CGRG Bibliography of Canadian Geomorphology
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Author : Brock, B.; Wolfe, B.; and Edwards, T.
Date : 2008.
Title : Present and past river discharge and spring flooding in the Slave River Delta, NWT, using water isotope tracers and lake sediments.
Publication : International Arctic Change 2008 Conference. December 9-12, 2008. Quebec City, Quebec.
Issue : Conference Programme and Abstracts
Page(s) : 190.
Abstract
The Slave River Delta (SRD), NWT, is a productive northern freshwater ecosystem in the Mackenzie River Basin. Recent concerns about the impacts of upstream water use, declining river discharge and the effects of climate variability on the hydroecology of the SRD have prompted the need to further understand the crucial role of water in this freshwater ecosystem. Stable isotope (18O, 2H) and suspended sediment data obtained from SRD lakes over three consecutive thaw seasons (2003-2005) provide a unique opportunity to tease apart the roles of the Slave River and climate on SRD hydroecology. While climate conditions were remarkably similar during the monitoring period, the spring break-up varied significantly. Moderate spring flooding occurred in 2003, flooding was absent in 2004, and a major flood occurred in 2005. floodwater serves as a key hydrological input to lakes in the active delta, where the spatial extent of flooding is positively correlated with discharge on the Slave River. Later in the thaw season, evaporation becomes one of the major hydrological factors controlling SRD lakewater balances. Sedimentary flood deposits from a delta lake, identified using peaks in C/N ratios, correspond to high magnitude events in the ~45-year Slave River discharge record, demonstrating the potential for reconstructing Slave River flood frequency using lake sediments. Notably, paleohydrological reconstructions from this lake sediment core are similar to records from the upstream Peace- Athabasca Delta (PAD) suggesting upstream snow accumulation, rate of snowmelt and discharge are the primary drivers of periodic ice-jam flooding in the PAD and SRD. To extend Slave River flood history beyond the instrumental record, a ~7 m sediment core was collected from another SRD lake adjacent to the Slave River using a vibracorer. The sediment core is laminated throughout and contains light grey sediment with frequent medium to dark brown beds and laminations. Light grey sediment is consistently very fine grained (clay to very fine silt). Medium and dark brown beds and laminations are <0.5 mm to ~8 cm thick (commonly 0.5-2 cm), and are typically fine to medium grained sand that fine upwards from a sharp lower contact, suggesting deposition during high energy events and subsequent suspension settling. X-ray imagery and magnetic susceptibility will be used to quantify changes in the sediment sequences and results will be used to hindcast Slave River flood frequency. Results will be compared to a ~600-year record of flood frequency from the PAD, and will be key to understanding drivers of historical deltaic evolution and anticipating future changes in the SRD in light of changing climate and river discharge.
Bibliography of Canadian Geomorphology