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Keywords:

  • Macroinvertebrates;
  • Hydrology;
  • Canalization;
  • Conservation

Abstract

This paper describes a study of a river regulated by past engineering schemes carried out for land drainage purposes: the River Welland in the East Midlands of England. Benthic invertebrate family richness and total biomass was measured in riffles, pools, and runs separately and then related to the frequency of these physical parameters. Changes which have occurred as a consequence of (a) loss of channel length through meander cut-offs and (b) alteration of substrate characteristics through dredging and lowering of the river bed, were quantified. Riffles comprised 20-30 per cent of the channel in reaches not seriously altered by engineering; elsewhere dredging has reduced or eliminated riffles and pools, leaving uniform sandy runs as the dominant channel feature. Riffles, pools, and runs all contribute to overall ecological value but the riffle and pool biotopes supported higher macroinvertebrate biomass and family richness. We show that proposals for river management that address the ecological needs of invertebrate communities can thus be expressed as numerical recommendations for maintaining or enhancing the key physical features of a river. In consequence, conservation recommendations can be simplified and considered in the same form as the engineering requirements of land drainage.