The effects of sampling techniques on the Gammarus: Asellus ratio

Abstract

Previous studies have shown the Gammarus: Asellus ratio to be useful in assessing organic enrichment in lowland rivers. Three types of artificial substratum colonization sampler i.e. Standard Autwuchs Unit (S.Auf.U), airbrick and basket samplers containing graded stones were compared with conventional Surber direct sampler data to determine the effects of passive sampling techniques on the ratio. The Standard Aufwuchs Unit and airbrick substratum colonization samplers provided Grammarus: Asellus ratios which showed some correspondence with the ratios derived from Surber data and performed well in the assessment of water quality at all sites. Basket samplers were found to have some degree of selectivity, particularly by Gammarus, for substrata having sizes of interstices corresponding with body size. The results from the basket sampler date therefore were inconclusive as colonization of these types of samplers are affected by factors other than pollution.