The ecology of invertebrate fauna of Manx streams in relation to pollution from disused mines

This investigation was carried out to inquire into the differences in the invertebrate fauna of two closely related streams in the Isle of Man. The Gleneedle stream is a clean mountain stream which drains the western slopes of Gleneedle. The Glendhoo stream drains the eastern sides of Gleneedle and collects runoff water from disused mine workings, it is slightly polluted by the presence of lead (mean annual concentration 0.26 mgl-1) and zinc (mean annual concentration 0.108 mgl-1). The two streams combine and the sampling areas are about 400 metres apart at an altitude of approximately 150m. The major components of the invertebrate fauna were determined for each stream, and observations of population changes recorded for a period of two years, from February, 1978, to January, 1980. Variations in the ionic concentration of lead and zinc, together with other chemical and physical parameters were also recorded. Laboratory experiments were carried out to determine the hatching success of eggs of the mayfly Baetis rhodani and of the trichopterans Hydropsyche instabilis, Rhyscophila dorsalis, Polycentrppus flavomaculatus and Potamophylax latipennis, incubated in water from the Gleneedle stream as a control, in water from the Glendhoo stream and in water to which had been added salts of lead and zinc. Observations were also made in the laboratory of the effect of rearing larvae of Potamophylax latipennis, Polycentropus flavomaculatus, nymphs of Baetis rhodani and the plecopteran Protonemura meyeri in conditions similar to those of the hatching experiments. Attempts to reproduce these experiments in the field did not succeed. The results suggest that small amounts of lead and zinc of the order of 0.15 mgl-1 act synergistically to prevent the hatching of aquatic insect eggs; whilst these amounts are not fatal during larval instar stages they appear to be lethal during metamorphosis. Protonemura meyeri and Baetis rhodani were unable to moult successfully and failed to survive. The trichopteran larvae Polycentropus flavomaculatus and Potamophylax latippnnis were resistant to lead and zinc and survived successfully in this stage. The rate of pupal emergence was low for Potamophylax latipennis, and those teneral adults which did emerge had underdeveloped wings and were incapable of flight. The existence of lead and zinc in the Glendhoo waters exerts a controlling influence on the ecology of the stream, colonization by insect larvae is prevented due to the eggs failing to hatch. The presence of P. latipennis larvae in the Glendhoo stream may be explained by the ovipositing behaviour of the imagines, eggs hatch on vegetation overhanging the water. The larvae of this species are therefore able to inhabit the stream but development is inhibited during pupation