NWT RESEARCH DATABASE

Regions: Inuvialuit Settlement Region

Tags: water quality, environmental impact, permafrost, aquatic ecosystems, landscape disturbance, hydrology, slumping, risk assessment, cumulative effects

Objective(s): To investigate the short and long-term impacts of permafrost instability on terrestrial and aquatic ecosystems and livelihood of communities on Banks Island.

Project Description: Thaw slumps are one of the most dramatic thermokarst features in permafrost regions. The number of thaw slumps on Banks Island has more than tripled in recent decades and it is likely that this change is altering terrestrial and aquatic ecosystems. This multidisciplinary research project investigates the short- (1960s-present day) and long-term (Medieval Warm Period to today) impacts of permafrost instability on terrestrial and aquatic ecosystems and livelihood of communities on Banks Island, NWT as well as determining the cause of the relations. The research project will 1) map the distribution of thaw slumps and assess physical thresholds related to their initiation and development to help predict areas susceptible to future change; 2) determine the degree of landscape disturbance necessary to significantly change water quality and assess the water quality thresholds associated with shifts in stream benthic communities and ecosystem health; and 3) determine long-term consequences of climate change on vegetation and geomorphic activity. Relating water quality parameters to stream health and benthic community composition is critical to understanding ecosystem response to disturbance, a requirement for the derivation of regionally relevant water quality guidelines. Objective 1. Map the contemporary distribution and level of activity of thaw slumps and other thermokarst disturbances. This objective will map the distribution of thaw slumps on Banks Island (number and size of active and stable slumps and other thermokarst disturbances) and estimate their growth rates since the 1985. The Tasseled Cap trend analysis of Landsat image stack will be used to map the distribution, level of activity and growth rates of thaw slumps on Banks Island following the methods described in Brooker et al. (2014). Mapping the distribution of disturbances will also help to identify landscape controls of slump activity and will provide a basis for producing watershed sensitivity maps that inform development planning and assessment. Objective 2. Determine the cause and impacts of thermokarst disturbances on the hydrological regimes, sediment load and geochemistry of streams and lakes. First, a regional dataset of the geochemical composition of stream and lakes will be developed. For summer 2015, this will be carried out in part by collecting stream and lake water samples along south and east Banks Island with helicopter support. Second, the research team will conduct local-scale measurements of water-level, turbidity, light penetration and UV attenuation and water quality in pristine and slump-impacted streams and lakes near Sachs Harbour and along southern Banks Island. The sites will be accessed using ATVs, where the research team will measure water-level turbidity, light penetration and UV attenuation using YSI hydrological sondes. Finally, 5-10 shallow permafrost cores (3-5m deep; 3.5 inch diamter) will be collected to assess biogeochemical variations in permafrost and the potential source of solutes to nearby water bodies following permafrost degradation. All water/permafrost samples, including those from the regional survey, will be analyzed in the laboratory for major and trace ions, stable O-H isotopes, DOC, 13CDOC, and 14CDOC and nutrients (phosphate, nitrogen). From these measurements, the research team will: i) establish geochemical tracers that can be used to track and quantify the contribution of runoff from thermokarst disturbances in the watersheds; and ii) determine if water quality of slump-impacted freshwater ecosystems is above the toxic threshold of drinking water quality, benthic macroinvertebrates and fish species. Participation of Sachs Harbour residents will enable the collection of bi-weekly water quality samples near that community and flow measurements to calibrate instrument readings. The geochemical data will be used to determine the relative impacts of different disturbance types on freshwater quality of freshwater ecosystems. Objective 3. Determine thermokarst disturbance thresholds relevant to the health of streams and lakes communities. To quantify the response of stream benthic communities to thaw slumps, the research team will sample benthic communities across a thaw slump activity gradient (undisturbed streams to heavily slump-impacted streams). Benthic communities along this gradient will be evaluated according to biological metrics related to species tolerance levels, ecological trait data and food web structure (i.e., carbon and nitrogen stable isotopes) that describe functional aspects of biological composition. First, an Extensive Spatial Study Design will be used to examine benthic communities from streams along the full disturbance gradient. Indirect gradient analysis will be used to determine whether disturbance levels can be differentiated on the basis of community composition (diatoms and macroinvertebrates), and direct gradient analysis will be used to discover the chemical and physical drivers of these patterns. Second, an Intensive Spatial Study Design will be used to more closely examine the mechanisms by which permafrost thaw slumping impacts benthic communities of streams. Benthic diatoms and macroinvertebrates will be sampled in a paired design of upstream and downstream of disturbances to control for the effects of among-stream variability. The research team will collect drift samples over 24-hour periods to determine the propensity of benthic macroinvertebrates emigrating from slump-impacted sites. Sediment traps deployed over the same period will estimate sediment movement. Benthic macroinvertebrate assemblages will be sampled and processed using well-established Environment Canada CABIN protocol to maintain consistency across the Arctic. Benthic diatoms will be collected and processed following the Eastern Canadian Diatom Index protocol. Objective 4. Determine long-term consequences of climate change on vegetation and geomorphic activity. Sediment cores from lakes and from peat deposits will be collected to determine vegetation changes since the Medieval Warm Period. Sediment sampling and lab methodology are standard, which permit comparison to previous work and to modern calibration samples. Cores are collected using a Livingstone sampler, processed for pollen in the lab and dated. Multivariate and time series statistical methods are used along with a modern pollen database to quantify changes in the vegetation. These results will be related to the results from the stream surveys, and permit the understanding of long-term impacts of slump activity on aquatic systems. Community members will be directly involved with the scientific program either as field assistants (i.e. taking stream discharge measurements, collecting stream water samples) or working as wildlife monitors. Several community members will be directly involved with the scientific program either as field assistants (i.e. taking stream discharge measurements, collecting stream water samples) or working as wildlife monitors. The research team are planning on presenting the results to the local communities through school workshops. Last year, we were the first to bring Let’s Talk Science, developed by Science Travels, to northern communities (Inuvik, Tsiigehtchic, Whitehorse) and the activity was well received. These outreach programs are mainly aimed at teenagers and school-aged children, but would be open to all interested members of the community. The project results will be shared within the scientific community through various conferences, both national and international, and peer-reviewed publications. The fieldwork for this study will be conducted from July 26, 2015 to August 7, 2015.