site structure by
Nick John Ford

The Importance of Water in Independent Quarry

  1. Wildlife Value

    1. Birds

      With so little opportunities on Portland to find drinking water the island's bird population will use any bodies of fresh water in the quarry immediately. Seed-eating birds such as Linnets and Greenfinches have particular need of water, as their food is so dry. All species need fresh water to bathe in regularly in order to keep their feathers in good condition. For these purposes the water needs only to be a few centimetres in depth. Seabirds such as Herring Gulls prefer slightly deeper water to wash salt from their plumage. The edges of ponds will attract wading birds such as Common Sandpipers, which like to feed on the mud exposed as the pond dries out in summer. Any trees or shrubs around the pond will provide good feeding for insectivorous birds such as Willow Warblers.

    2. Insects

      A wide variety of aquatic insects will find their own way into any body of fresh water. The most important species from a conservation point of view are the dragonflies and damselflies. These are predatory insects whose larvae spend up to 5 years in ponds feeding on other aquatic animals. 2 very rare species have recently spread to Portland from the continent, the Red-veined Darter and the Scarce Blue-tailed Damselfly. Both will breed in very small ponds, with the damselfly often breeding in the temporary ponds that form in wheel-ruts in quarries. It is very important that no fish are introduced that may feed on the larvae of these insects.

    3. Mammals

      All mammals in the UK need some source of fresh water for drinking. Ponds often provide the naturalist with opportunities for watching shy species such as Foxes when they come in to drink. Foxes will also be attracted by the chance to feed on aquatic animals such as frogs and toads.

    4. Amphibians

      Frogs and Toads are already common on the island, mainly in garden ponds. Here the Toads are often prevented from breeding by the larger Frogs. A large pond or a series of smaller ponds will give the Toads a chance to find a breeding area away from Frogs. Portland also has a declining population of Palmate Newts, which may be able to colonise a new pond. There may be a case for deliberately introducing newts if any of their current breeding areas (e.g. on the West Weares) is threatened by subsidence or development.

    5. Plants

      Seeds of aquatic plants find their own way to ponds soon after the pond is created, presumably on the feet of visiting birds. Many ponds suffer from deliberate introductions of unsuitable plants by well-meaning people. Canadian Pondweed and Water Fern are often introduced in this way and do great harm to a wildlife pond.

  2. Location

    The pond needs to be in an area that is naturally damp to maximise water collection. Shading by trees should be avoided as many species of insects, especially dragonflies, need warm conditions. The pond will dry up in summer unless ways can be found to direct run-off from the surrounding areas into the pond. Here are some suggestions:

    1. Water from the roofs of the stone works could be collected and piped to the pond. It would be important to ensure that in doing so the water was not contaminated in any way. As well as possible chemical contaminants from materials on the roof any source of nitrate should also be avoided. Roofs that are heavily contaminated by bird droppings would not be suitable.
    2. Natural run-off from surrounding areas could be encouraged by landscaping. If the pond were situated in the centre of a large depression it would naturally tend to be topped-up every time it rained. Similarly, a series of artificial gullies or channels could be dug to direct water into the pond during showers. These may be able to be created so that they form an interesting design when viewed from a vantage point. Such gullies would also provide breeding habitats for insects such as the Scarce Blue-tailed Damselfly.
    3. Water could be encouraged to condense out of the mists and low cloud that frequently envelope this end of the island. Trees are very efficient at this but artificial constructions may also help. "Mist curtains" are used in desert areas. It may be possible for some sort of installation to serve the dual purpose of collecting water whilst being making an artistic statement of its own.
    4. There is some evidence to suggest that dew ponds collect their own condensation by remaining slightly colder than the air above them. This would be most likely due to their being sited in a naturally cool spot, such as a windy hilltop or a shady corner. This would be incompatible with a wildlife pond, which needs to be as warm as possible, but such a dew pond could be used to supply water to an adjacent series of ponds.

  3. Construction

    The pond must be reasonably watertight, whilst incorporating features that will encourage wildlife to use it. The following points need to be adhered to as much as possible:

    1. The base of the pond must be constructed of thick clay to hold in water. Before filling this clay must be crushed into a solid, powdery layer ("puddling"). This may be achieved by the action of a vehicle's tyres, the feet of a group of helpers or a combination of both.
    2. The sides of the pond should be very gently sloping to a maximum depth of at least a metre. If the pond is more shallow than this it is likely to overheat and dry out. The gently sloping edges are absolutely vital to allow wildlife to enter and exit the pond and will also increase the supply of water when the level is low.
    3. Throughout the pond flat-topped rocks of a variety of heights should be placed to provide safe drinking areas for birds.

Once the pond has been constructed it can either be filled from the domestic water supply or left to fill on its own. On no account should any plants or wildlife be introduced to the pond, in case alien species such as Canadian Pondweed are accidentally introduced.

References:

  1. E. A. Martin "Dew Ponds" http://www.dewponds.co.uk/articles_dewponds_martin.htm
  2. J. and G. Hubbard "Neolithic Dew-Ponds and Cattle-Ways." Longmans Green, and Co. 1907
  3. Robert A. Nelson "Air Wells & Dew Ponds" http://www.bagelhole.org/article.php/Water/350/
  4. Jeremy Biggs et al "New approaches to the management of ponds";
    British Wildlife Vol. 5 No. 5 June 1994

Bob Ford 26/9/03