The ecology of some British rivers in relation to warm water discharges from power stations

A number of detailed studies of the effects of heated discharges from power stations on the temperature, chemistry and ecology of British rivers have been carried out since 1965. This paper deals mainly with the Rivers Severn and Trent. In the Severn, a relatively clean river, temperatures up to 28°C below Ironbridge Power Station outfalls have not affected the diversity of the invertebrate fauna. There were slight alterations in the hatching of insect nymphs which may have been attributable to temperature, though natural variations from year to year were much more obvious. Emergence of adult Ephemeroptera and Trichoptera was not affected by temperatures of 26 to 28°C. The River Trent is used for cooling by some 14 power stations. There are no obvious changes in the diversity of the invertebrate fauna which can be related to temperature, though pollution from other sources causes very marked changes. At Drakelow, in the most polluted reach, changes in the Oligochaete community were possibly attributable to temperatures below the outfall. Experiments showed that Limnodrilus hoffmeisteri had a wider temperature range for reproduction than Tubifex tubifex . Studies of fish populations at Peterborough have shown that many coarse fishes can withstand quite sudden and wide temperature fluctuations.