increases in Discostella abundance over time may be linked to earlier ice-off and a longer period of spring turnover, resulting from increased winter and spring temperatures. It is also possible that a trophic mismatch between the spring diatom bloom and zooplankton is occurring, thus reducing diatom loss rates, and resulting in greater overall abundance. Moreover, the spring dominance of Discostella in our study lakes occurred at a time of the year when nutrient concentrations were at their highest seasonally, suggesting that these taxa are neither limited directly by nutrients, nor responding to enhanced stratification during the summer months in these lakes.
authors.affiliation: Ausable River Association, PO Box 8, Wilmington, New York, 12983, USA.
authors.forename: Brendan
authors.initials: B
authors.lastname: Wiltse
authors.affiliation: Dorset Environmental Science Centre, Ontario Ministry of the Environment and Climate Change, 1026 Bellwood Acres Road, Dorset, Ontario, Canada, P0A 1EO.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Paterson
authors.affiliation: Freshwater Institute, 501 University Crescent, Winnipeg, Manitoba, Canada.
authors.forename: David L
authors.initials: DL
authors.lastname: Findlay
authors.affiliation: School of Environmental Studies, Queen's University, 116 Barrie St, Kingston, Ontario, Canada, K7L 3N6.
authors.forename: Brian F
authors.initials: BF
authors.lastname: Cumming
mesh_terms: D044822:Biodiversity; D017377:Diatoms / Q000502:physiology*; D060106:Lakes; D009864:Ontario; D011157:Population Dynamics; D012621:Seasons; D013696:Temperature
keywords: 
  Discostella stelligera
  ; Experimental Lakes Area; Seasonal; boreal lakes; climate change