Case Study: The Carbon and Water Cycles in Arctic Tundra

What is the carbon cycle like in the Tundra?

What is the water cycle like in the Tundra?

Changes due to oil and gas production in Alaska

Physical Factors that affect stores and flows of water and carbon

  1. Temperature
  • In winter, temperatures prevent evapotranspiration and in summer, some occurs from standing water, saturated soils and vegetation
  • Humidity is low all year
  • Precipitation is sparse
  1. Rock Permeability and Porosity
  • Permeability is low due to permafrost and crystalline rocks
  • Due to the impermeability of the permafrost, rock permeability, porosity and mineral composition of rocks have little effect on the cycles
  1. Relief and drainage
  • During the short summer, the meltwater forms millions of pools and shallow lakes
  • Drainage is poor so water cannot infiltrate the soil becuase of the permafrost at depth
  • Minimal relief (due to years of erosion and weathering) and chaotic glacial deposits obstruct drainage and contribute to waterlogging in the summer months
  1. Vegetation and Organic Matter in Soil
  • Carbon is mainly stored as decomposed plant remains in the permafrost, with most of it locked away for over 500,000 years
  • Carbon store of biomass is relatively small as low temperatures, the unavailability of liquid water and few nutrients in parent rocks limit plant growth; averaged over a year, NPP and photosynthesis are low
  • Waterlogging and low temperatures slow decomposition, respiration and the flow of CO₂ to the atmosphere

Permafrost is a vast carbon sink
Globally estimated to contain 1600GT of carbon

Low annual precipitation (50-350mm) where most of the precipitation is snowfall

Small stores of moisture in the atmosphere because of low temperatures which reduce absolute humidity

Limited transpiration becuase of the sparseness of the vegetation cover and the short growing season

Low rates of evaporation as most of the Sun's energy goes into melting the snow so the ground temperatures remain low and inhibit convection; also surface and soil water are frozen for most of the year

Limited groundwater and moisture stores; Permafrost is a barrier to infiltration, percolation, recharge and groundwater flow

Accumulation of snow and river/lake ice during the winter months; there is a sharp increase in river flow after the melting of snow, river and lake ice, and the uppermost active layer of the permafrost in spring and early summer

Extensive wetlands, ponds and lakes on the tundra during the summer; temporary store of liquid water is due to the permafrost (which stops drainage)

Accumulation of carbon is slow due to the low temperatures which slows down decomposition of dead plant material

The amount of carbon in soils is 5 times greater than in the above-ground biomass

Flux of carbon is concentrated in the summer months when the active layer thaws; the plants grow rapidly in the short summer and the long daylight hours allow them to flower and fruit within a few weeks

NPP is <200g/m²/yr

Biomass is small and ranges between 4 - 29 tonnes/ha depending on the density of the vegetation cover

During the growing season, plants input carbon-rich litter to the soil

Activity of micro-organisms increases and releases CO₂ to the atmosphere through respiration
Not just confined to the summer; even in winter, unfrozen soil and water in the permafrost act as a source of CO₂ and CH₄

Snow cover may insulate microbial organisms and allow some decomposition despite the low temperatures

Due to global warming, permafrost is becoming more of a carbon source (rather than a sink); outputs of carbon from permafrost have increased in recent decades but higher temperatures have increased the growth of plants and there is a greater uptake of CO₂ and this has increased the amount of plant litter entering the store so it is possible that the cycle has still remained in balance despite the warming of the Arctic

How is the Tundra managed?

How is the melting of permafrost managed?

Are the management strategies having a positive impact on the carbon and water cycle in the Tundra?

Changes to the carbon cycle

Melting of permafrost releases CO₂ and CH₄
On the North Slope, estimated CO₂ losses from permafrost vary from 7 - 40 million tonnes/year and CH₄ losses range from 24,000 - 114,000 tonnes/year

Gas flaring and oil spillages input CO₂ to the atmosphere

Industrial development

Destruction or degrading of tundra vegetation reduces photosynthesis and the uptake of CO₂ from the atmosphere

Thawing of soil increases microbial activity, decompositon and emissions of CO₂

As the vegetation is slow-growing, regeneration and recovery from damage takes decades

The localised melting of permafrost is associated with:

  • construction and operation of oil and gas installations, settlements and infrastructure diffusing heat directly to the environment
  • dust deposition along the rooadsides, creating darkened snow surfaces whcih increases the absorption of sunlight
  • removal of the vegetation cover which insulates the permafrost

Changes to the water cycle

Melting of permafrost and snow cover increases run-off and river discharge making flooding more likely

In summer, wetlands, ponds and lakes have become more extensive, increasing evaporation

Strip mining of sand and gravel for construction creates artificial lakes which disrupt drainage and expose permafrost to more melting

Drainage networks are disrupted by road construction and 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, reduces localised run-off