Article by Ken Ashley, Ph.D., R.P. Bio.
Climate change poses an existential threat to some of BC’s diverse ecosystems if it continues unabated. In the coming years it will influence BC’s lakes and reservoirs in variety of ways – some subtle and some dramatic.
In larger water bodies the effect will be muted, but will still be noticeable. Moderate increases in summer surface temperatures and slow minor warming of the hypolimnion will occur in large, cooler lakes (Anderson et al., 2021), such as Kootenay Lake and Harrison Lake, whereas large lakes in the Okanagan Valley will experience record high summer surface temperatures and stronger thermal stratification. Increased turbidity will occur in glacial-fed water bodies, such as Kinbasket Reservoir, Beaton Arm in Upper Arrow Reservoir and Duncan Reservoir, in late summer as glaciers melt and recede, which may be accompanied by increased nitrate loading (Williams et al., 2016) and release of persistent legacy contaminants (e.g., PCBs) stored in the glaciers (Blais et al., 2001). Glacial-melt inflows may not always be highly visible as cold turbid inflows will plunge to equilibrium depths due to their higher densities relative to warmer epilimnetic water. Overall water budgets will become a concern as winter precipitation transitions from snow to rain, especially in the Okanagan, South-East Vancouver Island and Gulf Islands, as the Cowichan Lake/River ecosystem experienced in the summer of 2023. Hydro-electric generation in snow-melt dominated reservoirs will also be affected as less winter precipitation will be stored as snow thus compromising annual generation capacity. Although BC imports the majority of its required electricity from Washington State, extended drought and low snowpack may result in BC importing electricity from Alberta (which is 89% fossil fuel generated) via the Western Interconnection grid network. As a result of the province wide drought in 2023, BC Hydro’s trading subsidiary Powerex imported 10,000 gigawatt hours – about 1/5 of the province’s energy needs (CBC, 2023).However, climatic effects in smaller lakes, especially shallow eutrophic lakes in the Southern Interior Plateau and Insular Lowland limnological regions will occur more quickly and be more discernable. In shallow lakes that do not stratify or mix repeatedly (polymictic), warmer summer temperatures and increased evaporative water loss will occur, and these lakes may no longer support cool/cold water fish such as trout, char and salmon in summer months. Quamichan Lake, near Duncan, is approaching this state (Moore, 2019). In lakes deep enough to stratify (~8-10 m) that historically experienced spring and fall circulation (i.e. dimictic), climate change warming will cause longer periods of summer stratification and shorter periods of spring and fall circulation. This will lead to lowered hypolimnetic oxygen concentrations in summer, and potentially in winter if winter ice cover forms following reduced fall circulation. The result will be increased frequency of summerkill and/or winterkill events of fish, especially trout, char and salmon. The frequency and severity of summerkill and/or winterkill events will be amplified or muted by the 12-18 month ENSO cycle (El Niño-La Nina) and multi-year warm and cold phases of the Pacific Decadal Oscillation (Di Liberto, 2016). Roche Lake, near Kamloops, which was historically dimictic, failed to fully circulate in the spring and fall of 2022-23, and experienced a winterkill event resulting in a loss of ~$3M to the local economy.
If hypolimnetic oxygen is reduced to zero and anaerobic conditions are established in the hypolimnion, a series of chemical reactions will occur that profoundly influence the lake’s ecology. The loss of the thin oxidized layer at the sediment–water interface will result in a significant increase in phosphorous and nitrogen releases, generation of toxic gases (i.e. H2S) and release of reduced metals, mainly iron (Fe+2) and manganese (Mn+2). The short term effect will be a positive feedback loop of internal nutrient loading which exacerbates any pre-existing eutrophic water quality conditions and offset efforts to curb external point and non-point source nutrient loading to the lake. If the reduction and/or lack of spring or autumn circulation continues for several years, the increase in hypolimnetic density from anaerobic sediment releases may form a chemocline and lakes will become increasingly resistant to complete circulation, causing some dimictic lakes to become monomictic, and some monomictic lakes to become meromictic. The onset of meromixis in a eutrophic lake represents a dramatic change in lake ecology, which can significantly degrade the lake for domestic use or recreational purposes. Traditionally, it was thought that transitioning to a meromictic state and establishment of a purple sulfur bacteria plate required decades, yet in the past few years, this scenario has occurred throughout southern BC at Lajoie Lake, near Bralone (Pritchard, 2023), and White Lake and Gardom Lake in the Thompson region. Once this occurs, meromixis is typically a very stable state. Meromixis developed in Mahoney Lake (near Okanagan Falls) about 9,000 years BP, and has been meromictic for ½ of the time since (Lowe et al., 1997).
If the increase in water temperature exceeds 250 C, virtually all salmonids will exceed their upper lethal temperature tolerance, or be forced to seek habitable strata between the low oxygen hypolimnion and high temperature epilimnion, which will experience temperature related reductions in oxygen solubility (Jane et al., 2021). Cultus Lake is predicted to reach this state by 2100, placing endangered Cultus Lake sockeye at risk of extinction if airborne non-point nutrient loading continues unabated (Barbati, 2023; Putt et al., 2019)). Replacement and/or competition of salmonid predators with expanded populations of native or introduced planktivorous fish may initiate a cascading trophic effect where large herbivorous zooplankton (eg. Daphnia) are increasingly targeted by planktivores, which can lead to increased algal abundance and degradation of water quality in terms of taste, odour and reduced transparency.
The long-term effect of continued positive feedback from internal loading in eutrophic lakes typically leads to increased algal density, more algal blooms including blue-green algae, increased organic loading, greater hypolimnetic oxygen demand, and more frequent summerkills and/or winterkills of salmonids and other native fish. The result will be impaired recreational use and loss of angling opportunities, and increased frequency of recreational closures. In the worst case scenarios, some small lakes will become fishless waterbodies dominated by blue-green algae as they transition to a permanent meromixis state.
In an upcoming article, I will discuss what can be done to mitigate/adapt to this unpleasant scenario.
Anderson, E.J., C.A. Stow, A.D. Gronewold. 2021. Seasonal overturn and stratification changes drive deep-water warming in one of Earth’s largest lakes. Nat Commun 12, 1688 (2021). https://doi.org/10.1038/s41467-021-21971-1
Barbati, J.A. 2023. Assessment of Hypolimnetic Oxygen Demand in a Peri-Urban Lake. M.Sc. thesis, BC Institute of Technology, 51.pp.
Blais, J.M., D. W. Schindler, D. C. G. Muir, M. Sharp, D. Donald, M. Lafrenière, E. Braekevelt and W.M. J. Strachan. 2001. Melting Glaciers: A Major Source of Persistent Organochlorines to Subalpine Bow Lake in Banff National Park, Canada. Ambio 30:410-415.
CBC. (2023, December 21). Drought is causing B.C. Utilities to import more power – and that will affect your bills in 2024 | CBC News. CBCnews. https://www.cbc.ca/news/canada/british-columbia/bc-electric-rate-changes-as-province-imports-power-1.7065802
Di Liberto, T. (2016, August 25). Going out for ice cream: A first date with the pacific decadal oscillation. NOAA Climate.gov. https://www.climate.gov/news-features/blogs/enso/going-out-ice-cream-first-date-pacific-decadal-oscillation
Jane, S.F. et al., 2021. Widespread deoxygenation of temperate lakes. Nature 594: 66–70.
Lowe, D.J., J. D. Green, T.G. Northcote and K.J. Hall. 1997. Holocene Fluctuations of a Meromictic Lake in Southern British Columbia. Quaternary Research 48: 100-113.
Moore, K.E. 2019. Restoring a culturally eutrophic shallow lake: Case study on Quamichan Lake in North Cowichan, British Columbia. M.Sc. thesis, BC Institute of Technology, 72.pp
Pritchard, S. 2023. Restoration of Lajoie Lake: Investigating Climatically Induced Meromixis M.Sc. thesis, BC Institute of Technology, 64.pp
Putt, A.E., E. A. MacIsaac, H. E. Herunter, A. B. Cooper and D.T. Selbie. 2019. Eutrophication forcings on a peri-urban lake ecosystem: Context for integrated watershed to airshed management. PLOS ONE https://doi.org/10.1371/journal.pone.0219241.
Williams, J.A. A. Nurse, J. E. Saros, J. Riedel and M. Beutel. 2016. Effects of glaciers on nutrient concentrations and phytoplankton in lakes within the Northern Cascades Mountains (USA). Biogeochemistry 131: 373-385.