USE OF CHIRONOMID DEFORMITIES TO ASSESS ENVIRONMENTAL DEGRADATION IN THE YAMASKA RIVER, QUEBEC

The frequency of morphological deformities in chironomid larvae was us ed to assess environmental degradation at 12 sites in the Yamaska Rive r, Quebec, that were known to be either impacted by agriculture or urb an centres, or were relatively clean and used as reference sites. A to tal of 2273 chironomid larvae were examined for deformities. The overa ll frequency of deformities at polluted sites was 2.7%, whereas no def ormities were observed at the reference sites. The highest incidence o f deformities was found downstream of two urban centres, site 9 at Act on Vale (5.1% deformed) and site 12 at Ste Hyacinthe (5.3% deformed). The frequency of deformities at the agricultural sites ranged from 0.8 to 2.5% and was comparable to sites receiving municipal sewage efflue nt. The occurrence of higher frequencies of deformities downstream of urban centres indicates that the frequency of deformities increases wi th environmental degradation.