The Study of Benthic Invertebrate Communities in: -(a) Lotic Eutrophic Waters (b) A River in Stages of Recovery from Past Pollution

Abstract

A two year survey into the ecological recovery of what was once one of the most grossly polluted rivers in Britain is documented. The R. Cole was subjected to gross organic pollution as a result of two sewage effluents, one of which was also metallically toxic, these effluents being abated in 1971 and 1972. The effect of the changing water quality on the recovery of the macro-invertebrate structure of the benthic communities has been studied, noting changes in the community structure and membership. Benthic macro-invertebrate communities living under different regimes of eutrophication in experimental streams and in natural rivers have been investigated with regard to numbers and diversity of species, productivity in terms of standing biomass, and the trophic dynamic aspect. The eutrophic conditions were simulated experimentally by mixing well oxidised sewage effluent with good quality river water, the resultant mixture being fed into three excavated experimental streams. Two rivers receiving well oxidisedsewage effluent (R. Tean, Staffs., and R. Ray, Wilts.) were also utilised for comparative purposes. One effect of eutrophication is to encourage huge growths of algae and mosses and in particular Cladophora, which may subsequently drastically affect the oxygen/carbon dioxide balance of a watercourse diurnally. An apparatus was developed capable of delivering and controlling fluctuating oxygen levels in both time and intensity while other parameters were kept constant. Using the apparatus, the reactions of the pollution sensitive amphipod Gammarus pulex was investigated. The importance of the chironomid larvae in benthic communities has been emphasised throughout, and preliminary investigations into their respiratory rates at differing oxygen concentrations have been made using a respirometric chamber designed and developed for this purpose. An appendix containing comprehensive drawings of taxonomic features of the Chironomidae encountered has been included. The literature has been reviewed,