Utilising our wilding approach, Somerset Wildlife Trust will make initial management interventions then allow nature to take the lead. By doing this we hope to rewet, improve water quality, reduce carbon emissions and potentially store new carbon on site.

As part of our commitments to Wilder Carbon and to demonstrate nature’s recovery and the return of ecosystem function at Honeygar, we will record initial baseline levels of greenhouse gas (GHG) emissions of carbon dioxide (CO₂) and methane (CH₄). Carrying this out prior to any drainage system alterations is key.

But why are we doing this?

Peatlands are captivating ecosystems. In Somerset, they are embedded into the very fabric of our culture, with many of us growing up surrounded by a plethora of artwork, music, myths and legends inspired by the ancient Isle of Avalon.

The lowland peatland habitats of the Somerset Levels and Moors (SLM) provide much more than just aesthetics. Somerset’s peatlands are recognised for providing a range of ecosystem services including, water storage, flood mitigation, climate adaptation, carbon storage and water purification. In addition to this, peatlands are also important habitats for a range of interesting plants and animals, particularly overwintering birds.

Until the 1980s in the UK, however, wetland habitats were largely regarded as wastelands and not recognised for the range of services they provide. As a result of this lack of recognition, over many generations and still today, Somerset’s wetland and peatland habitats were routinely drained to be utilised for agriculture, development or for peat mining.

Despite only covering 3% of the land’s surface, peatlands store over 30% of the world’s soil carbon and per hectare store more carbon than tropical rainforests. According to the most up-to-date science, peatland habitats store approximately twice as much carbon as the entirety of the world’s forests – nearly as much as is currently stored in the atmosphere. They are the biggest terrestrial store of carbon we have. This is important because peatland habitats are in crisis. The most up-to-date estimates suggest that every year over 300,000 tonnes of CO₂ e is emitted from Somerset peatlands. Currently, we predict that approximately 104,387 tonnes of carbon is stored within peat soils at Honeygar. As it stands, 80% of UK peatlands are either lost or damaged. Damage done to peatlands in the UK currently accounts for 5% of all anthropogenic emissions.

So, how did we monitor GHG emissions at Honeygar?

Working with the University of the West of England (UWE) 18 sampling points were spaced out evenly across Honeygar. These sampling points were monitored using a gas analyser on a seasonal basis between June 2021 and March 2022 utilising what’s called the surface flux chamber method.

To do this, a clear bucket (chamber) is fitted with two tubes, both connected to the gas analyser. One tube is an inlet, drawing air from inside the chamber and passing it through the gas analyser which detect both CO₂ and CH₄ in one second intervals using lasers. The second tube is an outlet which dispels analysed gases back into the chamber.

At each sampling location, two measurements are obtained. Firstly, a light measurement which captures net ecosystem exchange (NEE) is taken - this is a combination of plant photosynthesis and respiration in addition to soil respiration. In soils, respiration is driven by microbial decomposition of organic matter. Secondly, a dark measurement is taken by covering the chamber and blocking any light from entering, this stops photosynthesis so that only ecosystem respiration (ER) which is plant and soil respiration is recorded, simulating what would happen at night.

Each measurement is monitored for approximately 3 minutes during which a range of contextual data such as soil temperature, soil moisture, humidity, air temperature and air pressure were recorded. These measurements help to explain the resulting GHG fluxes (rate of change), whether the land be primarily emitting GHGs (a source) or primarily taking up GHGs (a sink).

What has our initial baseline monitoring shown?

The results from the initial baseline GHG monitoring at Honeygar show that overall, on the days monitored, the site was acting as a significant source of CO₂ emissions, with weighted average values ranging from 5.08 - 27.61 g/day/m² and a small, but significant source of CH₄ with weighted average values ranging from 18.19 – 965.34 µg/day/m².

In addition to this, Honeygar exhibited significant seasonal variability in fluxes of CO₂ and CH₄, with the highest fluxes recorded in summer and the lowest in winter. Furthermore, it was shown that the majority of the eastern side of Honeygar, previously under more intensive agricultural and land drainage practices was acting as a sink for CH₄. Contrastingly, the western, less intensively managed side of the site, was acting as a small source of CH₄.

What might explain the results?

The GHG fluxes exhibited in the initial baseline GHG monitoring at Honeygar are characteristic of drained peatlands. In drained peatlands, such as those present at Honeygar, groundwater levels are much lower. This creates aerobic conditions (with oxygen) within the soil. Under these conditions, organic matter is broken down by microbes releasing carbon dioxide. Vascular plants dominate the surface, further altering the composition of the soil and its microbial communities. Together these conditions mean, no new peat is actively forming and therefore no new carbon will be stored. Furthermore, our initial GHG monitoring shows the more intensively managed and drained eastern side of Honeygar is acting as a sink for CH₄ throughout the year. This is likely due to the breakdown of CH₄ by methanotrophic bacteria (bacteria that break down methane) in the aerobic zone of the soil into CO₂ which is subsequently emitted.

In a pristine or restored peatland, peat-forming plants such as sedges, rushes and sphagnum moss dominate. The decomposition of plant and organic matter present within the peat soils is inhibited due to anaerobic conditions (the absence of oxygen) resulting from high water levels. This process locks carbon away, and overtime facilitates the carbon capture (sink) function of peatlands. Contrastingly, pristine or restored peatlands are a natural source of CH₄ as microbes slowly break down organic matter within the anaerobic zone and convert it into very small quantities of CH₄, this is then either stored within the soil or emitted into the atmosphere. Furthermore, peatland vegetation such as sedges, rushes and reeds have been shown to be transport pathways for methane. Their deep roots penetrate the anaerobic zone enabling methane to be transported, bypassing the aerobic zone and into the atmosphere. Such pristine or restored lowland peatland does not currently exist anywhere in Somerset.

What’s next?

Water table depth and vegetation type are the main drivers for reducing carbon emissions from lowland peatlands. Honeygar aims to maintain water levels between 10-30cm below the soil surface. This has been shown to be the optimum water table depth to reduce carbon emissions from peatlands.

Somerset Wildlife Trust are doing this by isolating our ditch systems, utilising sheet piles set to our targeted depth to capture winter rainwater. In the short term, conditions in the soil will become more anaerobic altering microbial communities, and in the long term, new peat-forming vegetation will establish. Although this will lead to more CH₄ being released than before, due to the reduction in CO₂ emissions, overtime we predict that this will lead to an overall reduction in emissions across the site, restoring ecosystem function and potentially storing more carbon.

To learn more about Honeygar and the work we are doing as a trusted deliverer for Wilder Carbon visit: Honeygar Farm (wildercarbon.com)