Landscape variables influencing nutrients and phytoplankton communities in Boreal Plain lakes of northern Alberta: a comparison of wetland- and upland-dominated catchments

A review of headwater lakes in undisturbed watersheds on the Boreal Plain, with indirect gradient analyses of chemical data, indicated a clear separation between those in wetland-dominated watersheds (57-100% wetland with variable proportions of bog, fen, swamp, and marsh cover) and those in upland-dominated watersheds (0-44% wetland cover). In the former, percentage wetland cover in the watershed was positively correlated with total phosphorus (TP, r 2 = 0.78, primarily bog), total nitrogen (TN, r 2 = 0.50), and dissolved organic carbon (DOC, r 2 = 0.74) concentra- tions. Rich fens appeared to sequester both TP and TN. In upland-dominated lakes, the ratio of catchment area to lake volume (CA/LV) was the strongest watershed correlate of TP concentration (r 2 = 0.56), whereas most limnetic nitrogen and DOC were generated in situ. Colour concentration, being highest in wetland lakes, was correlated with the ratio of isotopically defined effective drainage basin area to lake volume (eDBA/LV, r 2 = 0.63). Drainage basin slope was only weakly associated with water quality, likely because of low topographic relief ( 11%). Higher Chlorophyta and Peridineae biomasses in wetland-dominated systems than in upland-dominated ones may coincide with greater NH4 + availability. 1299

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