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Presented at the NABS Annual meeting, Vancouver, British Columbia, 2004
in Disturbance Ecology 1
Macroinvertebrate and benthic organic matter responses to a hydrologic disturbance gradient in backwaters of a Mississippi River navigation pool
M.B. Flinn1, M.R. Whiles1, R.A. Adams1,2, and J.E. Garvey2. 1Department of Zoology, Southern Illinois University, Carbondale, Illinois 62901, 2Fisheries and Illinois Aquaculture Center, Southern Illinois University, Carbondale, Illinois 62901
Water level management in Mississippi River Pool 25 creates a hydrologic disturbance gradient in off-channel habitats whereby mid-pool backwaters dry for short periods (~10 days/yr) and lower-pool backwaters dry extensively (~60 days/yr). We examined the influence of this gradient on organic matter and macroinvertebrates during 2001-2003. Three samples were collected seasonally at three mid-pool and four lower-pool sites using a stovepipe sampler. Benthic organic matter values were stable at mid-pool, but lower-pool values were variable because of significant fluctuations in CPOM (P<0.01), especially in fall after vegetation grew on exposed mudflats. Lower-pool habitats had generally higher macroinvertebrate taxa richness, with significantly higher values in spring 2002 and fall 2003 (P<0.05), and responses of individual taxa varied. Multivoltine taxa dominated lower-pool habitats in spring, but had higher relative abundance and biomass at mid-pool in fall following summer drying. For example, Oligochaeta and Chironomidae abundance and biomass were higher at lower-pool in spring (P<0.05), but both had higher abundance and biomass at mid-pool in fall (P<0.05). Univoltine taxa preferred longer hydroperiods. For example, Hexagenia abundance and biomass were higher in mid-pool habitats throughout the study (P<0.01). Results show that water level management in this navigation pool influences backwater organic matter and macroinvertebrates.
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