Oxygen Conservation partnered with NatureMetrics to build a comprehensive eDNA baseline for the River Thet at its Shropham Estate in Norfolk. The data gives the team clear evidence to guide ambitious river restoration plans and a benchmark to measure their long-term impact.

The 694-acre former farm includes around 2km of the River Thet, which was historically straightened and confined to serve agriculture. Oxygen Conservation aims to restore this stretch to a more natural, dynamic state, potentially reconnecting it with its floodplain to create a thriving wetland ecosystem.

Before starting work, the team needed to understand what was already living in and around the river. By collecting detailed data on fish, mammals and aquatic invertebrates, Oxygen Conservation could shape its restoration strategy and set a baseline for tracking the success of its interventions.

Oxygen Conservation faced five key challenges in planning its river restoration project:

• Biodiversity data for the River Thet at the estate was out of date, with the most recent records dating back to the early 2000s.
• The team needed a non-invasive method that could survey multiple species groups without disturbing the sensitive river ecosystem.
• It wanted to balance ambitious restoration with evidence-based decision-making, and be able to quantify future biodiversity gains.
• It had to navigate stakeholder interests, including an existing angling syndicate using the on-site gravel pits, while prioritising overall ecosystem health.
• Non-native species in the adjacent gravel pits, including a potentially invasive catfish, raised questions about habitat connectivity and management.

Traditional survey methods were considered too invasive, resource-intensive and limited in scope for such a sensitive habitat. Oxygen Conservation needed a holistic approach that could capture the river’s biodiversity, address concerns around invasive species and habitat connectivity, and support evidence-based decisions.

NatureMetrics deployed aquatic eDNA sampling kits across multiple locations on the River Thet and its associated water bodies. The sampling was designed to capture biodiversity across the estate’s different habitats, including the main river channel, field drains and gravel pits.

We analysed the samples in our laboratories using two metabarcoding assays: one for vertebrates and one for freshwater macroinvertebrates. This dual approach detected a wide range of life, from fish and amphibians to elusive mammals and diverse invertebrate communities. We then delivered detailed reports and data, including species richness and evolutionary diversity metrics, to inform restoration planning.

The surveys revealed rich and spatially varied biodiversity across the River Thet and surrounding habitats.

A total of 54 vertebrate species were detected, with 72.2% identified to species level. These included 14 fish taxa, among them the European eel, which is listed as critically endangered on the IUCN Red List and was detected in 4 out of 12 samples.

The surveys also found evidence of important mammals. Water vole was detected in 9 out of 12 samples, and otter presence was confirmed at one location, giving valuable insight into how these protected species are distributed across the estate.

For aquatic invertebrates, the surveys identified 504 taxa, with 50.4% identified to species level. This rich invertebrate diversity is a powerful indicator of water quality and habitat condition. The data also pinpointed the sampling location with the highest invertebrate diversity, providing a potential reference point for restoration.

Finally, the results highlighted clear differences in biodiversity between habitat types on the estate, including the main channel, field drains and gravel pits. This spatial information is key to targeting restoration and understanding habitat connectivity.

The eDNA results gave Oxygen Conservation a robust biodiversity baseline, turning an ambitious restoration vision into a plan grounded in evidence.

Clear targets and measurable progress. With a detailed starting point, Oxygen Conservation can set specific, measurable biodiversity targets and track progress through repeat surveys, making it possible to show exactly what restoration has achieved.

Targeted restoration design. The invertebrate data and habitat comparisons give insight into water quality and condition across the estate. This will guide the design of in-channel improvements such as increasing channel sinuosity, adding large woody debris and reconnecting the river with its floodplain. The highest-diversity site offers a reference point for what good looks like.

Better connectivity decisions. Knowing where European eel, water vole and otter occur, alongside differences between the river, field drains and gravel pits, helps Oxygen Conservation make informed decisions about habitat connectivity, including how to manage links with the gravel pits where non-native species are present.

Adaptive management. Because eDNA detects a wide range of species, including those often missed by traditional surveys, it is well suited to assessing the effect of each intervention, so the team can adapt its approach as the project progresses.

Stronger stakeholder engagement. Concrete evidence of the site’s ecological value strengthens Oxygen Conservation’s position with potential partners and gives it a powerful tool for engaging anglers, conservation groups and other local stakeholders around the benefits of restoration.

Scaling across the portfolio. The success of the Shropham project has already opened discussions about using eDNA to answer conservation questions at other estates across Oxygen Conservation’s growing portfolio.