MEASUREMENT BY IN-SITU BIOASSAY OF WATER-QUALITY IN AN AGRICULTURAL CATCHMENT

This paper describes a study in which a battery of in situ bioassays was used to assess water quality in an agricultural catchment. The main aim of the study was to test whether experimental bioassays could provide information that complemented more traditional macroinvertebrate and chemical monitoring techniques. Two environmental quality assessments were undertaken in Curtisden Green Stream during 1992-1993, using macroinvertebrate monitoring techniques (hand nets or standard colonization units) and the following bioassays: Gammarus pules (L.) mortality and feeding rate, Anodonta cygnaea (L.) glutathione-S-transferase activity and Chironomus riparius (Meigen) emergence from sediment. The G. pulex and C. riparius assays provided useful information that complemented the macroinvertebrate survey data. The results revealed a system prone to considerable temporal and spatial variability in macroinvertebrate richness and abundance. Stretches of the stream that were consistently taxon-poor made it difficult to assess the effect of contamination using macroinvertebrate community monitoring alone. The experimental bioassays were able to identify particular stretches of the stream where pollution had occurred.