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

Michael J Lemke,Keenan Dungey,Heath M Hagy,Andrew F Casper,T D Vanmiddlesworth,Angela Kent,A Maria Lemke

doi:10.1007/s10750-017-3220-5

Abstract

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.

Highlights

A defining characteristic in the ecology of floodplain–river systems is the nature of the lateral water connection, especially the way riverine floods pulse into floodplain wetlands and lakes during the spring
Merwin Preserve is located on a former floodplain (484 ha) of the Illinois River that was isolated from the river by levees and farmed from the 1920s through 1998
The height of the breach at 133 m above mean sea level (AMSL) did not allow water to recede back into the river until a second, deeper notch was constructed in the levee at 129 m AMSL in mid-June

Summary

Introduction

A defining characteristic in the ecology of floodplain–river systems is the nature of the lateral water connection, especially the way riverine floods pulse into floodplain wetlands and lakes during the spring. These flood pulses increase species richness, diversity, and overall productivity (Bayley, 1995; Sparks, 1995; Galat et al, 1998; Robertson et al, 2001). Responses of abiotic and biotic factors to different flooding intensities need to be better understood in order to quantify tradeoffs among ecological services associated with benefits of restoring and reconnecting backwater lakes and wetlands, in hydrologically modified river systems (Ward et al, 2001; Tockner & Stanford, 2002). Increased understanding of the responses of the floodplain environment to inundation can be especially important when trying to ascertain the restoration capacity of highly altered river systems

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Results

Conclusion