Ecological Studies on Benthic Macroinvertebrates in Lowland Rivers in Relation to Water Quality

Abstract

The effectiveness of using macro-invertebrate communities as indicators of water quality and pollution in deep lowland rivers was investigated, and the effects of natural environmental changes on their ability to monitor pollution was assessed. Various sampling and data processing techniques were evaluated. The Standard Aufwuchs Unit (SAufU) colonization sampler was found generally to be the best sampler for monitoring purposes, as it yielded more species-rich samples than the grab. Hand-nets were only effective in stands of macrophytes. The Ponar grab was the best bottom sampler for direct sampling. Colonization studies showed that there was no need to leave SAufUs in deep rivers for more than four weeks, and that the widely used MacArthur-Wilson model was inappropriate for such evaluations. Seasonal changes were observed in the faunas, mostly related to changes in the discharge. In the autumn, extensive and rapid changes were recorded. It was concluded that monitoring is best carried out during the summer, when conditions are more stable and the faunas more diverse. The macro-invertebrate communities in many deep rivers in England were restricted. Naidid and tubificid oligochaetes, tanypodinid and chironominid midges, amphipod crustaceans and molluscs, many of which are regarded as tolerant of organic pollution, were dominant. Mayflies, stoneflies, beetles and caddis flies were restricted, these including most of the indicators of clean waters. This was because of their highly eutrophic nature, the naturally high organic loadings, and in some rivers, the physically stressful environment. A survey of the deep lowland rivers of Britain indicated that the natural environmental variations between them had a more profound effect on the structure of the macro-invertebrate communities than did gross pollution. Pollution indices based on taxonomic richness and saprobity were therefore found to be inappropriate for use in deep rivers. Multivariate statistics were useful, and were recommended in their place.