Flooding drives a macroinvertebrate biomass boom in ephemeral floodplain wetlands

Despite broad recognition of the importance of the Flood Pulse Concept to large river ecology, few studies have provided empirical evidence to support a number of its arguments. We compared and contrasted the responses of water quality, nutrients, and the macroinvertebrates of ephemeral and permanent wetlands to a 22-wk managed inundation. We hypothesized that inundation of ephemeral wetlands would mobilize higher concentrations of nutrients from floodplain sediments and C from organic matter, which would, in turn, fuel greater abundance and biomass of aquatic macroinvertebrates than in permanent wetlands. The response of ephemeral wetlands to flooding contrasted very strongly with that of permanent wetlands. Freshly inundated ephemeral wetlands had significantly higher dissolved nutrient and organic C concentrations than permanent wetlands and supported different aquatic macroinvertebrate communities. Macroinvertebrate diversity was higher in permanent wetlands, but ephemeral wetlands supported much greater macroinvertebrate abundance and biomass. Differences between macroinvertebrate communities in ephemeral and reference wetlands were driven primarily by Chironomidae. Chironomus tepperi was the dominant taxon among ephemeral wetlands, both numerically and by biomass. Early-colonizing Coleoptera contributed strongly to taxonomic richness among ephemeral wetlands. Analysis of functional feeding groups (FFGs) indicated that ephemeral wetlands contained a higher proportion of detritus-feeding collector–gatherers compared to permanent wetlands, suggesting an increased reliance on heterotrophic energy pathways. We showed that a managed flood pulse can mobilize latent terrestrial energy sources within ephemeral floodplain wetlands and support a boom of aquatic invertebrate biomass, with important implications for both terrestrial and aquatic food webs.