Wednesday, May 21, 2014
Wildlife in an old lead mine
Thursday's Guardian Country Diary describes some of the wildlife that has colonised the old disused lead mines at Westgate in Weardale. Many of the industrial processes that took place here (and ceased early in the 20th. century) involved the use of water, to power a hydraulic engine and to separate lighter stone from heavier lead ore (galena). The legacy is an excellent habitat for wetland wildlife which is now a Site of Special Scientific Interest.
I almost trod on this down-in-the-mouth toad, whose colour blended so well with the mosses around one of the shallow pools where it had spawned. You can see the ridge just behind its eye where the poison glands are located, which deter predators.
In this view you can see most of the main site, with Middlehope burn snaking through the valley. In the foreground you can see bridge parapets for the railway bridge that crossed the burn - ore was taken out on railway trucks pulled by horses. In the middle distance, just to the left of the third bend in the burn, you can see a rectangular depression with a pool of water in the centre. This was once a reservoir.
The reservoir is fed by water flowing out of this mine entrance, known as White's Level. The tunnel is just large enough to accommodate a small pony. Some of these mine levels stretch for miles under the hillside but are now lethal because some lead to vertical shafts where miners were winched down in baskets to tunnels that followed lead veins at lower levels in the strata.
The water flows out through a bed of watercress and into...
.... the silted up reservoir, mentioned earlier. This is a great site for dragonflies in summer, and also a breeding site for toads. The retaining wall on the left, like most of the walls of the mine ruins that were constructed from limestone blocks, is excellent habitat for ferns, like ....
... the dainty brittle bladder fern.
These are ruins of lead mine buildings downstream, with more waterlogged ground. The key elements for plant growth - soluble nitrogen and phosphorus - are rapidly washed from the soil by rainfall and flowing water, so some of the plants that grow here are adapted to obtaining these minerals by other means.
This is marsh lousewort, a partial parasite on the roots of grasses, that connects with their root systems and siphons off their mineral supplies, and ....
.... these are plants of butterwort. Those rosettes of sickly yellow-green leaves are covered in sticky mucilage glands that trap small insects, which are then digested by enzymes secrete by the leaves.
Downstream Middlehope burn flows through the sheltered, wooded valley known as Slitt woods and ....
...... when it reaches Westgate in Weardale flows over a series of picturesque waterfalls into the river Wear.