NWT RESEARCH DATABASE

Tags: physical sciences, carbon budget, carbon fluxes, organic carbon, erosion, weathering

Objective(s): The overall aim is to assess the carbon balance of the whole Mackenzie River basin and to place constraints on the role of climatic and physical erosion processes in driving certain CO2 source and sinks to the atmosphere and oceans.

Project Description: The objective of this study are to quantify the amount of chemical weathering that takes place in the Mackenzie River Basin, to quantify how much weathering of silicate rocks is done by carbonic acid versus sulfuric acid, and to quantify the chemical weathering of fossil organic carbon. The overall aim is therefore to assess the carbon balance of the whole river basin and to place constraints on the role of climatic and physical erosion processes in driving these CO2 source and sinks to the atmosphere and oceans. WATER VELOCITY TRANSECT At each sampling location, an Acoustic Doppler Current Profiler (ADCP) will allow the researchers to determine bathymetry, water velocity transect and concentration of suspended matter in the river water. All the data is instantaneously recorded and treated with a laptop connected to the ADCP. Establishing the ADCP transect (water velocity over the river cross-section) needs the boat to cross the river from a bank to another. To check the reproducibility of the transect, four to six transects will be made. Altogether, and including the ADCP setup, this procedure will take approximately two hours at each sampling location. SAMPLING Then, at each sampling location, the researchers aim to sample river water at various depths. This will be done thanks to a specific equipment built at the Institut de Physique du Globe de Paris: a point-sediment sampler. It consists in a one meter-long plastic tube, that can contain approximately eight liters of water, and that has one cap at each of its tips, attached via a steel cable to a winch mounted onto a boat. For some sampling locations, several vertical profiles will be made so as to assess the lateral variability of river material. To sample a river cross-section, several hours can be necessary. Finally, if possible, river bed material will be dredged using a simple home-made device. Coarse bank material will also be sampled if possible. FILTRATION Filtration will be achieved within a few hours after sampling, using under-pressure Teflon filtration units and PSE filter sheet, at 0.22 µm porosity. Filtering six to eight liters of water can be done in two or three hours. After filtration completion, filter sheets are brushed and rinsed so as to recover the solid material, which is poured with filtrated water into small glass bottles, to be brought back to the laboratory. Slightly less than a liter of filtrated water is also kept aside for chemical analysis. The researchers hope to initiate collaboration with members of the Aurora Research Institute and local academic institutions. They will be available to discuss their research to date and rational for this trip to local communities during their visit. They will also present findings of the study at international scientific conferences. They also intend to publish the scientific results in international peer-reviewed scientific journals. When possible, they will conduct interviews with the press to publicise their research in the Northwest Territories. The fieldwork for this study will be conducted from July 6 to July 30, 2009. The researchers plan to collect river water and sediment samples from the Mackenzie River and its main tributaries. For this purpose they intend to sample at three locations in the Northwest Territories: Mackenzie River at Tsiigehtchic, Liard River at Fort Simpson, and Slave River near Fort Smith.