Tuesday, June 5, 2007
508

Lateral Springtime Invertebrate Drift between a Restored Backwater and a Large Midwestern River

Laura A. Csoboth, HDR|LMS, 1 Blue Hill Plaza, Pearl River, NY 10965, Darrin L. Martin, Department of Zoology, Southern Illinois University, Life Sciences II, Room 351, Carbondale, IL 62901, James E. Garvey, Fisheries and Illinois Aquaculture Center, Southern Illinois University, Life Sciences II, Room 173, Carbondale, IL 62901, and Matt R. Whiles, PhD, Zoology, Southern Illinois University, Southern Illinois University, 326 Life Science II, Carbondale, IL 62901.

Despite their typically degraded state, backwaters are vital to many large river species, particularly when river connectivity remains intact.  During spring 2005, we quantified invertebrate drift into and out of a restored, 1,000-ha backwater, Swan Lake, at its confluence with the lower Illinois River.  Each week, drift nets were set bi-directionally within the constructed channel at the backwater-river confluence to reveal diel and taxonomic patterns of invertebrate drift and their relationship to abiotic conditions.  Invertebrates represented 17 orders and 1 phylum and were dominated by zooplankton.  No differences between drift into or out of Swan Lake occurred, although aquatic invertebrates drifted more at dusk and night (Time of day: F3,4 = 7.28, P = 0.04; Week: F8,10 = 4.53, P = 0.01; Time of day*Week: F23,10 = 2.44, P = 0.07).  Drift into, but not out of, Swan Lake was positively related to surface velocity and negatively related to water depth for macroinvertebrates.  Although high rates of zooplankton drifted at the backwater-river confluence, there were no diel patterns or significant relationships with abiotic variables measured.  These results suggest that lateral drift of invertebrates in large river systems occurs in a similar manner as downstream drift.

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