Identifying the Important Freshwater Areas of the River Thame Catchment

By Dr Pascale Nicolet & Hannah Worker

With continued pressures on the freshwater environment and limited resources, how do we prioritise conservation efforts to ensure the best gains can be achieve for freshwater biodiversity and reverse the decline of the freshwater environment?

Freshwater Habitats Trust has been working with national freshwater species and habitats experts to address this issue through the development of the Important Freshwater Areas (IFA) Concept. An evidence-driven and scalable approach to underpin the practical delivery of freshwater conservation projects through the identification of locations of regional or national importance for freshwater biodiversity.

This work supports the restoration of natural processes in river catchments: understanding where rare or special species live supports better decision making, and helps avoid potential conflicts between different priorities at catchment scale. More information the importance of natural ecosystem function for managing and restoring freshwater habitats can be found in the CaBA Biodiversity Pack.

At the heart of the IFA concept is the key principle that to stem the decline in freshwater biodiversity and prevent further extinctions of freshwater species, it is essential that we protect the remaining high quality habitats, the Important Freshwater Areas (IFAs), and strategically restore and create new high quality habitats to extend these areas, and so improve connectivity and resilience.

Analysis of the River Thame Catchment

Identification of the Important Freshwater Areas requires the collection, collation and analysis of existing data of both species (freshwater ‘Species of Conservation Concern’, of which there are about 1,000 nationally) and habitats of importance (e.g. Priority Habitats). The IFA are identified against a set of criteria and, depending on the data available, considerable expert knowledge. The identification method is still being trialled at different geographical scales, and the River Thame catchment is only the second river catchment in the UK with an IFA analysis to underpin conservation work.

Within the River Thame Catchment, 10 locations were identified as Important Freshwater Areas at the catchment scale (these are called ‘catchment IFAs’). Thame catchment IFAs include a wide range of freshwater habitats: the River Thame and its floodplain, areas of semi-natural woodland with clean water ponds, gravel pit lakes, chalk streams and fen habitat.

An additional four locations were identified as potential IFAs where there was insufficient data, but further survey may elevate them to full IFA status in the future.

Key findings

  • Species of Conservation Concern hotspots included a diverse range of habitats – floodplain, the river, ponds, fens, and gravel pit lakes – highlighting the importance of all freshwater habitat types within the landscape.
  • Spartum Fen SSSI, a small fen site, had the highest number of rare species in the whole catchment reflecting the specialism and vulnerability of many fen species. Restoration work is currently being undertaken at the fen through the Oxfordshire Fens Project.
  • As can be expected, the quality of the data was an issue: many species records were relatively old, and so we don’t know if these plants or animals are still living in the catchment or a particular location. There were also clear geographical gaps in data which could be due to the lack of survey and/or reflect the intensive land use of the catchment. Some species are either known or suspected to be extinct in the catchment, including for example the rare fen violet and submerged aquatic plants which are sensitive to water quality, like pondweeds. The report provides recommendations for further targeted volunteer and professional surveys which would help provide a more up to date picture of these populations, and support the development of a programme of freshwater species re-introduction or translocation to restore diversity.
  • Analysis of the habitat preference for the Species of Conservation Concern of the River Thame Catchment shows that all freshwater habitats, large and small, with standing or running waters, are important to maintain the diversity of freshwater wildlife at the landscape scale. Indeed, about a quarter of Species of Conservation Concern in the catchment live both in running and standing waters, and 20% use a wide range of freshwater habitat, including also marshes or wet ground. These results are consistent with other IFA analyses and illustrates how all types of freshwater habitats are connected biologically if not always physically.
  • Overall, the largest group of SOCC were invertebrates (47 species), with aquatic and amphibious beetles (34%) and true flies (30%) making up the largest proportion. All but three invertebrate species and most plant species in the Species of Conservation Concern dataset have a restricted or even very restricted in distribution nationally, so it is important that remaining populations in the River Thame catchment are protected and, if possible, expanded by creating or restoring high quality freshwater habitats, on and off the floodplain.

Next steps

This first IFA analysis for the River Thame Catchment provides an initial baseline for freshwaters in the River Thame Catchment, including all waters. It highlights:

  • the importance of protecting the floodplain and all different freshwater habitat types and the few semi-natural areas, like woodland or unimproved grassland.
  • the lack of survey or monitoring data in freshwater habitats other than for the river and its tributary streams – which are the only waterbodies included in the statutory national monitoring programme of the Environment Agency.

Based on the finding of the IFA analysis, to improve the water environment of the River Thame catchment in the short term and stem wildlife decline, we need to focus on creating new clean water habitats and floodplain mosaics in and around IFAs, increasing landscape connectivity and the extent of high quality freshwater habitats. A carefully thought out programme of species reintroduction and/or translocation should be considered at newly created or managed sites to restore catchment diversity and expand existing freshwater wildlife populations.

There are excellent opportunities to restore freshwater habitats and their associated wildlife throughout the River Thame Catchment, in particular along much of the length of the River Thame on the floodplain corridor. The wide floodplain, of low value for farming because of flooding, and the critical support of many large and small landowners along the river corridor, are both key elements to support the development of successful large-scale restoration projects. The River Thame Conservation Trust, in collaboration with the Freshwater Habitats Trust, The Environment Agency and others partners, has already started this work, with demonstration sites showing a range of habitat creation and management activities around Waddesdon and Waterstock, and through improved fish passage in the catchment.

To see the report on the Thame catchment IFAs visit the RTCT IFA page.

For more information on the IFA concept and to see the results of analysis in other areas please visit: www.freshwaterhabitats.org.uk/research/important-freshwater-areas