Resistance and resilience of winter-emerging Chironomidae (Diptera) to a flood event: Implications for Minnesota trout streams

Disturbances caused by rainfall are common in streams with the impact on stream inhabitants determined by the frequency, intensity, and predictability of the event. Here, we examine the response of winter-emerging Chironomidae (Diptera) to extreme flooding disturbance. In August of 2007, a severe flood impacted southeastern Minnesota, imparting stress on aquatic communities. Chironomid pupal exuviae collections were obtained biweekly from 18 southeast Minnesota streams during the following winter to assess resistance and resilience of winter-active chironomids to flooding. Streams examined were divided into moderate (2. 5-10 cm), heavy (10-20 cm), or extreme (20+ cm) rainfall categories with rainfall amounts in each category representing total precipitation during the 3-day storm. Post-flood samples were compared to samples obtained from the same localities during prior winters. Our findings contradict studies of responses by Chironomidae to flooding during warmer-water conditions and show that winter-emerging Chironomidae are resistant to stress imposed by summer spates. Significantly more taxa emerged during winter after flooding as compared to historic collections, and the number of species emerging in winter was positively correlated with rainfall severity, indicating that 15 species responded opportunistically to disturbance. This indicates that winter-active Chironomidae may be resistant to increased severity of summer spates associated with climate change predictions.