The Restoration of Berrington Hall Pool Will Watson

The Restoration of Berrington Hall Pool

- Will Watson

The National Trust property of Berrington Hall and its park and pool are located four kilometres to the north of Leominster on the western edge of the Herefordshire Plateau; the largest and highest of the county’s isolated flat topped hills. To the west of the pool are the Herefordshire Lowlands. The Ridgemoor Brook is situated 500 metres to the west within a wide floodplain which was formed before the last glaciation by the proto-Lugg and Teme1 . 300 metres east of Berrington Hall there is a wooded ridge, known as Long Wood, which forms the eastern boundary to the estate. The ridge is composed of harder sandstone of the St Maughan’s Formation from the Early Devonian Period. Three springs emanate from the surrounding higher ground. There are at least two small streams running through the park. In the 1770s, Thomas Harley, who acquired the estate, appointed the famous landscape architect Lancelot ‘Capability’ Brown to lay out the park with spectacular views to the west towards Wales and the Black Mountains2. It was his last commission. The pool was created in a natural hollow on the lower slopes of the plateau. The presence of fenland peat suggests that there was probably a marsh and possibly smaller pools present before its construction. Capability Brown constructed a five metre high dam to the west so that water could be impounded from the small streams which he had piped and directed into the pool. Some of the spoil from the construction of the pool was used to level the land to the north to create an open flowing vista from the Hall to the pool. The pool is 360 metres long by 220 metres wide and covers an area of 6.6 hectares (14 acres). Two islands were created, the round Main Island, and the smaller Rat Island to the north-west. The islands cover an area of about 2.1 hectares and both are wooded with tree canopies extending over the water. The total area of open water is 4.5 hectares and as such it is one of the largest areas of open water in the county. From the direction of the Hall the viewer is presented with the appearance that the pool is narrower towards the south. The pool was constructed so that the Hall is reflected in the water when viewed from the south.

In 1969 the pool was designated as a Site of Special Scientific Interest on account of it being one of a very few sizeable areas of open water in Herefordshire and because of its large heronry, at the time one of only two such breeding sites in the county3. The pool also has relatively rich and diverse flora in comparison with other lakes in Herefordshire. 46 species of aquatic plants were recorded during a detailed survey in 20124. According to the scoring system developed by the Freshwater Habitats Trust, it places the pool in the very high category for UK still water bodies5. The pool has several distinct aquatic plant communities. In the open water there are beds of native White Water-lily Nymphaea alba covering large areas of the pool. This is a local species in Herefordshire with just 29 records6. Around the margin, swamp vegetation has developed to the north and south of Main Island. The swamps are dominated by Lesser Bulrush Typha angustifolia with occasional Reedmace Typha latifolia. Branched Bur-reed Sparganium erectum is locally abundant especially along the east margin. Yellow Iris Iris pseudacorus is occasional in occurrence. On the upper margin of the pool is a zone of marsh vegetation which is broadest to the south where there is locally abundant Reed Canary Grass Phalaris arundinacea, Great Willowherb Epilobium hirsutum and Meadowsweet Filipendula ulmaria. Notable plants include Lesser Waterparsnip Berula erecta, which is rare in the county and the uncommon floating liverwort Ricciocarpus natans which was found to be plentiful in 2012 among the swamp margin to the north of the pool. This was the first county record for over 75 years.

Berrington Hall reflected in the pool viewed in July 2022 and White Water-lily bed (c) Will Watson

White Water-lily flower at Berrington Hall Pool June 2022 (c) Will Watson

Purple-fringed Riccia Ricciocarpus natans on the northern pool margin in 2012 (c) Will Watson

A Bechstein’s Bat captured after trapping being checked before release (c) Lindsay Harrison

The diversity and richness of the site’s flora is also matched by its animal life. A bat survey carried out the Herefordshire Mammal Group, under Natural England licence, in 2016 found 12 species of bat within the park with the main bat activity centred around the pool7. A significant finding was that of three Bechstein’s Bat Myotis bechsteinii roosts with the largest roost in a tree on Main Island; presence of juvenile bats demonstrated that a maternity colony was also present. Bechstein’s Bats are one of the rarest bats in western Europe. It is classified as near threatened and is on the IUCN Red List. 103 bird species were recorded around at the pool over a 20 year period by British Trust for Ornithology8. In addition to Grey Heron, Little Grebe, Moorhen, Coot, Sedge Warbler, Reed Warbler and Water Rail are regular breeders. The amphibian population has not been well studied but we know from seeing large shoals of Common Toad tadpoles in 2022 that they breed successfully in the pool. Up to 50 Common Frog spawn clumps have been seen in the pool at any one time. Six Smooth Newt tadpoles Lissotriton vulgaris were netted in August 2012; the relative population size of these amphibians within the pool is presently unknown. In 2012, 63 species of aquatic invertebrates were recorded over several visits. This included 20 species of water beetle which are all classed as Lower Risk Least Concern9, 14 species of aquatic bug, 13 species of dragonfly, six species of mollusc, four species of leech, one species of flatworm, one species of mayfly, one species of alderfly, one species of cranefly and one species of caddisfly. At least 20 Red-eyed Damselfly Erythromma najas were seen mainly basking on White Water-lily pads in August 2022. Also significant are the large numbers of common species of dragonfly present. In July 2012 over 100 Common Blue Damselflies Enallagma cyathigerum, and over 25 black-tailed skimmers Orthetrum cancellatum and, on 24th September, 20 common darter Sympetrum striolatum were present. The site is of local importance for Odonata. According to the scoring system developed by Freshwater Habitats Trust the recording of 63 species places the pool in the very high category for aquatic invertebrates; this is because more than 50 species were recorded at the site. In spite of the relative richness of the pool in the early 2000s there were clear signs that all was not well. Concerns were expressed about the water quality as the roadside drainage to the A49 main trunk road had been directed into the pool. This would have resulted in chemicals toxic to the wildlife entering the pool. In 2012 the Highways Agency re-routed the roadside drainage away from the pool. There were also large numbers of Common Carp Cyprinus carpio in the pool at the time with few, if any, other fish species present. Common Carp have been cultivated and moved around the world for hundreds of years and have been introduced into the pool. They are predatory on a large number of aquatic invertebrates and have a negative effect on species diversity and can cause local extinction of aquatic invertebrates. They also stir up the bottom sediment leading to increased turbidity particularly during the summer months when they are active. The other main issue was the spread of the Lesser Bulrush swamp. It was noted that it was spreading further out into the open water covering a greater area. In the south-east of the pool the channel between the main island and shore is very narrow and to the east of the island this swamp vegetation has closed the channel completely. There was also a very broad swamp to the north-east of the pool which was nearly contiguous with the island. The cause of its more rapid spread was the gradual silting up of the pool. This meant that water wasn’t able to circulate around the island as had been planned. If left, the swamp vegetation would soon cover a greater area than that of the open water.

Drone shot of swamp vegetation blocking the eastern channel and turbid water (c) Jenson Jones

Removal of large Common Carp from the pool in November 2012 (c) Will Watson

The numbers of breeding Grey Herons on the main island had also declined since a high of 20 to 30 breeding pairs in the 1990s, to a low of just eight breeding pairs in 2012. The exact cause of the bird’s decline is not known but it is likely to be connected to these significant management issues (see below). The majority of the fish were removed by seine net in November 2012 by Furnace Mill Fisheries with over 75 large Common Carp being taken out, and used for restocking elsewhere after full health checks. The average fish weight was 5½ pounds or 2.4 kilograms. The heaviest fish was 13 pounds in weight or 5.9 kilograms. This showed that the majority of fish present were too large to be caught by the herons. This imbalance in the fish population could have contributed to the heron’s breeding decline. In order to redress the balance Roach Rutilus rutilus, Rudd Scardinius erythrophthalmus, and European Perch Perca fluviatilis, all native species, were added to the pool. It took a further seven years to tackle the issue of the invading swamp vegetation. The National Trust finally managed to obtain funding from the National Highways through their Environment and Wellbeing Designation Fund. Berrington Hall Pool was dewatered and de-silted between November 2021 and February 2022 with the work being carried out by WM Plant Hire Ltd. at a cost of £260,000. The work was carried out with consent of Natural England and had been preceded by a water and sediment analysis carried out by ADAS, and an updated copy of the management plan10. During the de-silting approximately a third of swamp vegetation was removed and this included the unblocking of the eastern channel around the island. In total, many cubic metres of silt were removed and deposited in an area of plantation in Moreton Ride mainly below the dam. During the de-watering, all remaining large carp were removed by Furnace Mill Fishery, some for restocking. The de-silting was a major operation and at its peak there were four diggers in action each with a 30 metre reach.

De-silting of the eastern channel with two 30 metre reach diggers January 2022 (c) Will Watson

It was thought that the bird population might suffer. 38 bird species were recorded between November 2021 and February 2022. When the water was drawn down below the levels of the swamp, the fish had nowhere left to hide and were easy pickings for the birds. Great White Egret was seen on five separate occasions and sometimes up to five Grey Herons were present on the pool taking advantage of this situation, Kingfisher also took advantage and was also a regular winter visitor. One of the strangest things witnessed was Mute Swans feeding on young fish fry. The Water Rail stayed put and was seen foraging on the bare mud.

The exposed mud also attracted a pair of Green Sandpipers which were present for the duration of the work. As the water was drawn the Swan Mussels Anodonta cygnea started coming to the surface in order to breath. It was a great surprise to see 100s of them along the margin of the pool as we hadn’t been aware of their presence before. They are the largest freshwater bivalve in the UK, and those at Berrington didn’t disappoint with the largest reaching 20 cm in length.

Water Rail out in the open foraging and Kingfisher on a perch November 2021 (c) Will Watson

Live Swan Mussel over 20 cm in length rescued from the pool January 2022 (c) Will Watson

We managed to rescue 70 of them, returning them to the section of the pool which had been de-silted. Dozens of the mussels had been predated with evidence of canine teeth along the shell margin; the likely predator was Otter Lutra lutra which also left their tell-tale track signs across the mud. The de-silting work was completed in late February 2022. As if on schedule we then had steady periods of rain and it was amazing how rapidly the pool filled up just in the space of a couple of weeks. In February in time for the heron breeding season the pool was again restocked with Roach, Rudd, Perch and this time also Pike Esox lucius. The management work didn’t end there: following advice from an aftercare plan11 the bare gaps along the bank where the diggers loaded silt onto dumpers had to be filled with aquatic plants. The aquatic plants were obtained from the silt of settling lagoons in Moreton Ride which had began to sprout with all manner of native aquatic plants. Yellow Iris Iris pseudacorus was favoured for gap filling as it won’t spread across the open water like the Bulrushes and Branched Burreed which were not replanted in gaps. Water Mint Mentha aquatica, Brooklime Veronica beccabunga and Pink Water Speedwell Veronica catenata were also favoured for gap filling. It is hoped as a consequence of careful replanting and control measures there will be less aquatic plant management needed in future. The pool has recovered remarkably quickly. For the first time in decades (possibly living memory) the water actually cleared. There was a risk with all the rich organic sediment in partial solution after de-silting that the pool would be taken over by algae. In the event we saw an increase in algae on the base in June but this declined in a couple of weeks.

The pool viewed from the south with clear water May 2022 (c) Will Watson

What happened next in July and August was a botanical transformation. The entire base of the pool was colonised by submerged aquatic weed. First to appear was stonewort (probably Chara vulgaris) around the margin, then Fennel Pondweed Potamogeton pectinatus, Curled Pondweed Potamogeton crispus and Hornwort Ceratophyllum demersum appeared in great abundance. There was also frequent Horned Pondweed Zannichelia palustris a nationally declining species of aquatic plant. Seven submerged species were noted in total, as well two newly recorded species; Broad-leaved Pondweed Potamogeton natans, and Unbranched Burreed Sparganium emersum.

Abundant Fennel Pondweed observed in August 2022 (c) Will Watson

Unfortunately, in addition to the submerged species spreading, the emergent plants also began to march across the pool including in areas which had only months before been desilted. Branched Bur-reed was the main culprit; no doubt it was the clear water conditions that favoured this burst of flora activity. The decision was taken, again with Natural England consent, to apply contact herbicide to these emergent plants which are growing in the wrong place. So what future plans are there for the pool? The intention is now to maintain the pool in good condition and not allow the management to get behind schedule. So, regular smaller scale management will be carried out on a regular basis to maintain the pool in optimum condition. Ideally we will rely on hand management techniques; such as the removal of emergent species from the margin where and when they threaten to spread into the open water, but if that is not effective then herbicide treatment may again be considered. The other thing we want to continue is the biological monitoring and the water analysis of the pool. A detailed biological survey was not carried out in 2022 because it was thought that the pool would still be recovering. However, a full survey is planned for 2023. It will be interesting to see how these results will compare with the surveys carried out in previous years.

References 1. Brandon, et.al (1989). Geology of the country between Hereford and Leominster. British

Geological Survey. Her Majesty’s Stationery office. 2. National Trust (2022). Berrington Hall website. Available at: https://www.nationaltrust. org.uk/berrington-hall(accessed August 2022). 3. Natural England (1969). Berrington Hall Pool, SSSI Citation. 4. Watson. W. R. C. (2013). Berrington Hall Pool Management Plan and Biological Survey 2012. Unpublished report commissioned by the National Trust. 5. Williams, P.J., Biggs, J., Barr, C.J., et.al. (1997). Conservation assessment of wetland plants and aquatic macroinvertebrates. Pond Action and The Institute for Terrestrial Ecology. 6. Anon. (February 2001). An Atlas of the Vascular Plants of Herefordshire. Herefordshire

Botanical Society. 7. Foster, D & Lee, D. (2016). Berrington Hall 2016 Bat Breeding Report. Herefordshire

Mammal Atlas, Herefordshire Mammal Group. 8. Cooke, T. (2021). BTO volunteer conducting the Wetland Bird Survey. Personal communication. 21st March 2021. 9. Foster, G.N. (2010). A review of the scarce and threatened Coleoptera of Great Britain.

Part 3: water beetles. Species Status No. 1. Peterborough: Joint Nature Conservation

Committee. 10. Watson. W. R. C.2021. Berrington Hall Pool Management Plan 2021. Unpublished report commissioned by the National Trust. 11. Watson. W. R. C.2022. Berrington Hall Pool AftercareManagement Plan 2022.

Unpublished report commissioned by the National Trust.