turbid water and salmon: SETON LAKE, british columbia
More than 200 years of aquatic food web history in Seton and Anderson lakes in the southern Chilcotin area of British Columbia was reconstructed using a paleolimnological approach to assess the cumulative effects of a diversion of water from Carpenter Reservoir to Seton Lake that started in 1940-1960 and to assess effects of climate change on primary and secondary production in Seton Lake. Upstream Anderson Lake that is not affected by water diversion and is undisturbed was used as a control lake. The diversion of cool turbid water into Seton Lake from Carpenter Reservoir caused a decline in abundance of phytoplankton, a shift in algal composition associated with decreased light, and decreased flux of zooplankton that is food for sockeye salmon and Gwenish that rear in the lake. Equally large changes to Seton Lake productivity and sockeye salmon abundance occurred from natural processes in the 1800’s that were unrelated to any diversion. Those historical processes started a long term progressive decline in salmon abundance in Seton lake. The water diversion did not cause this decline but it has produced conditions that do not favour recovery of the salmon population, particularly under heavy predation pressure from Bull Trout. The Bull trout shown in the above image had 10 large Gwenish in its stomach. This work was a collaboration of scientists from across Canada, managed at Limnotek, and reporting to the St’at’imc First Nation of Lillooet, British Columbia and BC hydro, the hydropower utility that constructed the water diversion. It was a success for all concerned in showing the importance of large scale historical events influencing ecological changes from a major hydro power project and in adjusting people’s perceptions around that process.
Client: St’at’imc First Nation
Funding: BC Hydro
Sector: Reservoirs and lakes
Status: Completed 2017