Monitoring the effect of sewage effluent on the Oxford canal using chironomid pupal exuviae

Collections of chironomid pupal exuviae from the Oxford Canal were taken monthly from May to October 1991 at stations above and below the sewage effluent discharge at Kidlington, near Oxford. The chironomid exuvial assemblages showed clear changes reflecting the effects of the sewage, notably in the increased dominance of Parachironomus arcuatus and Chironomus riparius and other pollution-tolerant species downstream from the effluent inflow. A return to the pattern of taxa seen in the upstream stations was noted below the next canal lock, 2.8 km downstream from the effluent discharge. Environmental quality indices, calculated according to the Chironomid Pupal Exuvial Technique, also reflected the effects of the sewage inflow. The results show that chironomid populations, as sampled by collecting pupal exuviae, are potentially valuable for monitoring organic pollution in canals.