DISTRIBUTION AND PRODUCTION OF CHIRONOMIDAE (DIPTERA) IN THE LOWER COURSE OF THE GRABIA RIVER (CENTRAL POLAND)

1. A fifth-order section of the Grabia River was investigated over two years: 1984/85 (low water level) and 1985/86 (high spate). Chironomidae (thirty-nine species) dominated the macrobenthos in both years. 2. In 1984/85 (mean annual water temperature 10.2-degrees-C), the number of Chironomidae species in coarse sediment was highest in spring (thirty-three species) while in sand it was highest in summer (fifteen species). A decrease in species richness was recorded in autumn and winter at each of the established sites. The estimated Chironomidae production for the whole river section was 5.37 g dry wt m-2yr-1, but it differed widely amongst the study sites, ranging from 3.75 to 12.07 g m-2yr-1. 3. In 1985/86 (mean annual temperature 8.1-degrees-C) there occurred a summer spate which was more intense than any recorded over the previous 20 years. This substantially reduced the number of species, the greatest reduction being in the coarse sediment, which was buried with sand during the spate. Production for the whole section decreased to 1.17 g m-2yr-1, and the variability amongst sites ranged from 1.04 to 1.45 g m-2yr-1.