Dr. Patterson and Students Return from Yellowknife

Friday, July 17, 2015

Who Killed Frame Lake?

Tim Patterson awarded $27k by Tides Canada/RBC Bluewater to help develop remediation plan for urban Yellowknife lake

Frame Lake freeze cores


On the surface, Frame Lake appears to be a gem in the middle of Yellowknife. The green and lush shoreline is a magnet for bird life and nature lovers. There is a parkland and walking trail around the lake, and the Northern Frontier Visitor Centre on the shoreline is an attraction for tourists. But in the lake itself, all is not well. Prior to the early 1970s the lake was also a major attraction for beach goers and swimmers. In the 1970’s lake conditions degraded rapidly though and within a few years there were no fish. In imitation of a horror film an explosion in the leech population literally drove swimmers from the water.

With previous support from Tides Canada, the City of Yellowknife, Northwest Territories Geological Survey, NWT Environment and Natural Resources, Cumulative Impact Monitoring Program, the Geological Survey of Canada, The Giant Mine Team, and Trout Unlimited, Professor Tim Patterson’s research group has for the last two years been determining how the lake became degraded. They are using their findings to inform policy makers and planners as to how to best remediate the lake to once again support a year round fish population and provide an attractive destination for beach goers and fishermen. New funding from Tides Canada/RBC Bluewater will permit Patterson’s team to expand and accelerate their research efforts.

Additional Eckman Grabs collected in 2015

Prior to the 1930s when Yellowknife was established as an urban and industrial centre, the Yellowknives Dene caught whitefish and northern pike in the lake. They had a fish camp on the shoreline where they would smoke the fish. As Yellowknife became established and grew ever larger the community began to encroach upon the Frame Lake catchment. Through the last 90 years a variety of urban and industrial influences have negatively impacted the lake. These impactors include nutrient laden storm-water entering the lake through storm sewers, historical dumping of mine tailings and raw sewage into the lake, and use of the lake as a snow dump in winter. Nearly half a meter of sediments have been deposited in some parts of the lake through this interval, a remarkably high sedimentation rate for lakes in this region.

Tim Patterson and his students have thus far determined that the major tipping point for lake water quality occurred around 1970, which coincided with the construction of a causeway at the end of the lake where the only outflow is located. With water throughput impeded, nutrient levels in the water column increased, which resulted in massive expansion of aquatic plants. During winter the plants died under the snow covered ice as they couldn’t photosynthesize. As they decomposed oxygen levels in the lake declined. In only a few years winter oxygen levels became so low that fish were no longer able to survive. In the absence of large predators other organisms became extremely abundant, particularly leeches. The nature of the sedimentation in the lake changed as well with the 10 cm of sediments deposited since 1970 being black, sulfurous smelling and characterized by very high levels of metals, particularly arsenic. Using a variety of technologies, Patterson’s team are documenting at annual resolution the changes that occurred to the hydroecology of the lake, specifically identifying major causes of degradation and making recommendations as to how best remediate the lake (e.g. aeration, dredging, improvement of water flow).

Tim Patterson and Ph.D. student Nawaf Nasser carry out a seismic survey using a Syqwest Stratbox subbottom profiler

Tim Patterson and Ph.D. student Nawaf Nasser carry out a seismic survey using a Syqwest Stratbox subbottom profiler