Baselining and Estimating Ecosystem Services

Key Points:

• High Fen has been baselined using the Peatland Code (PC)’s field protocol for fens, and Defra’s Biodiversity Net Gain (BNG) UKHab survey assessment. 

• Nattergal has separated areas for registration under the PC and BNG according to both their nature market potential and ecological feasibility. 

• High Fen is the first lowland peat site to be validated under the Peatland Code, validated in July 2025. Current estimates suggest the site is capable of generating more than 60,000 peatland carbon units (PCUs) across two phases of restoration.  

• Nattergal has taken a conservative view on its BNG unit calculations due to its approach of using natural processes to re-establish habitats. It has confirmed that it will explore selling any unplanned uplift in the future, as the habitats become established. 

• High Fen’s main interventions are aimed at restoring the site’s natural hydrology, including the installation of a bund, blocking ditches and marl excavation.  

• Nattergal has established a control site on a neighbouring farm to compare biodiversity outcomes for the foreseeable future.  

 

Baselining and Use of Codes 

The two major methodologies with nature market potential that were used to baseline High Fen were the Peatland Code (PC)’s recently launched field protocol for fens, and Defra’s BNG metric.  

From its initial findings (Milestone 1), Nattergal identified separate areas that were likely to generate significant uplift under these methodologies, but needed to fully baseline these areas to confirm their suitability.  

 

Peatland Code 

Nattergal aims to achieve a ‘rewetted fen’ status across ~85 hectares of High Fen, aiming to certify in excess of 60,000 Pending Issuance Units (PIUs) across two phases of Peatland Restoration.  

High Fen is the first site to be validated under the new protocol – launched within Version 2.0 in March 2023. The site’s plans for Phase 1 were validated in July 2025. Planning and building the application took a significant amount of time as the team gathered the necessary data and came to grips with the protocol. 

Key to the site’s submission to the PC was a more detailed hydrological analysis – as raising the water table is essential for rewetting a fens site and its success affects the number of units generated. Nattergal worked with Haycock Environmental Consultants to analyse the site’s hydrology over two years. This exercise identified where rewetting and raising the water table would be feasible, to what depth, what interventions would be necessary, and generated a full monitoring plan for the site’s hydrology going forward.  

Another key component in baselining was the soil sampling, which defines the depth of the peat and therefore the duration of the project and how many PIUs it can sell1. Exo Environmental were commissioned to take core samples, measuring a depth for each peat core and other key details. Nattergal used this information to exclude areas of shallow peat depth from the carbon project. 

Overall, Nattergal has identified two separate areas to register with the Peatland Code: 

• Phase 1 began in December 2024 and will last for 45 years with average peat depths of 65cm, covering 30 hectares.  

• Phase 2 will begin in October 2025 and will last for 33 years with average peat depths of 55cm, covering 55 hectares. 

This phased approach has been taken to manage the overall baselining and implementation process – driven mainly by High Fen’s hydrology and peat depth differences.  

Figure 1: Map of Phase 1 of Peatland Restoration (Land App)

Figure 2: Map of Phase 2 of Peatland Restoration (Land App)

Biodiversity Net Gain 

Alongside the PC baselining, Nattergal assessed areas more likely for BNG uplift and made decisions over which areas would be more suitable under either scheme.  

Overall, Nattergal has submitted 114 hectares for BNG. 

Hay comments that a UKHab survey together with overlayed Natural England habitat types (Floodplain Grazing Marsh) was mostly sufficient for defining High Fen’s BNG offering – covering type and condition of habitats.  eCountability undertook the UKHab survey, showing that much of High Fen’s habitat is ‘coastal floodplain grazing marsh’ – a high distinctiveness mosaic habitat within the BNG metric. Nattergal’s in-house ecologist built on the UKHab survey’s findings with an assessment of what habitats could be more easily improved as per the BNG metric’s condition criteria, such as moving areas from ‘poor’ to ‘moderate’ condition. 

Due to its preference for natural re-establishment processes and the associated uncertainty, Nattergal has taken a conservative position on what habitats it expects to generate and therefore has covenanted a lower number of BNG units than what would be possible if the aim was to maximise unit yield. This conservatism allows natural processes to function freely, without creating a management burden and crucially will likely generate better outcomes for biodiversity. Once the future state and condition of the habitats are established, Nattergal has confirmed it has the ability to further enhance the habitats and sell the additional units once verified.  

Figure 3: Map of planned post-intervention habitats at High Fen (Nattergal)

Hay remarks that, as further detailed ecological, hydrological and soil data came to light, High Fen’s natural capital planning was a “balancing act” between the areas designated for either the PC or BNG. In some areas, High Fen has areas of high peat depth but also areas of greater BNG potential. In some cases, Nattergal has opted for BNG due to ecological factors, such as a reduced ability to keep the water table raised.  

It is important to note that the management of the site will be largely consistent across the site as a single unit – rewetting and a minimum intervention natural process led management approach – it is only the natural capital funding mechanism that is different based on habitats and soils.  

 

Other Methodologies and Data Collection 

Nattergal has partnered with several organisations to collect further data and guide its landscape restoration plans, including: 

• The Freshwater Habitats Trust for an assessment of flora species presence  

• The Centre for Landscape Regeneration for baselining biodiversity across separate sites and historic environmental searches and images.  

Nattergal has also used bioacoustics, LIDAR, satellite imagery, drone surveying, biodiversity transects and other ground surveys to gather more data.   

While these have often presented extra costs to date, Hay says that this data collection has given much more confidence in planning – such as the design and placement of the bund for High Fen’s hydrology.  

 

Interventions and Restoration Work 

Nattergal aims to use natural processes as much as possible to restore the site: “we are seeking more water, more nature and better climate resilience,” comments Hay.  

The most direct interventions for High Fen have been to raise the water table. These interventions include the establishment of a bund, blocking ditches, and marl excavation to create semi-permeable barriers within the soil. A competitive tender process was undertaken to appoint the contractors used for this work.   

Going forward, High Fen will require a winter water abstraction licence so that the site can be flooded each winter and ensure the water table remains sufficiently high in the summer and autumn, which is a key physical risk of the project. This abstraction is required because the Wissey has been fully and entirely disconnected from its floodplain. Nattergal has applied for this licence and, as of September 2025, is awaiting a determination from the Environment Agency (see Milestone 1 for further detail on required permitting). 

 

Figure 4: Image of ditch blocking to increase the water table (Nattergal)

 

Beyond changes to the site’s hydrology, Nattergal expects to see the establishment of a mosaic of fenland habitats, including reed beds, willow carr, scrub and species-rich grassland. While rewetting is key to some of this, grazing and deer management will also be critical interventions, to enable natural regeneration of vegetation in places while keeping habitats more open elsewhere.  

Nattergal is investigating the reintroduction of species native to the region, such as pool frogs, large marsh grasshoppers, corncrakes, fen raft spiders and a host of fenland flora. 

While a small herd of cattle are already present on-site, in the longer term, Nattergal intends to introduce further large herbivores, including ponies and potentially water buffalo. These will be used for natural grazing patterns that can support wider biodiversity. Nattergal will closely monitor the site to ensure that these herbivores do not have an adverse impact on the land – potentially culling populations where needs be.  

Figure 5: Map of Phase 2 project (Nattergal) 

To manage delivery and physical risks, Nattergal is exploring insurance options for habitat restoration, such as in the event of fire or catastrophic flooding. Carbon insurance is also under consideration for PIUs that have not yet been verified – and therefore not protected by the Peatland Code’s buffer. 

 

Monitoring, Reporting and Verification (MRV) 

High Fen’s formal monitoring and reporting plan combines the requirements of both the Peatland Code’s fens protocol and BNG.  

The Peatland Code requires the continuous monitoring of the water table through dipwells across the registered areas. Nattergal has installed digital loggers in its dipwells to record this data, which is downloaded every couple of months for reporting to the Soil Association – its validation and verification body.   

To convert the PIUs into verified carbon units, the site will be ground surveyed and assessed by the Soil Association every five years. 

Hay comments that as the fens field protocol was newly launched, it was difficult for the team to understand some of the monitoring requirements. Nattergal has fed this back to the Peatland Code team, which has offered clarity but has also highlighted that the fens protocol is based off early scientific data and will continue to evolve going forward. In response to this, Nattergal is trying to help actively plug knowledge gaps and has put more effort into monitoring and data collection, such as the installation of carbon dioxide sensors to measure emissions directly.  

Nattergal is also collecting data on water chemistry at five points across High Fen and conducting aquatic invertebrate surveys at these points periodically. 

For BNG, Nattergal will make annual assessments and reports to its Responsible Body (the Lifescape Project) on how the habitats are progressing, and re-baseline every five years. Between these years, Nattergal will continue with breeding bird surveys, bioacoustics, transects and other data collection to understand its species uplift.  

More broadly, Nattergal has agreed to establish a control site on a neighbouring industrial farm, undertaking the same activities for biodiversity monitoring to see if biodiversity trends found at High Fen can be attributed to local or regional trends, rather than its own restoration work.  

Although citizen science has not yet been implemented, it remains a future ambition – particularly for aquatic invertebrates, transects and other ground surveying. 

Figure 6: A Whooper swan at High Fen Wildland (Nattergal)