Echoes of a flood pulse: short-term effects of record flooding of the Illinois River on floodplain lakes under ecological restoration

The flood pulse drives primary productivity, biotic communities, and abiotic processes in large river systems; however, the effects of floods on restored floodplain lakes and associated wetlands are poorly understood. Record flooding of the Illinois River, Illinois, in 2013 reconnected two floodplain preserves under restoration that had been disconnected from the river by levees for >80 years. Differences in hydrological connections between sites created a natural experiment where field-based data collection could be employed to document flood effects. Levee failure and subsequent river connection at Merwin Preserve increased nutrient capture and floodwater retention, shifted microbial and invertebrate communities, increased fish species richness, spawning and nursery habitat, and stimulated production of moist-soil plant communities during summer drawdown that provided foraging habitat for spring-migrating waterfowl. However, increased hydrologic connectivity during the growing season resulted in loss of submersed vegetation and habitat for autumn-migrating waterfowl. In contrast, river water overtopped the levee at Emiquon Preserve during a 6-day event that resulted in marginal changes in the bacterial community and negligible changes in water quality and community diversity. Tradeoffs among ecological services should be carefully considered when reconnection of highly altered rivers to restored lakes and wetlands is proposed.