2.8 Threats to the carbon and water cycles

Why did the Madagascan government encourage farmers to clear more land in order to grow cash crops?

The growing international demand for tropical hardwood, an expanding population, and debt repayments

What impact does deforestation have on the terrestrial carbon store?

It can affect the total carbon absorbed by photosynthesis, which reduces the carbon stored in above ground biomass

What are the impacts of deforestation on the water cycle?

Infiltration decreases, runoff and erosion increases, flood peaks are higher and lag time is shorter, increased discharge leads to flooding, and more eroded material is carried in the river, and annual rainfall is reduced.

What are the impacts of deforestation on soil health?

The raindrop impact from a lack of infiltration washes finer particles of clay and humus away, and coarser and heavier sands are left behind. Biomass is lost due to reduced plant growth and rapid soil erosion leads to a loss of nutrients

What are the impacts of deforestation on the atmosphere?

Turbulence is increased as the heated ground induces convectional air currents. Oxygen content is reduced and transpiration rates are lower, and reduced evapotranspiration makes the air less humid

What are the impacts of deforestation on the biosphere?

Evaporation from vegetation is reduced, and less absorption of CO₂ means a reduced carbon store. Species diversity is reduced, as well as ecosystem services.

Why is the demand for corn so high right now?

Because ethanol from corn is used in 98% of all petrol, and this demand has kept prices high

What were the aims of the US Environmental Protection Agency’s Renewable Fuel Standard policy?

• Increase the amount of ethanol being used in petrol

• Boost the economies of rural US states

• Reduce US dependence on overseas oil imports

• Reduce CO₂ emissions from transport

Which biome has been most affected by the increase in corn production?

Grasslands, which were ploughed up, and in some states, the area of corn being cultivated more than doubled between 2007 and 2013

Give 3 benefits of natural grasslands.

• they trap moisture and floodwater

• they absorb toxins from soils

• they act as a carbon sink and a terrestrial carbon store

Give 3 disadvantages of converting grasslands to grow biofuel crops.

• Annual ploughing enables soil bacteria to release CO₂

• The carbon sink is reduced

• Biofuel crops are heavy consumers of water, so they need irrigation which has a significant impact on aquifers

What is afforestation?

The re-planting of trees when deforestation has occurred, or to establish forests on land not previously forested

How much of the CO₂ produced as a result of human activities since 1800 has been absorbed by the oceans?

Around 30%, and about 50% of that produced by burning fossil fuels

What impact does the increased absorption of CO₂ by the oceans have?

The pH decreases, becoming more acidic. This means that corals cannot absorb the alkaline calcium carbonate that they need to maintain their skeletons, and reefs begin to dissolve.

How much more acidic is the ocean as a result of this increased absorption of CO₂?

The pH has lowered by about 0.1, meaning it is now about 30% more acidic than it was in 1750

What happens to corals when the water gets too warm?

The algae, which live in the tissues of corals and provide food for them are ejected and the coral turns white, which is known as coral bleaching

What ecosystem services do corals provide?

• shelter 25% of marine species

• protect shorelines

• support fishing industries

• provide income from tourism

What are supporting services?

Services that keep ecosystems healthy by providing other services, including soil formation, photosynthesis, nutrient cycling and water cycling

What are provisioning services?

Products obtained from ecosystems, including food, fibre, fuel, genetic resources, natural medicines and pharmaceuticals

What are regulating services?

Benefits obtained from the regulation of ecosystem process, including regulating air quality, climate, water, erosion, disease and pollination

What are cultural services?

Non-material benefits that people obtain from ecosystems, such as spiritual well-being, recreation, education and science

What were the impacts on the carbon cycle in the Amazon from droughts?

The drought effectively shut down the Amazon’s function as a carbon sink. Forest fires broke out, burning trees and litter and releasing CO₂