CHIRONOMIDAE (DIPTERA) RESPONSES TO THE EXPERIMENTAL FLOODING OF PRAIRIE MARSHES

This study examined chironomid responses to the flooding of ten drained experimental marshes in Delta Marsh, Manitoba, Canada. Emergence traps were used to monitor chironomid emergence from three vegetation types (Symphyotrichum ciliatum, Scolochloa festucacea, and Schoenoplectus tabernaemontani) flooded at two water depths (shallow: 20–40 cm, deep: 50–70 cm) over a four-year period. The greatest number (7,651 m−2 yr−1) and biomass (20.3 g m−2 yr−1) of chironomids emerged from Schoenoplectus-deep sites in the fourth year of flooding. Numbers, biomass, and size classes of emerging chironomids were similar over the four years from the Symphyotrichum habitat. However, chironomid emergence from Scolochloa and Schoenoplectus habitats was dominated initially by the smallest size class but shifted steadily toward production of much larger species over the four-year experiment. The production of chironomids as a potential food resource for waterfowl was high from the Symphyotrichum habitat during all four years of flooding, but emergence from the Scolochloa and Schoenoplectus habitats did not reach comparable levels until the third or fourth year.