Biological Surveys

Macroinvertebrates are the most commonly used organisms when assessing water quality. They exhibit differential responses to physical and chemical changes in their environment (some aquatic organisms are sensitive to water quality changes while others are tolerant). Macroinvertebrate communities provide a realistic record of the prevailing conditions and are not affected by a temporary amelioration of pollution. It is, therefore, possible to investigate the general water quality over time.

In rivers and streams aquatic faunal collections are undertaken by a series of replicate kick samples by using a standard (1.0mm mesh) pond net or using a Surber sampler. Sampling is generally confined to riffle/glide areas although some projects adopt a multi-habitat sampling approach. The same sampling methods may be used for lake shore sampling, however, when sampling in deep water an Ekman-type grab sampler is used.

Following collection the organisms are preserved in 70% alcohol and returned to the laboratory. Here they are subsequently identified to the lowest possible taxon, using standard Freshwater Biological Association (FBA) identification keys for the British Isles. The Q-value index system, developed by the Environmental Protection Agency (EPA), for Irish rivers is then applied to the data.

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