CANAPE: Looking back at Barver Moor
What we did
Working on the drained bog grassland at Barver Moor, the partnership, operationally managed on site by Stiftung Naturschutz im Landkreis Diepholz (SNLD), created two polders for the cultivation of sphagnum moss. These large-scale polders, one covering one hectare, the other half a hectare, are carefully engineered to provide perfect growing areas for sphagnum moss – a bog plant that previously grew wild in the area. However, this time it would be cultivated with the objective of maximum plant growth and harvest. You can read about the early stages of the project in our previous articles here.
Each Polder has been carefully levelled to ensure a growing surface that will be approximately level with the water table in the polder. This is the optimum level for sphagnum cultivation. The water level inside the polder is maintained artificially constant by water pumped from a reservoir on the site, which is filled during times of plenty from the neighbouring ditch. This provides a buffer against the dry season.
The Polder at Barver Moor before the spreading of sphagnum plants, showing the underlying construction needed for sphagnum farming.
As the uncovered surface consists of compacted peat, water does not easily permeate laterally through it. Therefore, each polder is surrounded by a peripheral channel feeding irrigation ditches crossing the polder at distances of 6m apart to insure that the water is evenly spread across the area.
The crop that is established will be cultivated as a permacrop – after the crop is fully established, sphagnum will be harvested by cutting off the upper layers of the plant. The plant survives this process, and there will not be a need to reseed it.
Layout of the site at Barver Moor.
In nature, Sphagnum Moss is a central plant in raised bogs, and is the basis for the formation of peat, storing vast amounts of CO2 across the world. It is extremely well adapted to grow in the wet conditions we want to recreate in order to keep the carbon locked in the soil.
Once harvested, it is a highly versatile product, and has been used throughout the ages for its antimicrobial and absorbent qualities. Currently it is often imported from harvesting of wild bogs in South America, which damages important nature areas.
One potential market is as a growing media or substrate – in order for the world to achieve its climate goals, we need to stop the use of harvested peat as a compost for garden plants. Whilst amateur gardeners can easily use alternatives such as coir, there will be a need for high quality substrate for professional horticultural products. Sphagnum moss can be used as a replacement substrate for peat, and is already being trialled by some plant nurseries.
Another need for mosses comes from the large scale nature restorations planned for bogs across Europe – once they are rewetted there is a need for seed material to support the re-establishment of a natural sphagnum carpet. Farms like the one we have built at Barver Moor can provide this material.
The district of Diepholz, in the Federal State of Lower Saxony, contains many raised bogs. Many of these were drained for use in agriculture, or harvested for peat – originally for fuel, now to be sold as compost in garden centres around Europe. This all adds up to a significant carbon dioxide emission. Whilst some of these bogs have been rewetted, leading to a boost for tourism as the area is visited by tens of thousands of Cranes every year, the agriculture in the area has been suffering from a loss of employment. In part this is due to the loss of fertile soil and rising drainage needs as the peat soil degrades.
Taking Barver Moor as an example, there is less than a metre of peat left on the site, which has been lost at a rate of around 2cm a year over the last 20 years
The environmental benefits
The primary need to raise water levels on peatlands is the significant CO2 emissions associated with drained peatlands.
In the worst case scenario, cattle farmed on drained bogs can have an associated carbon footprint of 20kg of CO2 per litre of milk(1) – equivalent to driving an average new European car 185 Kilometres. The annual greenhouse gas emissions from organic soils in Lower Saxony amount to 10.6 million tonnes of CO2, which is about 11 % of the total greenhouse gas emissions in Lower Saxony. Rewetting of agricultural used lower Saxonian peatlands can reduce annual GHG-emissions by around 5 million tonnes of CO2
In contrast, a sphagnum lawn has a has a near-balance CO2 balance, and reduces the need for environmentally destructive peat harvesting.
Additionally, whilst still a monocultural agricultural field, the wet polders offer refuge for a lot of interesting wildlife, and the rewetting processes reduces the leeching of nutrients into surrounding waterways.
Finally, in a time of increasing unpredictability of the weather, the reservoir and rewetting of the soil increases the water storage in the catchment, and reduces the risk of wildfire as wet peat soil is unlikely to burn, unlike its dry counterpart.
The construction process
Cultivating Sphagnum mosses requires a well-prepared growing area. As noted above, the target is to have a wet growing surface where the growing surface for sphagnum is near the water level. At Barver Moor, particular care has to be taken to keep water in the field. For this, existing drainage tubes had to be detected and destroyed and topographic plannings had to ensure a sufficient layer of peat below any irrigation ditch, as the underlying material is porous sand, so without a layer of peat the water would rapidly drain away. This was a key factor in the design of the site.
First, we were required to move a small area of woodland on the edge of the site – whilst it would be preferable not to remove trees, this is sometimes necessary as the transpiration of the trees withdraws a lot of water from the moor and the species presented would not have flourished anyway on rewetted soil. This removal was counted into the GHG balance of the site.
Next, the construction of a reservoir. A rectangular polder was constructed, given an impermeable lining, and then filled from a nearby ditch. This is connected to the rest of the site with an automated control unit to ensure a uniform and constant water level, pumping water into the irrigation ditches whenever the level drops below a pre-set level. After some initial mishaps, it was learned to ensure that the control gear is reinforced against tampering by curious racoons.
Construction underway in the late winter in 2020.
Then the construction of the polders – these were levelled by mechanical earth mover, and the channels cut through the surface. Peat dug out of the polders was used to create the boundary or to dam ditches in the neighbourhood and the leftover was sent to be used as a soil improver. Reusing as much peat as possible on site reduces the carbon footprint associated with the conversion, however some losses were unavoidable.
The final step was the seeding of sphagnum material. To ensure that it was a local plant type, it was donated from three different sites near Oldenburg, the dutch border and from the nearby Netherlands. The Sphagnum was then spread onto the site. A roller was then pushed over the site to help peatmosses get in close contact with the wet surface. No straw mulching was applied as the irrigation system could keep the soil wet and cool from the start.
Material being spread on the site by hand, before being pushed in with a handpushed roller.
For this site the work had to be done mostly by hand – part of developing paludiculture in the future will be establishing mechanised planting, grooming and harvesting machinery to reduce the overall cost of establishing a sphagnum farm.
In general, a hectare of sphagnum farming can produce 2 – 8 t dry matter per year. This can be put to the following uses:
- Sustainable substrates
- Seeding material for bog restoration projects
- Bio-based sanitary towels
- Toxic waste absorber and water cleaner
- Ornamental floristics
- Use in exotic animal terrariums
Although the CANAPE project is wrapping up this year, this will not be the end of the road for our work at Barver moor. The site will continue to be used as a testbed and demonstrator, as part of the growing paludiculture movement around the world.
(1) Boxmeer et al (2021), Environmental and economic performance of Dutch dairy farms on peat soil