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

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 moistsoil 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 Electronic supplementary material The online version of this article

Energetic implications of floodplain wetland restoration strategies for waterfowl

“…timing of drawdown) were achieved. However, present hydrologic conditions within the IRV often prevent development of hydrophytic communities in partially connected and connected wetlands, regardless of previous restoration practices or active management (Lemke et al , ). Furthermore, hydrologic isolation of Emiquon Preserve behind levees prevented extensive flooding and hydrologic fluctuations during the growing season and allowed hydrophytic plant communities to flourish.…”

“…However, the short‐term effects of reconnection are dependent upon restoration of the health and hydrology of the main channel (Jackson & Pringle ). Partially connected moist‐soil wetlands can produce greater energy than semipermanent emergent marshes during years of successful vegetation growth, but variability of river flooding causes frequent loss of vegetation and may negatively impact quality of stopover habitat for migrating waterbirds (Lemke et al ; Yetter et al ). Wetland managers must weigh the trade‐offs of managing floodplain wetlands in isolation from the main river channel and allowing floodplain wetlands to be hydrologically connected in systems that have been highly altered from the historical states.…”

“…Hydrologic isolation can provide high‐quality habitat for waterbirds, while hydrologic connection provides flood storage, nutrient cycling, and a host of other services. Trying to accomplish all of these simultaneously through partial river‐floodplain connections will fail to produce high‐quality waterbird habitat in many years (Lemke et al ).…”

“…Based on food energy and other habitat needs provided by both seasonal moist‐soil and semi‐permanent emergent marsh wetland regimes, we recommend restoration and conservation of a diversity of wetland types within the Midwest, particularly restoration of semipermanent emergent marshes with energy‐rich SAV communities. In highly altered river systems, such as the IRV, maintaining hydrologic isolation from the main river channel during the growing season may be the only way in most years to ensure persistence of hydrophytic plant communities until system‐wide restoration of historic flows is feasible (Sparks et al ; Lemke et al ). Restoration of historical SAV communities in a large river ecosystem in the Midwest will not only increase energetic carrying capacity but will also support greater diversity of waterfowl and other waterbirds throughout the region (Hagy et al ).…”

“…Altered hydrology in the Illinois River creates frequent and high‐magnitude river‐floodplain connections during the growing season and periodically impedes the establishment of moist‐soil and other hydrophytic vegetation. Due to increasingly frequent and high‐magnitude flood pulses during the growing season, food for waterfowl and other waterbirds during subsequent autumn and spring migrations may be limited in some years in floodplain wetlands with partial connections to the Illinois River (Lemke et al ).…”