NWT RESEARCH DATABASE

Regions: Gwich'in Settlement Area

Tags: physical sciences, landscape disturbance, hydrology, slumping, geochemistry, ice thaw

Objective(s): To understanding cumulative effects of mega-slump development on the land and water of the Peel Plateau; and to establish a regional long-term monitoring program with the community of Fort McPherson to assess general environmental trends.

Project Description: In the Gwich’in Settlement Region, residents of Fort McPherson have identified the unusual size of the mega-slumps on the Peel Plateau as a serious concern to both water quality and aquatic ecosystem. In addition to research oriented objectives relevant to understanding cumulative effects of mega-slump development on the land and water of the Peel Plateau, the project team will pursue establishing a regional long-term monitoring program with the community of Fort McPherson to assess general environmental trends. The principal objectives of the project and purpose are listed below. Objective 1: Determine the distribution and growth rates of thaw slumps over the period of remote sensing record. The purpose of this component of the project is to determine patterns of thaw slump distribution and assess if the current distribution, number and size of slumps (and mega-slumps) has increased since the 1940s. Tracking patterns of slump growth may reveal linkages to changing climatic parameters. Mapping the distribution of slumps will also help to identify geological or environmental controls that can be used to produce sensitivity maps that will inform infrastructure planning and decision making. Disturbance maps will also allow us to estimate the magnitude of thermokarst impact on regional hydrological networks. A series of thematic maps will be produced for the community, Department of Fisheries and Oceans (DFO), Department of Transportation (DOT) and published at the NWT GeoScience office in geospatial format. Objective 2: To determine hydrological, sediment and geochemical regimes of disturbed and undisturbed streams (Stony Creek, Vittrekwa River) in the Peel Plateau to and evaluate long-term geochemical trends in the Peel River. This project objective investigates the impacts of mega-slumps and other disturbances on the hydrological regime, sediment load and geochemistry of local fish bearing streams in the Peel Plateau. a) The purpose of this objective is to monitor flow and turbidity and analyze water quality in undisturbed streams and in those impacted by mega-slumps of varying intensities. Flow and water quality of runoff will be monitored from varying sources (surface and subsurface flow from disturbances of varying type and age) and geochemical tracers will be utilized to determine the relative impacts of different disturbance types (Cumulative impacts) on stream water quality. b) Geochemical tracers (indicators) will be identified that can be used to track and quantify the relative contribution of slump runoff in the respective watersheds and in the Peel River utilizing geochemical hydrograph separation techniques. Long-term geochemical trends will also be investigated through statistical analysis of the 40 year Peel River water chemistry data set and causes of changes to water quality will be explored. c) Preliminary data from 2010 have revealed a new hydrological regime unique to the growing number of streams impacted by active and stabilized mega-slumps. In impacted streams, flow, sediment concentrations and geochemistry fluctuate on a daily basis following patterns of ground ice melt in thaw slumps. Describing and documenting this regime is very important in understanding the implications of these disturbances on stream ecology and fish habitat over broad areas of northwestern North America. Measureable outputs include the collection and archiving of data with the NWT Geoscience office database and publication of peer-reviewed and plain language reports related to this objective. Participation of local research partners will enable the collection of bi-weekly water quality samples and flow measurements to calibrate instrument readings. These datasets will provide aquatic ecologists and resource managers with quantitative information on how mega-slumps are altering variability in northern stream ecosystems. Outputs include a NWT Geoscience open file and series of peer-reviewed papers (by 2012-13). Objective 1: Determine the distribution and growth rates of thaw slumps (and other natural and anthropogenic disturbances) over the period of remote sensing record. Historical thaw slump distribution and relative change in the Peel Plateau (from Aklavik to south of Fort McPherson) will be reconstructed from aerial photographs acquired from the National Air Photo Library (Ottawa, Canada) and from satellite images (Landsat ETM7+, Quickbird). The following years have photos and images covering the Stony Creek watershed, 1944, 1952-54, 1970-71, 2008, 2009). The air photos will be scanned, georeferenced and imported in ArcGIS. The slumps will be traced to calculate their surface area for the different time periods. This information will be used to quantify the potential volume of sediments released during slumping. Using 15m resolution Digital Elevation Models, information relating to slope and orientation in slump distribution will also be extracted. From this database, thematic maps will be produced that will be made available to the community and decision makers. Objective 2: Determine hydrological, sediment and geochemical regimes of disturbed and undisturbed streams and groundwater in the Stony Creek and Vittrekwa River watersheds and evaluate long-term geochemical trends in the Peel River. Hydrological loggers equipped with turbidity, dissolved oxygen, pH, temperature, depth and conductivity will be deployed in June 2011 and retrieved in September 2011 at the outflow of Stony Creek and the Vittrekwa River and in tributary streams with catchments impacts to varying degrees by thaw slumping or other disturbances. Periodic water samples and discharge measurements will be obtained to calibrate the logger measurements of streamflow, chemistry and sediment concentrations. Bi-weekly collection of water samples and streamflow at the outlets of Stony and Vittrekwa creeks will be maintained by the Tetlit Renewable Resource Council. These data will also enable mass flux to be estimated from these watersheds. In order to explain variations in stream water chemistry the research team will aim to determine the impacts of disturbances on the geochemical nature of surface and subsurface runoff from disturbed and undisturbed slopes. Plot scale investigations of the hydrological and geochemical regimes of thaw slumps and adjacent undisturbed slopes will also be investigated around 2 mega-slumps that are easily accessible from the Dempster highway. The type of flow and geochemical characteristics of the runoff will be logged at regular intervals along a gradient of increasing distance from the headwall or hilltop. Water samples will be collected for geochemical and isotopic analysis. Runoff generated through the active layer can also contribute elevated solutes to nearby streams. In an effort to characterize active layer chemistry and separate its contribution from slump runoff and deep groundwater flow the team will monitor several slope types with 3-1 soil temperature, moisture and salinity sensors. Pore-water pressure sensors will be used to track vertical water migration through the active layer and Whipkey gutter-type apparatus will measure lateral discharge. Subsurface flow will be collected from piezometer wells and samples will be analyzed for isotope geochemistry, dissolved organic content (DOC) and nutrients. Since the maximum depth of active layer thickness is only reached in mid to late summer, this year sites will be instrumented and test methods but it will take two field seasons before reliable results are obtained. Following characterization of the various hydrological components in the Stony Creek watershed (unaffected streams, impacted streams, slump runoff, active layer runoff), an inverse mixing approach will be used (hydrograph separation) to evaluate the sources and pathways of flow from slump runoff and groundwater to the streams throughout the summer and quantify the contribution of slump and active layer runoff to impacted streams. All water sampling data collection and analytical methods will follow peer reviewed, standard methodologies. Data collected from the outflows of Stony Creek and Vittrekwa River will be placed on the NTGO water and sediment quality database. In 2010, the research team presented the project to a grade 12 class at the local school, and also discussed the project on the local CBC radio. This summer, they anticipate doing the same. Results of research will be published in scientific journals. From the results of 2009, the research team is currently preparing two scientific manuscripts to be submitted for publication shortly. The team also has a web site (http://ice-cave.tumblr.com/) showing images from the project. The fieldwork for this study will be conducted from May 28, 2011 to September 3, 2011.