Changes in the Emergence of Blackflies (Diptera: Simuliidae) over 50 Years from Algonquin Park Streams: Is Acidification the Cause?

Abstract

Studies on emergence of insect communities conducted in Mud Creek and Costello Creek in Algonquin Park, Ontario, Canada, over a period of 50 yr were analyzed to assess the changes that have occurred in blackfly populations in streams receiving long-term anthropogenic acidification. The headwaters of Mud Creek are currently experiencing pH depressions to 5.1–4.9 during snowmelt whereas pH depressions downstream in Mud Creek and throughout Costello Creek are less severe (to pH 5.6–5.8) compared with summer and autumn values of about 6.4. Since the time of the earliest collections, the total number of blackflies emerging has increased at the most severely acidified sites at the headwaters of Mud Creek, while emergence remains unchanged at all the less acidified sites. Large fluctuations from year to year in the emergence densities of many individual species were observed at all sites, making it difficult to determine which species may increase or decrease concurrent with elevated acidity.