Life on the Edge: Ecosystem Features of Lakes Across a Mountain–Prairie Elevation Gradient in Western Canada

ABSTRACT Ecological transition zones such as mountain elevation gradients can influence the function and productivity of lakes through changes in climatic characteristics and catchment composition (i.e., land use/land cover). However, surveys of limnological features along such ecological transition zones show variable patterns, making it difficult to extrapolate past results to regions such as the eastern slopes of the Canadian Rocky Mountains. To test the effect of elevation and gradients of environmental variability across such an ecological transition zone, we sampled 11 lakes spanning a 600 m elevation gradient between the prairies and Montane Cordillera of southwest Alberta. We analysed the catchment composition, water chemistry, lake metabolic rates (based on oxygen isotopic analysis), dissolved organic matter (DOM) composition, and zooplankton community composition and diet based on fatty acid analysis. Changes in catchment composition and water temperature along the elevation gradient were not clearly linked to DOM content or composition. Most lakes were autotrophic in summer. ERrates of gross primary production (GPP) and ecosystem respiration (ER) shifted modestly when scaled with elevation, and increased with DOM content and water temperature. Net ecosystem production (NEP = GPP − ER) decreased slightly at higher elevation and peaked at intermediate DOM levels. Zooplankton polyunsaturated fatty acid content was also unrelated to elevation but linked to lake trophic state. Overall, climatic and landscape shifts with elevation transmit inconsistent effects to the limnology of these regional lakes, possibly due to the region's overall low precipitation regime and lakes' weak hydrological connectivity with surrounding terrestrial habitats.