9.10.2018

Tuesday’s Soil Ecosystem Service – Carbon cycle (Global climate regulation)

 

 

Description: The carbon cycle is an important biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, and the Earth’s atmosphere. In this cycle, carbon is transformed from the atmospheric CO2 to plant tissue (photosynthesis), plant residues, and soil organic matter to be mineralised and released as CO2 back to the atmosphere. The soil carbon cycle ecosystem service refers to the ability of soils to enable the entire carbon cycle and to store/sequester atmospheric CO2 in a form of soil organic matter. Carbon sequestration is an important soil service that mitigates greenhouse gas problem and by this the effects of climate change.

Soil carbon cycle and soil processes: The soil organic carbon (SOC) storage is recharged by transferring carbon from the atmosphere via photosynthesis into plants and further as decaying litter into soils. SOC levels are directly related to the amount of organic matter in soil that is composed of soil microbes including bacteria and fungi, decaying material from once-living organisms such as plant and animal tissues, faecal material and organic products formed from their decomposition. These levels result from the interactions between ecosystem processes, such as photosynthesis, soil microbial respiration, and organic matter decomposition. SOC is determined from growth and death of plant roots, as well as indirectly from the transfer of carbon-enriched compounds from roots to soil microbes. Decomposition of biomass by soil microbes results in carbon loss as CO2 from the soil due to microbial respiration, while a small proportion of carbon is retained in the soil through the formation of humus, an important product that gives carbon-rich soils and acts as the largest carbon reservoir. If the humus decreases, additional CO2 is released into the atmosphere.

Carbon cycle and climate change: Carbon is the main component of many biological compounds and minerals and rocks (e.g. limestone). The carbon cycle comprises a sequence of events that are vital to making Earth capable of sustaining life, i.e. the movement of carbon as it is recycled and reused throughout the biosphere, as well as long-term processes of carbon sequestration to and release from carbon sinks. Human activities affecting these processes can lead to carbon loss or improved storage. CO2 emissions from fossil fuel energy are by far the largest source of greenhouse gas emissions. About 40% of these emissions have remained in the atmosphere; the rest was removed from the atmosphere and stored in the land (in plants and soils) and in the ocean. Increasing SOC increases soil health, fertility, drought resistance, biodiversity and other ecosystem benefits, including water quality and increased food security.

Relation to the entire ecosystem: In natural terrestrial ecosystems, the amount of organic matter and thus SOC storage considerably higher than those of vegetation, in particular in the uppermost 30 cm of soil. The highest amounts of SOC can be found in peatlands which therefore play an important ecological role. Whilst in forests high carbon storage of soils is supplemented by high carbon storage in the biomass, in agriculture, long-term carbon storage is largely limited due to unsustainable soil tillage and land use management.

Land use impacts: SOC storage is a vital ecosystem service. Human activities affecting these processes can lead to carbon loss or improved storage. Land use and poor soil management heavily influences global climate regulation. Deforestation, unsustainable agricultural practices, extensive soil sealing (urbanization) and other processes decrease or entirely eliminate soil carbon sequestration capacity. Furthermore, the extraction of peat or the drainage of wetlands is increasing CO2 emissions. Other ecosystem processes that can lead to carbon loss include soil erosion and leaching of dissolved carbon into groundwater.

Demand aspects In order to mitigate climate change with its myriad of negative impacts, this service should be of highest importance.

 

A short description:

Carbon cycle (Global climate regulation)

  • Output: Climate change mitigation
  • Provision: Carbon is withdrawn from the atmosphere by photosynthesis and via litter and root residues stored as organic matter in soils. The soil organic carbon storage is controlled by the organic matter accumulation (i.e. carbon sequestration) and decomposition (i.e. CO2 emissions) within soils. Soil contains globally more carbon than the atmosphere and terrestrial vegetation combined.
  • Demand: In order to mitigate climate change with its myriad of negative impacts, global climate regulation should be of the highest importance.
  • Threat: Inappropriate soil management can result in greater carbon emission than sequestration (e.g. drainage of bogs), which makes the soil a carbon source rather than a sink.