Study shows glacial melting changes mountain lake ecology

In the Rocky Mountains, researchers have been studying a pair of lakes–Jasper and Albino. While they are similar in size, location, and depth, there is one important difference: Jasper Lake is fed by glacier meltwater while Albino Lake is fed by snow. A report published in May reveals that this small difference has had a dramatic impact on the biology and chemistry of the lake itself, indicating that water source plays a much larger role in the ecological health of mountain lakes than previously thought.

Hallett Peak, Rocky Mountain National Park (source: NPS)
Hallett Peak, Rocky Mountain National Park (source: NPS)

Mountain lakes are an important source of regional water in the western United States, and are known for their historically high levels of biodiversity. Recently, these lakes have seen rapid changes which sparked concern from the scientific community. Last month the California-based Consortium for Integrated Climate Research in Western Mountains (CIRMOUNT) addressed the need for research on mountain lakes by publishing a special feature of Mountain Views, their biannual report compiling recent research on western United States mountains, that focuses exclusively on mountain lakes. The ten featured research articles all point to the importance of alpine lake conservation and investigate the impacts of climate change and other anthropogenic influences on regional ecology and environmental health.

One article— “Effects of Glacier Meltwater on the Algal Sedimentary Record of an Alpine Lake in the Central U.S. Rocky Mountains”— studied glacier-fed and snow-fed lakes and found drastic differences in the chemical compositions and species ecology between the two. The researchers, Krista Slemmons of the University of Wisconsin, Stevens Point, and Jasmine Saros of the University of Maine chose two alpine lakes in the Beartooth Mountains, Jasper and Albino, which are physically and geographically similar. However, Jasper Lake is fed by a glacier meltwater, while Albino Lake is only fed by snowmelt.

core samples (wiki)
core samples (wiki)

To determine differences in the lakes’ histories, sediment cores were taken from the bottom of the Jasper and Albino. Over time, organisms and nutrients accumulate on the lakebed and gradually build up as sediment in bodies of water. The layers of the core therefore tell a story about the history of the life within the lakes. By analyzing the sediment cores, the researchers were able to look back through time and see how the type of water feeding the lakes has led to differences in life history and biogeochemical cycling.

Within the Jasper core, researchers found high levels of plankton species that thrive in high nitrogen conditions, indicating that the lake has had higher nitrogen levels than Albino Lake over the past 3,000 years, with particularly high levels corresponding to periods of high glacial melting, most notably the 20th century.

fresh-water phytoplankton, used to determine historic water ecology and nutrient levels (wiki)
fresh-water phytoplankton, used to determine historic water ecology and nutrient levels (wiki)

Today, glacier-fed Jasper Lake has approximately 63 times more nitrogen than snow-fed Albino Lake. It is the high concentrations of nitrogen in the glacial meltwater that has led to the differences between the lakes. This trend will continue as glacier melting accelerates with climbing temperatures.

While nitrogen is an important nutrient, and often limited in alpine lakes, it is possible to have too much of a good thing. In Jasper Lake, the sediment cores also indicated that species richness, or the number of different types of species present in an ecosystem, was lower than in the nitrogen-limited Albino Lake. These findings suggest that a high influx of glacial meltwater into lakes may lead to eutrophication.

algal bloom from eutrophication (flickr)
algal bloom from eutrophication (flickr)

Eutrophication is a type of water pollution that occurs when high levels of nitrogen cause plant and algae to grow excessively. This phenomenon, known as an algal bloom, blocks sunlight from penetrating the water column, decreases the oxygen levels in the water, and can harm other species in the ecosystem. Eutrophication is most commonly seen as a result of nitrogen fertilizer runoff into bodies of water, but the nitrogen stored in glacier ice appears to have high enough concentrations to cause the same negative impacts.

While global water scarcity is enough cause for concern over glacier retreat, these findings suggest that glacier melt has wider reaching negative impacts on ecosystem function than previously recognized. Understanding the cascade of environmental impacts resulting from glacial melting will become increasingly important as temperature rise continues to break global records, and will play an important role in preserving the biodiversity of marine ecosystems.

Glacial Runoff: Bane or Boon for Aquatic Life?

As glaciers melt around the world, their waters carry high concentrations of sediments into glacial lakes and rivers. That glacial sediment brings some nutrients into the lakes, but also blocks sunlight– the energy source which organisms need to survive.

In a recently published paper in The Journal of Plankton Research, titled When glaciers and ice sheets melt: consequences for planktonic organisms, Dr. Ruben Sommaruga of  the University of Innsbruck, Austria, analyzed the relationship between sunlight, nutrients and organisms.

Glacial rivers and lakes often appear blue because of the particular mix of minerals and sediments, known as glacial flour, or glacial milk, that gets scraped up when glaciers expand and grind the bedrock surface over which they move. Glacial retreat releases that glacial flour into rivers and lakes at unprecedented rates. At the same time, new glacial lakes and rivers are forming, providing scientists with an opportunity to observe if and how life will thrive in these bodies of water.

Figure of turbid glacial lakes transitioning to clear oligotrophic lakes.
Figure of turbid glacial lakes transitioning to clear oligotrophic lakes. Figure by RUBEN SOMMARUGA 2015

High concentrations of glacial flour in young glacial lakes makes them  turbid, or cloudy, blocking sunlight. These lakes become clearer as they age, as glacial flour settles to the lakebed. This process increases sunlight penetration in the water. Combined with an increase in other forms of nutrients entering the lake over time, such as bird droppings, this process results in a clear blue glacial lake with a healthy ecosystem. These clear lakes, called oligotrophic lakes, can support plankton and small fish, but do not have many aquatic plants. Eventually, if nutrients keep increasing in oligotrophic lakes, they can develop into highly biologically active lakes, called eutrophic lakes, with abundant aquatic flora and fauna.

An image of Kurtkowiec Lake, an oligotrophic lake in the Tatra Mountains of southern Poland.
Kurtkowiec Lake, an oligotrophic lake in the Tatra Mountains of southern Poland, via Wikipedia.
An image of Lake Waahi, a eutrophic lake in Huntly, New Zealand.
Lake Waahi, a eutrophic lake in Huntly, New Zealand, via Flicker.

In order for this eutrophication to occur, organisms at the base of the food chain, particularly  plankton, need to survive in the water during its early phase with low sunlight penetration.

Once a lake loses its connection with its original glacier, either because the glacier completely melted or because its runoff ceased, it changes more rapidly from a cloudy glacial lake to a clear oligotrophic lake. The location and size of the lake and glacier influence the pace of this process and the potential for eutrophication.

Research on these processes–which integrate climatic, hydrological, chemical and biological components–contributes to a more general understanding of the ecological consequences of climate change.

In the article, Dr. Sommaruga states “ . . . estimates based on a scenario where all glacier ice disappears in the Swiss Alps, predict 500 new lakes, which represent 30% more lentic [stillwater] systems for Switzerland. In other regions, such as in northern Patagonia, total glacial lake area has increased by 65% from 1945 to 2011.”

This research shows that plankton and other small organisms survive, though not always thrive, in young cloudy glacial lakes and rivers. Future research will extend current understanding of these ecosystems, and trace the implications for our planet’s freshwater ecosystems.

Other posts at GlacierHub have described glacial lakes in Switzerland and Greenland.