Carbon sequestration

What is it?

Ecosystems can play an important role in capturing greenhouse gas (carbon dioxide, CO₂) as carbon in soil and vegetation. They also regulate the amount of CO₂ in the atmosphere and thus help ensure a more stable climate. It is estimated that the total stock of carbon in the soil in the Netherlands comes to 357 megatons.

Forests figure prominently in capturing CO₂, because they put it into the wood as carbon and this creates a multi-year stock. Each year Dutch forests sequestrate 2.7 megatons of CO₂. This equals only 1.3% of the total emission by sources such as traffic, households and industry.

A large quantity of carbon was captured in peat land in ancient times. We can look upon this as an ecosystem service delivered in the past. Some of the peat land has been cleared and reclaimed since the Middle Ages, and even now groundwater levels are actively being lowered for agricultural purposes. This causes the oxidisation of the peat (as a reaction to oxygen), which releases a lot of CO₂. This mounts up to 4.2 megatons of CO₂ per year in the Netherlands, more than the quantity sequestrated by forests.

Sustainability

CO₂ is sequestrated as carbon in nature areas. This occurs not only in forests, but also in other types of nature. Damp forests hold the biggest stock of carbon per hectare, but the largest stock of carbon in the soil can be found below natural rough grazing land and reed marshes. In most types of nature (except forests), the carbon stock below ground in the soil is many times greater than the stock above ground in trees and plants.

Dutch forests make a modest contribution to the capture of CO₂, when compared to emissions (1.3%). Using forests solely to capture CO₂ (as production forests) might be at the expense of other ecosystem services, such as green recreation and life-cycle maintenance.

Peat land contributes significantly to Dutch CO₂ emissions as a result of oxidisation of the peat. Prevention of peat oxidisation by wetting slows down this process and reduces the amount of released CO₂. But this has the disadvantage of releasing more methane, a strong greenhouse gas.

In real life

CO₂ emissions from peat lands are reducible by raising the groundwater level in the area. A higher water level impedes the use of heavy equipment in agriculture, so the agricultural land yields less. If the costs of actively lowering the water level are high and the returns from agriculture are relatively low, one option might be to turn the agricultural area into nature. The water level can then be raised, ensuring that CO₂ remains captured. This will be a less preferred option in areas where the returns from agriculture are relatively high.

Although capturing CO₂ in forests makes a modest contribution, it is possible to strengthen this ecosystem service by looking for the optimum configuration of wooded areas. This will necessitate making a choice between different ecosystem services, such as green recreation and life-cycle maintenance.

In agriculture, too, there are ways of improving carbon sequestration. Conservation tillage and an improved alternation of crops have the greatest potential for carbon sequestration. This potential is not being fully utilised due to the costs involved and agricultural limitations. The maximum attainable carbon sequestration in Dutch agriculture might be approximately 1 megaton of CO₂ per year. This equals 5.5% of current emissions by the agricultural sector.

Real-life examples:

Maps

Carbon in the soil: