Lakes in Hot Water: The Impacts of a Changing Climate on Aquatic Ecosystems

Abstract

Our planet is being subjected to unprecedented climate change, with far-reaching social and ecological repercussions. Below the waterline, aquatic ecosystems are being affected by multiple climate-related and anthropogenic stressors, the combined effects of which are poorly understood and rarely appreciated at the global stage. A striking consequence of climate change on aquatic ecosystems is that many are experiencing shorter periods of ice cover, as well as earlier and longer summer stratified seasons, which often result in a cascade of ecological and environmental consequences, such as warmer summer water temperatures, alterations in lake mixing and water levels, declines in dissolved oxygen, increased likelihood of cyanobacterial algal blooms, and the loss of habitat for native cold-water fisheries. The repercussions of a changing climate include impacts on freshwater supplies, water quality, biodiversity, and the ecosystem benefits that they provide to society.

Keywords: climate change; ecology; environmental science; limnology; water resources.

Figure 1.

Historic and future projections of lake ice cover, thermal stratification, and water temperature. Temporal and spatial variations in (a, b) the duration of winter ice cover, (c, d) the duration of summer stratification, and (e, f) annually averaged surface water temperature. The temporal changes are shown (a, c, e) from 1901 to 2099 under historic and future climate forcing. The future simulations include three climate change scenarios: representative concentration pathway (RCP) 2.6 (low-emission scenario where emissions start declining at around 2020), 6.0 (medium-high-emission scenario where emissions peak at around 2080 and then decline), and 8.5 (high-emission scenario where emissions continue to rise throughout the twenty-first century). The thick lines show the average across numerous lake-climate model projections, and the shaded regions represent the standard deviation across the model ensemble. Panels (b), (d), and (f) show the spatial patterns by the end of the twenty-first century (averaged over all years from 2070 to 2099) under RCP 8.5. Anomalies are quoted relative to the 1970–1999 average (e.g., a positive value in panel (c) represents warmer conditions than estimated during the period 1970–1999). Source: The projections of lake ice cover and water temperature are from Grant and colleagues (2021), and the lake stratification projections are from Woolway and colleagues (2021b).

Figure 2.

Projected and observed change in water quantity. Shown are simulated future changes (2071–2100 relative to 1971–2000) in (a) lake evaporation, (b) land P–E (precipitation minus evaporation), and (c) lake volume (based on the P–E balance over land and lake surfaces), under representative concentration pathway (RCP) 8.5. Model projections are from Zhou and colleagues (2021). Shown in panels (d) and (e) are what were previously permanent High Arctic ponds (Cape Herschel, Canadian High Arctic), that are now evaporating because of climate change. Pictured here is one of these sites, which used to be more than 100 meters long in the 1980s (d) but, since 2005, is dry by mid-July (e). Source: Reproduced with permission from Smol and Douglas (2007b). (f, g) Satellite images of Lake Mead (United States) taken on 2 September 1989 (Landsat) and 18 October 2019 (Sentinel 2), respectively, showing the decline in lake level or extent, as well as the expansion of Las Vegas to the west. (h, i) Satellite images of Lake Chad (bordering Chad, Cameroon, Niger, and Nigeria), taken on 5 November 1984 (Landsat) and 31 October 2018 (Sentinel 2). (j-l) Satellite images acquired from ESA's Proba-V minisatellite of Lake Poopó (Bolivia) acquired on 27 April 2014, 20 July 2015, and 22 January 2016, respectively. Images: Panels (f)–(i) contain modified Copernicus Sentinel data, processed by the ESA, CC BY-SA 3.0 IGO. Panels (j)–(l) contain modified satellite images from ESA/Belspo, produced by VITO.

Figure 3.

Cyanobacterial bloom in Dickson Lake (Ontario). (a) Aerial view of the Dolichospermum bloom on remote Dickson Lake (Algonquin Provincial Park, Ontario) in September 2014. Photograph: Courtesy of Alison Lake, Ontario Parks. (b) Concentrations of cyanobacterial akinetes (resting stages) in a high-resolution sediment core collected from Dickson Lake, scaled by age of sediment estimated from ²¹⁰Pb dating, showing the unprecedented increases in cyanobacteria in the most recent sediments. Source: Redrawn from data presented in Favot and colleagues (2019).

Figure 4.

Expected climate change responses of key lake ecosystem processes. Shown are the level of additional risk to important physical, chemical, and ecological lake processes due to global warming, based on our expectations. White indicates an undetectable level of risk, meaning that lake ecosystems will be somewhat resilient to change under those specific levels of warming, and dark red illustrates a very high risk of ecosystem response. We stress that there will be exceptions to these expected changes, as is highlighted in our review.