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Zones and Habitats

Geology of the Springs near Duncton
Dr Andy Swan President, Haslemere Natural History Society

The landscape of the South Downs results from the underlying geological sequence. The higher part of the escarpment is formed from the relatively hard and porous Middle and Upper Chalk, below which are gentler slopes underlain by the grey and clay-rich Lower Chalk. Below this is a lower but well-defined escarpment of the hard and porous Upper Greensand (30m thick), on the top surface of which are sited the villages of Cocking, Barlavington and Sutton.

Underlying the Upper Greensand and forming the lower ground on which Heyshott, Graffham and Duncton are sited is the very soft and impermeable Gault Clay. All of this geological sequence was deposited in seas during the Cretaceous period, around 110 to 80 million years ago, and the layers have since been affected by earth movements so that, in this area, they are now inclined to the south.

A consequence of the geology is that there are two spring lines. Rain falling on the South Downs soaks through the Upper and Middle Chalk, but is partially impeded by the clayey Lower Chalk, so water is “ponded-up” in the pore spaces of the Middle Chalk and seeps from the bottom of the hillside at the top of the Lower Chalk. Some water does slowly percolate through the Lower Chalk and finds its way into the Upper Greensand and this, plus rainwater that has soaked directly into the Upper Greensand terrain, is “ponded-up” at the top of the underlying highly impermeable Gault Clay, and so there is a very strong spring line at the base of the Upper Greensand escarpment.

Whilst water may seep to the surface all along the two spring lines, there are particularly strong springs where the aquifers (the water-soaked porous rocks) are especially permeable, probably as a result of fracturing. The stream at Botany Bay emerges from a particularly strong spring. The action of water emerging from rocks at a spring is an erosive force, and this was accentuated during the ice ages by annual cycles of freeze-thaw fracturing the damp rocks, with the spring water washing away the resulting debris. The original position of the spring would have been in-line with the rest of the Upper Greensand escarpment base (i.e. currently near the A285 bridge), but the intense and focused erosion at the spring has eaten into the Upper Greensand terrace, probably working along a line of fractured rock, and has formed the current gorge.
The Chalk Stream
r2 : Rivers and lakes/rivers and streams
The springs rising from the base of the Downs in Beechwood Lane merge to form the stream which flows through the ghyll in Botany Bay. In the stream is a small population of wild Brown Trout, many Bullheads and riverfly larvae. The stream is surveyed regularly for The Riverfly Partnership. Riverflies, along with other freshwater invertebrates, are at the heart of the freshwater ecosystem and are a vital link in the aquatic food chain. Their common characteristics of limited mobility, relatively long life cycle, presence throughout the year and specific tolerances to changes in environmental conditions make them good biotic indicators of water quality and useful indicators of change in local environmental conditions such as pollution, siltation and low flows. The Riverfly Partnership interest focuses on three key groups of riverflies: the up-wing flies or mayflies (Ephemeroptera), caddisflies or sedges (Trichoptera) and stoneflies (Plecoptera). Advised by Andy Thomas from The Wild Trout Trust, we improved the flow of the stream, creating pinch points to form spawning areas for the brown trout. In 2017 Botany Bay received an award from The Wild Trout Trust for the restoration project.
The Fishing Lake
r1b : Rivers and lakes/Mesotrophic lakes
Portsmouth Services Fly Fishing Association (PSFFA) has leased the lake since 2007. Since that time their volunteers have helped with many of the improvements to Botany Bay: initially helping to clear the infrastructure from the old fish farm, enhancing the stream bed for the small community of wild trout, and enabling the fish passage to the stream’s upper reaches of clear gravel to spawn. The lake is stocked with triploid Rainbow Trout that are unable to breed. This allows the diploid native Brown Trout to thrive in this unique environment, whilst providing adequate fishing for members of PSFFA. The rainbows, averaging 1.5 to 2lbs, are stocked according to its usage, the browns are always carefully returned. The use of barbless hooks is encouraged. Native brown trout are now regularly caught of about 1lb, showing the fishing/environmental balance; a fine example of where the fishing and environmental interests coincide.
The Still Ponds
r1a : Rivers and lakes/Eutrophic standing waters
There are six still ponds on site which were originally dug out for the fish farm. These deep steep sided fish ponds have been re-profiled to increase their diversity, creating ponds of differing sizes and depths with shallow edges and undulations. We have constructed a dipping platform on one of the ponds and have regular visits from school groups for pond dipping. Toads, frogs, palmate newts, dragonfly and damselfly nymphs can be found in these ponds.
The Lake Edges
f2d : Wetland/Aquatic marginal vegetation
The margins of the stream and lake are largely steep, so that there is little room for the development of emergent vegetation and this is dominated by Hemlock Water Dropwort and Horsetail. To provide additional opportunity for other riparian species, a small number of bankside areas on the sunny northside of the lake have been dug out to encourage a variety of emergent plants to flourish. Species introduced to these areas include Purple Loosestrife, Marsh Marigold, Ragged Robin, Meadowsweet and Devil’s-bit Scabious.
The Meadow
g2a : Grassland/Lowland Calcareous grassland
In 2019 part of the meadow was stripped of turf and some of the topsoil to remove the coarse grasses present and decrease its nutrient level to make it suitable for sowing wildflower seeds. This was done because the meadow sward consisted only of coarse grasses and very few flowering plants such as Stinging Nettle and Hogweed. Most wildflowers cannot compete with the plants that grow in rich soils. Wildflower seeds were sown and in the following year the area was dominated by Ox-eye Daisy and Wild Carrot. These two species still dominate, but in 2023 over 50 wildflower species were recorded. Furthermore, the meadow now supports a range of meadow butterflies, such as Meadow Brown and Marbled White. In addition, other groups of insects have been found utilising the pollen or nectar o the wildflowers, such as bees, hoverflies and beetles including wood eating species. We hope to increase the area of wildflowers in the near future.

A south facing bank to provide warm bare earth was built in 2022 to provide an area where solitary bees could dig out their nesting tunnels. The bank was surrounded by an area of wildflowers that have been shown to be particularly attractive to bees wild and in its first summer it has proved to be popular with bees and other insects, many warming up on the south facing soil early in the morning.
The Apple Orchard
c1e : Cropland/intensive orchards
A small apple orchard was planted in 2006 when the family had a fruit and vegetable garden on the west side of the meadow. Varieties include Bramley, Egremont Russet, Worcester Pearmain, Laxton’s Superb, Charles Ross and Blenheim Orange.
The Woodland
w1f : Woodland and forest/Lowland mixed deciduous
A headwater chalk stream flows north-eastward through the steep-sided wooded ghyll. The stream is fast-flowing and rocky-bottomed in places. The chalk stream has carved out a deeply incised and steep-sided ravine, the sides of which are cloaked in ancient woodland. There is a good diversity of trees and shrubs. The southern part of the wood is mainly Ash with some Field Maple, Oak and the coppiced Hazel along the west bank.There are also a few large old limes in the west and a particularly large Sweet Chestnut in the far south. Northwards, Oak is more frequent, and there are some fine veteran trees. There are also some mature Yew, a small number of Alder and Sycamore. The narrow belt of woodland north of the lake includes Grey Poplar and Corsican Pine over an understorey of Goat Willow and Hazel. Regional plant ancient woodland indicators on site include Bluebell, Moschatel, Wood Anemone, Yellow Archangel, Opposite-leaved Golden Saxifrage, Ramsoms, Sanicle, Primrose, Dogs Mercury, Common Dog Violet, Herb-Robert and Greater Stichwort.
The Riparian Woodland
w1d : Woodland and forest/Wet woodland
Most of the lake banks rise uniformly out of the water leaving little space for emergent vegetation. Three small areas on the north bank of the lake have been modified to provide habitat for such wetland species, and also contain small ponds for additional species. The plants introduced to these areas include Water Forget-me-not, Marsh Marigold, Ragged Robin, Purple Loosestrife and Yellow Flag Iris.
The Hedgerows
h2a : Heathland/Hedgerow
There are approximately 590 metres of hedgerow around the site. Some of the Hazel has been laid, thanks to Graham West and our SDNPA volunteers. We have planted over 200 metres of mixed native hedging plants from The Woodland Trust’s Trees for Schools and Communities scheme including: Holly, Hazel, Crab Apple, Downy Birch, Hawthorn, Goat Willow, Hazel, Blackthorn, Elder, Dog Rose and Rowan.