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1 2007

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Effect of flow manipulations on benthic fauna communities in a lowland river: interhabitat comparison

Dukowska Małgorzata, Szczerkowska Eliza, Grzybkowska Maria, Tszydel Mariusz, Penczak Tadeusz

Polish Journal of Ecology

2007

Vol. 55, nr 1

101-112

In order to estimate the impact of flow manipulations on abiotic and biotic variables two sites of the fourth-order section of a lowland river (Drzewiczka River, in central Poland) with five dominant habitats each were selected downstream of a dam reservoir: the former just downstream of a canoeing track (CT), marked as disturbed (D), and the latter, control one (C), 10 km farther downstream. At the disturbed site water from the reservoir was released in afternoons to operate the CT (3-5 times higher volume than the natural median, i.e. from 4.3 (most frequently) to over 12.0 m[^-3] s[^-1] (exceptionally), which lasted for 2-3 hours per day while no flow fluctuations were observed in the control. The habitats were sampled over an annual cycle. Variables that have a great impact on macrozobenthos, like current velocity, water depth, substrate composition, presence of macrophytes and standing stock of food resources (BPOM - benthic particulate organic matter, TPOM - transported particulate organic matter, periphyton) were measured. As showed by our results (MANOVA) permanent moderate disturbance caused macrobenthos to be 2-4 times more abundant and diverse at the disturbed site (D), than at nearby natural river site (C), especially at the high-flow area. A lower abundance was recorded at the stagnant and pool habitats of both sites. Chironomidae dominated at all habitats, and Oligochaeta (gathering collectors) at the stagnant and macrophyte habitats; Trichoptera (mainly filtering collectors), Ephemeroptera and Simuliidae (filtering collectors) were the next most abundant among insects, depending on the habitat type. Although Chironomidae dominated at both river sites, they were represented by taxa belonging to various functional feeding groups; at site D chironomids - mainly periphyton scrapers (Orthocladiinae), while at site C - deposit feeders (Chironomini), connected with either silt sediment or sand.