A Case Study of Large Floodplain River Restoration: Two Decades of Monitoring the Merwin Preserve and Lessons Learned through Water Level Fluctuations and Uncontrolled Reconnection to a Large River

Large riverine systems are diverse and dynamic and are made up of multiple habitat types of lentic and lotic water. They are also heavily modified by humans and today nearly all habitats in many large rivers have been drastically altered. These modifications often include disconnecting lentic habitats either permanently or intermittently from the main channel. The Merwin Preserve at Spunky Bottoms (Merwin) began as a connected backwater that was leveed and drained for agriculture in the 1920s and restored in 1999, with restoration allowing it to become a disconnected backwater habitat. This status changed in 2013 when record flooding on the adjacent Illinois River overtopped and breached the levee creating an unmanaged and intermittent connection allowing the river access at moderately high river stages. During the past 20 years, the fish community at Merwin has undergone several changes that follow three drought events pre-breach, the exchange of fishes from the mainstem following the breach in 2013, and subsequent low water conditions of much of the area as river levels drop. Long term data and more intensive sampling efforts during the drought of 2012 showed relative abundance of sport fishes declined during, or immediately following, pre-breach drought events and post-breach low water conditions while relative abundance of non-sport and non-native fishes remained stable. The unique story of Merwin can provide a case study for other large river restoration projects on the effects of drought, climate change, and impacts of an unmanaged connection of a previously disconnected habitat to an adjacent large river.