Primary Production and Carbon Dioxide Metabolic Balance of a Lake-Rich Arctic River Floodplain: Partitioning of Phytoplankton, Epipelon, Macrophyte, and Epiphyton Production Among Lakes on the Mackenzie Delta
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The Mackenzie River Delta, a floodplain system in the western Canadian Arctic contains approximately 45,000 lakes used by resident and migratory fish, aquatic birds, and mammal populations, which are critical resources for aboriginal peoples. Our results show the Mackenzie Delta is a remarkably productive aquatic ecosystem, not out of place relative to other large river floodplains and unusually productive for its Arctic latitude. Along with other such deltas of north flowing rivers to the Arctic Ocean, it represents a critical habitat of high productivity to support dependent consumers. Our results also showed a consistent under-saturation of CO2 in lake waters of the delta, co-occurring even with high concentrations of dissolved organic carbon, and indicating P:R greater than 1 during the open water period. In less turbid lakes, abundant macrophytes provide a considerable surface area for supporting production of epiphyton, but epiphyton production is constrained strongly by macrophyte shading, when macrophyte biomass is high. Despite this, epiphyton represented a greater supply of non-macrophyte algal carbon than phytoplankton, and thus explains why benthic algae may be a more important food source for primary consumers than phytoplankton, except in the most turbid systems. Most importantly, the high autotrophic production in the Delta lakes relative to nearby lakes on the arctic tundra suggests the extended ice-free season of the floodplain lakes and their landscape setting on, and replenishment by, nutrient-rich river sediments, is the strongest influence on aquatic production levels.