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 [36-38] resulting from global change [1]. The delta contains 45,000 lakes [6] 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 [24]. Circumpolar river deltas are lake-rich because of thermokarst effects [6]. These systems are complex [39-41] and represent thousands lakes [42] 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 [26], and because deltas are affected by processes occurring throughout the drainage basin [1]. Significant advances in this research over the past 4 yr includes improved understanding of (1) aquatic autotrophs, underwater light, bacteria, & zooplankton; (2) transparency of water-types (mixtures of colored (CDOC) & non-colored (NCDOC) dissolved organic carbon) to UV-radiation; (3) photochemical effects on 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; and (6) formulation of 89 hypotheses on responses of delta lakes to combined stresses of global change. Next 5 years will involve continuing efforts to assess the strength and direction of ecosystem responses in delta lakes to individual stresses of global change. Specific goals include assessing (1) sources and fates of dissolved organic carbon in delta foodwebs via isotopic modeling; (2) foodweb controls on plankton heterotrophic nanoflagellates (HNAN) in delta lakes; (3) photochemical production of H2O2 and biolabile-DOC in delta lakes; (4) responses of aquatic bacteria to photochemical effects and high pH in delta lakes; and (5) further work on delta effects on river outflow to the Beaufort, needed for independent but collaborative IPY investigations. DG funds, with requested NRS, will facilitate training & research of 2 PhD & 3 MSc students plus 5 field assistants in arctic-based research.