Cobbaert, D.D. (2012). Factors driving switches in the primary producer communities of shallow lakes of the Boreal Plains, Alberta, Canada. Ph.D. Thesis, University of Alberta, Edmonton, Alberta, Canada. 196 pp.

508703

10.7939/R3M902B6R [view]

Cobbaert, D.D.

2012

196 pp.

Publication

Available for editors  

The mechanisms that contribute to the frequent switching of primary producer communities in shallow lakes on the Boreal Plains of Alberta, Canada were explored. The lakes tend to be clear and macrophyte-rich (61% of lakes) or turbid and phytoplankton-rich (30% of lakes). The study is based on surveys of twentythree lakes on the Boreal Plains, Alberta, Canada monitored from 2001 to 2007. I examined the effect of annual fluctuations in precipitation on the limnological conditions of the study lakes and the primary producer communities. Drought concentrated nutrients, phytoplankton biomass and turbidity, decreasing macrophytes cover and promoting a phytoplankton-rich regime. Macrophyte abundance was better predicted by lake depth. During the study SAV cover increased with lake depth and was significantly higher in 2007 following three years of high water levels. Precipitation-induced switches occur because the lakes are small, isolated and the water budget is dominated by precipitation inputs and evaporative outputs with little surface or groundwater fluxes. The lake and landscape factors affecting the persistence of the macrophyterich regime and phytoplankton-rich regime were assessed. The macrophyte-rich regime was more persistent in shallow lakes (max. depth < 112 cm) with high macroinvertebrate predator biomass (> 580 µg L-1 ) and low TP concentration (< 58 µg L-1 ) (variance explained = 0.66). Lakes with high Daphnia dominance (> 61% of the Cladocera community) and higher TP concentration (> 67 µg L-1 ) were associated with a more persistent phytoplankton-rich regime (variance explained = 0.50). I examined the importance of food web structure in maintaining the alternative regimes. Food web structure appears important in maintaining the resilience of the macrophyte-rich regime in fishless lakes on the Boreal Plains. The macrophyte-rich regime is reinforced (stabilized) by top-down control of phytoplankton and periphyton by macroinvertebrates and zooplankton. In contrast, food web effects appear weak or absent in the phytoplankton-rich regime.

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