CASE STUDY | Arctic Tundra

Question 1

Water cycle in the Arctic Tundra

Answer 1

• Low annual precipitation (50-350mm), most falls as snow
• Small stores of moisture in the atmosphere, caused by low temperatures which reduce absolute humidity
• Limited transpiration due to sparseness of vegetation cover and short growing season
• Low rates of evaporation, much of the sun’s energy in summer is used to melt snow so that ground temperatures remain low and inhibit convection, surface and soil water are frozen for most of the year
• Limited groundwater and soil moisture stores, permafrost is a barrier to infiltration, percolation, recharge and groundwater flow
• Accumulation of snow and river / lake ice during winter months, melting of snow, river and lake ice and the uppermost active layer of the permafrost in spring and early summer results in a sharp increase in river flow
• Extensive wetlands, ponds and lakes on the tundra during summer, temporary store of liquid water is due to permafrost which impedes drainage

Question 2

Carbon cycle in the Arctic Tundra

Answer 2

• Permafrost is a vast carbon sink, globally it is estimated to contain 1600GT of carbon, accumulation of carbon is low due to low temperatures which cause slow decomposition of dead plant material
• Overall, amount of carbon in tundra soils is five times greater than in above ground biomass
• Flux of carbon is concentrated in summer months when the active layer thaws, plants grow rapidly during the short summer, long hours of daylight allow them to flower and fruit within just a few weeks
• NPP is less than 200 grams/m^2/year-1, consequently tundra biomass is small, ranging between 4 and 29 tonnes/ha-1 depending on density of vegetation cover
• During the growing season, tundra plants input carbon-rich litter to the soil, microbial activity increases releasing CO2 to the atmosphere through respiration, however CO2 and methane emissions are not just confined to the summer, even in winter pockets of unfrozen soil and water in the permafrost act as sources of CO2 and CH4, meanwhile snow cover may insulate microbial organisms and allow some decomposition despite the low temperatures
• In the past permafrost functioned as a carbon sink but today global warming has raised concerns that it is becoming a carbon source, while outputs of carbon from permafrost have increased in recent decades, higher temperatures have stimulated plant growth in the tundra and greater uptake of CO2, this in turn has increased amount of plant litter entering store, it is possible therefore that despite the warming Arctic climate, the carbon budget in the tundra today remains in balance

Question 3

What three main physical factors impact flows and stores of water in the Arctic Tundra?

Answer 3

Temperature
Relief
Rock permeability

Question 4

How does temperature affect flows and stores of water in the tundra?

Answer 4

Average temperatures are around -30 degrees celsius, meaning that water is stored as ground ice in the permafrost layer, during the short summer the shallow active layer (top layer) thaws and liquid water flows on the surface, meltwater forms millions of pools and shallow lanes which stud the tundra landscape, drainage is poor and water cannot infiltrate the soil due to the permafrost at depth, during winter sub-zero temperatures prevent evapotranspiration, in summer some evapotranspiration occurs from standing water, saturated souls and vegetation, humidity is low all year round and precipitation is sparse

Question 5

How does relief impact the flows and stores of water in the tundra?

Answer 5

The ancient rock surface of which underlies the tundra has been reduced to a gently undulating plain by hundreds of millions of years of erosion and weathering, minimal relief and chaotic glacial deposits impede drainage and contribute to water logging during the summer months

Question 6

How does rock permeability impact the flows and stores of water in the tundra?

Answer 6

Permeability is low, owing to the permafrost and the crystalline rocks which dominate the geology of the tundra in Arctic and sub-Arctic Canada

Question 7

What three main physical factors impact flows and stores of carbon in the Arctic Tundra?

Answer 7

Vegetation
Temperature
Rock permeability / mineral composition

Question 8

How does vegetation impact the flows and stores of carbon in the Arctic Tundra?

Answer 8

Carbon is mainly stored as partly decomposed plant remains, frozen in the permafrost - most of this carbon has been locked away for at least 500,000 years

Question 9

How do temperatures impact the flows and stores of carbon in the Arctic Tundra?

Answer 9

Low temperatures contribute to the limiting of plant growth, slow decomposition and slow respiration, which all contribute to limited CO2 flowing to the atmosphere

Question 10

How does rock permeability / mineral composition impact the flows and stores of carbon in the Arctic Tundra?

Answer 10

The lack of minerals and nutrients present in rocks in the Arctic Tundra limit plant growth, therefore the total carbon store of the biomass is relatively small (NPP 200g)

Question 11

How do seasonal changes in the Tundra impact the water cycle?

Answer 11

• Average temperatures are well below freezing for most of the year so water is stored as ground ice in the permafrost layer, during the short summer the shallow active top layer thaws and liquid water flows on the surface, meltwater forms millions of pools and shallow lakes which stud the Tundra landscape
• Drainage is poor, water cannot infiltrate the soil because of the permafrost at depth, in winter, sub-zero temperatures prevent evapotranspiration, in summer some evapotranspiration occurs from standing water, saturated soils and vegetation, humidity is low all year round and precipitation is sparse

Question 12

How do seasonal changes in the Tundra impact the carbon cycle?

Answer 12

• Carbon is mainly stored as partly decomposed plant remains frozen in the permafrost, most of this carbon has been stored away for at least the past 500,000 years
• Averaged over the year, photosynthesis and NPP are low, with the growing season lasting for barely 3 months, however there is some compensation for the short growing season in the long hours of daylight in summer

Question 13

What impacts has the developments of the oil and gas industry in the Tundra had on the water cycle?

Answer 13

• Melting of the permafrost and snow cover increases run-off and river discharge making flooding more likely
• This means that in summer, wetlands, ponds and lakes have become more extensive, increasing evaporation
• Strip mining of aggregates for construction creates artificial lakes which disrupt drainage and also expose the permafrost to further melting
• Drainage networks are disrupted by road construction and by seismic explosions used to prospect for oil and gas
  -Water abstracted from creeks and rivers for industrial use and for the building of ice roads in winter reduce localised run-off

Question 14

What impacts has the developments of the oil and gas industry in the Tundra had on the carbon cycle?

Answer 14

• Oil and gas industries have contributed to the melting of permafrost, on the North Slope, estimated losses from the permafrost vary from 7-40 million tonnes per year-1, while CH4 losses vary 24,000 to 114,000 tonnes per year-1
• Gas flaring and oil spillages also input CO2 to the atmosphere
• The destruction or degrading of tundra vegetation reduces photosynthesis and the uptake of CO2 from the atmosphere
  -The thawing of soil increases microbial activity, decomposition and emissions of CO2
• Slow growing nature of tundra vegetation means that regeneration and recovery from damage takes decades

Question 15

What strategies are being implemented to manage the impacts of the oil and gas industry in the Tundra?

Answer 15

Insulated ice and gravel pads
- roads and other infrastructural features can be constructed on insulating ice or gravel pas thus protecting the permafrost from melting
Buildings and pipelines elevated on piles
- constructing buildings, oil/gas pipelines and other infrastructure on piles allows cold air to circulate beneath these structures
- this provides insulation against heat-generating buildings, pipework, etc which would otherwise melt the permafrost
Drilling laterally beyond drilling platforms
- new drilling techniques allow oil and gas to be accessed several kilometres from the drilling site
- with fewer sites needed for drilling rigs, the impact on vegetation and the permafrost due to construction is greatly reduced
More powerful computers can detect oil and gas bearing geological structures remotely
- fewer exploration wells are needed thus reducing the impact on the environment
Refrigerated supports
- they are used on the Trans-Alaska pipeline to stabilise the temperature of the permafrost
- similar supports are widely used to conserve the permafrost beneath buildings and other infrastructure