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Régions: Inuvialuit Settlement Region, Gwich'in Settlement Area

étiquettes: physical sciences, biology, limnology, food web, habitat, carbon

Objectif(s): The objectives of this project are: (1) Resolution of the sources and fates of dissolved organic carbon (DOC) in aquatic food webs of the Mackenzie Delta (year 3 of PhD thesis - S. Tank); (2) Assessing importance of dissolved organic matter transformation into microscopic transparent exopolymer particles (TE-particles) among lakes of Mackenzie Delta (year 2 of MSc thesis - A. Chateauvert); (3) Tracking of changes in dissolved organic carbon (DOC) composition and nutrient content available for aquatic bacteria among delta lakes used for bacterial growth efficiency experiments (BSc project of S. Magee);(4) Assessing the annual effect of Mackenzie Delta on riverine nutrient outflow to Beaufort Sea (year 1 of PhD thesis project of J. Gareis).

Description du projet: Specific activities for this field season include the following: (1) Resolution of the sources and fates of dissolved organic carbon (DOC) in aquatic food webs of the Mackenzie Delta (year 3 of PhD thesis project of S. Tank). This information is needed to ultimately understand the relative role of bacterial (fueled by DOC) versus photosynthetic organisms and their importance in ultimately supporting fish and aquatic birds in this system. With climatic warming, water levels in the Mackenzie River are expected to decrease because of reduced ice jamming in the river channels during spring break up. Such a change in flooding regime will significantly alter the DOC regime among delta lakes and the fuel available for aquatic bacteria. During summer 2007 this study will (a) assess the hypothesis that older DOC, derived from river-water and thermokarst melting of permafrost, is an inferior bacterial substrate than newer DOC derived from macrophyte production; and (b) assess the hypothesis that in lakes where new DOC predominates, bacteria are a greater contributor to higher trophic levels such as zooplankton. This research will be conducted at the Aurora Research Institute and will entail the following. (i) Laboratory incubations at the Inuvik Research Centre will be used to assess aquatic bacterial growth on various DOC substrates. Water will be collected from 9 lakes, ranging in character from river-connected to macrophyte-rich (no direct river connection) to strong thermokarst effects. DOC will also be extracted from macrophyte tissue, and permafrost adjacent to the lakes. Incubations will measure the growth rate, respiration rate, and growth efficiency of the resident bacteria populations. (ii) Micro-zooplankton samples will be collected (mid-July) from the same set of 9 lakes near the peak of open-water productivity, and will be analyzed for fatty acid biomarkers. These results will be used in combination with stable isotope data collected in the 2 prior summers to resolve the relative importance of old versus new DOC in supporting higher organisms. (2) Assessing the importance of dissolved organic matter transformation into microscopic transparent exopolymer particles (TE-particles) among lakes of the Mackenzie Delta ((year 2 of MSc thesis project of A. Chateauvert). This study will investigate the chemical transformation of dissolved organic carbon (DOC) directly into particle form that may then be removed from the water via sedimentation. This process may be very important for removing DOC from river-water that otherwise would be transported to the Beaufort Shelf, plus such transformation to particle form may also affect the quality of food for aquatic bacteria among the lakes. During summer 2007 this study will further assess the hypothesis that sediment-rich river-water mixing with lake waters will enhance TE-particle removal via enhanced particle aggregation and sedimentation. Experiments on mixtures of lake-waters will be conducted at the Inuvik Research Centre where lake-water and river-water will be mixed together in combinations of - (i) whole lake-water + whole river-water, (ii) whole lake-water + river sediments added, (iii) whole lake-water + filtered river-water, (iv) filtered lake-water + whole river-water. Treatments will be batch mixtures with standardized slow mixing rates approximating in situ lake conditions and tracked for two days each. The general set of experiments will be conducted during early summer when in aquatic photosynthesis has taken off, first using water from a lake with high photosynthesis and then from another lake with low photosynthesis. (3) Tracking of changes dissolved organic carbon (DOC) composition and nutrient content available for aquatic bacteria among delta lakes used for bacterial growth efficiency experiments (BSc project of S. Magee). This work is complimentary to the PhD project of Tank and is needed to interpret her experiments on suitability of carbon sources as fuel for aquatic bacteria. During summer 2007, this study will (a) measure the weekly changes (mid- June through August) in levels of DOC and other nutrients among the 9 lakes selected for the experiments; and (b) conduct various measures of DOC quality and water optical properties on the water samples from the suite of lakes back at the Inuvik Research Centre. (4) Assessing the annual effect of Mackenzie Delta on riverine nutrient outflow to Beaufort Sea (year 1 of PhD thesis project of J. Gareis). The Arctic Ocean receives high river inflows and this has major ecological implications. The researcher’s general hypothesis to be investigated over next 3 years (NSERC-DG funds) is that off-channel river-water in the delta is a substantial portion of river discharge during breakup, and such temporary storage reduces particulates and dissolved inorganic nutrients, but enhances dissolved organic nutrients, resulting in nutrient quality that differs from prior reports on Mackenzie River water. During 2007, Field work will include (a) monitoring of delta floodwater depths at peak water levels (early June) (b) Lake depth estimates will be improved via measuring depths in lakes, other than the ones that have been routinely worked on. (c) Assumptions about floodplain geometry from lake-water's edge to local levee tops, and relations of floodplain area to lake area will be assessed via ground survey. (d) Nutrient compositions of floodwaters at peak water levels will be improved via sampling of lakes and floodplain areas during the latter breakup period (prior to peak water) before boating is possible in the delta, and via sampling of rill-waters in areas surrounding several delta lakes during the early falling water period. The researchers generally make an effort to publish the results of their work in top-ranked scholarly journals that are subscribed to by the library at the Aurora Research Institute. To make research results more accessible to communities in the NWT, they have posted a website on their Mackenzie Delta research <http://www.sfu.ca/limnology>. This highlights their research and student opportunities for training in arctic based research. The principal investigator’s students have given presentations at the Inuvik Research Centre, Summer Research Forum. He has also given presentations in Inuvik and expects to give a presentation on their work on the Mackenzie Delta to the Inuvik Hunters and Trappers Committee when he is in Inuvik this summer. This project will also benefit local communities by advancing the general understanding of how the lakes in the Mackenzie Delta will respond to global change stresses such as climatic warming, sea-level rise, changes in Mackenzie River flow, and arctic regional changes in ultraviolet radiation. Fieldwork will be conducted from May 15 to August 30, 2007 within the Mackenzie Delta in the vicinity of Inuvik.