Lowland Peat Mesocosm Experiments

The mesocosm experiments used intact soil cores collected from lowland field sites across South Yorkshire and East Anglia. These core samples were placed into outdoor water-controlled mesocosm bins, each with pre-drilled outlets to maintain precise water-table levels. Experiments ran for one year with the water table levels at 0 cm and another year with water table levels at 20 cm below the surface. 

1. Raising the water tables – We tested higher water tables (at around 0 cm,15 cm and 20 cm below the surface) versus lower water tables.
2. Biochar and iron sulfate addition – Biochar and iron sulfate were applied directly to the peat cores to explore whether different types of soil treatments can prevent the release of stored carbon from the peat under different water table levels. The experiments compared Miscanthus biochar with Miscanthus cuttings, treated sewage waste, barley straw and paper waste. This is the first time mesocosm experiments have been used to study the effect of biochar in peatlands.
3. Simulating crop planting – Lettuce crops were planted and observed over 4 months to explore whether food production can continue under high water tables and biochar treatments.
    

1. Higher water tables and biochar reduce emissions

While raised water tables do reduce carbon dioxide and nitrous oxide emissions, this also increases methane emissions and result in a net increase in greenhouse gas emissions. However, raising the water table to 0 cm and  10-15cm below the soil surface, and adding biochar, significantly reduces overall greenhouse gas emissions and increases soil organic carbon. This supports the peatland’s natural role as a carbon store.

• Highest carbon preservation: Miscanthus biochar showed the highest capacity to retain carbon in the peat soil (18.9 tonnes of carbon per hectare) with the lowest net carbon loss compared to the other treatments.
• Combined treatment: The most effective approach for peatland restoration was found to be a combination of higher water tables, biochar treatments, and adding iron sulphate.  
• Microbial effects: Raising the water table limits oxygen, which suppresses aerobic decomposers and prevents the dominance of certain microbial groups that accelerate peat breakdown. Biochar addition directly changes the microbial community structure and function, significantly reducing the activity of enzymes responsible for breaking down organic matter. Iron sulphate provides an alternative pathway for microbial respiration that is not reliant on methanogenesis (methane production). It also increases the amount of carbon that is chemically bound to iron, making it more resistant to decomposition.  Overall, these microbial effects create better conditions for long-term carbon preservation and is a new finding in the context of peatlands.
• Practical application: Combining rewetting with biochar and iron sulphate offers a practical strategy for restoring degraded agricultural peatlands and improving their carbon storage capacity.  

2. Agricultural production can be maintained

A water table level of around 15 cm below the surface, with the addition of biochar, can still maintain agricultural productivity while reducing emissions. 

• Improved growth: Lettuce grown with biochar had improved shoot and root growth compared with control plants where no biochar was added. This was regardless of the height of the water table.
• Increased microbial diversity: With the addition of biochar, there was increased diversity of microbes, which changes the structure of the soil so it benefits plants.

Combining a raised water table with biochar and iron sulfate is a practical and scalable strategy to help peatlands store more carbon. In fields with lettuce, biochar is an effective soil treatment for improving yields across different water table heights. 

The experiments show that peatland restoration is more complex than simply raising water tables and adding carbon, it’s about changing microbial hotspots, enzyme activity and stabilising soil organic carbon with iron. The studies did not look at the overall greenhouse gas emissions of producing and transporting biochar.