Community Composition and Dissolved Oxygen Dynamics in a Disconnected Bottomland Swamp

In the early 1900’s, drainage activities in Southern Illinois divided the Cache River in half, effectively separating the river into the upper and lower Cache Rivers. The lower Cache River is about 36 miles long with a flat gradient (0.2 ft/mile) and contains a remnant of a vast wetland system, commonly called Buttonland Swamp. The combination of river disconnection and a flat gradient has severely limited flow of water from the upper Cache River into the lower Cache River, resulting in drastically changed hydrology. Depending on the water level, Buttonland Swamp can flow naturally downstream or reverse course and flow upstream into a drainage ditch.  Currently a water level of 326 feet AMSL is maintained throughout Buttonland Swamp with the use of two instream channel weirs.

Historical anecdotes suggest Buttonland Swamp was once a popular fishing destination for local residents. However, in recent years fish kills have become more frequent, a possible result of low dissolved oxygen levels stemming from the disconnection of the river from its upstream flow sources and expansion of duckweed and other vegetation. Fish species composition relative to dissolved oxygen concentrations were evaluated in Spring and Summer of 2011 in Buttonland Swamp. Sampling stations were distributed across Buttonland Swamp.  Dissolved oxygen concentrations in 2010 ranged from 0 to 20 mg/l in the peak of the summer. Forty-eight species have been documented from previous sampling events (1892-2009), mostly obligate swamp species. Three state-listed species of concern (Cypress minnow [Hybognathus hayi], Bantam sunfish [Lepomis symmetricus] and Redspotted sunfish [Lepomis miniatus]) have repeatedly been found in Buttonland Swamp as well as three invasive species (Common carp [Cyprinus carpio], Grass carp [Ctenopharyngodon idella] and Silver carp [Hypophthalmichthys molitrix]). It is hypothesized that fishes with behavior and morphological adaptations to hypoxia, such as gar, bowfin and pirate perch, will persist in sites with lower dissolved oxygen concentrations while those fishes maladapted for hypoxia will be found in low abundance. Results will help determine if river reconnection or use of aeration equipment to improve dissolved oxygen levels are effective in increasing species richness, abundance, and possibly angling opportunity.