Biogeochemistry of lakes in the Mackenzie delta

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The long-term goal is to develop a general ecosystem model for lakes in the Mackenzie Delta to facilitate assessing the effects of multiple stresses on major river floodplains [28-30] resulting from global change [1]. The delta contains 45,000 lakes [11] and is representative of floodplain lakes among major river deltas of the circumpolar arctic [1], a region of the world where climate is changing more rapidly than anywhere else [31]. Circumpolar river deltas are lake-rich because of thermokarst effects [11]. These systems are complex [32-34] and represent thousands lakes [35] that function as critical aquatic habitat for fish, birds, and mammals. They are sensitive to global change because thermokarst and jamming of river-ice are highly temperature dependent [36], and because deltas are affected by processes occurring throughout the drainage basin [1]. Significant advances in this research over the past 5 yr includes improved understanding of (1) aquatic autotrophs, underwater light, bacteria, & zooplankton; (2) transparency of water-types to UV-radiation; (3) photochemical effects on dissolved organic C (DOC) & aquatic bacteria; (4) Mackenzie Delta effects on riverine nutrient fluxes to the Beaufort Sea; (5) Mackenzie Delta fit within ecological models of large river floodplains; (6) formulation of 89 hypotheses on responses of delta lakes to combined stresses of global change; & (7) detection of significant changes in water level regime. Next 5 years will involve continuing efforts to assess the strength and direction of delta lake responses to individual stresses of global change. Specific goals include assessing (1) sources and fates of DOC in delta foodwebs; (2) abundance & bacterial colonization of transparent exopolymer particles; (3) foodweb controls on heterotrophic nanoflagellates; (4) photochemical production of H2O2 and biolabile-DOC; (5) responses of aquatic bacteria to declining flooding regime; & (6) delta effect on annual nutrient fluxes to Beaufort Sea, to capitalize on upcoming IPY. DG funds, with requested NRS, will facilitate training & research of 2 PhD & 3 MSc students plus 5 field assistants in arctic-based research.