Responses by benthic macroinvertebrates to prolonged flooding of marsh habitat

This study examined the seasonal differences in benthic invertebrate densities and biomass within the dominant vegetation types in a series of 5-ha experimental marshes in south central Manitoba. Following periods of normal water depths, the marshes were flooded to 1 m above the existing cattail beds for up to 2 years to determine the benthic invertebrate response to prolonged above-normal flooding of the marsh habitat. Benthic invertebrate densities and biomass were low during periods of normal water depths when compared with levels later during flooding. The benthic response to flooding was primarily within the herbivore–detritivore group, especially nonpredaceous chironomids. All cover types other than former open-water sites showed increases in benthos densities, biomass, and numbers of taxa following flooding. The increases following flooding appear to be related to the death of the belowground components of the emergent vegetation, the availability of coarse organic litter early in flooding, and the development of fine particulate organic matter during flooding.