Short-term Effects of Initial Flood Disturbance on Restoration Projects: Waterbirds and Wetland Vegetation Final Report Period 1 September 2013 – 31 August 2015

During spring 2013, record flooding occurred on the Illinois River. Emiquon and Merwin Preserves, two restored but hydrologically-isolated floodplains, were reconnected to the Illinois River for the first time in >80 years. Both Preserves are owned and managed by The Nature Conservancy and have been the focus of monitoring efforts since restoration began. Moreover, flooding intensity was not equal at these locations. Levees at Merwin Preserve breached, establishing a two-way hydrologic connection between the floodplain and the Illinois River at moderate river stages (i.e., partial connection). Conversely, levees held at Emiquon Preserve, facilitating a one-way input of water into this floodplain over top of levees (i.e., limited connection). These conditions created two case studies under which a natural experiment unfolded. Our objective was to document and assess site-specific post-flood changes in biotic communities from pre-flood states and trajectories. We hypothesized that waterbird communities would remain unchanged at Emiquon Preserve, but these communities would be negatively affected by the partial river connection at Merwin Preserve. Consequently, we anticipated less overall waterbird use, lower species diversity, and a shift in dominant species from herbivorous and granivorous waterbirds to piscivorous birds at Merwin Preserve. Likewise, we hypothesized that vegetation communities would be negatively affected by the partial river connection at Merwin Preserve resulting in decreased submersed and emergent aquatic macrophyte coverage, but vegetation communities would remain resilient to the limited connection at Emiquon Preserve and change minimally.