The Future of Arctic Lakes

It is now commonly understood from paleo records that much of the Arctic began to warm in the mid-19th century, that the warming will likely intensify in the future, and that arctic ecosystems are extremely sensitive to such warming and its associated ecological effects. This sensitivity is due mainly to the fact that the Arctic lies at the cusp of change from solid to liquid water. The indirect, physical consequences of even slight increases in temperature that will melt lake ice, thaw permafrost, and increase evaporation are certainly grander in their effects on organisms and system function than is the temperature change alone.

The first threshold we are crossing is the melting of ice cover, which immediately alters the mixing patterns

Shallow Lakes Ecosystem
Figure 5 Recently dried lakes on the North Slope of Alaska (left, shallow thermokarst pond ~69° N; right, small lake in glacial till nearToolik Lake, 68.4° N). Photos by G Kling.

of lakes, increases the growing season, and greatly enhances the UV exposure of aquatic organisms; these changes have led to increased productivity and shifts in the community structure of many lakes, especially in the high arctic. If water temperatures warm above 4 °C in summer, lakes that now mix continuously in the icefree season may start to stratify. One biological consequence is that under warmer temperatures lakes that now stratify may have increased oxygen depletion in bottom waters, and if coupled with warmer surface waters this could physiologically stress fish and shrink their effective habitat.

A second threshold includes the thawing of permafrost and the net balance of precipitation and evaporation that allows lakes and ponds to persist. There is evidence of both pond desiccation due to increasing temperatures and evaporation, and of the drainage of lakes assisted by melting permafrost and altered hydrological patterns (Figure 5). Thermokarst ponds have a relatively short life span, and are constantly draining and reforming on time scales of hundreds of years mainly as a result of altered drainage or river capture. Permafrost thawing may initially increase thermokarst activity and pond formation, but in the long term there appears to be a distinct shift in the balance of these processes that has allowed thousands of lakes to shrink or disappear completely just in the last 30-40 years.

The melting of massive ground ice will have other potentially marked impacts on aquatic ecosystems,

Alaska Thaw Lakes Aerial

Figure 6 Left: Aerial views of Lake NE-14 (0.24 km2 area, 68.41 ° N) near Toolik Lake, Alaska with a glacial thaw slump on shore adding sediment to the lake; prior to the slump in 2006 the lake color was the same as the lake in the lower left of the photograph. Note the visual evidence for previous slumping scars to the left of the current scar (lower left picture). Top right: Ground view of massive land failure associated with the slump. Bottom right: Aerial view of a thermokarst slump on the shore of a lake near the Sagavanirktok River, Alaska (—69° N). Photos by B Bowden (a - top left and d - lower right), A Balser (c - bottom left), G Kling (b - top right).

Figure 6 Left: Aerial views of Lake NE-14 (0.24 km2 area, 68.41 ° N) near Toolik Lake, Alaska with a glacial thaw slump on shore adding sediment to the lake; prior to the slump in 2006 the lake color was the same as the lake in the lower left of the photograph. Note the visual evidence for previous slumping scars to the left of the current scar (lower left picture). Top right: Ground view of massive land failure associated with the slump. Bottom right: Aerial view of a thermokarst slump on the shore of a lake near the Sagavanirktok River, Alaska (—69° N). Photos by B Bowden (a - top left and d - lower right), A Balser (c - bottom left), G Kling (b - top right).

such as land failure and catastrophic slumping of soils into lakes (Figure 6). Even without such slumps, the implications of permafrost thawing and deepening of the surface active layer include: (1) chemical changes such as increased carbonate minerals and P released from weathering of previously frozen mineral soils; (2) biological changes in vegetation, demonstrated by increased shrubs in low-arctic tundra, which can alter the amount and character of DOM exported from land to lakes; and (3) warming of lake sediments and soils, some of which are extremely C rich (especially the Yedoma soils in Siberia) and could substantially increase the source of both CO2 and methane to the global atmosphere. This C has been locked up in permafrost and not participating in the global C cycle, but the tremendous stores of C in wetlands and sediments of the Arctic (estimated as up to one-third the mass of C in the entire atmosphere) may provide strong positive feedbacks to climate warming in the future. Finally, there are indications that fire

Figure 7 Aerial views of two tundra fires on the North Slope of Alaska. Top (a) shows a small fire in 2004 near the Sagavanirktok River (photo by R Flanders), while bottom (b) shows a gigantic fire (> 1000 km2) near the Anaktuvuk River that burned in August and September 2007 (photo R Jandt, BLM).

Figure 7 Aerial views of two tundra fires on the North Slope of Alaska. Top (a) shows a small fire in 2004 near the Sagavanirktok River (photo by R Flanders), while bottom (b) shows a gigantic fire (> 1000 km2) near the Anaktuvuk River that burned in August and September 2007 (photo R Jandt, BLM).

frequency and magnitude on the arctic tundra has recently increased (Figure 7), and although the implications for both tundra C budgets and lake ecosystems could be considerable, they are currently unknown.

While the island continent of Antarctic suffers from extreme biogeographical isolation, the Arctic faces more serious threats from both species invasions from the south and a truncated northern border of ocean. Unlike current boreal species with the opportunity to survive climate warming by shifting distribution patterns northward, the arctic species have nowhere to go. This presents an interesting aspect of research, especially for the future and in terms of arctic biodiversity and its controls, and determining which species have enough genetic flexibility to adapt to the rapidly changing (with respect to evolutionary time scales) environment.

Nomenclature

g

gram

mg

milligram

m

meter

km

kilometer

km2

square kilometer

mm

micrometer

day

day

a

annum (year)

BP

before present

a BP

years before present

°C

degrees Celsius

°N

degrees North latitude

J

Joules

MJ

megajoules

Ca

calcium

Mg

magnesium

Na

sodium

Cl

chloride

HCO3

bicarbonate

CÜ2

carbon dioxide

C

carbon

N

nitrogen

P

phosphorus

DOM

dissolved organic matter

See also: Abundance and Size Distribution of Lakes, Ponds and Impoundments; Antarctica; Effects of Climate Change on Lakes; Geomorphology of Lake Basins; Meromictic Lakes; Origins of Types of Lake Basins; Saline Inland Waters.

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