The Changing Colours of Mountain Lakes in the Twenty-First Century
Aerial View of Egypt Lake, Banff National Park. Photo: Clark Monson
When viewed from above or in a postcard, the mosaic of different colours of lakes in the Canadian Rockies appears serene – but their pristine and idyllic looks can be deceiving. Multiple novel and extreme environmental changes related to human activities are increasingly altering many of these lake ecosystems. Some of these “stressors” date back to the mid-twentieth century while others have more recently become pronounced, such as those arising from global warming. These stressors often interact with one another so as to confound predictions of their cumulative ecological impacts if based on the sum of their known individual effects. Such non-additive “ecological surprises” are not only altering the appearance of mountain lakes, but also their ecology.
Contrasting lake colours caused by glacial meltwater inputs in the Devon Lakes in the northeastern corner of Banff National Park. Photo: Patrick Thompson.
“Such non-additive “ecological surprises” are not only altering the appearance of mountain lakes, but also their ecology.”
Clarification of many glacial mountain lakes is occurring as reduced inputs of eroded rock flour from shrinking glaciers result in a shift from a milky turquoise to more translucent blue appearance.[1] As a consequence, these lakes are becoming less reflective of sunlight, and in turn also warmer. Evidence from sediments obtained from alpine lakes suggests that the ablation of glaciers actually amplifies the effect of recent higher air temperatures so as to promote several- fold increases in the growth of algae. However, less glacial meltwater may also result in less nutrients (e.g., phosphorus) entering these lakes, thereby offsetting the positive effects of warmer and more well-lit conditions on their food webs.[2] For example, glacially fed, turbid streams entering the Columbia River contain elevated levels of phosphorus relative to those streams fed by only snowmelt.[3] Consequently, recession of glaciers appears to be leading to more nutrient-poor and translucent water conditions, which surprisingly can fuel the proliferation of certain nuisance algae, termed “rock snot” in along the shorelines of mountain lakes and streams.[4]
Brownification of certain mountain lakes is also expected to eventually occur as vegetation (e.g., advancing treelines) replaces melting glaciers under a warming climate, resulting in greater inputs of brownish organic substances from soils.[5] Here, loss of glacial meltwaters may actually amplify brownification by eliminating the potential for rock flour to adsorb to, and thereby remove, the brownish organics from the water column. The effects of brownification on mountain lakes likely depend on the balance between the nutritional quality versus natural sun-screening capacity of the organic material.[6] For example, brownification may be most pronounced at or below treeline where organically rich soils and wetlands release more rich concentrations of darkish organics. In contrast, higher concentrations of relatively translucent organics were linked to increased growth of phytoplankton in alpine lakes along the eastern Front Range of the Canadian Rockies.[7]
McConnell Lake, also in Banff National Park, where our sediment core showed that the loss of a small pocket snowfield or glacier (note the depression left in the moraine above the lake) resulted in a fast transition from a turbid to clear lake state. Photo: Patrick Thompson
Greenification of small naturally fishless lakes is also occurring in the Canadian Rockies as a consequence of stocking with non-native sportfish. Populations of non-native sportfish have persisted in certain lakes within the national mountain parks despite stocking programs having been terminated in the 1980s following their designation as UNESCO World Heritage Sites. Elsewhere, provincial sportfish stocking programs continue in the Canadian Rockies. These novel predators biologically impoverish naturally fishless mountain lakes by preying on filter-feeding herbivorous invertebrates. In addition, they increase cycling of nutrients through their foraging for prey. Therefore, reduced grazing pressure and increased nutrient availability then stimulate the growth of golden green algae in heavily stocked, small mountain lakes.[8] Here, climatic warming appears to synergistically increase the fertilizing effect of introduced sportfish on such lakes.[9]
Air pollution involving nitrogen as seen at more southern latitudes (e.g., Colorado) appears to have not had much of an effect on lakes in the Canadian Rockies. Deposition in nitrogen in rainfall remains relatively low in the Rockies where the lakes are more sensitive to aerial inputs of phosphorus, which can arise from wildfire ash.[10] Interestingly, nitrogen deposition does however appear to exert a potential greening effect on alpine ponds because they are more starved of nitrogen compared to the lakes.[11]
“Collectively, these changing colours point towards these lakes becoming more productive ecosystems with an increased potential for concerns over water quality under a rapidly changing climate.”
In summary, regional and local environmental changes are interactively affecting the mountain lakes of western Canada in complex ways. These interactions are shifting many lakes from a turquoise to a more translucent blue, and eventually greenish or brownish appearance. Collectively, these changing colours point towards these lakes becoming more productive ecosystems with an increased potential for concerns over water quality under a rapidly changing climate. Although the mosaic of lake colours across the Canadian Rockies is changing, it will continue to be a fascinating feature of the landscape because of the natural high environmental heterogeneity that translates into a diversity of lake responses to global change.
Chester Lake, Kananaskis Country/Peter Lougheed Provincial Park. Photo: Travel Alberta / Paul Zizka
AUTHOR
Rolf Vinebrooke is a Professor in the Department of Biological Sciences at the University of Alberta, where his research focuses on the cumulative impacts of multiple environmental stressors on biodiversity and ecosystem functioning in mountain, boreal, and arctic lakes.
References
[1] Wolfe, A.P., et al. Stratigraphic expressions of the Holocene- Anthropocene transition revealed in sediments from remote lakes. Earth Science Reviews 116, 17-34 (2013); Vinebrooke, R.D. et al. Glacially mediated impacts of climate warming on alpine lakes of the Canadian Rocky Mountains. Verhandlung International Verein Limnology 30, 1449–1452 (2010).
[2] Elser, J.J., et al. Key rules of life and the fading cryosphere: Impacts in alpine lakes and streams. Global Change Biology 26, 6644–6656 (2020).
[3] Brahney J. et al. Glacier recession alters stream water quality characteristics facilitating bloom formation in the benthic diatom Didymosphenia geminate. Science of the Total Environment 764, 142856 (2021).
[4] Brahney et al., 2021
[5] Olson, C.R. et al. Shifting limitation of primary production: experimental support for a new model in lake ecosystems. Ecology Letters, 23, 1800-1808 (2020); Olson, M. et al. Landscape-scale regulators of water transparency in mountain lakes: implications of projected glacial loss. Canadian Journal of Fisheries and Aquatic Sciences 75, 1169-1176 (2018).
[6] Olson et al., 2020
[7] Parker, B.R., Vinebrooke, R.D., Schindler, D.W., 2008. Recent climate extremes alter alpine lake ecosystems. Proceedings of the National Academy of Sciences of the United States of America 105, 12927–12931 (2008).
[8] Parker, B.R. & Schindler, D.W. Cascading trophic interactions in an oligotrophic species-poor alpine lake. Ecosystems, 9, 157-166 (2006).
[9] Loewen, C.J.G. et al. Climate warming moderates the impacts of introduced sportfish on multiple dimensions of prey biodiversity. Global Change Biology, 26, 4937-4951 (2020).
[10] Cook, J. et al. Concordance of chemically inferred and assayed nutrient limitation of phytoplankton along a depth gradient of alpine lakes in the Canadian Rockies. Aquatic Sciences, 82, 17-31 (2020).
[11] Cook et al., 2020