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 [33-35] resulting from global change [2]. The delta contains 45,000 lakes [16] and is representative of floodplain lakes among major river deltas of the circumpolar arctic [2], a region of the world where climate is changing more rapidly than anywhere else [36]. Circumpolar river deltas are lake-rich because of thermokarst effects [16]. These systems are complex [37-39] and represent thousands lakes [40] that function as critical aquatic habitat for fish, birds, and mammals. They are sensitive to global change because thermokarst and river-ice breakup effects are highly temperature dependent [41], and because deltas are affected by processes occurring throughout their drainage basin [2]. Significant advances in this research over the past 6 yr includes improved understanding of (1) aquatic autotrophs, bacteria, and zooplankton; (2) under-water irradiance; (3) photochemical effects on dissolved organic C (DOC) and aquatic bacteria; (4) sources and fates of DOC in delta foodwebs; (5) Mackenzie Delta effects on riverine nutrient fluxes to the Beaufort Sea; (6) Mackenzie Delta fit within ecological models of large river floodplains; (7) 89 hypotheses formulated on responses of delta lakes to combined stresses of global change; and (8) detection of 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) delta aquatic habitat modeling through dynamic range of water levels; (2) lake flooding, land/water ratios, and landscape changes in delta; (3) photochemical production of H2O2 and biolabile-DOC; (4) responses of aquatic bacteria to declining flooding regime; (5) foodweb controls on heterotrophic nanoflagellates; and (6) abundance and bacterial colonization of transparent exopolymer particles. DG funds, with requested NRS, will facilitate training and research of 2 PhD and 3 MSc students plus 5 field assistants in arctic-based research.