Preliminary observations on the benthic macroinvertebrate communities of Ross Bay,a polluted area of lough leane,south-west Ireland

The physical, chemical and biological water quality characteristics of Ross Bay, monitored during the period July 1974–May 1975, are described. The benthic macroinvertebrate standing crop of the littoral zone was sampled quantitatively during July 1974. The results are described in terms of biomass distribution and the distribution of taxa. The sampling stations are placed in an ordinal series based on their respective pollutional status. Changes in community structure and taxonomic composition along the series are described in terms of species diversity and the distribution of “indicator” organisms. Based on this distribution, a scheme of biotic indices is devised in order to reduce complex community composition to simple numerical terms. For this purpose, individual organisms are given a water quality rating which is dependent on their relative tolerance or intolerance to pollution. Significant correlation is shown between the ordinal series, water quality, Diversity Index ($\text{d}\text{?}$) values, Community Similarity (τ) values and Biotic Quality (qb) values. The biological evaluation of water quality in lakes is discussed and it is suggested that the littoral benthos may serve in any future assessment of organic pollution and enrichment in Lough Leane.