How much carbon is stored in the soil, and how does this compare to other carbon stores?
- Soil = ~1500-2400 Pg carbon
- Vegetation = ~450-640 Pg carbon
- Atmosphere = ~ 589 +- 240 Pg carbon
Soil contains more carbon than vegetation and atmosphere combined
What ecosystem services do soils provide for humans?
- Carbon sequestration
- Climate regulation
- Water purification and soil contaminant reduction
- Nutrient cycling
- Provision of food, fibre and fuel
- Cultural heritage
- Provision of construction material/human infrastructure
- Flood regulation
- Habitat for organisms
- Source of pharmaceuticals/genetic resources
What is soil made up of?
Soil is either mineral or organic - we are mainly focused on organic elements:
Soil organic matter:
- Stable SOM
- Readily decomposible SOM(ready to decompose and be released back into atmosphere). 20-40% is living organisms - e.g., bacteria, fungi, yeasts, algae, insects etc
How much carbon is stored in different soils?
- Surface of soils are more rich than lower down - need to make sure you compare same depths
- Tundra higher %C than forest soils
- BUT: Peatlands: have significantly larger %C - up to 50% carbon - can increase with depth
- Peatlands cover - 3% of land area - but store around half of soil carbon
Where are the largest peat deposits?
Mainly at high northern latitudes
- But also some in northern europe - e.g., Scotland and Scandinavia
- But recent discoveries have found large peatland stores in tropical areas
- But is so challenging to find out any of this information remotely
How does peat impact the climate?
Near natural bog:
- Releases methane but stores lots of carbon = Net global warming potential is negative
Drained bog: e.g., for agricultural use
- Very substantial change: source of methane and carbon = net positive effect
Restored bog:
- Rewetting them - bog still emits lots of methane - but now stored carbon = starts to swing net effect over time
How can deforestation have a knock-on effect on carbon loss?
Deforestation is a source of carbon on its own - but it also means carbon cannot accumulate in the soil without any vegetation/litter - exacerbates effect
- The soil will also now be more susceptible to erosion - providing another source of carbon
How can you measure soil carbon dynamics?
Diachronic:
- Sampling same site at different moments
- Tracking site location
- Long-term experiments
Synchronic:
- Different land use and management, same soil, climatic conditions
- Space substitutes time
- Chronosequences/paired comparions
- Better with shorter time period
Discuss how long does it takes for land use change from forest to pasture in Brazil to re-coup the carbon lost from deforestation?
High uncertainty - but average around 3 years
How will climate change affect soil organic carbon?
Positive climate feedback - bad
- Higher temp = faster microbial decomposition of SOM - and release of carbon to atmosphere
Potential negative climate feedback: good
- Higher temp = increase nitrogen availability (via enhanced SOM decomposition) which alleviates N limitation for plant growth + increases photosynthesis rates
But we dont know which feedback will be stronger - all very uncertain
How can we increase soil carbon?
4 per 1000 initiative: e.g.,
- Not leave soil bare
- Add hedges at boundaries
- Optimize pasture managment etc
- UK Farm and Soil Carbon Code - UKFSCC - people receive more credits for putting more carbon in soil
- But how do we make sure they stay there? Can be easily released by disturbance
What are the wider benefits of increasing/maintaining SOC?
- Improves water availability to plants - drought resistance
- Soil structure - reduction in losses by runoff/eroision and increase in root growth and proliferation
- Nutrient retention - decrease nutrient loss and increase nutrient use efficiency
What are some of the caveats of SOC sequestration as a mitigation strategy?
- Upper limit of stable soil carbon storage
- Soil carbon sequestration can be reversed
- Potential for soil carbon sequestration depends on initial conditions
- Challenges with Measuring, Reporting and Verifying changes in SOC
