Using Paleolimnology to Assess the Impacts of Historical Insecticide Use on Chironomid Assemblages in the St. Lawrence River, Montreal, Quebec, Canada
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In 1962, Montreal was awarded the host site of the 1967 World Exhibition. Considered one of the most successful fairs in history and a part of Canada’s centennial celebration, preparations for the event were extensive and included a project in collaboration with Agriculture Canada to control pest populations of mayflies, shadflies, and midges that would frequently swarm Montreal in the summertime. Between 1965 and 1967, over 16,000 kg of the larvicide dicholorodiphenyldichloroethan (DDD) were applied directly to the St. Lawrence River around the around Île Saint-Hélêne. The purpose of this paleolimnological study is to assess the chironomid (non-biting midge) community of the St. Lawrence River prior to, during, and post DDD inputs related to the 1967 World Exhibition. No thorough ecological study was performed prior or following the application of DDD, and so in the absence of long-term monitoring, a paleolimnological approach is the only technique capable of reconstructing how invertebrate insect assemblages responded to such intensive pesticide inputs. Subfossil chironomid assemblages preserved in a sediment core recovered from the affected area of the St. Lawrence River were studied to assess the biological impacts of the World Expo DDD applications. This study found that while total chironomid abundance remained low in sediments associated with elevated DDD levels, abundance levels were not out of the range of natural variability. However, certain taxa were found to have increased, while others decreased in response to the increasing DDD levels during the 1967 World Exhibition, but interpretation of species changes was difficult due to the complex history and continually changing state of the water quality of the St. Lawrence. The results of this study suggest that chironomid may be effective indicators of tracking the impacts of pesticide use in fluvial systems.