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• VISION FOR THE LYE VALLEY

The Lye Brook was once the centre of a large boggy area known by various names including 'Hogley Bog' and ‘Bullingdon Bog. It is a very rare environment:  a wet area, fed by lime-rich springs along the valley walls, making it technically a 'calcareous fen'. It is home to many unusual plants that are adapted to this environment, including the marsh helleborine, an orchid which flourishes here, and grass of Parnassus, a very rare species in this part of the UK. It is also abundant in wild-life: unusual insects including the brown hairstreak butterfly and glow-worms, birds such as the reed warbler, reptiles (grass snakes, slow-worms and lizards) and of course foxes, badgers, and occasional deer. The importance of this area has led to the designation of two Sites of Special Scientific Interest, the North and South Fens, which are protected by national legislation.

For centuries this was common land used for grazing animals, which kept grass and reeds short, allowing the flowers to flourish. But over the last century, the valley has changed: large estates have grown up around it, trees have colonized it, and the vegetation has changed. Now there is a major threat to its continued existence because of hydrological issues. The fen is wetted by natural springs, but the catchment area for these springs, once open country, is now very much built up – and threatened by further development. In addition, water run-off from the surrounding area, instead of percolating gently into the ground, is now captured in large drains and fed into the brook. When there is heavy rain, the brook becomes a raging torrent, and the bed and the walls are being eroded. This increased flow is threatening the fenland.  As the brook sinks lower between its banks, water drains off the fen, leading to a gradual drying out of the fens.

 

How does a Calcareous, Valley-head Spring-fen like the Lye Valley Work? New document by Dr Judy Webb, explaining why the catchment areas should stay as green as possible.

 

Grass of Parnassus




Marsh helleborine

Two dissertations for the degree of Master of Conservation Ecology at Oxford Brookes University:

(1) Adam Bows: Assessing the biodiversity outcomes of Wild Oxford: An alkaline fen ecosystem restoration project

Abstract The study investigated the effects of the Wild Oxford ecosystem restoration project on the plant communities, floral nectar resource and invertebrate pollinators of three small valley-head Alkaline Fens in Oxford, Chilswell Valley, Lye Valley and Raleigh Park. It found that the Wild Oxford project has substantially increased biodiversity, with a shift to more biodiverse plant communities and the establishment of Oxfordshire Rare Plant Register species in the areas undergoing restoration within 4–7 years. These were not the target M13 Schoenus nigricans-Juncus subnodulosus mire characterising undisturbed Alkaline fens in the region, but novel ecosystems closest to M22a Juncus subnodulosus-Cirsium palustre fen-meadow. A substantial increase in floral units, nectar resources and visits by flying insect pollinators was also recorded in Chilswell Valley and Lye Valley, demonstrating by proxy the value of fens for invertebrates. This effect was not recorded at Raleigh Park as a consequence of high intensity grazing which drastically reduced the floral and nectar resource of the Alkaline fens under restoration.
    Comparison with pre-restoration plant communities and control plots determined that these changes are largely explained by ecosystem restoration activities. The intensity of cut and collect biomass removal activities, application of hand-collected seed and grazing were found to have the strongest influence on biodiversity uplift. The role of rewetting could not be fully evaluated but the high mean annual water table recorded is an essential pre-requisite for the biodiverse wetland plant communities found.
    Abiotic variables also influenced biodiversity with effects of water table depth and potassium detected for all sites as a whole and a small negative effect of nitrates observed at Chilswell and Lye Valley. Calcium concentrations are high in all plots and play an important role in aiding restoration activities by limiting phosphate and significantly neutralising the effect of elevated nitrates.
   Compelling evidence was found of the effectiveness of fen ecosystem restoration techniques and similar sites with high water tables and calcium rich groundwaters offer good prospects for the ecosystem techniques to be successfully replicated in other local, degraded Alkaline fens at low cost primarily using volunteers.

• The full dissertation (PDF)

2. Darcey Haldar: Estimating the carbon stock in the Lye Valley's Peat fen

• The full dissertation (PDF)
• Carbon in the Lye Valley SSSI, North Fen Unit 1:
  Estimate by Dr Judy Webb on 7 February 2022 using Darcey Haldar's project data

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Plants in Lye Valley with Red List status

The Botanical Society of Britain & Ireland (BSBI) has released a new Red Data list for Vascular plants in England – see http://bsbi.org.uk/england.html

According to this re-assessment of threat status to plants, fourteen of the plants in the Lye Valley fens have now a national status – either Near Threatened or Vulnerable. Previously, when considered in the context of the whole of Great Britain, their status was LC – least concern.

Losses in England have been so great that the BSBI have felt it important to highlight the dire straits in which some wild flowers are in England, hence the new Red List.

• Table of plants in the Lye Valley with the new Red List status

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The Catchment of the Lye Valley North Fen

This map shows Surface and Groundwater Catchment Limits combined (thick black line) on a street map for the Lye Valley North fen area. This is the ground area within which rainwater falling on the soil, infiltrates and moves down into the limestone aquifer (store) to later emerge as special calcium-rich water in the springs which feed the Lye Valley SSSI and LWS fens (northern part of old Hogley Bog).

This map is drawn by J. Webb from a street map and the calculated catchment limits in the hydrological report of Curt Lamberth carried out for Oxford City Council (2007)*. 

Surface water travels through the top layers of the soil, ground water travels in the limestone at a deeper level. Obviously surface water feeds down into groundwater after a time.

The limit lines for the two types of catchment are slightly different but they have been combined for simplicity and because they are both important. Please see Lamberth’s original report* for the separate catchments.  He has checked this map for accuracy and states that the surface water limits are indicative only and has suggested a probable extension (red dashed line) of the groundwater limit, but as yet the data is not available to prove this.

Do you live within the catchment limits? If you do it is important what you do with your garden areas.  If you want to help save the Lye Valley wetland, it is important not to pave over either front or back garden, because the soil in these areas will feed water to the springs. If you pave it you prevent rainwater entering the soil and this will deprive the springs, eventually (even if your paving has a tiny effect, imagine the combined effect of all the gardens in your street paving their green areas).
Paved areas, roads, pavements (hard surfacing) shed rainwater into surface water drains which pour out into the Lye brook to erode the stream banks and cause the fens to dry out. 

Within the catchment area all green spaces, gardens and road verges are vitally important because they are freely permeable to rainwater. The playing fields of Wood Farm School and Peat Moors recreation field are particularly important as they are big green areas. But all green back gardens, allotments etc. are also important.

Within the catchment, all verges should remain green and uncompacted i.e. not parked-on or tarmacked. The springs need every drop that currently infiltrates because many of them have already dried up as a consequence of previous housing development.

Videos of the Lye Valley during heavy rain

The stream

The source (grating) and the contribution from road run-off (stream from right)

The cascade (among trees near the source)

Constitution of the Friends of Lye Valley (PDF)

Gerard Manley Hopkins, ‘Inversnaid’