A new method of monitoring water quality in a stream receiving sewage effluent, using chironomid pupal exuviae

The midge family Chironomidae (Diptera) are of prime importance in fresh waters, and have over 450 species in Great Britain. They live in all types and conditions of rivers and lakes, and occur in large numbers. Their great potential in biological assessment of water quality has been offset by taxonomic difficulties, and especially by problems of larval identification, and by the labour of sorting benthos samples.It is proposed that the chironomid fauna of a river may be adequately sampled by collecting the floating pupal exuviae which accumulate along the banks and against obstructions. This technique is simple, quick, and is applicable to large, deep rivers as well as to small, shallow streams. Such samples provide enough material for examining the percentage composition of species, and for calculating diversity indices. The pupal exuviae are much easier to identify to species or species group than are the larvae.An examination of the effect of a sewage discharge into a small stream in South West England is given as a practical example of the method.