AbstractThe effects of a kraft paper mill effluent discharge on the benthic invertebrates in the Rivers Llynfi and Ogmore were determined by regular collection of biological samples from six sites. One site was upstream of the effluent discharge, two downstream on the Llynfi, one on the Ogmore before the confluence with the Llynfi and two further sites downstream of the confluence. The effluent tended to reduce the dissolved oxygen concentration and BOD 5 concentrations in the water immediately below the discharge and this adversely affected the benthic invertebrate community at these sites.
The Chironomidae and more particularly the Oligochaeta were very important constituents of the benthic macro-invertebrate community at the sites immediately downstream of the effluent. The most common oligochaetes were the Enchytraeidae, Tubifex tubifex and Nais elinguis. The most common species of Chironomidae recorded during the survey were Brillia longifurca. Tvetania calvescens. Orthocladius(O) rubicundus. and Eukiefferiella clarripennis. Cricotopus bicinctus was very numerous in the summer collections.
With improving water quality downstream of the discharge species belonging to the Plecoptera, Ephemeroptera and Trichoptera tended to become more important members of the benthic community.
The biological results were analysed with standard statistical tests, various biotic indices and computer programs.The results of the survey undertaken indicated that the river was polluted immediately below the effluent outfall but to a lesser extent than was expected. However, a typical pollution fauna was found to be associated with Sites 2 and 3 and as such this is attributable to the organic effluent discharge from the paper mill at Llangynwydd.
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